PSN-L Email List Message

Subject: Re: New Station Questions
From: "Jonathan Peakall" jpeakall@............
Date: Wed, 28 Aug 2002 08:22:24 -0700


Wow, neat stuff. I took a brief look, will look in depth soon. Sounds like a
great project!

> It's great that you've set up a seismograph station in your
> school!!!  There is a
> national effort to promote school-based seismic recording which is
supported by
> the NSF through IRIS 
>  and the USESN
> US Educational Seismograph Network .
> Your efforts and feedback to these groups would be very helpful to the
> At 06:56 AM 8/27/2002 -0700, you wrote:
> >So, onto the questions:
> >
> >1) What is the average sample rated used by stations?
> This relates to the sensor period and the type of earthquake that one
> to record.  For local events a sensor with a natural frequency of 1 to 2
Hz is
> ideal and sample rates of  50 Hz to 100 Hz are typically used.  Keep in
> that a filter is required prior to the AD that will eliminate frequencies
> the Nyquist frequency
> which is one half of the sampling frequency.

All new to me. Great page about Nyquist stuff. Still digesting it, but is
the bottom line to keep my sample rates above the Nyquist frequency, right?

> For recording distant (teleseismic) events a sensor with a period of about
> 15 - 20
> seconds is good because the surface waves have a lot of energy in this
> Due to limited dynamic range the higher frequencies are often filtered out
> a long-period system, so a high cut filter might be set to 1 Hz and the
> sampling
> rate set to 6 Hz.
I live in northern CA, about 289kms from Larry's site in Redwood City. My
goal is to make a system sensitive enough to record moderate quakes that
Larry does. If we get a hit or two a week, that would be fine. So should I
be able to do this with a 2 sec pendulum sensor of reasonable functionality?

> >4) How can I convert magnitude to UG or MM?
> If you system is calibrated so that you know what the peak amplitude
> is in microns for a local event, then you can use Richter's original
> magnitude formula to estimate the magnitude.  See:
The main thing I want to do is to be able to use Larry's site to check my
system. His site shows the most recent/largest event in accelration units. I
want to be able to convert that to magnitude, or otherwise know when Larry
has recorded and event that I should have.

Thanks for the help!

Jonathan Peakall


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