PSN-L Email List Message

Subject: Re: Earthquake strength
From: John Lahr johnjan@........
Date: Tue, 08 Jul 2008 21:07:02 -0700


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:
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


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


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