Seismicity, b-values and focal depth distributions of earthquakes in the Andaman-Nicobar Island region

Abstract

An analysis of seismic data of the Andaman-Nicobar Island region that lies between 4°-16°N and 90°-98°E has been made for the 1900 – 1982 period. A seismicity map has been prepared for the aforesaid period. The major features of the seismicity of the region are well seen from this map. It shows a well-defined pattern almost parallel to the structural trend of the basin. The b values as determined from the earthquake frequency-magnitude relationship of Gutenberg and Richter are found to be in good agreement with the result obtained in northeast India. The depth-distance cross-sections, measured eastwards from 92°E at the latitudes 7°N, 9°N, 11°N and 13°N, have been made to understand the foci distribution and the nature of seismic zones and their geometry beneath the Island arc system. These seismic cross-sections reveal some interesting results on the oblique subduction of the Indian plate beneath the Andaman sea plate and rifting of the central Andaman through.