PSN-L Email List Message

Subject: New Station Questions
From: "Jonathan Peakall" jpeakall@............
Date: Tue, 27 Aug 2002 06:56:23 -0700

Hi All,

I'm new to seismology. Spent a while looking through the archives. Whew! A
little intimidating! I looked for a newsgroup more oriented to beginners,
but no luck. If these questions are too basic for this group, let me know
where I might ask them, if you can.

A little background: I am a science teacher in a small rural elementary
school. As part of an Earth Science unit I am developing, I have made a
simple seismic station. My goal is to be able to record events, determine
magnitude and use the data to determine location and time of origin.
Accuracy of wave form depiction is not that important, just time and

Station specs:

2 sec pendulum style sensor (NIB magnets suspended over a 1.1kOhm buzzer
Dampening: small sheet of brass between the magnet and the coil
741 op amp amplifier
DATAQ 194RS A/D board
133 mHz laptop to log
WWVB clock with photo diode pickup (puts minute marks into log)

The sensor is very sensitive to local events. Background noise seems OK. I
could detect logging activity a couple of miles away (trees hitting the
ground look very different from seismic activity).  Jumping in my house 50'
away is visible if magnified, and dropping a rock nearby is huge.

So, onto the questions:

1) What is the average sample rated used by stations?
2) What level of compression is usually used to examine results?
3) Where can I find information to determine an ideal or reasonable level of
4) How can I convert magnitude to UG or MM?
5) Does anyone know of quakeware  that will work with this A/D board?

Sample rate/compression/signal amplification and dampening are obviously
related in trying to examine the wave form. Is there a formula, rule of
thumb,  or does one tweak the system till it "looks right"?

Larry Cochrane has been very helpful, and says that if my sensor is usefully
sensitive, I should be able to record quakes that he detects in Redwood City
(289 kms as the crow flies from me) of magnitude 3.5 or greater. His web
site shows the events in mg and cm's (actually, I thought it was ug and mm'
s, but I just looked). How can I convert these figures to magnitude? I just
need a way to figure out when Larry's site is showing an event that I should
have picked up.

I have seen some Geosource model MD-31 geophone sensor for sale cheap.
Anyone know if these are useful in my application? Frequency wasn't stated.
Unfortunately, price is a major restriction for me, so buying a nice sensors
is out of the question. I am going to build a Leham type at some point, but
part of the fun is going to be the students building the sensor for their
station, so I am committed to the pendulum style (due to ease of
construction) unless it is absolutely useless.

Thanks for your time!

Jonathan Peakall


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