Global Inversion of Phase and Group Velocities of Fundamental Mode Rayleigh Waves in the Period Range 20 to 100 sec

Abstract

We have applied to the extensive phase and group velocity data compiled in a first stage of this work (Rosa, 1986; Rosa & Aki, 1991) the stochastic inverse method in order to obtain the global distribution of Rayleigh wave phase velocity values. This is the first attempt to invert globally a data set consisting entirely of R1, which does not suffer from polar passages which tend to complicate the waveform by multipath interferences. Toe resultant anomalies of the phase velocity correlate well with major tectonic features and with previous regional studies made for similar periods. It was demonstrated that these results at relatively longer periods can now be used for determining the moment tensor of events in most regions around the globe. Shorter period results, however, cannot be used in this fashion, due to large residual data variance. ln the case of our group velocity study, we found that since the standard deviation of the regionalized values were very similar to those obtained in the phase velocity regionalization (Rosa, 1986; Rosa & Aki, 1991), the large, unacceptable error bounds achieved after the application of the stochastic inversion to the group velocity data, are related to the larger errors involved in the measurement of group velocity. This makes it much harder to obtain geophysical meaningful results from group velocity data.