PSN-L Email List Message

Subject: Fwd: Re: Iris Waveform Chart
From: John or Jan Lahr johnjan@........
Date: Sun, 06 Feb 2005 22:06:35 -0800

John Taber, below, points out two sources of information on caustics that
are on the web.  

The upper set if figures on Paul Richards's page (second URL below) shows how caustics can develop when even when the velocity increases continuously with depth. 

The lower set of figures shows how a shadow zone and caustic are created when there is a low velocity zone.


Date: Sun, 6 Feb 2005 22:17:39 -0500
Subject: Re: Iris Waveform Chart
To: John or Jan Lahr <johnjan@........>
From: John Taber <taber@........>


That is my understanding as well. It is a point where energy will be focused.  Rick Aster has a fairly complete explanation at  ..  One website which shows an example, but without defining it is I had unsubscribed from the PSN list while I was away so your email reminded me to resubscribe.


On Sunday, February 6, 2005, at 08:13  PM, John or Jan Lahr wrote:


My understanding is that a caustic is formed when the derivative of Distance with
Take-off angle is zero.  ("Distance" is the angular distance from the earthquake
to the place where the ray reaches the surface of the Earth and Take-off angle
measures the direction with respect to vertical that the ray leaves the earthquake

Other cases of constructive interference are not termed caustics as far as I
know.  I'm traveling now, so can't refer to any seismology books and have
yet to find a good explanation on a web site. 

Maybe John Taber or Alan Jones can double check me on this!


[ Top ] [ Back ] [ Home Page ]