## PSN-L Email List Message

Subject: Re: Earthquake strength
From: Barry Lotz barry_lotz@.............
Date: Wed, 9 Jul 2008 18:34:19 -0700 (PDT)

```Steiner
S-T Morrissey posted a discussion about this to psn on 13 nov 1999. I plotted a log-log sheet
with "sensor count" on the y axis and distance from sensor on the x axis and drew magnitude lines (m =3.0,3.5,4.0, etc) . I then plotted individual points for each quake I recorded on this graph. I got pretty good correlation.
Regards
Barry

John Lahr  wrote:
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
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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Steiner  S-T Morrissey posted a discussion about this to psn on 13 nov 1999. I plotted a log-log sheetwith "sensor count" on the y axis and distance from sensor on the x axis and drew magnitude lines (m =3.0,3.5,4.0, etc) . I then plotted individual points for each quake I recorded on this graph. I got pretty good correlation.  Regards  Barry  John Lahr <johnjan@........> wrote:  Steiner,You could use the equation for Ms magnitude to compute the expectedsurface wave amplitude at your location. The equation is given in thisspread sheet:http://jclahr.com/science/psn/magnitude_files/ML_magnitude.xlsunder Sheet 2.This will just be an rough estimate of the amplitude you may seebecause the radiation pattern of the earthquake will also effect
theamplitude.Cheers,JohnAt 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/__________________________________________________________Public Seismic Network Mailing List (PSN-L)To leave
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