PSN-L Email List Message

Subject: Re: WinQuake
From: The Lahrs johnjan@........
Date: Sat, 09 Jun 2001 17:46:25 -0600

Hi Larry,

Here's a suggestion for WinQuake.  It would be nice to have a marker for
the beginning of the Love (LQ) and Rayleigh (LR) waves.  Based on the
"Principles Underlying the Interpretation of Seismograms" travel time
chart, you could easily compute their approximate start times from:
origin time plus (distance in degrees)/2.43 for LQ and the same
formula, but divide by 2.2 for LR.  You could plot these phases for
distances of 20 degrees and greater.  This would certainly work for depths
as deep as 50 km.  For deeper depths, down to at least 200 km, one can
often see surface waves.  I'm not sure if the arrival times would need to be
delayed for these depths, but you could use the same formulas and
people would have to understand that these are the earliest start times,
that the arrivals are emergent, that the duration of the waves increases
with greater epicentral distance, that the start times are somewhat
dependent on how much of the path is oceanic and how much is
continental, and that surface waves become weaker and weaker as
the depth increases.  Clearly surface waves are not helpful for locating
an earthquake, but it would be nice to know approximately when
they should start arriving.

Just a suggestion.  Others may have a better approach.

John C. Lahr
1925 Foothills Road
Golden, CO 80402
Phone: (303) 215-9913

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Larry Cochrane <cochrane@..............>