PSN-L Email List Message

Subject: Re: computer time sync
From: "Larry Cochrane" lcochrane@..............
Date: Thu, 15 Apr 2004 21:02:22 -0700

Good question. I would say it depends on the type of earthquakes you will be
recording. If you only record teleseismic events, then anything under 1/4 of
a second is probably overkill. If you record local events, then the timing
should be more accurate. The travel-time tables that WinQuake uses can be
very accurate. If an agency accurately reports the location and time of a
teleseismic event, WinQuake can place the P and S markers to within a few
seconds of the actual arrival time of the wave. Now picking the location of
the P and especially the S is another story....

Larry Cochrane
Redwood City, PSN

----- Original Message ----- 
From: "Ian Smith" 
Sent: Thursday, April 15, 2004 1:40 AM
Subject: Re: computer time sync

> for the purposes of our psn uses (plotting quake location etc) what is the
error budget for timing?  I've never seen this discussed.
> There must be a fundamental limit caused by the variation in travel times
through the earth.  Ie, if the same quake happened twice some thousands of
miles away, what would the typical variation in travel time through the
earth be?
> Another limit will be the algorthms used to calculate the distance from
the S and P waves.  Also, the accuracy on our traces with which we place the
S and P pointers.  I suspect that this is the largest source of error and
may be the equivalent of many many seconds.
> Ian Smith


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