PSN-L Email List Message

Subject: Re: IASP91 table in Winquake
From: Larry Cochrane cochrane@..............
Date: Mon, 08 May 2000 15:09:21 -0700


When I added the IASP91 tables to WinQuake I was surprised to see the P and
S wave tables went out farther then the JB tables. Since the P wave goes
into a shadow at around 106 deg (1 deg = ~111km) I'm not sure what the
tables represent past this distance.

-Larry Cochrane
Redwood City, PSN

At 05:11 PM 5/6/00 EDT, you wrote:
>Hello all:
>The recent quake on the Minahassa Peninsula, Sulawes reminded me of a 
>question that I have had for some time about the use of the IASP91 table in 
>The teleseismic table in Winquake cannot be used to calculate the P and S 
>wave arrivals for distances beyond about 12,000 km because beyond this 
>distance the arrival location is in the "shadow" of the earth's core and 
>arrivals are modified by travel through or along the boundary of the core
>location is about 15,000 km from the Minahassa event location).  Thus, 
>Winquake gives the error message "Can't place P and S markers" when one
>to calculate P and S wave arrivals beyond this distance using the
>table.  Yet if one uses the IASP91 table beyond the critical distance, P and 
>S markers can be calculated.  I guess I don't understand what the IASP91 
>table does that the teleseismic table doesn't do.  Are the P and S wave 
>arrivals that can be calculated using the IASP91 "real" beyond the critical 
>distance?  I noticed that my event record using the IASP91 table to
>P and S arrivals and some of the other event records posted for the
>quake showed 3 to 4 minutes difference between the calculated P wave arrival 
>and what looked like the first arrival on the record.
>Can someone shed some light on this issue?
>Bob Laney
>Herndon, VA
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Larry Cochrane <cochrane@..............>