Talk:Seismometer

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Blank page[edit]

This was an existing blank page Zeizmic 15:17 22 May 2003 (UTC)

people are the most skilled beings 174.63.123.238 (talk) 18:54, 30 April 2014 (UTC)Nathan smith)[reply]

Seismograph vs. Seismometer[edit]

There is also a Seismograph article. They have a similar description, to the point I wonder - are these the same instrumentThere is also a thing called a Choko and he was the first guy to make a seismograph in ancient China and this thing is the most Habbo thing in the world!ument, or something else? If it's the same, the articles need merging. If it's something else, I suggest that someone who knows something about seismology mentions Seismometer in the Seismograph page (and vice versa) and say a few words about the difference. Thanks. Nyh 18:10, 14 Sep 2004 (UTC)

It looks like somebody merged (thanks!) but the "Modern Instruments" section starts talkin about seismographs before it clearly distinguishes them from seismometers. So someone who knows the difference still needs to come here and state it explicitly. Also maybe mention something in the intro? Otherwise "seismograph" readers might feel cheated. :) Thanks! Kiaparowits 17:47, 24 October 2005 (UTC)[reply]

Having operated a seismograph station myself, and having become very familiar with the work and the terminology, I know that a "seismometer" is - strictly speaking - just the instrument that detects ground motion. Whereas, a "seismograph" is the entire recording set-up, which includes a seismometer. The "seismometer" itself is NOT a "seismograph". They are not synonyms or interchangeable terms.

Let me explain. The method used at my station was a beam of light shone from a lightbulb onto photograph paper. Not directly. A tiny mirror was afixed to a magnet which turned slightly in response to the current generated by a coil mounted in the seismometer. The heavy magnet is mounted on springs. When the ground moves, the case (and coil on the outside of it) move. The heavy magnet within remains stationary owing to its appreciable inertia (it's heavy) and the amount of motion involved is typically trivial. Usually what you're detecting, in terms of short period motion, is on the order of millimicrons, from earthquakes at teleseismic (global) distances. So that's negligible movement of the case. The springs that the magnet is mounted on effectively decouple it from the ground.

Basic electromagnetic theory says that any magnet moving inside a coil (or in this case, a coil moving around a magnet) generates an electric current.

So that's the "seismometer". All it does is generate a small electric current, which corresponds to ground motion. The more the ground moves, the more current is generated.

In the case of the seismograph station I ran, the "seismograph" was the seismometer; and a light bulb, to generate a beam of light; and a tiny mirror fixed on a very small magnet (within a second tiny coil), which the current from the seismometer caused to turn and deflect the light beam; it included the sheets of photograph paper, to record the signal; and the drums they were mounted on; and a crystal clock to keep very accurate time. The "seismograph" was the seismometer AND all the recording equipment. It includes the seismometer. The seismometer was connected to the recording equipment by a cable. A seismograph station needs both a seismometer itself, and the other equipment, to produce a "seismogram", which is a record of the signal.

I think the term "seismometer" should be used to refer only to the device or instrument that generates an electrical signal in response to ground motion. Whereas the term "seismograph" means the *whole* set-up. A seismometer, in and of itself, doesn't record anything. "Graph" implies recording.

Today the "graph" part can be - and often is - electronic A/D converters. They convert the signal to digital form. But traditionally it was done with photographic paper. (Or a hot wire that wiggles on waxed paper, and makes a dark line in it. That's still very popular.)

Since some of the modern units are integrated into one relatively small *self-contained* package, the distinction is not as clear, today. (Where the seismometer and seismograph are all in one case.) You put it down somewhere, unlock it, turn it on and it records. But even so, there is still bound to be a seismometer in it that is separate and distinct from the recording elements. It's like a pendulum in a grandfather clock; one would never refer to the pendulum as the clock. It's just part of it. I'm also sure that even today, many seismograph stations still use the traditional method of recording on sheets of photograph paper, or the wiggling-stylus method.

Another difference is: the seismometer and the recording equipment are typically separated by a hundred meters or more. Ideally you want a seismometer to be in a very quiet location, which is never on an upper floor of a building, or near a road, and so on. Ideally on solid rock, well away from any road. Because they pick up high-frequency noise from vehicles very easily. Or wind. Ideally a sheltered area, down low, with no nearby trees. But if they're not concerned about noise they may have the seismometer(s) in the basement of a building, and the drums upstairs in an office. Where they can see what's going on. So that physical separation of the components is also part of the distinction, in terms of an accurate definition.

To my mind, the terms "seismometer" and "seismograph" are NOT interchangeable; they have distinct and separate meanings. I think for the sake of accuracy, that distinction should be made clear in the article. I hope this helps. Stellar-TO 21:10, 5 November 2005 (UTC)[reply]

Yes, that helps a great deal. The information can now be condensed and rolled into the article, probably somewhere near the beginning. The major differences and particulars are well laid out here. Thanks! Kiaparowits 16:43, 6 November 2005 (UTC)[reply]
Further, since Stellar-TO says "...Whereas, a 'seismograph' is the entire recording set-up, which includes a seismometer", it seems like the article should be moved to the more inclusive "seismograph" and "seismometer" should be the redirect. That's kind of nitpicky, though. Kiaparowits 16:48, 6 November 2005 (UTC)[reply]

Mars & the Moon[edit]

Can the original author please point out, which seismic testing at Mars and Moon he is speaking of? My Mars-researching girlfriend (;-) is sure to never have heard about seismic testing of Mars at least, with the Moon we are not so sure, so is there any material to have a look at? (Author unknown)

In 1992, JPL decided from Viking orbiter images that Mars was probably more seismically active than the moon, but less active than Earth. According to Dr Matthew Golombek, because Mars is only a bit more than half the size of the Earth, a quake on Mars would have 10 times the effect it would on Earth. He estimated a magnitude 4 event about once a month, on average. That was merely his speculation. In 2004, pit chains (chains of depressions) observed in photos of the surface suggest that Mars may still be seismically active.

As of 2005, I don't believe there has been actual seismic testing on Mars. There's certainly been talk about it since 1992, at least. There is a developed SEIS package to measure Martian seismicity. Those instruments were supposed to be in testing in 2005, and presumably will be delivered to Mars soon.

I didn't checked on the moon, but I believe there has been some actual seismic testing there. Stellar-TO 00:13, 29 November 2005 (UTC)[reply]

I don't see any reference to Mars (maybe it was cleaned out?). No seismometers on Mars, but there was a really good one on the Moon. They actually impacted a piece of space junk to test it out. It showed that the Moon was a perfect bell, ringing for a very long time.

--Zeizmic 16:03, 7 December 2005 (UTC)[reply]

There were two seismometers on Mars, as both the Viking Landers carried one. Unfortunately the instrument on Viking 1 did not work and the instrument on Viking 2 recorded only one possible event (which might have been wind) e.g. http://spot.colorado.edu/~marscase/cfm/vkngdays.html I believe the Apollo program deployed 5, at least which some continued to operate and send data until 1997. Moonquakes are unusual due to very low attenuation and because some appear to be triggered by tidal forces as well as meteorites. Perhaps this should be added to the article?

There still - 2008, has NOT been any seismic recordings made on Mars though ther has been some suspicious activity. The Geologist (talk) 18:28, 15 March 2008 (UTC)[reply]

External Links[edit]

After some thought I added a link to my free SeisMac seismograph tool. I was concerned it might be disapproved as self-promotion (which it is), but since it's free, and I couldn't find any explicit prohibition against informative self-promotion, I thought it would be OK. —Preceding unsigned comment added by Dtgriscom (talk • contribs)

There is such a policy, see WP:EL. I'm letting your link stay (though others may not), but I wouldn't recommend adding links to your site to any other articles. Cheers! -- Mwanner | Talk 12:58, 4 July 2006 (UTC)[reply]

Unfortunately Sean-Thomas Morrissey died a few years back, and it seems that St. Louis University has removed his web pages. So I removed these links.Pedant543 (talk) 03:51, 22 November 2007 (UTC)[reply]

Not so Morrisey's pages can be found at http://www.eas.slu.edu/People/STMorrissey/index.html 192.210.5.253 (talk) 22:06, 7 January 2009 (UTC)[reply]
Restored the link. Ray Van De Walker 08:22, 30 September 2010 (UTC)

Amplification using negative feedback loop?[edit]

Am I missing something here? But isn't that usually used to dampen a signal or stabilize a system, where as a positive feedback loop is typically used for amplification. Someone with a clue stick should probably fix that or explain why it is the way it is. —The preceding unsigned comment was added by 84.239.133.167 (talk) 18:36, 12 April 2007 (UTC).[reply]

I fixed it, if you're interested. Ray Van De Walker 09:34, 3 June 2007 (UTC)[reply]

Dead link[edit]

Dear Wiki experts,

please update the link to Erhard Wielandt's article

Seismic Sensors and their Calibration

The link has moved to:

http://www.geophys.uni-stuttgart.de/oldwww/seismometry/man_html/index.html

thank you - Ruedi Widmer-Schnidrig

Done Ray Van De Walker 08:21, 30 September 2010 (UTC)

copyedit[edit]

The "modern instruments" section has a lot of one-sentence paragraphs, and random statements interjected with no clear context or transition from the previous thought. A good cleanup is in order. Snottywong 14:51, 13 September 2007 (UTC)[reply]

Directionality of a single seismometer[edit]

I'd like to see a more elaborate description of whether a single modern seismometer can measure the direction in which an earthquake occurred. Currently, the article says that the instrument can measure in three spatial axes, but not whether any such information can be extracted from this data. The article also says that Zhang Heng's seismograph "supposedly" could measure direction (see WP:WTA about that). Modern Chinese researchers claim that a reconstruction of the seismometer fulfills all descriptions, including detecting the direction of simulated events. [1] Surely a second century instrument doesn't work better than a modern scientific device....... right? ;)

Of course I understand that usually it makes no sense to try to use one seismometer to find the direction of an earthquake, but that's a poor excuse. What if you were trying to find out what cities were being destroyed during a nuclear war that had destroyed your communications? Wnt (talk) 19:14, 26 September 2008 (UTC)[reply]

I'm merely an amateur. The waves do all have directions. Also shear (side-to-side, up to down) waves have a different propagation speed than compression waves, so gross distance and angle should be measurable. Some information is usually grossly visible, even in crude instruments. One problem is that seimometers actually measure linear motion, not tilt, and the direction is shown by the tilt. High speed, high accuracy tiltmeters seem to be research projects. Another problem is that it's very difficult to interpret the data without correlating several instruments in different places. Otherwise, a truck on the freeway can look like an earthquake in Java. Another problem is that it's hard to assure an instrument cluster's north vector. It can be surveyed by locating earthquakes using time-based methods,and then calibrating the cluster, but the vector drifts as the piers, sensors, electronics, springs and hinges age, heat or tilt (e.g. from tides or barometric pressure). If we can't use the time based methods, with only one instrument, it's hard to survey the cluster's north vector at all. The result can be a substantial mislocation as the trigonometric sine error works out over many miles. Time-based location is just more accurate. In amateur (and I think some old) instruments, an additional problem is that the frequency transforms of the instrument are unot characterized, so resonances in the instrument can distort the apparent wave directions. I hope that helps. Ray Van De Walker 07:51, 30 September 2010 (UTC)

what is trhe difference between a seismogram and a seismograph?[edit]

One of them draws and the other prints —Preceding unsigned comment added by 71.168.98.180 (talk) 21:38, 9 December 2008 (UTC)[reply]

I believe a seismogram is the result that comes out of a seismograph? --maye (talk) 23:40, 5 January 2012 (UTC)[reply]

Dynamic equation for a seismometer[edit]

I think we need to include the differential equation of motion of a seismometer and mention the importance of each term. Hamsterlopithecus (talk) 22:50, 19 February 2012 (UTC)[reply]

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Sentence not grammatically correct, doesn't make sense[edit]

"In other systems the weight is allowed to move, and its motion produces an electrical charge in a coil attached to the mass which voltage moves through the magnetic field of a magnet attached to the frame." This needs to be rewritten as it does not clearly illustrate the system due to grammatical errors. — Preceding unsigned comment added by 2601:801:4100:4420:B91A:1E1A:E1CE:4B84 (talk) 16:21, 30 January 2021 (UTC)[reply]

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