EXPLORING DEEP INTERFACES BY SEISMIC WIDE ANGLE MEASUREMENTS*

Abstract

ABSTRACT Amplitudes of the vertical ground motion are larger in the critical angle region than in the near vertical region, especially amplitudes coming from deeper boundaries or interfaces with small velocity contrast. Four basic boundary models are used to derive specific travel time patterns for first order and higher order interfaces. The transition from reflected waves to diving waves in the supercritical angle region is shown for the different models. Examples from wide angle surveys in Bavaria and in the Buchara region in the USSR have many characteristic similarities. Travel time patterns and asymptotic velocities are almost identical. The most important boundaries of the continental crust ‐ the Mohorovč Ić discontinuity and the top of the crystalline basement ‐ correspond to two boundary models mentioned before. Amplitude and frequency investigations have been used to derive items of the M‐discontinuity. It is certainly a gradient zone and seems to have a lenticular structure with material of stepwise different velocities.