REFLECTION AND TRANSMISSION OF SURFACE WAVES AT A VERTICAL DISCONTINUITY AND IMAGING OF LATERAL HETEROGENEITY USING REFLECTED FUNDAMENTAL RAYLEIGH WAVES

Abstract

We present a technique for the determination of approximate reflection and transmission coefficients of surface-wave modes for a vertical plane discontinuity that is simple to use. It is applied to different models of lateral heterogeneity. Furthermore, a method for the localization of lateral heterogeneity using the coda of the fundamental Rayleigh mode is proposed. In particular, the frequency content of surface waves enables the investigation of the lower crust and the uppermost mantle. Lateral changes of the S-wave velocity, density, and P-wave velocity lead to the formation of the coda of the fundamental Rayleigh mode that contains delayed surface waves that reach the recording station indirectly. The complicated structure of the coda makes it impossible to identify reflected surface waves visually using a small number of recordings only. Coda waveforms of a large number of sourcestation pairs are inverted simultaneously for experimental reflection coefficients. The method is successfully tested using an ultrasonic model experiment. Finally, it is applied to Central Europe and especially to the Tornquist zone (TZ), mainly using records of the German Regional Seismological Network (GRSN). The resulting reflection coefficients depend on frequency and give an image of the location of reflectors.