The table format is basically that developed by Klein for his Hypoinverse earthquake location program. Program Hypoinverse assumes a flat-earth velocity structure, and the tables for that program can handle velocity gradients within layers but not first-order discontinuities. Program Hypotable allows for spherical-earth ray-tracing for locating earthquakes with program Hypoellipse. The table generation uses the iaspei-tau software developed by Ray Buland (USGS). In principle it can be used with any velocity structure with a two-layer crust, but it is not stable for all such models. This distribution includes only the iasp91 velocity model.

Input required are both the .tbl and .hed files produced by the iasp91 package, as well as the .mod file used to generate those files. These three files are assumed to be in the directory from which the program is run (in this case, directory ./build-tables). One can either create a single P-velocity table and use a single P/S velocity ratio to calculate S traveltimes from that table, or create a second S-velocity table, thus allowing for variations in the velocity ratio with depth. In this distribution, the separate S-velocity-table option is used.

One is prompted for ranges in both depth and epicentral distance (both in kilometers). One can input up to two ranges in each case: generally one set of ranges with a finer spacing for shallower depths and smaller distances and a second set of ranges for greater depths and distances with coarser spacing. Because Hypoellipse uses interpolation to calculate both the focal depth and event-station distances from these tables, one should fine-tune the ranges based on the focal depths of interest and the event-station distances involved. Two applications I have used these tables for are event locations in the western South American subduction zone where the focal depths were over 100 km, and the location of very shallow rock bursts associated with gold mines in South Africa. For this distribution we include only a set of tables for which the focal depths are assumed to be shallow.

The scripts for generating the tables in ./build-tables are self commented. By comparing them with the listing file created and the tables themselves, it should be clear what the entries mean. One can also look at the documentation which comes with the Hypoellipse package.

The files (with their most recent modification dates) in directory ./build-tables are as follows:

Modif.  date     name            comment
Oct 28  1991    IASP91.hed      1st of two table files for the iasp91 model
Jun 22  1992    iasp91.mod      v-z file for iasp91 velocity structure
Oct 28  1999    IASP91.tbl      1st of two table files for the iasp91 model
Apr 27  2002    iasp91_P.lst    listfile from hypotable from rht_iasp91_P
Apr 27  2002    iasp91_P.table  table output from rht_iasp91_P
Apr 27  2002    iasp91_S.lst    listfile from hypotable from rht_iasp91_S
Apr 27  2002    iasp91_S.table  table output from rht_iasp91_P
Apr 21  2001    rht_iasp91_P*   script to run hypotable for iasp91 P model
Apr 21  2001    rht_iasp91_S*   script to run hypotable for iasp91 P model