John,

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
effort.
>
>
> 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
wants
> 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
mind
> that a filter is required prior to the AD that will eliminate frequencies
above
> 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
range.
> Due to limited dynamic range the higher frequencies are often filtered out
from
> 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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