From: S-T Morrissey Subject: thermal convection in LP sensors Date: Thu, 31 Dec 1998 14:58:45 -0600 (CST) Regarding thermal convection in LP instruments: This has long been a problem with high gain observatory instruments, even in large secure vaults. The earths' heat flow out of the ground is always present, even when a large pier is in the way. If the environment above the pier is cooler, problems result. In a cavern or mine, the temperature difference is minimal if the area is closed off, but it can still be present. Within an instrument enclosure, the base will warm up a boundary layer of air, which will eventually peel away and invert with the cool air in the top of the case, usually at periods of 10 to 100 seconds. Insulation inside, on top of the baseplate, as well as baffles within the case, will help, but more often just make the problem more interesting. The most common system with the problem came with the WWNSSS (Worldwide network of standard seismograph stations) in the 1950s, where a set of 30-second long period sensors was connected to 90-second galvanometers. The steel cases of the LP sensors were equipped with small 10-watt cartridge heaters in the very top of the case, and a small variac transformer was used to adjust the heat so that the convective noise just disappeared from the (photographic) record. Too much heat would set up its own noise. Thermostatic arrangements only added another cycle to the problem, not only to the thermal convection but to radiant heating of the sensor. To minimize the heat required, as much fiberglass insulation as possible was installed under the seismometer baseplate, which was usually about 2cm above the pier. In a small underground vault in the Ozarks, the LPs are on 10cm high piers on the rock floor, but the vault is a heavy aluminum streem culvert and a big heat sink, so more heat was needed. I use 220-volt, 50 watt band-style air-conditioner case heaters running on 110v for 25 watts and an indefinite life, and resting on the outside of the steel case, where the mice loved them. For lower wattage and indefinite life, regular 10 watt bulbs can be used in series; we want the heat, not the light, and a burned out bulb can make a very mysterious transient in the data. Strip heaters can be found in surplus stores, and when used in series they don't burn out or burn your hand. Regarding insulation: fiberglass matting gives much greater protection than lighweight styrofoam panels because it has significant thermal mass along with its insulation properties. As Meredith notes, large R-values can be realized with a lightweight plywood box with 4" of fiberglass (or other heavy closed-cell panels) on each side. The more mass in the thermal barrier, the longer the time constant is. To remove the daily thermal noise in 3m deep tiltmeter pits in the Aleutians, we bagged up the volcanic soil and packed it around the sensors, and it reduced the diurnal thermal noise by a factor of 100. So if you can sand-bag your vault ..... or go deeper underground ...! Regards, Sean-Thomas _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "David A. Nelson" Subject: new year Date: Fri, 1 Jan 1999 10:00:12 +1300 Happy new year to all from new zealand i trust that 1999 will bring new challenges and great advances for the PSN and for all in their family lives cheers Dave Co-ordinator: New Zealand Public Seismic Network Dave A. Nelson ZL4TBN 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm IF there indeed are other parallel universes... I can now rest in the knowledge, that in at least one of them, I am filthy rich and drive a red Ferrari _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: macsmith Subject: Re: thermal convection in LP sensors Date: Thu, 31 Dec 1998 11:28:39 -1000 For the professionals with budgets, I would have thought that enclosing instruments in a vacuum would eliminate all of theses problems. Has anyone use such things? Happy New Year Ian Smith _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: JIm Hannon Subject: Re: thermal convection in LP sensors Date: Thu, 31 Dec 1998 18:25:07 -0600 macsmith wrote: > For the professionals with budgets, I would have thought that enclosing > instruments in a vacuum would eliminate all of theses problems. > > Has anyone use such things? > > Happy New Year > > Ian Smith > I am busy working on a vacuum enclosed seismograph. There is not too much expense except for the pump to pull the vacuum. But eventhough a vacuum eliminates a lot of problems with convection currents and barometric pressure changes. I suspect that it will have its own set of problems starting with leaks and case flexture. We shall see. Happy New Year -- Jim Hannon http://soli.inav.net/~jmhannon/ 42,11.90N 91,39.26W WB0TXL _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: KACAMACHO@....... Subject: Re: new year Date: Thu, 31 Dec 1998 20:09:47 EST HAPPY NEW YEAR TO YOU TOO! _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Fred Subject: Re: thermal convection in LP sensors Date: Thu, 31 Dec 1998 17:11:41 -0800 That would be an ideal housing but a fairly expensive undertaking. That would have to be a pretty strong box. If anyone in the bay area wants to try this, I own a pretty good pump that I could loan out. I wonder if the amp's would have to be outside if the tank as the thermal dissapation will be much different. Happy New Year all Fred -- How much choice did God have in constructing the Universe? If the no boundary proposal is correct, he had no freedom at all to choose initial conditions. He would have only had the freedom to choose the laws the universe obeyed. Albert Einstein _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: macsmith Subject: Re: thermal convection in LP sensors Date: Thu, 31 Dec 1998 16:51:05 -1000 I should urge a little caution about using a vacuum. Firstly, one wouldn't use a "box", but a "vacuum vessel", these are usually aluminium, whose walls are 0.25 to 0.5 of an inch thick. Otherwise there is a risk of implosion. Secondly, some vacuum pumps have an exhaust port which has to be vented to the outside, the fumes (evapourated vacuum oil) are poisonous (I can't remember how to spell carsogenic!). One might also think of adding a vacuum guage, to see how good the vacuum is - more expense. All our instruments at the telescopes use these, and we have (working) amps inside, not just at vacuum, but close to Liquid Nitrogen temperature - now there's a thought, low noise amps. Happy New Year. Ian Smith _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Robert Avakian Subject: Re: thermal convection in LP sensors Date: Thu, 31 Dec 1998 21:38:24 -0800 Question. As long as thremal events had periods several times the period of the longest waves, I would think they could be filtered out quite effectively after the fact. So all one would need would be a box which slowed or damped the enviornmental changes effectively. Might a water jacket with a circulating pump be a cheaper and easier alternative to the vacuum scheme? I assume the circulating water could cause a problem, but the pump would not need to run continuously, perhaps several seconds every few minutes? Bob A. macsmith wrote: > > I should urge a little caution about using a vacuum. > > Firstly, one wouldn't use a "box", but a "vacuum vessel", these are usually > aluminium, whose walls are 0.25 to 0.5 of an inch thick. Otherwise there is > a risk of implosion. > > Secondly, some vacuum pumps have an exhaust port which has to be vented to > the outside, the fumes (evapourated vacuum oil) are poisonous (I can't > remember how to spell carsogenic!). > > One might also think of adding a vacuum guage, to see how good the vacuum is > - more expense. > > All our instruments at the telescopes use these, and we have (working) amps > inside, not just at vacuum, but close to Liquid Nitrogen temperature - now > there's a thought, low noise amps. > > Happy New Year. > > Ian Smith > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@.............. with the body of the > message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: S-T Morrissey Subject: evacuated containments Date: Fri, 1 Jan 1999 01:34:00 -0600 (CST) Re vacuum contaiment for seismometers: They have been used since the 50's for high gain long-period sensors, but because these sensors were large (50 cm or more), they were large and dangerous (30" steel tanks), and had serious problems with flexure of the interface between the seis and the pier. But a pressure contaiment for the vertical is necessary to reduce the barometric buoyancy noise by a factor greater than 100. So the current long-period configurations of the major commercial VBB sensors are much smaller, with dimensions within 10 cm, and have isolated bases of Stainless steel or aluminum that are 1 to 2 cm thick, and the covers are coupled to the base with large, often double, O-rings so that flexing of the covers is not transmitted to the base. For barometric noise control, the cover does not have to be evacuated, just vacuum tight. THis however, does not provide thermal control. Most commercial VBB sensors are not evacuated. Even the 1965 gravimeter we are operating to record earth tides is simply sealed in a cylinder of 1/2" plexiglass with double active heaters for stability. (and remote control centering, etc.) The major exception is the STS-1, the cadillac of VBB seismometers, which operates at 360 seconds with a noise level below the low noise earth model. This sensor has a thick Pyrex baseplate that is vacuum-grouted to the pier itself, and a 30cm dia glass bell jar over the sensor for the vacuum. All three components are evacuated, so both barometric and thermal (as well as humidity) control are provided. The vacuum needs to be good, but not "high", like better than 29" of Hg. Recently, the Albuquerque lab has been making a "warpless" baseplate for field re-installation of the STS-1 without the grouted pyrex plates. Photos of such can be found at: http://www.eas.slu.edu/People/STMorrissey/ stmmisc.html PSN INFO ... SLU Seismic Network and a photo of the STS-1s installed on a pier at CCM can be found through: stmiris.html St. Louis Univ. IRIS Broadband Stations I recently re-installed a set of STS-1 at a station near Nashville using the warpless baseplates; I will post the photos when I get them. OTher notes: (repeating some observations by others) 1. Evacuating any container has to be done with great care and a certaity that it will not implode: it should probably be designed for such. Atmospheric pressure on the end of a 12" diameter surface is a total force of 1700 pounds. The container should hold the vacuum indefinitely, since the pump makes vibrations, and a dial vacuum gauge is needed. For the short run of the pump, the vapors are not a problem, no more than automotive oil. While I was working on the cyclotron, we had pumps coating oil vapor on everything, which maybe helped our electrical arcing problems; however, I'm sure that any chance of oil vapor deposition around a telescope is a no-no. 2: Enclosing the seismometer means that the container base has to be rigid enough that it doesn't significantly flex with external pressure changes. To get a feel for the rigidity required, consider a barometric pressure change of 1/2" on the Hg scale of 30" = 1 atmosphere = 15 lbs/square inch. The 1/2" change is about 1/4 lb/sq.in. So if the area is 1 square foot, this is a total change of force of 36 pounds. Suppose (for the discussion), that 1/4 of this is applied just at the center of the side of the box, just like putting a gallon jug of water on it. It should not measurably deflect within the tilt sensitivity of the sensor, usually less than a micron. 3. Once you have your seis in a suitable container, you will need some method to remotely center it, like a small toy motor geared down to a fine threaded rod arranged to move a trim mass along the boom. (The motor itself could be designed to be part of the effective mass; power would have to be minimal to be able to be connected through the fine wires across the hinges). If you even partially evacuate a suitable container, the mass will float down, so remote centering would be a must. 4. You will also need to arrange a vacuum tight method of getting the electrical signals through the wall of the container. A good electronics surplus store might help with connectors. Also, a practical note: If one uses a steel container, like the domed end of a steel tank that I use for vacuum grouting, I have found that a plexiglass porthole or two to allow lighting and viewing the inside of the container can be quite handy. Especially if your "remote centering" consists of a rod through a tight feedthrough that reaches over the boom and allows manual positioning of the centering trim weights. 5. So what am I considering for the next STM design? I need to make it shorter than 11" to get it to fit into a large pressure canner. The canner is all cast aluminum, seals tight, etc. In the mean time, I'm looking at a 20 gallon aquarium with a 1/2" acrilic cover. At the 20 gallon size, some are available with 3/8" thick glass sides and bottoms for lt. $50. Regards, Sean-Thomas _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: RLLaney@....... Subject: Lehmans and cold weather/thermal convection Date: Fri, 1 Jan 1999 14:52:31 EST Meredith, Greg and Sean-Thomas: I appreciated the notes on your experiences and the suggestions concerning thermal interference. I would love to have a vault and have even considered devoting some garden space to one. But, I have a hunch that I would generate a whole new set of problems for myself. So, I think I will keep the sensors on the garage floor, but will try additional insulation and baffles. Thanks. Bob _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Arie Verveer Subject: Station near you. AutoDRM Date: Sat, 02 Jan 1999 18:56:28 +0800 Hi All, I've just finished writing a "DOS" program that converts the "AutoDRM" waveform files to a file compatible with Winquake. This means you [YOU] have access to over 1,200 professional seismograph channels, World wide. You can request Waveform data from these instruments. If you need to check out that small local event, you now can, via email. Or if you are interested in an event on the other side of the plant and would like to see the original data, you can. See http://www.iinet.net.au/~ajbv/ The test data from Alaska should be "FFT" filtered with a 1.5Hz high pass filter, (Winquake) before you can see the event. I did this to demonstrate that the data from professional seismographs suffer from all the noise problems the PSN community does. Anyhow, this is essentially my first "C" program, so if you find a major bug, please let me know. I hope to eventually locate my local events All the best Arie _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Edward Cranswick Subject: Re: Update on Dominica Date: Sat, 02 Jan 1999 12:47:54 -0700 John- Happy Holidays & New Year! We're ... back in the USSA ... Do you have the reference for Dave Hill's paper? -Edward John Lahr wrote: > Hi Wayne, > > One possible source of the noise is the P-phase itself. I was > in the Imperial Valley of California during a swarm of earthquakes > that were shallow and not far away. I could hear them before > I felt them. Some microphones were added to one channel of the > seismic recorders and it was determined that we were hearing the > P-phase and then feeling the S-phase. Dave Hill wrote a paper on > this and showed that the earth was acting like a drum head and > amplifying the vertical motion of the P-phase. > > The earthquakes sounded like thunder in the distance. > > If people are hearing events now, but they did not hear them > in the past, this could be due to a change in earthquake location, > magnitude, or focal mechanism. > > JCLahr > ################################## John C. Lahr > ################################# Seismologist > ################################ U.S. Geological Survey > ############################### Geologic Hazards Team, MS966 > ############################## PO Box 25046 > #############################/############################## > ############################/############################### > Denver, Colorado 80225-0046 ################################ > Phone: (303) 273-8596 ################################## > Fax: (303) 273-8600 ################################### > lahr@........ ##################################### > http://giseis.alaska.edu/lahr > http://lahr.org/john-jan > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@.............. with the body of the > message: leave PSN-L -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: John Hernlund Subject: Re: Station near you. AutoDRM Date: Sat, 02 Jan 1999 18:12:03 -0700 (MST) On Sat, 2 Jan 1999, Arie Verveer wrote: > Hi All, I've just finished writing a "DOS" program that converts the "AutoDRM" > waveform files to a file compatible with Winquake. Arie, What is the difference between AutoDRM files and SAC files? I usually use the latter, so I haven't come across this file type. Who is using it? ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ http://www.public.asu.edu/~hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Arie Verveer Subject: Re: Station near you. AutoDRM Date: Sun, 03 Jan 1999 10:48:48 +0800 Hi John John Hernlund wrote: > > What is the difference between AutoDRM files and SAC files? I usually use > the latter, so I haven't come across this file type. Who is using it? > It appears that "AutoDRM" outputs are given in plain text while SAC outputs are in binary(?). I assume that the plain text is given, so as to cover all possible types of data transfer. There is a good smattering of countries around the world that use AutoDRM and each of these have many professional stations connected to them. Most likely they give there outputs in SAC and AutoDRM and whatever form, the profession geophysical community needs. The good thing for a PSN user is that we can get very, nearly real time waveform data from all over the world. In Western Australia this sort of data access is marvellous, I can now confirm any possible local events. Normally I had to wait until the middle of the next month before the states Geophysical Centre would publish there findings. But since that centre is going to close down in about a year, that will be it, no more data. The seismic stations are going to be controlled from the eastern side of the country. The AutoDRM site. All the best Arie See http://www.iinet.net.au/~ajbv/ if you are interested. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Arie Verveer Subject: Update: Station near you. AutoDRM Date: Sun, 03 Jan 1999 13:32:25 +0800 Hi All, Sorry about this, but it turns out that if you have multiple requests in a AutoDrm request and the station name stays the same then the program "GSEtoPSN.exe" will overnight file name with next decoded data block. I've now fixed this, by making the extension the same as the channel name. I've latest software is at. http://www.iinet.net.au/~ajbv/ Oh well.......... Arie _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Mark Robinson" Subject: New Zealand event and links to IGNS Date: Sun, 3 Jan 1999 21:20:50 +1300 Hi folks A couple of related events near Wellington today. 4.2 and 5.1. see http://www.gns.cri.nz/news/earthquakes/latest_drum.html http://www.gns.cri.nz/news/earthquakes/recent_quakes.html regards Mark G Robinson | ZL2TOD | other@............... Box 8770, Auckland 1035, New Zealand Phone +64-9-846-3296 | Fax +64-9-849-7408 ------------------------------------------------ 03 Jan 1867 Te Whiti released from prison in the South island. 03 Jan 1959 Alaska becomes the 49th state of the U.S.A. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: barry lotz Subject: Re: Capacitors Date: Sun, 03 Jan 1999 09:51:24 -0800 Brett & Fred Thanks for your capacitor input. I haven't checked your links yet Brett. I have been using Don Lancaster's Active filter cookbook to design my instrument filtering. I just went from a 4 pole Butterworth lowpass(10 hz) to a 6 pole. I now seem to be getting more periods of 10 hz oscillations. I guess they are triggered by transient input or/and low damping? They are configured similar to Larry's board but with different values. Currently all the caps are equal (0.15u) . To all: Would decreasing the feedback cap slightly reduce the oscillations? Regards Barry _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: macsmith Subject: Pacific Rim Quakes Date: Sun, 03 Jan 1999 08:12:02 -1000 here's an interesting news report on the recent Pacific rim quakes: http://www.news.bbc.co.uk/hi/english/world/asia-pacific/newsid_247000/247363.stm _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: S-T Morrissey Subject: VBB and filters Date: Sun, 3 Jan 1999 14:04:57 -0600 (CST) Barry, I am uncertain where you are using the filter, why, or why you seem to have an undamped response. As I recall, you are using the latest triple feedback VBB configuration, as used for the STS-1, the Guralps, and the STM-8. I justed looked at the transfer function I have here for your 6" design, based on some of the parameters you sent some time ago. It has an r = 234 000 V/m/sec. G=12.65 N/A; M=0.35kg; Cp=24uf; Rp=1 meg ohm; RI=0.107 meg ohm, and Ti= 80 seconds. and To = 1.7 seconds. ... and looks like it should be quite stable, with Tn = 90 seconds. (most of the numbers are defaults from the STM-8; you can update them). It is important to know the sensitivity of your displacement transducer to properly use the Mathcad model of the transfer function. The resulting response quite accurately reflects what you get, as I have previously shown in the calibration data. The transfer function will indicate an oscillator if either end of the flat velocity response has an inflection in it. If the damping term zeta is much less than 0.6, the oscillation will be at the effective period, like 20 to 100 seconds, depending on your configuration. If the response has a bump at the short period end, several instabilities are possible due to "out of range" selection of the feedback components, like the value of Cp is too large or r is too small or too large. The response should be quite flat. The usual cause of oscillation or ringing is because r is too large. As Brett's effort shows, there is little in the loop to damp the high-end oscillation if the loop has the gain to oscillate there. To determine the actual value of r, the gain(s) of the displacement amplifier(s) need to be known; this is readily determined from the elements in their feedback per your schematic. Like for one of the VBBs here, the transducer is 58mv/micron, the first amp is x3, the second is x10, so the value used in the Mathcad function (which uses MKS units) is 1 740 000 volts/meter. (1.74 million V/m sounds hugh, but it is a reality of the VBB). My old transfer function response indicates an oscillation at 300-400hz, which I can hear, but I killed it with appropriate low-pass filtering (a larger feedback capacitor) in the 2nd X10 displacement amp. To control (= live with) local cultural noise (= the street) I use 2-pole filters at 2 hz (or so) in the line driver amplifier, which is a high-pass (1000 second) output of the VBB signal. These are outside the loop, so only affect the "cosmetic" appearance of the data, reducing the local noise so I can see microseisms and teleseisms. So determining their parameters is mostly a trial and error activity. Lancaster's book is a good resource; it shows different damping options for the filters on pages 75-77; you might want to use what he calls the "compromise" between best delay and flattest response, which is (referring to the NASA Active filter Design Handbook (SP-5104; 1977), a "Legendre" response, somewhat between a Bessel and a Butterworth response. Anything with ripple in the passband (the Chebyshev filter) will have a sharper cutoff, but will ring in response to an impulse. Regards, Sean-Thomas _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: barry lotz Subject: Re: VBB and filters Date: Sun, 03 Jan 1999 13:24:23 -0800 Hi Sean Thomas Thanks for your response. I'll spend some time reviewing the content. I'm not having a problem with the VBB, it's with the Lehman when it comes into the house. The sensor is in the garage (~50 ' away) and when it comes in on a shielded cable I filter it with a 6 pole low pass. The circuit inside was a 30k load resistor followed by a noninverting 10X preamp, 6 pole butterworth, 1 pole 0.008 hz highpass, 18X amp, and 10 hz single pole lowpass, and computer. I put a single pole 10hz low pass just as the cable comes into the house and it seems to help. I have more problems during the day, probably traffic. On a separate subject, I finally ordered some parts from digikey to take my VBB off the solderless bread board. Regards Barry _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Marchal van Lare Subject: TEST - please IGNORE Date: Sun, 3 Jan 1999 17:07:18 -0500 TEST= _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: RADIOTEL@....... Subject: LEHMAN RESPONSE Date: Sun, 3 Jan 1999 23:22:42 EST Any List members I have just finished a Lehman seismograph, placed it in a plywood enclosure with form insulation on sides and top and a 10 watt light bulb. The seis is sitting on a cement slab that about 6 X 3 Feet and 4 inches deep. I am temporarily using a tupper-ware bowl filled with brake fluid to dampen the boom. I have the seis connected to an amp with about 1800 gain and a 15Hz filter. Watching the trace on the screen, there is a slow undulation wave pattern (almost straight across the screen). My problem (at least I assume it is a problem) is when I walk on the ground around the seis it generates a very large undulating wave pattern going off the screen and slowly returning until it finally returns to the wave pattern where it was before detection. I have tried minimum damping and maximum damping. Based on a geophone that I installed recently I assume this wave pattern is not normal. The geophone has essentially a straight wave pattern until detection and then the wave is closely spaced in the traditional pattern routinely seen from other. Thanks Jim Allen _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: meredith lamb Subject: Re: LEHMAN RESPONSE Date: Sun, 03 Jan 1999 23:14:10 -0700 RADIOTEL@....... wrote: > My problem (at least I assume it is a problem) is when I walk on the ground > around the seis it generates a very large undulating wave pattern going off > the screen and slowly returning until it finally returns to the wave pattern > where it was before detection. I have tried minimum damping and maximum > damping. Based on a geophone that I installed recently I assume this wave > pattern is not normal. The geophone has essentially a straight wave pattern > until detection and then the wave is closely spaced in the traditional pattern > routinely seen from other. > Thanks > Jim Allen > Jim, What is the period of the undulations? Could be long period microseisms....mine in Denver are running roughly 6-8 seconds. Regardless......congratulations on building the seismo......hope future adjustments improve it to your satisfaction. Meredith Lamb _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: meredith lamb Subject: Re: LEHMAN RESPONSE Date: Sun, 03 Jan 1999 23:29:01 -0700 Jim, Forgot to add.....of course walking around a seismo will make it tilt.....that is normal. With time you will recognize all the floor and car and etc., tilting "noise" as such. What you get out of the total system without inducing tilt is what counts. You should see activity all the time with the gain high enough....adjust it to the least gain, but, enough to see some activity most of the time on the computer screen. Then......you can adjust the damping oil levels. Damping with oil I've never done, but I suppose the only way is alot of experimentation....filling, lowering. It could be that you may need alot more fluid than you've already tried. Again.....Congratulations. Meredith Lamb _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "David A. Nelson" Subject: 2 M5+ New Zealand events Date: Mon, 4 Jan 1999 22:12:57 +1300 for those of u not on the PSN events list some info on the 2 recent NZ events........ M5.7 Near Rotorua upper central Nth Is NZ 144 km deep on the subducting slab under the volcanic zone M5.4 NW of Wellington City Sthrn end of the Nth Island (epic in Cook Strait) this 54 km deep event is also part of the subduction zone but at its southern end this region around cook strait has very complex tectonics as its the boundary between the subduction zone under and to the north of the Nth Island and the oblique slip zone in the south island that has thrust up the southern alps. the oblique slip Alpine Fault has a 3:1 ratio for every 3 metres of horizontal movement there is 1 metre of vertical movement. The subduction under the North Island is ~ 40 mm (4 cm 2 odd inches / yr) the convergence of the pacific plate against the indo-australian plate along the South Is's Alpine Fault is ~ 30 mm (3 cm 1.25 " / yr) Dave Co-ordinator: New Zealand Public Seismic Network Dave A. Nelson ZL4TBN 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm IF there indeed are other parallel universes... I can now rest in the knowledge, that in at least one of them, I am filthy rich and drive a red Ferrari _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: robert barns <75612.2635@..............> Subject: LEHMAN RESPONSE Date: Mon, 4 Jan 1999 10:36:16 -0500 Jim Allen, My Lehman behaves pretty much as you describe. It sits on the concrete= floor of my basement. If I walk within 5 feet of it, I see a fairly larg= e signal. Within 2 feet, it goes off scale. A Lehman is very sensitive to tilt and these signals are undoubtedly du= e to bending of the concrete floor. Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Norman Davis WB6SHI Subject: Re: LEHMAN RESPONSE Date: Mon, 04 Jan 1999 08:03:55 .. > A Lehman is very sensitive to tilt and these signals are undoubtedly due >to bending of the concrete floor. >Bob Barns I'll drink to that. I had mine in the back of the garage. On the outside is sat on a slab that had been poured around the outside like a sidewalk. Whenever the ground got wet and swelled the slab would tilt and eather bottom out the lehman or run it out of the coil. I moved it into the garage and that stoped that. Next project... Slab buy it self away from the whole house and garage. Norman Davis WB6SHI Shingle Springs, Ca normd@............. http://www.directcon.net/normd/index.htm _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: John Lahr Subject: Re: Update on Dominica Date: Mon, 4 Jan 1999 12:58:27 -0700 (MST) Hi Ed, Welcome back! The Hill reference is: BSSA, August 1976, v 66, pg 1159-1172. John _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: S-T Morrissey Subject: Lehman tilt sensitivity Date: Mon, 4 Jan 1999 14:31:55 -0600 (CST) Jim, Congratulations! Some thoughts on your Lehman horizontal seismometer: (I have edited together some previously posted information; you may already have seen this) The Lehman is a "real-world-boys'" version of the Columbia-Sprengnether S5000 long-period, of which there are over 1000 in use; Meredith has a set; but I think there are others out there in the PSN. I have scanned a pictorial drawing of it to my web site on the psn info page. http://www.eas.slu.edu/People/STMorrissey/ stmmisc.html Some formulae of interest for the horizontal pendulum: (assuming that the restoring force by the hinges and/or pivot are minimal): The natural period: Tn = 2*pi*sqrt(l/(g*sine i)) where l is the boom length in cm, g=980cm/sec^2, i is the angle that the boom makes wrt the horizontal, measured in radians, (where sine i = i). For example, a 40 cm boom hanging vertically as a simple pendulum ( an angle of 90 degrees) has a period of 1.3 seconds, likr a SG. (a one second clock pendulum is 24.8 cm). When tilted horizontally to about 4 degrees, the period is 5 seconds. At about a 1 degree angle (sine i = 360deg/(2*pi) ), it is 10 seconds, and at about 0.23 deg. it is 20 seconds. So the period is changing with inverse of the square root of the angle, which is why long periods are so unstable. But unstable also means sensitive to smaller ground motions, which is why geophones fall short for LP sensitivity. So the stability question for a horizontal seismometer depends mostly on the mechanical period and the working range of the velocity coil; ie how far it can drift before touching. The old S5000s that I operate at 15 seconds in vaults rarely need to be recentered. (the working range is +,- 5mm for these horizontals). Years ago we ran them at 30 seconds, and had to center them about every other month. I understand that most Lehmans operate at 10 seconds give or take, but that some can be workable at 20 seconds with more frequent adjustment. Of course, the quality of the base, the rigidity of the boom support, and the stability of the pier then become a major concerns. Also, thermal effects on the base and frame of the instrument can cause major drifting. I don't have any information on the actual sensitivity of the Lehman designs that are in use. But for comparison to the S5000s I am operating at 15 seconds, which have a 32 tpi (turns per inch) leveling screw, about 1/100th turn (the leveling knob happens to have about a 100 mm circumference) is about 16 microradians, and moves the mass about 1mm. One can calculate how much the mass should move when tilted at a given period. This is a useful calculation for the tilt sensitivity of the horizontal pendulum (which can be used to calibrate the displacement detector) z = (g * Tn^2 / 4 * pi^2) * phi where z is the horizontal displacement of the mass, Tn is the natural period, and phi is the tilt of the base at right angles to the boom, again measured in radians. From my example above about the S5100: the base is 500 mm, so the tilt from 1/100 turn of the screw ( which is 0.008 mm) is 0.008/500 = 0.000016 radian. If Tn = 15 seconds, the mass will move 0.88 mm, which is close to my approximation. Evaluating this on my STM-8 horizontal, with l = 40 cm, and Tn = 10 seconds, 1/12 turn of the 28 tpi leveling screw is 0.9mm/12 = 0.075mm; the base width is 130mm, so the tilt is 0.075/130 = 0.00058 radians. This calculates to an offset of the mass of 1.43 cm, which is about what I measure. At 20 seconds, the offset is about 4 times, or 5.7 cm. Two points are clear: the stability is inversely proportional to the square of the period, or conversely, the sensitivity increases with square of the period. And the amount of the mass is not a consideration for the period or the displacement sensitivity. As long as it is significantly greater (like 10x) than the weight of the boom, it will work. And a final thought: I would forgo the hydraulic damping and simply use resistive damping with the main coil by shunting it with an appropriate resistor, which is what is done in modern seismology. The value of the resistor can be readily calculated; the voltage loss of the resistive damping is easily made up for with additional gain of the preamplifier. You can also add a separate moving coil/ magnet to accomplish the damping. Some LP high-gain sensors have a 100 000 ohm signal coil, which won't pass enough current to damp the seis, and a standard 500 ohm coil, for which the damping is calculated. For your fconvenience, I will re-post the formulas for calculating damping with a moving coil. One last note: since the LP horizontal IS so tilt sensitive, and will wander off scale at most "practical" sites, one could consider using a single high-pass filter at the input to the recording amplifier, like 1000 uf with 1 megohm, which will remove the long period drift that even a moving (velocity) coil will produce, and allow higher gains in the 1 to 20 second range. regards, Sean-Thomas _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: S-T Morrissey Subject: Lehman damping Date: Mon, 4 Jan 1999 14:33:14 -0600 (CST) Here is an edited repeat of a previous mote about damping seismometers: Re electromagnetic damping: Most moving coil seismometers only use resistive damping. If properly calculated, no other damping is needed or should be used. Damping is generally expressed in relation to what is needed for "critical" damping, which means that after a step input, the output returns to a zero output voltage as rapidly as possible without overshooting. This damping has a value of 1. But it has a price, namely significant loss of the signal in the damping resistor. So generally damping is set at 0.8 of critical, which cuts the loss by about half, but the overshoot to an impulse input is minimal. Much less than 0.8, the natural period of the seismometer will dominate the response. On the other hand, if a fairly broad response is desired, and the seis and the amplifier have enough output and/or gain, damping as high as 2 can be used. Note that actually calculating the proper resistor depends on how much you know about the geophone or seismometer. The manufacturers data will sometimes even give the value for critical damping. But if the geophone is a mystery device, a generally good approximation is to measure the resistance of the coil and use that value for the damping resistor. To calculate the value of the damping resistor to be used, one first has to know or determine the open circuit damping, called Bo. It is the mechanical air-dashpot function of the coil movement, and is often listed in the specifications for the seismometer. For most seismometers, it ranges from 0.2 to 0.4, where a value of 0.8 is for critical damping. It can also be determined from the logrithmic decrement of the free oscillations of the undamped seismometer. (write for details on logrithmic decrement; you need a recorder or oscilloscope to do it. It involves measuring the successive amplitudes of undamped oscillations). Then the motor constant and resistance of the main coil have to be determined or found in the specifications. The electromagnetic damping Bem needed is determined by subtracting the Bo from the required total Bt. Bem = Bt - Bo (If you don't know your Bo, use a value of 0.3) Then the damping resistor is calculated by: Bem = G^2 / (2*omega*M*(Rs + Rd), or Rd = [G^2 / (Bem*2*omega*m)] - Rs Where Bem is the electromagnetic damping, G is the main coil constant, omega is the angular frequency, equivalent to 2*pi/Tn, where Tn is the natural period, and M is the mass. For an L4-C, with a 5500 ohm coil, with G = 270 V/m/sec, Bo = 0.27, we want Bt to be 0.77, so Bem = 0.5, M = 1 kgm, omega = 2*pi, we calculate a damping resistor Rd of 6102 ohms for critical damping. For an S5000 Long Period Seis, with a 500 ohm coil, G = 100 V/m/sec, Bo = 0.1, we want a flatter response with Bt = 1, so Bem = 0.9, omega = 2*pi/15 (seconds), M = 11 kg, we calculate a resistor of 705 ohms for Bt = 1 (the LP is over damped for a broader response). For an HS-1 4.5 hz geophone with a 1250 ohm coil, G = 41 V/m/sec, and Bo = 0.28; we want critical damping with Bt = 0.8, so Bem = 0.52, omega = 2*pi*4.5 (hz), M = 0.022kg, we calculate Rd = 1348 ohms. This method of damping is the only method currently being used on velocity sensors. The method is so exact that often the resistor for Rd is installed inside the smaller geophones at the factory. Metal-film resistors are used for lower noise. When one is connecting a seismometer to an amplifier with a low input impedance Ra, that value is in parallel with the seismometer, so must be taken into account. So if Ra = 10k ohms, and Rd is to be 5k ohms, the actual resistor to be used is Rs = Rd*Ra/(Ra-Rd), or in this case Rs = 10k ohms. Generally very high input impedance amplifiers are not used because of noise considerations, so this detail is often overlooked. Unfortunately I have no idea what the constants for a Lehman might be. I note that the coil is 1/4 pound of # 34 wire which has 8310 feet per pound and 2168 ohms per pound at 20 deg.C. So assuming the coil is about 500 ohms, I would try a damping resistor of about 1000 ohms, unless you already know the constant G of the main coil and can calculate the value. With this type of damping, the response should be flat to velocity from roughly the natural period to whatever low-pass filter you have in your amplifier. (BTW another place to check to see if the shorter p-wave phases are being filtered out). The drawback of resistive damping, other than the loss of part of the signal from the coil (made up for with less attenuation in the recording circuitry) is that it is dissipative, and makes noise. This is the reason it is not used in the VBB configuration, where the damping is a dynamic process in the feedback loop. The noise from the damping resistor is primarily Johnson or thermal noise, which can be estimated, as well as 1/f noise. A low noise metal film resistor does help. This noise is generally not a problem for most seismometer sites. Regards, Sean-Thomas _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: RADIOTEL@....... Subject: Re: Lehman tilt sensitivity Date: Mon, 4 Jan 1999 23:29:25 EST Meredith, Norman,Bob and Sean-Thomas Your suggestions and experiences that you shared were very helpful. I had not realized that the lehman would be so sensitive (even showing those microseisms). Next weekend I will connect a varible resistor (10 turn 0 -30k variable wire-wound resistor) across the coil which is 9.7k. That certainly should dampen it adequately (if I am reading the formulas given in Sean- Thomas' response, right? I will also follow the recommendation by Sean-Thamas to use a high pass filter to help remove the long period drift. Jim Allen radiotel@....... _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Francesco" Subject: R: Station near you. AutoDRM Date: Tue, 5 Jan 1999 12:37:09 +0100 Hello Arie. I had download your C programm for AUTODRM, but I'haven't understand a = thing. I have required a file to PIDC ORG for example. I have received the = mail, with inserted the file in GSE2.0 format, but not attached. =20 This way, I have a file of mail (uencode, ecc.ecc.) but not a named file = available to convert with your program. =20 How do I have to do? =20 Regards Francesco Nucera - I.ES.N. PSN ITALY
Hello Arie.
I had download your C programm for = AUTODRM, but=20 I'haven't understand  a thing.
 
I have required a file to PIDC ORG = for example.=20 I have received the mail, with inserted the file in GSE2.0 format, but = not=20 attached. 
This way, I have a file of mail (uencode, ecc.ecc.) = but not=20 a named file available to convert with your program. 
How do I = have to=20 do? 
Regards
 
Francesco Nucera -  = I.ES.N.  PSN=20 ITALY
From: Arie Verveer Subject: Re: R: Station near you. AutoDRM Date: Tue, 05 Jan 1999 21:23:02 +0800 Hi Francesco > I had download your C programm for AUTODRM, but I'haven't understand a thing.I have required > a file to PIDC ORG for example. I have received the mail, with inserted the file in GSE2.0 > format, but not attached. > This way, I have a file of mail (uencode, ecc.ecc.) but not a named file available to convert > with your program. > How do I have to do? If your mail program has an edit feature then you could open the AutoDRM message, mark the text, and then go to your edit menu and press the copy option. Then go to a text editor and paste the document. Then you should be able to save the data as a file. This may be one solution. Are you running Eudora lite ? I do understand its a strange way to get data but once you master the technique its really worth it. This is especially true when you are in an area where data is hard to get. If you have any more troubles please let me know. Its worth persevering with the AutoDRM, especially the method of getting the data. All the best, a please let me know how it worked out. Arie Today I used the AutoDRM to confirm a small event as coming from a mining area 140km from my station. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: RADIOTEL@....... Subject: LEHMAN RESPONSE Date: Tue, 5 Jan 1999 22:13:31 EST Meredith, Norman, Bob and Sean-Thomas My new lehman picked up its first earthquake today. Meridith,Norman and Bob's suggestions that the undulations and tilt were normal was correct. I did need more damping as Meridith suggested and I took Sean-Thomas' suggestion to get rid of the oil damping. The installation of resistive damping made a world of difference especially using a variable resistor which I can adjust from inside the house while the seismo is outside. When I dont get near the seismo I now find that the wave trace is essentially straight. Next weekend I plan to add a 1000 uf cap and 1 meg res. filter to the amp input to ensure that drift will be minimal. Your help and encouragement was invaluable. Jim Allen radiotel@....... _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Arie Verveer Subject: Year 2000 Calendar Date: Wed, 06 Jan 1999 14:21:50 +0800 Hi All, I was looking up some information on the year 2000 calendar dates when I came across this interesting bit information. The years 1876, 1944, 1972, 2000, 2028 all have the identical calendar. The 1st of those years all start on a saturday and years following are in the calendar sequence. So just set your old computer clock to -28 years and all will be well? Just remember to add 28 years. Just an observation. - Arie _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Wayne Abraham J73WA Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 07:51:35 -0400 Arie I thought the calendar repeated itself every 11 years. Wayne Arie Verveer wrote: > Hi All, > I was looking up some information on the year 2000 calendar dates > when I came across this interesting bit information. > > The years 1876, 1944, 1972, 2000, 2028 all have the identical calendar. > The 1st of those years all start on a saturday and years following are in the > calendar sequence. > So just set your old computer clock to -28 years and all will be well? > Just remember to add 28 years. > > Just an observation. - Arie > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@.............. with the body of the > message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Brett Nordgren Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 09:25:58 -0500 Arie, I may be way wrong, but I thought, unlike the other four years you mention, that 2000 is *not* going to be a leap year. Does anyone remember for sure? Brett At 02:21 PM 1/6/99 +0800, you wrote: >Hi All, >I was looking up some information on the year 2000 calendar dates >when I came across this interesting bit information. > >The years 1876, 1944, 1972, 2000, 2028 all have the identical calendar. >The 1st of those years all start on a saturday and years following are in the >calendar sequence. >So just set your old computer clock to -28 years and all will be well? >Just remember to add 28 years. > >Just an observation. - Arie > > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@.............. with the body of the >message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: bc Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 09:49:42 -0500 At 09:25 AM 1/6/99 -0500, you wrote: >Arie, > >I may be way wrong, but I thought, unlike the other four years you mention, >that 2000 is *not* going to be a leap year. Does anyone remember for sure? > >Brett Typically century marks are not leap years. I'm not absolutely sure about 1000 year marks but i don't remember them being treated special so my best educated guess is that it is not a leap year. However, I'm not sure I'm actually following this thread? Is it the contention that by advancing one's date to the year 2028 that we will avoid a year 2000 problem? If that's the assumption than I'm afraid its incorrect. If not, my apologies for sticking my nose in where it doesn't belong (a bad habit I seem to have) bc > > >At 02:21 PM 1/6/99 +0800, you wrote: >>Hi All, >>I was looking up some information on the year 2000 calendar dates >>when I came across this interesting bit information. >> >>The years 1876, 1944, 1972, 2000, 2028 all have the identical calendar. >>The 1st of those years all start on a saturday and years following are in the >>calendar sequence. >>So just set your old computer clock to -28 years and all will be well? >>Just remember to add 28 years. >> >>Just an observation. - Arie >> >> >> >>_____________________________________________________________________ >> >>Public Seismic Network Mailing List (PSN-L) >> >>To leave this list email listserver@.............. with the body of the >>message: leave PSN-L > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@.............. with the body of the >message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: bzimmerman@............ Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 09:59:03 -0500 (EST) The calender on my desk shows 29 days in February 2000. Brian Zimmerman _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: bc Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 10:19:47 -0500 At 09:59 AM 1/6/99 -0500, you wrote: > >The calender on my desk shows 29 days in February 2000. > >Brian Zimmerman I stand corrected on 2 counts. First, I understand the thread now. Its to correct OLD calendar clock systems to just get the correct day of the week. Second, it is a leap year. The following is from Leap Year FAQ at http://aa.usno.navy.mil/AA/faq/docs/faq1.html The Rule According to the Gregorian calendar, which is the civil calendar in use today, years evenly divisible by 4 are leap years, with the exception of centurial years that are not evenly divisible by 400. Therefore, the years 1700, 1800, 1900 and 2100 are not leap years, but 1600, 2000, and 2400 are leap years bc _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Canie Brooks Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 08:29:22 -0800 At 09:25 AM 1/6/99 -0500, Brett Nordgren wrote: >Arie, > >I may be way wrong, but I thought, unlike the other four years you mention, >that 2000 is *not* going to be a leap year. Does anyone remember for sure? > >Brett I'll also add my 2 cents worth - I'm a programmer and this is one of the issues creating part of the 'millenium bug' ! The year 2000 IS a leap year and lots of programs, operating systems don't recognise it as such.. One of the big things to fix... Canie > > >At 02:21 PM 1/6/99 +0800, you wrote: >>Hi All, >>I was looking up some information on the year 2000 calendar dates >>when I came across this interesting bit information. >> >>The years 1876, 1944, 1972, 2000, 2028 all have the identical calendar. >>The 1st of those years all start on a saturday and years following are in the >>calendar sequence. >>So just set your old computer clock to -28 years and all will be well? >>Just remember to add 28 years. >> >>Just an observation. - Arie >> >> >> _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Wayne Abraham J73WA Subject: [Fwd: MessageShip Response to MSG_ID=All] Date: Wed, 06 Jan 1999 15:46:54 -0400 Arie This is a message I received when I tried a request from autodrm. Just thought I would pass it on. Wayne From: John Hernlund Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 12:56:44 -0700 (MST) On Wed, 6 Jan 1999, bc wrote: > At 09:25 AM 1/6/99 -0500, you wrote: > >I may be way wrong, but I thought, unlike the other four years you mention, > >that 2000 is *not* going to be a leap year. Does anyone remember for sure? > >Brett > Typically century marks are not leap years. I'm not absolutely sure about > 1000 year marks but i don't remember them being treated special so my best > educated guess is that it is not a leap year. However, I'm not sure I'm > actually following this thread? Is it the contention that by advancing > one's date to the year 2028 that we will avoid a year 2000 problem? If > that's the assumption than I'm afraid its incorrect. If not, my apologies > for sticking my nose in where it doesn't belong (a bad habit I seem to > have) I think the only rule for leap years is an extra day in February (the 29th) every four years. This is because the year is approximately 365 and 1/4 days long. I think we also have leap seconds every year, but I am not sure if that is just rumor or truth... For those using WWV though, these leap seconds could be a hassle; that is, if they exist. Also, the only thing special anyone is doing for 2000 that I have heard about is going to Jerusalem and vowing to die in a violent fight to prepare the way for the second coming... I have a feeling that this type of thing will be a problem for governments worldwide this year... ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ http://www.public.asu.edu/~hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Greg Subject: Re: [Fwd: MessageShip Response to MSG_ID=All] Date: Wed, 06 Jan 1999 13:27:53 -0700 Wayne Abraham J73WA wrote: > This is a message I received when I tried a request from autodrm. Just > thought I would pass it on. I'm not Arie, but I'm guessing you wanted the binary file sent to you directly? If so it's possible you requested it wrong. It looks like the server put it on a FTP server for you to download. From what it says, try this: ftp into pidc.org username anonymous with an email address for the password cd to /pub get 5264365.msg.Z Then you gotta get tar for DOS unless you have Linux or Solaris or something. The Z means the file is compressed. Check out gnu.org if you need it. It's probably in lots of other places also. It is there. I just checked. Good luck, Greg _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Greg Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 13:34:48 -0700 John Hernlund wrote: > long. I think we also have leap seconds every year, but I am not sure if that > is just rumor or truth... For those using WWV though, these leap seconds > could be a hassle; that is, if they exist. I found this just now: http://www.dtic.mil/doctrine/jel/doddict/data/l/03463.html "Leap Second (DOD) A second of time that is added to or removed from Coordinated Universal Time (UTC) to keep UTC within 0.9 seconds of UT1 (see Universal Time). Leap Seconds are normally introduced at the end of June or December if required. The decision to introduce a Leap Second is announced by the International Time Bureau (Bureau International de l'Heure, or BIH) approximately eight to ten weeks in advance. See also Coordinated Universal Time." Neat little military biased dictionary. I remember hearing other people talking about adding them at one of my former jobs. I've never been involved myself. I would think that WWV would handle this pretty much automatically. Same for GPS. It might take a full minute or two for the computer to catch up to the signal time though. ,Greg _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Subject: Re: Year 2000 Calendar Date: Wed, 6 Jan 1999 14:49:38 -0600 (EST) See http://tycho.usno.navy.mil/leapsec.html for a detailed description of the leap second and how it affects GPS wwV etc. Jim Hannon http://soli.inav.net~jmhannon/ 42,11.90N,91,39.26W WB0TXL On Wed, 6 Jan 1999, Greg wrote: > John Hernlund wrote: > > > long. I think we also have leap seconds every year, but I am not sure if that > > is just rumor or truth... For those using WWV though, these leap seconds > > could be a hassle; that is, if they exist. > > I found this just now: > http://www.dtic.mil/doctrine/jel/doddict/data/l/03463.html > > "Leap Second > > (DOD) A second of time that is added to or removed from Coordinated > Universal Time (UTC) to keep UTC within 0.9 seconds of UT1 (see > Universal Time). Leap Seconds are normally introduced at the end of June > or December if required. The decision to introduce a Leap Second is > announced by the International Time Bureau (Bureau International de > l'Heure, or BIH) approximately eight to ten weeks in advance. See also > Coordinated Universal Time." > > Neat little military biased dictionary. I remember hearing other people > talking about adding them at one of my former jobs. I've never been > involved myself. > > I would think that WWV would handle this pretty much automatically. Same > for GPS. It might take a full minute or two for the computer to catch up > to the signal time though. > > ,Greg > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@.............. with the body of the > message: leave PSN-L > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Greg Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 14:14:31 -0700 jmhannon@............. wrote: > > See http://tycho.usno.navy.mil/leapsec.html for a detailed description of > the leap second and how it affects GPS wwV etc. That page mentions that GPS is not corrected for some reason, but it doesn't mention WWV. I did find that also. WWV is corrected (I hope that is correct) ;) GPS is off by about 13 seconds right now. http://www.bldrdoc.gov/timefreq/pubs/sp432/s_appa.htm What time is it? ;) ,Greg _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Kevin J. Rowett" Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 13:32:45 -0800 >I would think that WWV would handle this pretty much automatically. Same >for GPS. It might take a full minute or two for the computer to catch up >to the signal time though. WWV distributes time on the UTC scale, which includes leap second insertions. GPS time is not on the UTC scale because it doesn't insert any (more) leap seconds. The GPS messages do contain both an indication that a leap second will be inserted into the UTC scale at the end of the month, and how many have been inserted so far. This allows a GPS receiver to produce a pretty accurate estimate of UTC directly. I noted any more leap seconds because when GPS time was first synchronized in 1980, 19 leap seconds were already inserted, and GPS included those. So GPS time is now 13 seconds ahead of UTC. KR _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Greg Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 14:40:06 -0700 "Kevin J. Rowett" wrote: > So GPS time is now 13 seconds ahead of UTC. Larry C., is SDR using the offset in it's time with your GPS reciever? It would probably be pretty obvious if it's not. It would be kinda fun to watch it handle the leap second as it happens, if it does look at that. ,Greg _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Kevin J. Rowett" Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 14:04:37 -0800 At 01:40 PM 1/6/99 , you wrote: >"Kevin J. Rowett" wrote: > >> So GPS time is now 13 seconds ahead of UTC. > >Larry C., is SDR using the offset in it's time with your GPS reciever? >It would probably be pretty obvious if it's not. It would be kinda fun >to watch it handle the leap second as it happens, if it does look at >that. It was fun, especially since the USNO clock 'tick.usno.navy.mil' didn't update properly (tick did, clepsydra.dec.com didn't). BTW, the proscribed insertion method is to duplicate the last second of the month, hence the leap second was in 1998, *not* 1999. Some clocks will display 23:59:59 23:59:59 24:00:00. Some display the dup :59 as :60. You'll have to wait 17 months and a few days now to see the next one mostly likely. Check with IERS in July. KR _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Larry Cochrane Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 14:05:22 -0800 At 02:40 PM 1/6/99 -0700, you wrote: >"Kevin J. Rowett" wrote: > >> So GPS time is now 13 seconds ahead of UTC. > >Larry C., is SDR using the offset in it's time with your GPS reciever? >It would probably be pretty obvious if it's not. It would be kinda fun >to watch it handle the leap second as it happens, if it does look at >that. > >,Greg When I added the GPS support too SDR I didn't notice a 13 second offset problem, so the ONCORE GPS receiver must be handling this.... -Larry Cochrane Redwood City, PSN _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Kevin J. Rowett" Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 15:23:48 -0800 >>> So GPS time is now 13 seconds ahead of UTC. >> >>Larry C., is SDR using the offset in it's time with your GPS reciever? >>It would probably be pretty obvious if it's not. It would be kinda fun >>to watch it handle the leap second as it happens, if it does look at >>that. >> >>,Greg > >When I added the GPS support too SDR I didn't notice a 13 second offset >problem, so the ONCORE GPS receiver must be handling this.... It does, as long as it has satt lock, and the ephemeris acquired during the leap second event. Most GPS receivers output time (the PVT message) on the UTC scale. You have to fiddle with them in propietary ways to get them to output the true GPS time. KR _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: John Hernlund Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 16:47:05 -0700 (MST) On Wed, 6 Jan 1999, Kevin J. Rowett wrote: > So GPS time is now 13 seconds ahead of UTC. I wonder what happens to files that are archived from seismograph stations receiving GPS time correction then, are they all normalized to UTC after retrieving the data??? ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ http://www.public.asu.edu/~hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Kevin J. Rowett" Subject: Re: Year 2000 Calendar Date: Wed, 06 Jan 1999 16:05:56 -0800 At 03:47 PM 1/6/99 , you wrote: >On Wed, 6 Jan 1999, Kevin J. Rowett wrote: >> So GPS time is now 13 seconds ahead of UTC. > > I wonder what happens to files that are archived from seismograph stations >receiving GPS time correction then, are they all normalized to UTC after >retrieving the data??? I think some confusion exists here. GPS receivers normally issue time messages (the PVT message) using the UTC scale, which includes leap seconds. The time "flowing down" from the satt is on the GPS time scale which doesn't include leap seconds past 1980. The receiver "subtracts" the number of leap seconds (it's a lot more complicated than this, read the GPS spec!) presently indicated in the difference between UTC and GPS time. As Larry noted, his use of the Moto oncore GPS receiver is the normal one -> UTC time scale. The original point was WWV and GPS run on different time scales. The subsequent point is that GPS receivers normally are the devices that apply the correction. Now, if you want to talk about being able to set an alarm clock for a future event, that's an interesting discussion. What interval should I set the timer for? :-). KR _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Walt Williams " Subject: PSN-L: Solar Super Flares Date: Wed, 6 Jan 1999 17:20:43 -0800 All, Little off-topic post, but very interesting. FYI. Cross posted from the Search for ExtraTerrestrial Intelligence - League (SETI-L) open list. Walt Williams, 99.01.06 PSN Stn 63 dfheli@.............. ============================================ Date: Wed, 6 Jan 1999 22:39:40 GMT From: Ron Baalke To: astro@.................... Subject: Yale Astronomers Study Superflares on Stars Just Like Our Sun Sender: owner-astro@......................... Reply-To: Ron Baalke Subject: Re: Year 2000 Calendar Date: Thu, 07 Jan 1999 09:49:35 +0800 Hi All, The year 2000 is a LEAP year. Our passage through the seasons is called a "tropical" year of 365.24.. days long. This awkward fraction 0f 0.24... days is nearly a 1/4 of a day. So Pope Gregory on the advice of the astronomer Clavius adopted this solution. Every forth year we add a day (leap year). To correct for the errors in the fraction we make the century years that are divisible by 400 a leap year. (There is also a 4000 year correction). So 1900 was not a leap year but 2000 will be a leap year. Calendars that are the same: Look identical (other than festivals) 1) ..,1989, 1995, 2006, 2017 (not a leap year) 2) ..,1990, 2001, 2007, 2018 "" 3) ..,1991, 2002, 2013, 2019 "" 4) ..,1997, 2003, 2014, 2025 "" 5) ..,1998, 2009, 2015, 2026 "" 6) ..,1999, 2010, 2021, 2027 "" 7) ..,2005, 2011, 2022, 2033 "" 8) ..,1928,1984, 2012, 2040 (LEAP YEAR) 9) ..,1968,1996, 2024 L 10) ..,1952,1980, 2008,2036 L 11) ..,1908,1964, 2020,2048 L 12) ..,1948,1976, 2004,2032 L 13) ..,1904,1960, 2016,2044 L 14) ..,1944,1972, 2000,2028 L ******** Ragards Arie _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: John Hernlund Subject: Re: Year 2000 Calendar: simple algorithm for leap yrs. Date: Wed, 06 Jan 1999 19:25:46 -0700 (MST) A simple algorithm for determining leap years would simply be to see if the year is divisible by four and the result be a whole number... eg. 2000/4 = 500 leap 2001/4 = 500.25 not 2002/4 = 500.5 not 2003/4 = 500.75 not 2004/4 = 501 leap 2005/4 = 501.25 not etc., as long as they keep doing it every four years... ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ http://www.public.asu.edu/~hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Kevin J. Rowett" Subject: Re: Year 2000 Calendar: simple algorithm for leap yrs. Date: Wed, 06 Jan 1999 18:59:01 -0800 At 06:25 PM 1/6/99 , you wrote: >A simple algorithm for determining leap years would simply be to see if the >year is divisible by four and the result be a whole number... > >eg. 2000/4 = 500 leap > 2001/4 = 500.25 not > 2002/4 = 500.5 not > 2003/4 = 500.75 not > 2004/4 = 501 leap > 2005/4 = 501.25 not >etc., as long as they keep doing it every four years... Yet, 1900/4 = 475 "evenly divisible", 1900/400 = 4.75; 4 with a remainder of 75 (1900 wasn't a leap year). 2100 is similiar. KR _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Mark Robinson" Subject: Re: Year 2000 Calendar Date: Thu, 7 Jan 1999 16:39:31 +1300 Just a wee vote for Arie's leap year algorithm. What he states is what I was taught at univeristy while learning to program. Shame that certain more successful programmers didn't. Happy New Year Mark G Robinson | ZL2TOD | other@............... Box 8770, Auckland 1035, New Zealand Phone +64-9-846-3296 | Fax +64-9-849-7408 ------------------------------------------------ 07 Jan 1924 George Gershwin composes Rhapsody in Blue. 07 Jan 1952 Ike offers to accept GOP Presidential Nomination. ----- Original Message ----- From: Arie Verveer To: PSN-L Mailing List Sent: Thursday, 7 January 1999 14:49 Subject: Re: Year 2000 Calendar >Hi All, > >The year 2000 is a LEAP year. Our passage through the seasons is >called a "tropical" year of 365.24.. days long. This awkward fraction >0f 0.24... days is nearly a 1/4 of a day. So Pope Gregory on the advice of >the astronomer Clavius adopted this solution. Every forth year we add a >day (leap year). To correct for the errors in the fraction we make the century >years that are divisible by 400 a leap year. (There is also a 4000 year >correction). So 1900 was not a leap year but 2000 will be a leap year. > >Calendars that are the same: Look identical (other than festivals) > > 1) ..,1989, 1995, 2006, 2017 (not a leap year) > 2) ..,1990, 2001, 2007, 2018 "" > 3) ..,1991, 2002, 2013, 2019 "" > 4) ..,1997, 2003, 2014, 2025 "" > 5) ..,1998, 2009, 2015, 2026 "" > 6) ..,1999, 2010, 2021, 2027 "" > 7) ..,2005, 2011, 2022, 2033 "" > > 8) ..,1928,1984, 2012, 2040 (LEAP YEAR) > 9) ..,1968,1996, 2024 L >10) ..,1952,1980, 2008,2036 L >11) ..,1908,1964, 2020,2048 L >12) ..,1948,1976, 2004,2032 L >13) ..,1904,1960, 2016,2044 L >14) ..,1944,1972, 2000,2028 L ******** > >Ragards Arie > > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@.............. with the body of the >message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Dewayne Hill Subject: Y2K Date: Thu, 07 Jan 1999 08:11:14 -0700 I'm not one that gets upset very easily but I think all of the E-Mails about Y2K problems would be better communicated on one of the Y2K user groups rather that filling up the PSN server and my mail box. Regards, A nagging old man Dewayne (n0ssy) & Linda (n0uqf) Hill Westminster, Colorado USA 39.83569n 105.06270w. Elev 5460ft. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Roger Griggs Subject: Re: Year 2000 Calendar Date: Thu, 07 Jan 1999 16:46:08 -0800 John, Our Electric Transmission Control system log showed a leap second added via GPS TIME at 16:00 PST, Dec 31, 1998. This would have been 00:00 Jan 01, 1999 GMT. And yes, in a realtime control system, these leap seconds are a hassle. Roger At 12:56 PM 1/6/99 -0700, you wrote: >On Wed, 6 Jan 1999, bc wrote: >> At 09:25 AM 1/6/99 -0500, you wrote: >I think the only rule for leap years is an extra day in February (the 29th) >every four years. This is because the year is approximately 365 and 1/4 days >long. I think we also have leap seconds every year, but I am not sure if that >is just rumor or truth... For those using WWV though, these leap seconds >could be a hassle; that is, if they exist. > >Also, the only thing special anyone is doing for 2000 that I have heard >about is going to Jerusalem and vowing to die in a violent fight to prepare >the way for the second coming... I have a feeling that this type of thing >will be a problem for governments worldwide this year... > >*************************************************************************** *** > > John Hernlund > E-mail: hernlund@....... > WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ > http://www.public.asu.edu/~hernlund/ > >*************************************************************************** *** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: peaches@............ (Donna Whitaker) Subject: USGS Geological Hazards Report Date: Thu, 7 Jan 1999 15:06:37 -1000 (HST) News Release U.S. Department of the Interior U.S. Geological Survey Office of the Eastern Regional Geologist 953 National Center Reston, VA 20192 Release: Upon Receipt (Jan. 7, 1999) Contact: Diane Noserale dnoseral@........ 703-648-4333 Fatalities Increase in 1998, but . . . Earthquake Death Toll Still Below Long-Term Average Note to editors: Because of the nature of earthquake data collection, information on these events should be considered preliminary. We will issue an update if necessary. At least 8,928 people were reported killed from earthquakes world wide in 1998, according to the U.S. Geological Survey National Earthquake Information Center (NEIC) in Golden, Colo. Although this is a three-fold increase over the 1997 toll of 2,907, and a twenty-fold increase over the 1996 total of 419 deaths, it is still under the long-term average of about 10,000 earthquake-related deaths in the world each year. "This is the 5th consecutive year in which the death toll has been below average world wide," said Waverly Person, Director of the USGS NEIC. "The border area of Afghanistan and Tajikistan bore the brunt of fatalities in two events (at least 6,323 fatalities), neither of which was the strongest earthquake for the year or even classified as a major earthquake," Person explained. The strongest earthquake in 1998, one of only two great earthquakes recorded in the world in 1998 (magnitude 8.0 or above), occurred on March 25 in the Balleny Islands region, between Australia and Antarctica. Its magnitude was 8.3. The other great earthquake occurred on Nov. 29 in the Ceram Sea, near Sulawesi, Indonesia. That earthquake's magnitude was 8.1 and at least 34 people were killed. Only ten earthquakes were classified as "major." Major earthquakes have a magnitude of 7.0-7.9. According to long-term records, an average of 20 major earthquakes occur in the world per year. "No fatalities occurred in the U.S. in 1998 from earthquakes; however two people were reported injured in the August 12, magnitude 5.3 earthquake in southern Santa Cruz County, California," said Person. Three earthquakes of magnitude 6.2 were the strongest recorded in the U.S. in 1998. All occurred in Alaska: July 9 in southern Alaska, Aug. 20 and Sept. 14 in the Aleutian Islands. "A magnitude 5.2 earthquake on the Ohio-Pennsylvania border on Sept. 25 generated the greatest number of inquiries to the NEIC. Although this earthquake did not cause very much damage, it was felt strongly throughout northern Ohio and most of Pennsylvania. It was also felt in Illinois, Indiana, Michigan, New Jersey, New York, and southern Ontario, Canada," said Person. "We continue to hear from many people throughout the world that earthquakes are on the increase. Although it may seem that we are having more earthquakes, this is not the case. In fact, earthquakes of magnitude 7.0 or higher have remained fairly constant throughout this century," Person noted. A partial explanation for the impression of increased earthquakes may be that in the last twenty years, we have definitely had an increase in the number of earthquakes USGS has been able to locate each year. This is because of the tremendous increase in the number of seismograph stations in the world and the many improvements in global communications. Besides enhancing public safety, this increase in the number of stations and the more timely receipt of data has allowed seismological centers to locate many small earthquakes which were undetected in earlier years, and we are able to locate earthquakes more rapidly. Also, because of the improvements in communications and the increased interest in natural disasters, the public now learns about more earthquakes. Also, the effect that earthquakes have when they strike is generally more pronounced. Although we have gained much knowledge in building safer structures, when earthquakes occur today, losses (both human and property) are greater in many areas of the world. This is not because the earthquakes are stronger; it is simply because the Earth's population is increasing and more property (much of it not built to withstand earthquakes) exists that can be destroyed in an earthquake. USGS estimates that several million earthquakes occur in the world each year. Many of these earthquakes go undetected because they occur in remote areas or have very small magnitudes. The USGS locates about 18,000 to 20,000 earthquakes each year (about 50 per day). Additional information on the year's earthquakes is available on the USGS NEIC Homepage at: http://wwwneic.cr.usgs.gov/ As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, to contribute to the conservation and the sound economic and physical development of the nation's natural resources, and to enhance the quality of life by monitoring water, biological, energy, and mineral resources. ### USGS ### This press release and in-depth information about USGS programs may be found on the USGS home page: http://www.usgs.gov. To receive the latest USGS news releases automatically by email, send a request to . Specify the listserver(s) of interest from the following names: water-pr; geologic-hazards-pr; biological-pr; mapping-pr; products-pr; lecture-pr. In the body of the message write: subscribe (name of listserver) (your name). Example: subscribe water-pr joe smith. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Steve Jones Subject: Re: Year 2000 Calendar Date: Thu, 07 Jan 1999 19:30:51 -0800 Larry Cochrane wrote: > > At 02:40 PM 1/6/99 -0700, you wrote: > >"Kevin J. Rowett" wrote: > > > >> So GPS time is now 13 seconds ahead of UTC. > > > >Larry C., is SDR using the offset in it's time with your GPS reciever? > >It would probably be pretty obvious if it's not. It would be kinda fun > >to watch it handle the leap second as it happens, if it does look at > >that. > > > >,Greg > > When I added the GPS support too SDR I didn't notice a 13 second offset > problem, so the ONCORE GPS receiver must be handling this.... > > -Larry Cochrane > Redwood City, PSN > > > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@.............. with the body of the > message: leave PSN-L Just thought I'd add my .02 re: the "GPS offset". If you fire up a "cold" (non-initialized) Oncore (or any other, I suppose) GPS receiver, you can watch the offset correction from GPS time occur a few minutes after the receiver first acquires a complete time solution. It is simply a (currently) 13-second decrement in the seconds output message. From the Oncore tech manual: "...The UTC [GPS offset] parameters are broadcast by the satellites as a part of the almanac, which is repeated every 12.5 minutes...The value reported is the integer number of seconds between UTC and GPS time..." Steve Jones _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: CARRJJ@....... Subject: Assistance?? Date: Thu, 7 Jan 1999 21:45:06 EST Can anyone direct me to sources of information on seismic instruments, hardware and their application suitable for amateur or hobbyist level people? Joseph J. Carr POB 1099 Falls Church, VA 22041 CARRJJ@....... _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Wayne Abraham J73WA Subject: Re: Assistance?? Date: Thu, 07 Jan 1999 23:07:03 -0400 Joseph Visit the PSN site at: http://psn.quake.net/ Wayne CARRJJ@....... wrote: > Can anyone direct me to sources of information on seismic instruments, > hardware and their application suitable for amateur or hobbyist level people? > > Joseph J. Carr > POB 1099 > Falls Church, VA 22041 > CARRJJ@....... > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@.............. with the body of the > message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: JIm Hannon Subject: Re: Assistance?? Date: Thu, 07 Jan 1999 21:41:45 -0600 CARRJJ@....... wrote: > Can anyone direct me to sources of information on seismic instruments, > hardware and their application suitable for amateur or hobbyist level people? > > Joseph J. Carr > POB 1099 > Falls Church, VA 22041 > CARRJJ@....... > > Just start asking questions on this list. Also it is well worth the time to read the archives of the list at http://psn.quake.net/maillist.html#archives -- Jim Hannon http://soli.inav.net/~jmhannon/ 42,11.90N 91,39.26W WB0TXL _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: barry lotz Subject: Re: Assistance?? Date: Thu, 07 Jan 1999 20:01:46 -0800 Hi Joe Scientific American - Amatuer scientist.( Older editions) Barry CARRJJ@....... wrote: > Can anyone direct me to sources of information on seismic instruments, > hardware and their application suitable for amateur or hobbyist level people? > > Joseph J. Carr > POB 1099 > Falls Church, VA 22041 > CARRJJ@....... > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Edward Cranswick Subject: Re: box to dominica Date: Thu, 07 Jan 1999 23:13:19 -0700 Meredith- I apologise for taking so long to get back to you on the subject, but now that I've been back from Dominica for a week, I figured I'd tell you just what happened to your box (I'll start with a short background for the blissfully innocent). [Meredith arrived at my USGS Golden, Colorado, office on Saturday afternoon, 19 Dec, the day before Jody and I departed for Dominica, with a large cardboard box, ~30x20x60 cm, i.e., 12x8x24 in, that was also quite heavy, ~10-15 kg, i.e., 20-30 lbs. When I saw how big his box was relative to the heavy-duty plastic shipping case I was planning to pack all the seismic equipment I was bringing to Dominica -- including a 3-channel amplifier board, an SDR board, a PC-LABS A/D board & manual from Larry Cochrane; a L-28 vertical geophone from Roger Vaught; an antenna mount from Rick Curtis; and a 3-component L-22 geophone on loan from USGS -- I suggested to Meredith that maybe I could leave the box itself and only pack the contents, but he did not look particularly enthusiastic about that idea.] It was only in my typically last-minute rush of packing the next morning a couple of hours before our departure that I looked in the box and realized that it contained many of the pieces in semi-kit form of a Lehman seismometer -- including what looked to my hasty inspection like a LARGE MAGNET -- and that all the components were carefully and securely packed in their respective bags and plastic jars. So I packed the whole box as it was in the shipping case and everything else fit in quite snugly as well, and I wrapped up the shipping case with meters of fiber tape so that it looked like a bandage-swathed plastic coffin holding a PVC Mummy from the petrochemical swamps of New Jersey industrial wasteland. However, as soon as we started to checkin at the Denver airport, the man at the counter wanted to know if the shipping case contained "any magnets". Since I have shipped literally tons of seismic equipment using the same shipping cases while chasing earthquakes with USGS and have never been questioned about their contents, I was, in terms of speaking the truth, caught with my pants down, and I answered that it contained one magnet weighing several pounds (i.e., half that many kilograms). That triggered several long telephone consultations with various airline experts and other officials during which I was questioned -- causing me to babble about working for the USGS even though all our other statements indicated that we were on a personal vacation -- and which included discussions of "compass checks". That made me think that perhaps Meredith's supermagnet might misnavigate us to Cuba rather than Dominica. And then of course, there were all the questions about whether anyone unknown had given us any items to carry (of course not, I know all these people on the PSN-L whom I have never met face-to-face and who have sent me these strange boxes better than I know my mother). Anyway, everything arrived safely, and shortly before I left Dominica when I explained to Wayne that he could use your pieces to build a Lehman to monitor teleseisms, he got enthusiastic about that project. Though the groundmotion theshhold detector you sent Wayne was described to me in Dominica, I never actually saw it because it and Jody & I were never quite in the same place at the same time as we made our respective journeys around the island, though I understand it is at residence at Andre'&Joyce's, which is a shaking kind of place. Anyway, I have a couple of items from Dominica* to give to you and Lee Ann (maybe Chipper might also like them?), and I am planning to ride my bicycle over to your home (I need the exercise after not being able to ride on Dominica because the roads were just as crazy for the naive American as I was told they would be by Wayne and Clem) this weekend and drop them off. What would be a good time for you? -Edward * I also have a couple of things for others who contributed equipment but I am not planning to ride my bicycle to Texas and California. meredith lamb wrote: > Hi Edward, > > Have box for Wayne in Dominica ready for pickup. We maybe in > and out over the next few days....maybe if I leave it out front just > in case, we miss meeting? Hope you remember address here.... > 715 S. Pecos St. Denver, Co. ph 303-936-6221 > > or......we can deliver to your place? > > Thanks, Meredith, Lee Ann and Chipper the dog. > > -- > Meredith Lamb > <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> > > Main Web site: http://www.users.uswest.net/~psnseismograph52/Index.html > > <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Edward Cranswick Subject: Re: Baffled Date: Fri, 08 Jan 1999 00:22:31 -0700 Wayne- Four seconds of first motion of the seismogram you sent me 990101j.dm[1-3] is shown in the plot below (using my old VECTOR prog ram): ftp://groundmotion.cr.usgs.gov/PSN/Dominica/01jan1999/FIRSTMOT.GIF All three components are plotted at the same amplitude scale. Note that the Z- (Ch1) and N- (Ch2) components are similar and th at their first arrivals precede that of the E-component (Ch3) by 0.10-0.15 s but then the E is much larger and more impulsive. All the c omponents are very monochromatic, and you can see from the WinQuake FFT that the spectra peak at 4-6 Hz. In short, this is another weird seismogram, and I am not sure what is P & S and what is what (are all the channels connected 1, 2, 3? ... a rude question but I had to ask) . It maybe something idiosynchratically volcanic, but I am not very familiar with those seismograms. Have you recorded anything as simple as that first event on 27 Dec, i.e., large P on Z followed by large S on N&E? If you have, please send it to me. You should be able to use SDR as a voltmeter. Take a sinusoidal signal, e.g., Delores tapping the Z-component of the L-22 and i nput that directly into Ch1 of the SDR. Take the same signal in parallel and input it into the amplifier and then take the amplifier outp ut and input that into Ch2 of the SDR. Calculate the amplification by dividing the digital counts of Ch2 by those of Ch1. By controlli ng how hard she taps, Delores should be able to produce a signal that is on-scale in both straight and amplified versions. Save both record s and send them to me, and I will calculate the overall response of the amplifier using spectral ratios. -Edward Wayne Abraham J73WA wrote: > Ed, > > I will take up the direction finding subject with you again later because I am definitely going to have to use it alot and I want to > understand it properly. > > Larry told me how to change the frequency from 10 to 20hz which I did today. I also increased the sampling rate to 100. The m inute I > changed the frequency, my trace seemed to become at least 5 times wider than it was. I guess I will now have to reduce my gai n some > more. I have asked Larry how I can use my multimeter to know my gain. If he replies tomorrow, I will to back to Roseau to get it done. > > Seismic activity seems to have subsided somewhat. That's good because I want to be well calibrated when it decides to return. > > Take care, > > Wayne -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Al Allworth" Subject: Test Date: Sun, 10 Jan 1999 00:40:11 -0800 Real quiet for 2 days. ____________________________________ Al Allworth allworth@.............. Gold Beach On The Beautiful Southern Oregon Coast ____________________________________ _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Bob Fryer Subject: Re: Test Date: Sun, 10 Jan 1999 01:07:01 -0800 Hi Al, Yeh, real quiet. I got dumped from another list the other day. Bob -- in the dripping PNW (Beaverton, OR) >Real quiet for 2 days. >____________________________________ > >Al Allworth allworth@.............. > >Gold Beach > >On The Beautiful Southern Oregon Coast > >____________________________________ ----- earthquake WARNING research ----- --- animals, people, scientific evidence --- --- http://www.teleport.com/~bfryer --- _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "anthony p. giunta" Subject: event in New England Date: Sun, 10 Jan 1999 18:23:49 -0500 @ 5:52 am quake measuring 2.7, epicenter was located at Merrimac, Massachusetts A. P. Giunta Norwood, Mass _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Larry Cochrane Subject: New WinQuake beta release Date: Sun, 10 Jan 1999 17:22:32 -0800 Hi Everyone, Happy New Year. In the last few months I have been working on a new Winquake (WQ) release. With some help from Arie Verveer (thanks Arie!) I think I have a stable beta release ready.I sent Arie a pre-beta release so he could checkout one of the new features in this release. I used the code he wrote to convert GSE2.0 files to the PSN format to allow WQ to view event files in that format. He ended up finding a few major bugs that where not happening on my system. Heres what's new in this release (Version 2.5.7 Beta): Mapping and Event Location: This is the main new feature in this release. After opening one or more event files and picking the P and S phase, a map can be drawn showing the stations with a distance circle. This can be used, if you have good P and S picks, to locate the event. To open a map window, click on the new map tool bar icon next to the RST (Reset) icon or use the "View/Locate Event" menu item. After opening a map window, you use the Zoom menu to zoom in and out. To move the globe around, double click on a point on the globe. This will move the map so that this point is now centered in the window. I still need to add some tool bar icon controls and come up with a better way of moving the map around. GSE2.0 support: WinQuake uses the keyword "BEGIN GSE2.0" to see if a file is in the GSE2.0 format. This keyword must be within the first 512 bytes of the file. WQ supports both single and multiple seismograms in one GSE2.0 file. If there is more than one seismogram in a file, it will be treated the same way as a PEPP or SEED volume data set. IASP91 travel time model: The option, controlled by the Travel Time Table and Display Phase control dialog boxes, uses the IASP91 travel time tables instead of the JB tables. There isn't much difference between the two sets of tables except that the IASP91 P and S tables go past the 107 degree point. Apparently they use some other first arrival P and S phases once the main P and S go into the earth's core shadow. Too enable this option, the file IASPI91.DAT must be in the WQ root directory. New Event Window Look: The Event Window now is divided into two sections using a splitter window. The text or header information is displayed in one window and the seismogram is displayed in another. Using the Options menu items you can control the colors and font of each window. You can download the new beta release at ftp://ftp.drnet.com/users/psn/software/wqbeta257.zip. If you are having problems with that link, the FTP server is hanging sometimes, you can download the file at ftp://ftp.seismicnet.com/software/wqbeta257.zip. The file is about 1.3 meg bytes in size. The zip file only contains a new winqk32.exe and some new and old data files. To use this release you must have an older version of WQ installed. After unzipping the beta release file in a temp directory copy all of the files to your main WQ root directory. You might want to rename the exciting winqk32.exe file before you do the copy. Note: The beta release is only for Windows 95/98 or NT. I won't be supporting the 16 bit version any more. Also, since this is a beta release the program will time out at the end on April. That's it. Let me know if you find any problems, have any suggestions or need any help with the new features in this beta release. -Larry Cochrane Redwood City, PSN _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Wayne Abraham J73WA Subject: Re: New WinQuake beta release Date: Sun, 10 Jan 1999 23:42:00 -0400 Larry Will I lose my registration when the program times out in April? Wayne _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Larry Cochrane Subject: Re: New WinQuake beta release Date: Sun, 10 Jan 1999 21:07:46 -0800 At 11:42 PM 1/10/99 -0400, Wayne wrote: >Larry > >Will I lose my registration when the program times out in April? > >Wayne No... -Larry _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: S-T Morrissey Subject: VBB transducer sensitvity Date: Mon, 11 Jan 1999 00:59:20 -0600 (CST) For those interested in the displacement detector used for the triple-feedback broadband seismometer: An update on the VRDT used for the STM-8 VBB seismometer: THE Conclusion: experiments indicate that configuring it per pervious specifications may make it TOO sensitive. I have re-evaluated the oscillator frequency question and gathered this information, some of which has been previously noted: a: The inductance of the VRDT when made with the TL021 transformer with the vane centered in a 2mm gap is 125 millihenries (per side). This calculates to an impedance of 3.9k ohms at 5khz, and 470 ohms at 600 hz. This would be the effective bridge impedance. b: With the borrowed digital LCR meter, I measured the inductance change as the vane is moved with the micrometer. Of course one side increases as the other decreases, so the changes need to be summed. They average 70 micro-henry per micron. This is a change of the reactance of each side of the bridge of 2.26 ohms per micron at 5 khz, and 0.27 ohms per side at 600 hz. Clearly the 5 khz (or even higher?) frequency gives much more sensitivity. c: The 600 hz option is used for the tiltmeters because it greatly reduces reactive changes caused by temperature, etc, of the long (over 10 meters) cables that are used. For the seismometer, the bridge can be within a few cm of the VRDT, so this is much less a problem. (Also, the tiltmeters are electrolytic resistive bridges, whose output was not frequency dependent.) As long as the bridge excitation is a clean sine wave, without high frequency harmonics, reactive changes should be minimized. d: SO... It seemed that the sine frequency should be 5 khz for maximum sensitivity. This makes the bridge impedance 4.02k ohms (at 1%), which is what it was designed for, and how I have drawn the schematic. BUT.... THis makes the transducer so sensitive that it is almost impossible to calibrate. (I actually changed one oscillator to 10khz for an application to a geophone, then studied the noise with the TL021 coils.) e: SO... It seems that for the present the 600 hz frequency is preferred. With the output of the oscillator at the transformer set to 350mv RMS, or 1 volt p-p referred to common, the transducer output is about 120 mv/micron. THe sensitivity does scale with the drive level. This sensitivity can be very roughly checked by turning the 30-turn, 100 ohm zero potentiometer in successive 1-turn steps. Since the transducer net reactance change is 0.5 ohms/micron at 600 hz, 3 ohms will represent 6 microns, or 720mv. (The "calibration" resistors and switch will produce the same result if they are installed.) So with the differential micrometer calibration, which is really only useful at 5 or 10 micron steps, the +,- 7 volt working range is spanned in 10 or 20 steps, which limits the statistics of the direct VRDT calibration. With the displacement gain amplifier at 20X, which is needed for the very high value of "r" in the feedback system, a level of 2400 mv/micron requires calibration by much higher resolution devices. However, its output is an indication of the system noise, which is about 1 mv p-p from 10 hz to DC. This is an equilavent ground noise of about 0.4 nanometers. I have recently operated the STM broadband vertical with a r value as high as 2 000 000 V/m. This extends the frequency response to above 100 hz. And of the differential capacitor Cp is reduced for a shorter natural period. like 50 seconds, the flat response level is very high, like 11 700 v/m/sec. It makes for very large 6-second microseisms. Regards, Sean-Thomas _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "Francesco" Subject: R: New WinQuake beta release Date: Mon, 11 Jan 1999 12:19:20 +0100 Hello Larry, very good the new release of WQ! =20 One suggestions for the definitive version: the automatically save of = the files map in gif format . This option would be useful, because it = would simplify the job of conversion with clipboard and another graphic = programm. A question. New Winquake read automatically the GSE2.0 file? =20 Regards Francesco Nucera - I.E.S.N. PSN ITALY
Hello Larry,
very good the new release of = WQ! 
One=20 suggestions for the definitive version: the automatically save of the = files map=20 in  gif format . This option would be useful, because it would = simplify the=20 job of conversion with clipboard and another graphic = programm.
 
A question. New Winquake read=20 automatically  the GSE2.0 file? 
 
Regards
Francesco Nucera  - I.E.S.N. = PSN=20 ITALY
From: "Francesco" Subject: AutoDRM and GSE2.0 Date: Mon, 11 Jan 1999 12:23:23 +0100 Arie, wich is the system now, with the new beta release of Winquake, to read = the GSE2.0 file, via AutoDrm and e-mail request? Bye Francesco Nucera - I.E.S.N. - PSN ITALY
Arie,
wich is the system now, with the new = beta=20 release of Winquake, to read the GSE2.0  file, via AutoDrm and = e-mail=20 request?
 
Bye
Francesco Nucera   -  = I.E.S.N. -=20 PSN ITALY
From: Arie Verveer Subject: Re: AutoDRM and GSE2.0 Date: Mon, 11 Jan 1999 21:00:28 +0800 Hi Francesco, > wich is the system now, with the new beta release of Winquake, to read the GSE2.0 file, via > AutoDrm and e-mail request? You will still need to send your Email requests to your AutoDRM provider and save the returned data as a file. From then on I would use Larry's new release of Winquake. Its the complete package. The only thing you should be aware of , GSE2.0 files do contain checksum errors. They appear to be some sort of marker in the GSE2.0 file data. If you get a checksum error its better to decode the data via the "dos" program. It has some "fudge" code to ignore the checksum and extract the data that doesn't comply with the GSE2.0 standard. It only happens occasionally. I found using AutoDRM files in Winquake to be a grand way of locating epicentres. I used that feature today to locate a epicentre from a mine blast. All the best Arie. > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: robert barns <75612.2635@..............> Subject: MA 'quake Date: Mon, 11 Jan 1999 10:02:39 -0500 Hi gang, An item which might tickle the risibilities of you Californians-- = There was a 'quake yesterday near Merrimac, MA which registered 2.7 on t= he Richter scale! This made the CBS TV 11PM news in NYC. Any questions about what we do for excitement in this part to the worl= d? Bob Barns = = _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Bonnie Subject: 75612.2635@.............. Date: Mon, 11 Jan 1999 22:29:02 -0600 MA 'quake Hi, I can remember, when I was living in Oregon, that I thought that a 2 quake was a biggy! Then I moved to CA and got reedgucated real fast. Bonnie the crafty crafter Net-Tamer V 1.10 - Registered _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: "anthony p. giunta" Subject: Re: 75612.2635@.............. Date: Tue, 12 Jan 1999 20:02:08 -0500 Well thats how it is in New England, Our observatory has quakes all of the time but not like your area...............Thanks Tony -----Original Message----- From: Bonnie To: psn-l@.............. Date: Tuesday, January 12, 1999 01:56 AM Subject: 75612.2635@.............. >MA 'quake > >Hi, I can remember, when I was living in Oregon, that I thought that a 2 >quake was a biggy! Then I moved to CA and got reedgucated real fast. > > >Bonnie >the crafty crafter > >Net-Tamer V 1.10 - Registered > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@.............. with the body of the >message: leave PSN-L > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email listserver@.............. with the body of the message: leave PSN-L From: Arie Verveer Subject: Little quakes from distant BIG quakes Date: Wed, 13 Jan 1999 11:24:18 +0800 Hi, This may be a silly question but has anyone noticed that on some occasions a small local quake occurs very