PSN-L Email List Message

Subject: Re: Large earthquake near cost of Canada
From: John Lahr johnjan@........
Date: Sun, 06 Jan 2008 18:20:01 -0800

Not really.  At my station the P-wave amplitude was about 1.5 
micrometers zero to peak.  Based on this, I computed an mb of 7.0, 
using AmaSeis' built-in magnitude calculations:

I added an image showing the calculation window to this page:
(You may have to refresh your browser to see the new image at the bottom.)

Given all of the factors that can influence the magnitude 
calculation, such as the approximate station calibration that we use 
for the AS-1 and the event radiation pattern (the USGS mb is computed 
from an average of for stations at many azimuths and distances), 
coming within 0.5 units is not too bad.  The computed USGS mb was 
6.2, so my amplitude was, if anything, a bit too large.  The USGS 
preferred magnitude of 6.5 is an Mw.


At 05:17 PM 1/6/2008, Thomas Dick  wrote:
>Wouldn't  P be expected to be larger for this magnitude of a quake 
>and the nearness to the epicenter?


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