## PSN-L Email List Message

**
Subject: Re: Earthquake strength**

From: John Lahr johnjan@........

Date: Tue, 08 Jul 2008 21:07:02 -0700

Steiner,
You could use the equation for Ms magnitude to compute the expected
surface wave amplitude at your location. The equation is given in this
spread sheet:
http://jclahr.com/science/psn/magnitude_files/ML_magnitude.xls
under Sheet 2.
This will just be an rough estimate of the amplitude you may see
because the radiation pattern of the earthquake will also effect the
amplitude.
Cheers,
John
At 02:08 AM 7/8/2008, you wrote:
>For my web page I automatically retreave current earthquake data from
>USGS and NORSAR in order to make a table of earthquakes which my
>instrument should be able to detect. I then calculate arrival times
>for the P and S waves and add that to my plot as well.
>
>Quakes that satisfy the equation sqrt(10)^(m+2.5) > d, where m is the
>magnitude and d is the distance in km, are currently in my list, and
>that limit seems roughly to correspond to what I can detect.
>
>That is, I'm assuming that the strength of an earthquake drops by the
>square of the distance. Is that a valid assumptation for earthquakes?
>
>--
>Steinar Midtskogen
>http://voksenlia.net/met/seismometer/
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