Deep structure and seismotectonics of the Wharton Basin, Indian Ocean

The deep seismic sounding materials on the structure of the earth's crust and upper mantle in the Wharton Basin of the Indian Ocean are generalized and reinterpreted. The bulk of the deep seismic sounding data in the Wharton Basin were obtained during American expeditions using two-vessel techniques. The sections of the earth's crust and upper mantle were compiled with the use of the To method assuming a horizontally layered medium with constant seismic velocities in each of the layers. The time-distance curves of the first arrivals of refracted waves published by Francis and Raitt [23] were digitized and reinterpreted with the two-dimensional modeling method with account for the vertical velocity gradient in the layers of the earth's crust and upper mantle. In so doing, the changes in the bottom topography and thickness of the sediments over the deep seismic sounding profiles were also taken into account. The results of the modeling over selected profiles are presented in the form of a combined seismic cross section along a sublatitudinal transect 3250 km long; it suggests a significant variability in the deep structure of the Wharton Basin. A database on the earthquakes of the region considered was compiled; it contains 77 events that have occurred from 1903 up to the present. It was used to plot histograms of distributions of magnitudes and hypocenters of the earthquakes in the basin. A conclusion is made about the correlation between the seismicity and tectonics of the region.