Category Archives: Seismology
In this post I am not talking about the chopped audio method used in all my previous devices. This one is just straight audio – directly into the PC’s sound card.
Some time ago I had bought into the idea that “you can’t record earthquakes through a PC’s sound card because they don’t respond to low frequencies,” in fact I had repeated it myself. But recently I’ve found that this is not strictly true for all sound cards. Very long period waves from distant quakes will certainly not register much through any sound card, but on some cards, quite good results can be obtained with local quakes and P waves from strong, distant quakes. (The trace in the above photo shows P waves from a 7.3 quake in Japan, a little left of center. Ignore the other stuff to the right of it; that’s “student quakes”.) Continue reading
After about a year and a half of messing around, I finally got this very cheap seismometer system working and displaying real-time data under both Windows and Linux (More on how to set up Linux later.) Educationally, it has great potential.
It consists of the sensor and an interface box. This interface is radically different from traditional digitizing methods. The earthquake signal, after being amplified, then modulates a fixed 5 KHz audio tone. That plugs into the microphone socket of a computer running three pieces of software under Windows (XP in the one shown here). They are, 1) the one I put together – “seismochop”, which retrieves the earthquake signal from the audio tone and converts it to serial data, 2) a virtual serial port package called com0com which acts as a relay, and 3) Amaseis – software that records and displays earthquake data. These three can be downloaded free.
This very cheap and rather unusual way to digitize an earthquake signal was inspired by my experience in ham radio, when AM transmitters were common. When I found the same principle (amplitude modulation of a carrier wave, or more correctly here, pulse amplitude modulation) used in “cheapchop“, even including the basic software, I was able to get it working.
Here is a screen shot of a local quake I recorded today. There’s a DOS window I brought to the foreground for the screen shot. That’s seismochop showing the data samples at about 11 samples per second. Continue reading
I made this video to show how an elevator affects the magnetometer trace. This is something, for those using a magnetometer to detect earthquake precurors, to be aware of. Notice the characteristic of the trace. Not to be mistaken as an earthquake precursor.
(Editor’s note: Simon is using the magnetometer described in this post. He lives on the 7th floor and sees very little traffic noise on his daily recordings, but at certain times of day he had been plagued by some very regular signals, always about the same size. In this video he shows how he finally tracked down where they’re coming from.)
Student Seismology Research Station – Seismometer and Magnetometer Recording Via Computer Sound Card
One cannot ordinarily record earthquakes via a computer sound card as they don’t respond much to the slow vibrations experienced in earthquakes. (Update: not strictly true. See my latest on this: Simplest Seismometer – Experiments with direct recording through PC sound card) However, with some cheap electronic trickery and clever software, it can be done, and very adequately for the purposes of study. The seismometer above, made by a high school student, in its first night of testing recorded this local 3.8 quake – a magnitude 1 in Taipei:
(click on the pictures for larger versions)
and as a surprise bonus, some filtering of background noise revealed this distant quake as well. It was a 5.9 from 1000 km away in the Philippines.
magnetometer: n. [Magneto- + -meter]
An instrument for measuring the intensity of magnetic forces [1913 Webster]
precursor: One who, or that which, precedes an event, and indicates its
approach; a forerunner [1913 Webster]
Scientists, particularly in Japan, have for many years been gathering evidence of electromagnetic signals that come from under the ground before earthquakes. The bigger the signal, the bigger the quake is likely to be. This can occur hours before, and in some cases, days or even weeks before the quake itself. Why it happens is not well understood but current theory is that it has to do with rocks creating large electric currents as a result of crushing or grinding under high pressure. Several methods have been used to detect these reportedly erratic, electromagnetic pulses. The method described here is one of the simplest. Technically, it’s called a “search coil magnetometer.” This does not respond to very slow magnetic changes, but it can sense short-term ones, making it suitable for detecting earthquake precursors. Continue reading
In my search for educational projects that can engage a kid’s interest, I recently began looking into seismology (from Ancient Greek, “seismos”, an earthquake and “logia”, study of.)
Being a rather high-tech subject, I was skeptical of my chances of reducing it to something kids could do, but I gave it a shot anyway, since it’s very applicable here in Taiwan, where earthquakes average a couple a day. (You can see them on this website: http://www.cwb.gov.tw/eng/index.htm )
The goal was to come up with some kind of a detector; the simplest and cheapest design possible that a student could plug into a computer and record real earthquakes. Although still in progress I wanted to share what I’ve done so far as it’s a fascinating field and full of good, observable data that will give anyone a deeper understanding of the planet we live on. Continue reading