Title

MODELING OF THE KOYNA, INDIA, AFTERSHOCK OF 12 DECEMBER 1967.

Abstract

Short-period teleseismic and near-regional long-period waveforms from a large aftershock (m//b equals 5. 3, origin time 06:18:36. 8 UTC) of the 10 December 1967 Koyna main event were modeled to determine source depth and focal mechanism. Identification of pP and sP on the short-period waveforms yielded a well-constrained source depth of 3. 5 to 4. 0 km. The focal mechanism was determined using a systematic trial and error (grid-testing) technique in which seven P first motions, two SH first motions, two teleseismic pP/P ratios, one teleseismic sP/P ratio, and one regional SH/P ratio were included. This heterogeneous, but sparse, data set yielded a constrained normal fault mechanism at 100 degree plus or minus 20 degree strike, 40 degree plus or minus 10 degree dip, and 240 degree plus or minus 20 degree rake. Rupture directivity is inferred from consistently high surface reflection/direct wave amplitude ratios. A circular fault of 1 km radius with a rupture initiation point at the lower edge and an assumed rupture velocity of 0. 9 V, explains the anomalously high amplitude ratios and yields a seismic moment of 3. 8 multiplied by 10**2**3 dyne-cm.

Publication Title

Bulletin of the Seismological Society of America

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