Isodirect1 is a MATLAB-language function for modeling seismic directivity at user-selected sites around a user-defined fault. Isodirect1.m implements the Spudich and Chiou (Earthquake Spectra, 2008) directivity model. The results of isodirect1.m should be combined with the ground motion predictions of a non-directive predictive model like any of the four NGA models. Input to isodirect1.m consists ... of the coordinates of a set of sites where directivity predictions are desired, the coordinates of the corners of one or more fault segments, hypocenter location, earthquake magnitude and slip rake, desired periods for output. Output consists of directivity amplifications for all input sites, plus many intermediate results, such as the points on the fault closest to the input sites, rupture distances, etc.
[Summary provided by the USGS.]