calc_crust_corr
Called by: correct_ttime for each phase if crust_corr_on =1.
Includes: iscloc.h, jb_model.h, crust_type.h, crust_type_key.h.
Input arguments:
Character indicating whether the phase is P or S.
Latitude of either source or station.
Longitude of either source or station.
Depth of source. 0 for station.
Elevation of station if elev_corr_on =1. NULLVAL otherwise and for source.
dt/dd for the phase.
Structure members updated: None.
Return: Travel time correction in seconds.
Gabi Laski has made available on the REM web site a global crustal
model on a 2 x 2 degree grid. (http://mahi.ucsd.edu/Gabi/rem.html or
Bassin, C., Laske, G. and Masters, G., The Current Limits of Resolution
for Surface Wave Tomography in North America, EOS Trans AGU, 81, F897, 2000.)
Each 2x2 degree 'tile' of the Earth's surface is assigned one of 360 crustal
structures each made up of 7 layers. Each layer has a P velocity, an S velocity
and a density.
Here, the crust types are stored in crust_type.h in a two dimensional
array which has indexes corresponding to latitude and longitude. The velocity
profiles for each crust type are stored in crust_type_key.h in an array of
suitable structures. For each phase the time to traverse the crust of the
homogenious earth model in use is subtracted from the travel time and the
time taken to traverse the crust from this model is added on. This is done
for both the source and the station, taking the depth of the former into
account and allowing for non-radial take off angle.