PSN-L Email List Message

Subject: Re: WinQuake display phases
From: "Larry Cochrane" cochrane@..............
Date: Fri, 15 Jun 2001 19:56:02 -0700

John and others,

WinQuake has LR and LQ phase display markers. These phases are part of the
JB travel-time tables that comes with WinQuake. You can display them by
going to the Phase Control dialog box (View/Phases/Phase Control menu items)
and deselecting IASP91 check box. You should see the LR and LQ phases in the
Select From or Selected Phases list boxes. If you don't see them you will
need to download the complete set of jb tables here After unzipping
the file, copy all of the JB table files to the directory location displayed
in the Phase Control dialog box.

Once you add the phases to the Selected Phases list box they should show up
when you display the phases in the event window. I don't know what the
travel times are of the LR and LQ phase in the JB tables. They could be
calculated and compared to the formula John provided below. If they don't
match a new set of LR and LQ JB tables could be created using the formulas.
I don't have time right now too look into this. If someone out there would
like to work on this I can help out.

-Larry Cochrane
Redwood City, PSN

----- Original Message -----
From: "The Lahrs" 
To: "Larry Cochrane" 
Sent: Saturday, June 09, 2001 4:46 PM
Subject: Re: WinQuake

> 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
> 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.


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