John & John,

Thanks.

I reviewed your two references and then found this one:
http://wwwrses.anu.edu.au/seismology/SHon2002/sp4sw.pdf which has some
revealing graphics as well.

Based on some of the stuff I've been reading, it looks like a lot of =
this
work was done ca. 1911. It still seems remarkable that so much was =
(could
be) done prior to the advent of the computer.

Regards,

-Tim-

=20

=20

-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@............... =
On
Behalf Of John or Jan Lahr
Sent: Monday, February 07, 2005 1:07 AM
To: psn-l@..............
Cc: taber@........
Subject: Fwd: Re: Iris Waveform Chart

=20

John Taber, below, points out two sources of information on caustics =
that
are on the web. =20

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. =20

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

Cheers,
John




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

John,=20

That is my understanding as well. It is a point where energy will be
focused.  Rick Aster has a fairly complete explanation at
www.ees.nmt.edu/Geop/Classes/GEOP523/Docs/rays2003.pdf  .  One website =
which
shows an example, but without defining it is
http://www.ldeo.columbia.edu/~richards/ARhtml/add_to_Sec9.4.html. I had
unsubscribed from the PSN list while I was away so your email reminded =
me to
resubscribe.=20

John=20


On Sunday, February 6, 2005, at 08:13  PM, John or Jan Lahr wrote:=20




Tim,=20

My understanding is that a caustic is formed when the derivative of =
Distance
with=20
Take-off angle is zero.  ("Distance" is the angular distance from the
earthquake=20
to the place where the ray reaches the surface of the Earth and Take-off
angle=20
measures the direction with respect to vertical that the ray leaves the
earthquake=20
source.)=20

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=20
yet to find a good explanation on a web site. =20

Maybe John Taber or Alan Jones can double check me on this!=20

Cheers,=20
John=20

















John & John,

Thanks.

I reviewed your two references and =
then
found this one: http://w=
wwrses.anu.edu.au/seismology/SHon2002/sp4sw.pdf
which has some revealing graphics as well.

Based on some of the stuff I've =
been
reading, it looks like a lot of this work was done ca. 1911. It still =
seems
remarkable that so much was (could be) done prior to the advent of the
computer.

Regards,



-Tim-

 



 

-----Original =
Message-----

From: =
psn-l-request@..............
[mailto:psn-l-request@............... On
Behalf Of John or Jan Lahr

Sent: Monday,
 February 07, 2005 1:07 AM

To: =
psn-l@..............

Cc: taber@........

Subject: Fwd: Re: Iris =
Waveform
Chart

 

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.



Cheers,

John







Date: Sun, 6 Feb 2005 22:17:39 =
-0500

Subject: Re: Iris Waveform Chart

To: John or Jan Lahr <johnjan@........>

From: John Taber <taber@........>



John, 



That is my =
understanding as
well. It is a point where energy will be focused.  Rick Aster has a =
fairly
complete explanation at www.ees.nmt.edu/Geop/Classes/GEOP523/Docs/rays2003.pdf 
..  One website which shows an example, but without defining it is =
http://www.ldeo.columbia.edu/~richards/ARhtml/add_to_Sec9.4.html.
I had unsubscribed from the PSN list while I was away so your email =
reminded me
to resubscribe. 



John 





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








Tim, 



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 

source.) 



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! 



Cheers, 

John