Theoretical seismograms for block structures

Abstract

In constructing theoretical seismograms for large models with block structures, approximate methods are particularly efficient. For example, in treating Earth's crust block models, the ray method with various modifications for including diffracted waves can be used. Smaller block structures, of dimensions comparable to a wavelength, are efficiently treated by direct numerical methods. In this way practically important problems of engineering seismology, seismic microzoning, etc., can be solved. The method of so-called conservative diference schemes combines effectively the advantageous features of both the standard finite element and finite difference methods. The basic properties of the method, as well as some features of the corresponding Fortran IV program LATER, are explained on a computational example. The example concerns a highly simplified evaluation of the seismic response of the earth fill. In the frequency range under study two resonance frequencies are identified. Moving along the surface of the fill, from the base to the peak, the predominant frequency decreases. Some prospects of direct numerical methods in seismology are briefly discussed in concluding section.