Theoretical Seismogram Calculation for Laterally Varying Crustal Structures

Abstract

Summary A modification of the reflectivity method for calculating theoretical seismograms is introduced. This technique enables allowances to be made for differing crustal structures beneath the source and the receiver. The method has been applied to the 1971 long range refraction profile across France, and it is shown that the observed effects can only be accounted for by structure in the upper mantle. In this paper we develop a computational method which enables us to make such an allowance for the propagation effects of the different crustal structures beneath the source and the receiver using a modification of the reflectivity method. We then apply this technique to the results of the long seismic refraction profile in France in 1971 (Hirn et al. 1973) and use the experimentally determined crustal structures (Sapin & Prodehl 1973) to show that the observed effects can only be accounted for by structure in the upper mantle. Varying crustal structure and the reflectivity method The reflectivity method in its usual form (Fuchs & Miiller 1971) provides an effective computational technique for approximating the response of a horizontally layered elastic half space to excitation by a near-surface source. Since the com- putation of the complete response is exceedingly time consuming a number of simplifications are made. Only in the lower part of the layered half space, referred to as the ' reflection zone ' are all multiple reflections and interconversions of wave