Abstract

Seismic P-wave velocity (Pn) of the uppermost mantle beneath the Shillong Plateau has been studied using a temporary seismographic network. Refracted Pn arrivals of shallow distant earthquakes (M > 3.0) recorded at pairs of stations, lying within 2° azimuthal differences with respect to a given epicenter, are used in this study. Since the method is based on relative travel-time differences, the measurement is independent of origin time and location errors. The average Pn velocity is found to be 8.57 ± 0.02 km/sec, which is higher than the average mantle velocity 8.13 km/sec under other areas of the Indian subcontinent. The observed high Pn velocity beneath the plateau may be attributed to the presence of high density material.

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