Files 'prem*.*': B-spline approximation of PREM by Dziewonski and Anderson (1981). Guide to the input data for the complete ray tracing program. By Ludek Klimes Date: 1998, October 5 The spherically symmetric Earth model is a B-spline approximation to PREM. The model consists of 13 complex blocks (layers) limited by Earth's surface (surface 1), and separated by 9 interfaces of the first order and 3 interfaces of the second order. The values of parameters at grid points are taken from the table II of the paper by Dziewonski and Anderson (1981). Some values, specified in the table II of the paper, which will likely be accurately fitted by cubic splines are left out. Between the given points within each complex block, the parameters are interpolated using natural cubic splines. The model is specified in geographic spherical coordinates: X1=longitude (in radians), X2=latitude (in radians), X3=radius. Four elementary waves passing through the core are computed for the source in the depth of 200 km. To change the source depth, see the note in input data file 'prem-crt.dat'. Two-point rays, coming to the receivers at the Earth's surface in the epicentral distances from 110 to 178 degrees with the step of some 2 degrees, are determined. Sample History file to run the complete ray tracing program: 'prem-crt.h'... History file running 'crt.for' to trace the two-point rays and then rewriting the resulting travel times at the given receivers by means of program 'crtpts.for' into formatted output files. Files 'prem-*.dat' listed below contain the sample input data for the complete ray tracing program. The input data consist of the 7 data sets (1) to (7) listed in file 'crtdoc.htm' (corresponding to lines (2) to (8) of input data for 'crtin.for'). Note that several data sets may be located in a single file. 'prem-crt.dat'... file containing the data sets: (1) CRT (3) DCRT (4) INIT 'prem-mod.dat'... File containing the data set: (2) MODEL 'prem-cod.dat'... File containing the data set: (5) CODE 'prem-rpa.dat'... File containing the data set: (6) RPAR 'prem-wri.dat'... File containing the data set: (7) WRIT 'prem-src.dat'... File containing the source coordinates. 'prem-rec.dat'... File containing the receiver coordinates. Remarks within the input data files: The comments in brackets situated at the ends of lines, after the input items, are not the part of the input data. They are just remarks placed so as to be skipped when reading the input data. The last input line of a data file is usually followed by (a) Empty line, line '====' and empty line, or by (b) Empty line, line '----', empty line, text describing the input data, empty line, line '====' and empty line. Reference: Dziewonski A.M., Anderson D.L.(1981): Preliminary reference Earth model. Phys. Earth Planet. Inter., 25, 297.