[irised] wells nevada record, station SHMT

[Jeff Barker]

Hi all,

Without making measurements of your particular seismograms, I think 
John Taber has it right.  At regional distances, beyond say 150 km 
out to several hundred km, you are likely to see a small arrival, Pn, 
which is the head wave or critical refraction from the top of the 
Mantle arriving before the larger Pg, which is a combination of the 
direct wave and multiple reflections within the crust.  There are 
comparable S phases but you are unlikely to see Sn on a 
vertical-component seismometer.

John Lahr's website has a link to a USGS site where you can calculate 
arrival times of many phases (waves) at your station from recent 
earthquakes.  The URL is
http://neic.usgs.gov/neis/travel_times/artim.html
Set the maximum distance to something like 10 degrees and choose an 
appropriate minimum magnitude (5.0 is good).  Be sure to click the 
radio button for "All branches".  You get lots of predicted arrival 
times, but look for Pn, Pg and Sg.  For Jerry's station the arrival 
times from the Wells earthquake are 48, 57 and 98 seconds after the 
earthquake's origin time.

On my website is an animation that shows Pn and Pg propagating in a 
model of the crust.  It's the second animation on the following page:
http://bingweb.binghamton.edu/~jbarker/animations.html
Pn is the "head wave", a weak, linear wave seen arriving first at the 
surface for distances beyond about 150 km (for this model).

By the way, it was exactly this sort of data that Mohorovicic used to 
interpret that there was a difference between the Crust and the 
Mantle.  That's why we call this boundary "the Moho".

Jeff Barker

P.S. - Craig, your SAC file didn't include the station lat and lon, so 
I couldn't look it up.  I did notice that the station name is defined 
as SUNYB.  This must be the default from AmaSeis, because that stands 
for SUNY Binghamton.

-- 
----------------------------------------------------------------
Jeffrey S. Barker
Assoc. Prof. of Geophysics      jbarker at binghamton.edu
Dept. of Geological Sciences    geology.binghamton.edu/~barker
SUNY Binghamton                 (607) 777-2522
Binghamton, NY  13902-6000      FAX (607) 777-2288