What is the physics behind seismometers?

[qspeechc]

Hello everyone.

I am trying to research seismometers for a project. I need to know the physics of the seismometer. Preferably the older, mechanical ones, not the modern electronic ones I won't understand. I need to bring in ideas of resonance, forced oscillations etc. I have tried googling this topic, but I have not found anything on the physics. Sure, many sites, including Wikipedia, give a lot of backround material, and explain the general idea of a seismometer, but I have not found a website that gives a type of seismometer and explains the physics.

I tried looking for a book in the university library but found nothing. Similarly with online journals. Any help at all in finding sources would be ery much appreciated. Thanks.

 

[mersecske]

Hi, what is "rubber mandrel" in fiber optic seismometers?

 

[Darryl]

I was just trying to find an electronics mag's article, where they presented a project for a seismometer. I though it was quite a nifty design. What a seismometer is basically a mass that does not move when the Earth is moving, so you can record to amount and type of movement.

The design was simple, it was a bolt, threaded fixed to the central magnet of a big, (low frequency) speaker, keeping the diaphram in place, on that threaded shaft to add nuts to give the central shaft the necessary mass, you then have a speaker (dynamic speaker, with a mass on it making it a sort of low frequency microphone, the speaker will generate EMF when the mass of the shaft/nuts moves in relation to the base of the speaker.

There are two main kinds of Earth movement, (you probably know better than me), the P wave and the 'other one', one I know is the up/down motion and the other is the sideways motion or back and fourth.

The speaker/mass combination is able to measure and differentiate between the two types of motion, the sideways motion will cause the mass to swing side to side creating a different signal to the up/down motion which will drive the coil/magnet up and down.

It also makes for easy logging of the collected data, as its basically an audio signal, that you can feed into you sound card.

It was either "silicon chip" or "elecktor" or "electronics world" that featured it.

Make a whole bunch of then, give them to your friends and loved ones, get them to install them in their back yards, sync your clocks, and then you have a cheap, internet connected detection network, you might be able to determine things like epicenter and things.

Good luck with your research..