Abstract

Surface waves from aftershocks (magnitude>5) of the great Sumatra Earthquake recorded at the STS-2 broad-band seismometer, located at Hyderabad, are used to estimate the average shear wave velocity structure of the Bay of Bengal. The fundamental mode Rayleigh waves are used to construct Rayleigh wave group velocity distribution maps of the region using multiple filtering techniques. These group velocities are plotted against the corresponding periods, and thus obtained the dispersion curve for each of these events. Later these events are classified into two clusters based on source location and similarity of structure sampled. An error weighted average, group velocity dispersion curve is obtained for each of these clusters and are inverted individually to look at the one-dimensional shear wave velocity structure beneath the Bay of Bengal. Two velocity models were obtained for each cluster with a good match between the calculated and observed dispersion curves. The first is the model that gives the number of interfaces while the second yields a model in terms of the number of layers. In order to have a good resolution between the layers including the thin strata, the velocity gradient need not be extremely smooth which otherwise will produce an average effect. In determining the model with the minimum number of layers, the early stage inverted models were examined and adjoining layers that had similar wave speeds were merged into a single homogeneous layer. This model was used as the starting model for subsequent inversion. This process was repeated until satisfactory model whose forward solution matched the significant features of the measured dispersion curves. The final models suggest a thick continent-like crust beneath the Bay of Bengal. The average depth to the crust-mantle boundary is 30