Seismic Sensors - Page 1
Forum section: electronics / projects

author: radioactive
author_rank: Regular Contributor
timestamp: January 05, 2019, 02:51:47 am
content: I've been thinking it would be kind of fun to stick a seismometer out under the lawn somewhere around the house and log the data. I've looked briefly on ebay and search engines for sensors and nothing really stuck out. Anybody here done this just for fun? Would love to hear about your experiences and advice on the sensors.

author: boB
author_rank: Frequent Contributor
timestamp: January 05, 2019, 03:03:05 am
content: You might want to try adding strain gage to your search. I think that's what they use for seismographs mostly.https://engfac.cooper.edu/pages/tzavelis/uploads/Strain-Gage%20instrumentation0.pdf

author: EEVblog
author_rank: Unknown
timestamp: January 05, 2019, 05:29:25 am
content: What you need is called a geophone, like this:https://www.ebay.com.au/itm/Geophone-RTC-4-5hz-395ohm-Vert-Geophone-in-case-with-1m-lead-Mueller-clips/361665013385?hash=item5434ea2689:g:S6QAAOSw9V1ac4hf:rk:14:pf:0For underwater they are called hydrophones.

author: coppercone2
author_rank: Super Contributor
timestamp: January 05, 2019, 11:01:54 am
content: if you were to do this in a slightly more urban then suburban area with lots of rock/elevation, where you live on a hill, would you be able to get useful seismic data or would it be completely polluted by cars and roads/

author: EEVblog
author_rank: Unknown
timestamp: January 05, 2019, 01:10:15 pm
content: Quote from: coppercone2 on January 05, 2019, 11:01:54 amI used to work at the largest seismic water tank in the southern hemisphere, and we often had to schedule tests in the middle of night and to avoid passing trains many km away. Passing trucks were also a pain.And that was with a properly vibration isolated tank (no such thing as infinitive attenuation).

author: coppercone2
author_rank: Super Contributor
timestamp: January 05, 2019, 02:03:57 pm
content: does the structure of the land matter. i live in an area littered with lots of granite.i always thought about seismic sensors and magnetic earth antennas.there is a highway some one point five miles away or so, and train tracks near the same location. i am maybe fifty or more feet elevated from the highway, living on a high point in the area. not a gradual lump but more like on top of a finger poking out of the land with a significant slope towards the flat land and highway.also does a river effect things/ in a sense that is usable geological data possible, the interstate has traffic all the time pretty much.what would be a reasonable low cost primer test to see the type of hardware that can be used in the area, i will naturally tend to blow alot of money on precise equipment and over design noise floors and resolutions, so it would be good to have some kind of proofing test to discourage this kind of stuff if its going to end up being swamped with transit noise in the end.

author: EEVblog
author_rank: Unknown
timestamp: January 05, 2019, 02:24:42 pm
content: Sorry, don't know, I wasn't in the geology side of things, all I know is that our tank measurements got affected pretty easily.

author: coppercone2
author_rank: Super Contributor
timestamp: January 05, 2019, 03:29:38 pm
content: as far as sensitivity i understand urban areas have a problem, i spoke to a professor that told me despite a floating granite table on air his laser measurements were obstructed by trucks passing across the street, however it was a much more urban area.guess a ninety dollar gamble is not so bad

author: coppercone2
author_rank: Super Contributor
timestamp: January 05, 2019, 03:41:52 pm
content: what would be a good starter circuit for a geophone that works well with the one you linked/maybe a eevblog video/

author: mark03
author_rank: Frequent Contributor
timestamp: January 06, 2019, 03:14:41 am
content: Instrumentation for local events (frequencies > 1 Hz) is easier but IMO less interesting than the teleseismic band below 1 Hz. With even a rudimentary long-period seismometer you can see magnitude 6+ events in the same hemisphere and magnitude 7+ events worldwide, learn how the different wave components propagate, how we know that the Earth has a liquid core, etc. As a bonus that frequency range is less susceptible to local noise sources. The stuff you have to watch out for is not so much cars and footsteps as things like wind, or sunlight hitting the concrete slab you've placed the seismometer on.For a geophone-based solution (mainly high frequency but maybe some teleseismic capability too), I recommend checking out the Raspberry Shake product.The classic amateur long-period design, of amazing simplicity, is Lehman's "garden gate" seismometer from the Amateur Scientist column in Scientific American, July 1979. Speaking from experience, this is an excellent gateway drugFor a really serious, vertical broadband design with force feedback, google "FBV seismometer"; sadly there has never been a proper web site designed for this but several of the builders have nice pages describing theirs, e.g.http://www.groundmotion.org/main.html. The "Yuma" is the most recent design for home builders and competes favorably with professional instruments costing tens of thousands of $$. It has a flat response from 20 mHz to 30 Hz. From a location in Seattle, mine sees most M5+ anywhere on the Pacific rim of fire, usually several events every day. At this level the limiting factor is not the instrument but the site. It helps if you are in the middle of a big continent to reduce microseism noise from the oceans, as does placing the instrument in a temperature-stabilized vault cut into bedrock. OTOH mine sits on a concrete basement floor atop hundreds of feet of glacial till, and I'm happy with the results.

author: cdev
author_rank: Super Contributor
timestamp: January 06, 2019, 03:22:31 am
content: I've wanted to do this for years.. Tell me, how do you know the thickness of your glacial till, were you able to figure that out from your seismographs? I also live on glacial till (between two long basalt outcroppings).Quote from: mark03 on January 06, 2019, 03:14:41 am

author: mark03
author_rank: Frequent Contributor
timestamp: January 06, 2019, 03:38:45 am
content: Quote from: cdev on January 06, 2019, 03:22:31 amI don't actually have a measurement---that [very round] number comes from a geological map and conversations with local geologists. Be careful BTW, you might inadvertently give away your top-secret locationIf you can blast a pit or a vault out of the basalt, that would be a great place for a seismometer. But the best "easy" place is usually your basement, if you have one. You want to avoid big temperature swings.

author: texaspyro
author_rank: Super Contributor
timestamp: January 06, 2019, 04:20:55 am
content: My seismic sensor is a "JM jug". It is basically a magnet suspended on springs in a large coil of wire (with a neon light bulb across the coil to prevent handling damage from voltage spikes). One problem with these is the coil can pick up interference from AM radio stations...I also have a Worden gravity meter...

author: coppercone2
author_rank: Super Contributor
timestamp: January 06, 2019, 09:53:46 am
content: probobly a bad idea, but can you put it in a home well

author: max_torque
author_rank: Super Contributor
timestamp: January 06, 2019, 01:50:05 pm
content: Quote from: EEVblog on January 05, 2019, 01:10:15 pmI've googled "seismic water tank" and all i get is lots of links to how to design water storage tanks that are earthquake proof! I assume the test tank you are talking about Dave is to provide isolation for precision measurements? Be interesting to hear more!

author: babysitter
author_rank: Frequent Contributor
timestamp: January 06, 2019, 03:19:12 pm
content: Subscribe thread.Just got some people at (A)Schaffenburg Makerspace interested in citizen science, have ordered 3 geophones from ebay, played with 1-20 Hz Sound reception, fired off a email to a nearby visitors mine for seismic setup.

author: rhb
author_rank: Super Contributor
timestamp: January 06, 2019, 05:46:24 pm
content: I spent my career in reflection seismology as a research scientist and programmer in the oil industry. You will want to get the CWP/SU package. You *might* want SLT/SU also, but it's unlikely to be of much help for your use case. I supported CWP/SU for over 10 years and SLT/SU for 6. I also arranged for SLT/SU to be transferred to Mines.There is a wonderful wiki archived on the wayback machine of seismicunix.com with lots of usage examples.Stockwell has retired and moved SU from the CWP site to github.https://github.com/JohnWStockwellJr/SeisUnix/wikiR. T. Clark has been the main equipment broker in the US for 30+ years.. I bought a 3 axis geophone from them 8-10 years ago for around $135. I don't happen to see it on their website at the moment, but not much to them. Plastic box w/ 3 spikes and 3 geophones inside.Exploration seismology is very nearly on its death bed., so used land survey gear should be very cheap.https://rtclark.com*Everything* effects the response. Topography is particularly difficult to deal with as it produces strange raypaths.The most important question is what do you want to do? Hobby science is easy. Using multiple sensors to detect someone walking in the yard is a whole different ball game.Exlporation geophones have poor low frequency response. So if you're interested in earthquakes they are not suitable.If you live somewhere reasonably quiet building a LaCoste-Romberg vertical and a pair of orthogonal horizontal axis seismographs would make an interesting project. Most of the cost would be in mounting the units solidly.Using ambient noise as the source is called "seismic interferometery". I never understood that naming. But it stuck.

author: vindoline
author_rank: Unknown
timestamp: January 06, 2019, 08:00:05 pm
content: I don't know if it's the same thing, but Charles Wenzel has been experimenting with infrasound recently. He has lots of info, including diy microphones at his site:http://www.techlib.com/area_50/infrasound.htm

author: cdev
author_rank: Super Contributor
timestamp: January 06, 2019, 08:31:47 pm
content: This is also an amazingly cool program thats super useful in the time/frequency domain as a fine grained spectrum analysis tool.https://www.qsl.net/dl4yhf/spectra1.html

author: radioactive
author_rank: Regular Contributor
timestamp: January 07, 2019, 08:28:16 am
content: Quote from: mark03 on January 06, 2019, 03:14:41 amThe Yuma FBV design and related looks really amazing. Thank you for the information and links. That helps a lot.

author: radioactive
author_rank: Regular Contributor
timestamp: January 08, 2019, 04:43:46 am
content: Interesting document comparing various sensor types.Review of sensors for low frequency seismic vibration measurementhttps://cds.cern.ch/record/1322403/files/CERN-ATS-Note-2011-001-TECH.pdfAfter reading about the FBA type sensors, I'm wondering if this video from AppliedScience might be relevant. Any thoughts on if it would be possible to use this approach for a vertical arrangement? Please watch all the way to the end where it is demonstrated that you can pull the wavelength a few nm either way from center via supply modulation.

author: GK
author_rank: Super Contributor
timestamp: January 11, 2019, 02:18:49 am
content: Spent ~13 of my 15 years in government assisting in upgrading and maintaining the (since disbanded) seismic monitoring network for the whole state of South Australia and have been on more field trips to deploy temporary equipment for aftershock surveys than I can remember.I've never seen a geophone used to monitor natural seismicity. I've only had anything to do with geophones for induced seismicity, such as when letting off charges or for teaching purposes banging a metal plate on the ground with a sledgehammer. I have some geophones which I've collected and have thought about sticking them in the ground, but they are just too insensitive and really don't have the low frequency response required to make a decent seismometer.We always operated on a shoestring budget and the state seismologist kept quite a large amount of antique/legacy equipment in active use just to keep the monitoring network as large as practically possible. We had a lot of Ranger SS-1 short-period seismometers in use - originally developed for the moon (the lunar Ranger Missions) and only recently (a few years ago) finally discontinued by Kinemetrics. From a hobby perspective with a limited budget, a used SS-1 from ebay or some specialist test/scientific equipment reseller would be a excellent start. They are mechanically simple and easily repaired. An SS-1 suitably installed will pick up those 7 and 8s overseas no problem.The best seismometers for distant earthquakes though are the long-period units with huge/heavy sprung masses. The farther away the epicenter of the earthquake, the lower the frequency of the shock waves. Think of a stone dropped into a body of water - as the ripples radius outwards they dissipate as the wavelengths grow longer and longer. We had some long-period Benioff seismometers dating back to the 50s/60s that weighed, IIRC, a couple of hundred kg each. They had no high-frequency response to speak of so the noise was really low. These were installed in concrete bunkers on huge concrete plinths. Probably not practical for the average hobbyist, but in response to a big enough overseas wobble (our in-house technical term for earthquakes in general) they could continue to respond for an hour or more.A couple of our modern sensors for picking up local seismicity, that I recall, were the 3ESP and the CMG-5T from Guralp:http://www.essearth.com/product/weak-motion-seismometer/http://www.essearth.com/product/strong-motion-feedback-accelerometer/

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2019, 02:38:56 am
content: Quote from: max_torque on January 06, 2019, 01:50:05 pmYes, above ground test tanks vibration isolated on huge rubber mounts and other mechanisms. IIRC the one on the Thomson Marconi Sonar site was maybe 6-8m in diameter and 20m deep. I think the Marconi one was a bit smaller, but also above ground.I've tried but can't find any photos of them, this was in the days before digital cameras and the photo happy craze we have these days.Maybe I should try and ask if it's still there and get a tour?

author: radioactive
author_rank: Regular Contributor
timestamp: January 11, 2019, 02:52:32 am
content: QuoteI would like to watch that!

author: diegogmx
author_rank: Contributor
timestamp: January 11, 2019, 06:37:31 am
content: One interesting method i know modern seismometers use is to have a test mass as an lvdt moving element, and using a control loop and a coil to keep the lvdt output at 0, the seismometer output waveform would be the output of the control loop, they use one of these for each axis, buying one of these would most likely be prohibitively expensive yet it would be an interesting (and probably damn hard) project for summer (unless you are in the north hemisphere)

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2019, 12:50:06 pm
content: BTW, yes, the test tank was for precision measurements on all sorts of active and passive underwater sonars and hydrophones etc.We also has "flow tanks" that were more suited to towed arrays.There is only so much you can in a test tank, even a large one, as the wall effects dominate very quickly.Larger scale tests were always preferred but were logistically harder, so the test tank was handy for testing out new ideas and revisions to validate numbers etc.We had a lake test facility in Jarvis Bay.

author: radioactive
author_rank: Regular Contributor
timestamp: January 11, 2019, 09:44:51 pm
content: Quote from: diegogmx on January 11, 2019, 06:37:31 amFrom what I've read so far, this is the approach that interests me the most. It appears you get similar low-frequency performance to the long-stroke type sensors without the larger mass/coils in the sensor. @mark03 mentioned this type of sensor earlier in the thread (e.g. Yuma design). FBA (force balance accelerometer). The Yuma design appears to use a differential capacitive sensor for the PID control loop in vertical configuration (FBV). Sounds like capacitive is probably the best way to do this.The reason I brought up the video with the laser interferometer measurement earlier in the thread, is that it seems like it might be another way to pick up the displacement. I was thinking that a voice-coil (speaker) with retro-reflective tape (like in the video) could be used for the correction. I have no idea if this could be made to work as well as the capacitive type sensor (probably not I'm guessing), but it seems like it would also be fun to play with. I also ran across something describing Michelson interferometer involving a couple of mirrors / beam splitter to get higher resolution measurements, but that looks like it would be a bit much for a first attempt.

author: rhb
author_rank: Super Contributor
timestamp: January 11, 2019, 11:06:36 pm
content: A few comments:Take a look at this thread:https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1531160/#msg1531160in particular the differential capacitance sensing. The results achieved are quite amazing. You could sense the movement of a dielectric core. So basically a capacitance version of an LVDT.Making an LVDT would not be hard if you can wind a coil and allow generous clearance for the core. There are lots of plans around for coil winding machines.Dead CD/DVD drives are an excellent source of beam splitters and first surface mirrors for a Michelson interferometer. There are laser diodes which have enough coherency length to serve for a seismometer. IIRC these are the ones with a photodiode in the back and it requires a circuit to stabilize the frequency of the diode.A cheap He-Ne laser will have a coherency length of 8-12" which is enough for a small ring gyro.Finally there is the La Coste suspension. There's a picture of the first LaCoste seismograph here:https://web2.ph.utexas.edu/utphysicshistory/LucienLaCoste.htmlI recall seeing a version made using 3 screen door springs.

author: diegogmx
author_rank: Contributor
timestamp: January 12, 2019, 06:42:23 am
content: the problem i see with the interferometer approach (at least the open air one) is that you may very well measure air temperature fluctuations too, just thinking out loud but maybe if you use a REALLY high resolution and dynamic range sensor you could send the beam into a reasonably short fiber and measure a "linear sagnac effect" also using an interferometeralso if you want to sacrifice some resolution i figure maybe a laser diode / photo diode like the one in the applied video would sufficethe other disadvantage i see from a design like that would be that the low frequency response would be pretty pretty low since the sagnac is a consecuence of velocity, and at low frequency and low amplitude velocity is really lowi figure the highest resolution approach would be a michelson interferometer in vacuum with the mirror in a suspended test mass, pretty much like LIGO but without seismic isolation

author: rhb
author_rank: Super Contributor
timestamp: January 12, 2019, 12:48:11 pm
content: Once you start playing around measuring motions at sub-micron levels, *everything* becomes an issue.One of the interesting aspects of a seismograph is that an amateur can build a research grade instrument. It's challenging project because there are so many factors which must be taken into account. But the cost is low if you have a suitable location and the necessary skills.Where I live the traffic noise would be pretty bad, so I'll probably content myself with measuring deflection of the ground as the water level in the lake a mile from me changes. No real value to that, but I *am* a retired geophysicist. But then there are probably very low magnitude earthquakes associated with sudden loading from major rain events. So if I ever get my workshop organized who knows what might happen.

author: Rerouter
author_rank: Super Contributor
timestamp: January 12, 2019, 01:04:15 pm
content: You can also go all the way to the extreme with a laser tractor beam, essentially a tiny spherical lens is held in place by the photon momentum, and by measuring the deflection of the light you can measure extremely tiny forces.

author: radioactive
author_rank: Regular Contributor
timestamp: January 13, 2019, 07:28:59 am
content: Quote from: rhb on January 11, 2019, 11:06:36 pm@rhb, thanks for pointing to that thread and the other thoughts. That simple capacitive sensor is pretty amazing. I assume that is just water/air (80/1) in the vials based on the Ames description? I think I might start with this sensor and see if I can get similar results in the garage.@diegogmx, thanks for thoughts on the laser. After watching the appliedscience video, I was thinking that it might be possible to utilize the idea of modulating the power supply + DSP to get some higher resolution measurements. I'll be doing a digikey order soon. I might pick up a diode with the integrated PIN to play around with.@RerouterQuoteThen profit!

author: Rerouter
author_rank: Super Contributor
timestamp: January 13, 2019, 10:32:00 am
content: Sorry, the more correct term was Optical Tweezers, Its how they measure extremly small forces

author: rhb
author_rank: Super Contributor
timestamp: January 13, 2019, 01:26:14 pm
content: Spirit levels are filled with alcohol so they won't freeze and break. Hence the name. It's probably worth spending a little extra and getting the UK made vials. The interior finish on the Chinese vials is a bit rough and leads to erratic movement. Not important in a machinist's level, but JBeale found it problematic for a monitoring application.If you happen to live near a volcano or a major fault zone you can do serious science by setting up an orthogonal pair on a bedrock mounting. If you've got a good setup with the vials accurately oriented USGS will be glad to get data from you. I'd talk to USGS before making the permanent mount. They may know from experience that there are some wrinkles to getting good data. Also they'd probably want to do a calibration of your unit before installation.I dropped my membership in the Seismological Society of America some years back so I don't know the current details, but USGS has a sizable network of tiltmeters all over California.It's a good bit of work to calibrate and integrate a new instrument, especially a seismograph installation, into the network so to work with them you'd need to be very professional in your dealings with them. That mostly requires that you read and understand the relevant recent literature. Those papers will also tell you who to contact.I strongly suspect that the same circuit and electrode arrangement with a piece of teflon rod would be equally sensitive in a seismograph application.I'm used to seeing ads in the geophysical journals for microradian tiltmeters for many years and understood how they worked, but I never imagined it was as simple to make one as it is. The commercial units are quite expensive.

author: mark03
author_rank: Frequent Contributor
timestamp: January 13, 2019, 10:04:15 pm
content: Quote from: diegogmx on January 11, 2019, 06:37:31 amThis is known as "force feedback" and is a staple of all modern broadband seismometers, including the amateur FBV instruments mentioned up-thread. It's analogous to negative feedback in electronic amplifiers, yielding a flat response over multiple decades of frequency. Older and simpler designs like the Lehman, and I believe also the Benioff mentioned by @GK, are merely second-order damped pendulums whose bandwidth can only be expanded through post-processing. With force feedback, it is possible to achieve the same (actually, much better) performance at low frequencies, without the heavy seismic mass.

author: mark03
author_rank: Frequent Contributor
timestamp: January 13, 2019, 10:22:06 pm
content: Quote from: radioactive on January 11, 2019, 09:44:51 pmYou might have seen the same paper that I recall, where they used the guts of an STS-1 (?) retrofitted with optical position sensing, and DSP to keep track of the fringes using quadrature signals. My recollection is that they were running this open-loop. I have been assured by people who know this stuff much better than I do, that a digital control loop (for force feedback) is impractical because any realizable D/A will sacrifice too much dynamic range. This may be an insoluble issue with the interferometric measurements. OTOH with sufficiently low measurement noise you may be able to achieve what you want without force feedback... which I think was the point of that paper.Ok, found the quote I was looking for, from Erhard Wielandt,Design considerations for broadband seismometers(http://ds.iris.edu/stations/seisWorkshop04/PDF/Wielandt-Design3.pdf)Quote

author: rhb
author_rank: Super Contributor
timestamp: January 14, 2019, 12:38:47 am
content: FWIW An interferometer based seismograph produces an FM signal. The larger the amplitude, the faster the fringes change. Much better than trying to count fringes to just use regular FM demodulation.

author: radioactive
author_rank: Regular Contributor
timestamp: January 19, 2019, 03:25:13 am
content: QuoteI noticed that right away (FM signal) from watching the applied science video too.. for the stable laser power supply. Still *very* cool response for pretty small measurements. Later in the video where it was demonstrated that wavelength could be manipulated via power supply, I started thinking about DSP and what might be done with that. (even though he wasn't very optimistic about it being useful). As mark03 pointed out, this is probably not something to be optimistic about for a closed loop system.Thank you both for your inputs. Much appreciated. I'm still working on another unrelated project, but I hope to transition to playing around with a seismic sensor soon. That capacitive inclinometer from the other thread is going to be the first thing I want to experiment with I think.Quote@Rerouter, sorry I thought you were being sarcastic or something. That is a *very* interesting video. Also wayyy out of my capabilities..

author: rhb
author_rank: Super Contributor
timestamp: January 19, 2019, 01:00:59 pm
content: Also look into the Zeeman effect with lasers.http://wanda.fiu.edu/teaching/courses/Modern_lab_manual/zeeman_effect.htmlHP uses this in their optical measuring system to derive absolute position from the interferometer fringes. There's an HP application note describing it in detail.

author: max_torque
author_rank: Super Contributor
timestamp: January 19, 2019, 02:13:06 pm
content: Quote from: EEVblog on January 11, 2019, 02:38:56 amIt would be interesting to see that! It's a field (should that be a "lake"?) i know nothing about and looks to have quite a few interesting challenges and solutions

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 20, 2019, 12:17:58 am
content: Several years ago there was a post on hackaday about a project of a home made raster tunneling microscope.I believe it used an isolation scheme built from several layers. A heavy plate (granite?) on 2 meter long springs, with some extra dampening hardware added, but also with half filled bycicle inner tubes. (Edit: Triggered my memory from a post below me).He had to make do with local situations (urban area?) but managed to get quite decent results.

author: rhb
author_rank: Super Contributor
timestamp: January 20, 2019, 12:35:52 am
content: A large box of sand on partially inflated inner tubes is a popular isolation table design in the hologram community. It's cheap and much easier to move than a block of stone of similar mass (around 3000 kilograms for a 4' x 8' x 2' table).

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 20, 2019, 02:05:16 am
content: Over the years several intersing projects have been hacked together and posted via Hackaday.It may have someting you like.https://hackaday.com/?s=seismograph

author: 3roomlab
author_rank: Frequent Contributor
timestamp: January 20, 2019, 10:23:48 am
content: that yuma2 LTspice model is fun to play with

author: rhb
author_rank: Super Contributor
timestamp: January 20, 2019, 02:02:19 pm
content: It occurs to me that a survey volume of professional seismograph designs would be very interesting. Unfortunately, I cannot think of a single earthquake seismologist whom I know. A search with Amazon turned up nothing but reflection seismology books and SSA has no publications except the bulletin and research letters.Earthquake seismology and reflection seismology have almost no contact. I was a member of the Seismological Society of America for a number of years but dropped most of my professional society memberships when I retired as it costs quite a lot. And in my case I simply could not deal with managing 37 publications even if many of them were quarterly. I'm getting ready to do a major purge of journals from my library as I am running out of space.I already have far too many projects, but the SSA bulletin and Seismological Research Letters finally got scanned so members have electronic access. While I was a member they were just starting on making it available electronically. But had not yet scanned back volumes.The Society of Exploration Geophysicists which is the major reflection society routinely assembles important papers into review volumes on various topics. It's very convenient to have all the major papers in a single volume so you can read a citation just by flipping pages.If anyone reading this has a serious interest in seismograph design I'd like to urge joining SSA and collecting all the papers on seismograph design and testing into a review volume available through a book on demand service. I'd buy a copy in a heartbeat. Designing a new seismograph is now pretty rare. Most networks settle on an instrument and use that same instrument throughout the network. That greatly simplifies the process of calibrating the installation as you only have to model the earth coupling at that location. Getting an amateur station accepted into one of the official networks would be real badge of distinction.