Another FYI, in case you didn't
notice in the notes on the USGS pages,  the IASP91 is based on what
they term a
spherically-symmetric model, the ellipsoid is not taken into account. 
Those pages are apparently not going for ultra-high accuracy, just for
a simple average.  I guess, they assume, those pages are close enough
for government work, for the public, HA!

 Stephen

 PSN Station #55 



GPayton wrote:

  
  
  
  
Thank you, Stephen & Kathy,
  
 
  
No, that had not been mentioned and is good information.  I
guess I could say that if it is good enough for the USGS, it should be
good enough for me!
  
 
  
However, as accurate as it presently may be, it IS a table of
averages and the wave plane would still propagate differently each
event through different conditions within the mantle.  Therefore, as I
said, either JB or IASP91 is accurate enough for my primitive needs.
  
 
  
Thank you again & Happy New Year.
  
Jerry
  

    
-----
Original Message ----- 
    
From:
    Stephen & Kathy 
    
To:
    psn-l@.............. 
    
Sent:
Friday, January 01, 2010 12:56 AM
    
Subject:
Re: And Now A Simple Question
    


    
    FYI, (sorry if this was already
mentioned), the USGS Earthquake time travel calculator uses the IASP91
model, as per the note at the bottom of the page; see the following
link.

    http://neic.usgs.gov/neis/travel_times/artim.html

    

The USGS "Theoretical P-Wave Travel Times" map with shadow zones, also
says it uses the IASP91 model.  Following is a link to an example for
the 6.0 Banda Sea quake on Dec 26...  see notes below map.

    http://neic.usgs.gov/neis/bulletin/neic_qrat_t.html

    

     
Stephen

  PSN Station #55

    

GPayton wrote:
    

      
      
      
Thanks to you, Larry and all that answered.  I've searched
and can only find that the IASP91 is the newer, but cannot discover
that it would matter that much in my limited sensor setup and
environment.  Looking at other posts, the JB seem to be the favorite,
if not be default.
      
 
      
Regards & Happy new Year to All
      
Jerry