abstract

Seismicity of peninsular India is studied from a detailed consideration of the historical as well as recent earthquake data, and a catalog of earthquakes from the earliest time through 1974 occurring within the region, 5°N-28°N; 67.5°E-90°E, is prepared. Separate epicenter maps showing instrumentally located earthquakes and the earthquakes located by using macroseismic observations are presented. A number of seismic zones, based largely on the distribution of earthquake epicenters but, also, partly on local geology and fault-plane solutions, are tentatively identified. Some of the zones of weakness may be related to the plume-generated triple- or four-armed rifts formed at different times in the geological past. Recent seismicity is related to the rejuvenation of activity along some of these zones of weakness. Fault-plane solutions for six earthquakes, widely separated geographically and related to different seismic zones, obtained by using teleseismic observations from the records of worldwide standardized stations network, show two consistent features. One of these features is that the axis of pressure, P, trends nearly in the north-south direction, and the other is that one of the nodal planes, in at least one possible solution for each event, strikes in a northnortheast to east direction and shows a left lateral sense of motion. The former observation indicates that the high stresses generated by the continental collision, caused by the northward movement of India, have affected the entire Indian peninsula. The latter observation suggests that the whole region may be under a state of left lateral shear. This shear is believed to be a consequence of the geometric disposition of the Indian and Eurasian continents at the time of collision and the subsequent plate kinematics. The latter observation also suggests that the orientation of the zones of weakness with respect to the ambient stress field may be an important factor in determining the faults along which the earthquakes are likely to occur.

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