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Surface-wave radiation pattern and source parameters of Koyna earthquake of December 10, 1967

NATIONAL GEOPHYSICAL RESEARCH INSTITUTE, HYDERABAD 7 A.P., India

Abstract

The fundamental-mode Rayleigh waves for the Koyna earthquake of December 10, 1967 recorded on long-period vertical component seismograms of 30 WWSSN stations have been Fourier analyzed. The radiation patterns have been plotted at six wave periods. Comparison of these data with the theoretical radiation patterns computed for various fault parameters favored the strike of the fault in N10°E direction, dip 78°W, slip 175°, and the depth of focus to be 10 km. Strike-slip faulting on a near-vertical fault plane has been inferred. The S-wave polarization angles, which have been obtained for 13 stations, also favor the above solution. Surface-wave magnitude has been determined to be 6.3 and the fault surface area to be 252 km². Using the Rayleigh-wave spectral amplitude for 50-sec period, the seismic moment, M_o, is determined to be 0.82 x 10²⁶ dyne-cm. The values of average dislocation, seismic energy, apparent stress, and apparent strain are calculated to be 108 cm, 2.25 x 10²¹ ergs, 15.4 bars and 5.3 x 10^–5, respectively. For a rupture velocity of 1.5 km/sec, the values of fault length and stress drop are found to be about 23 km and 19.8 bars, and for a rupture velocity of 3.0 km/sec these values are about 40 km and 6.2 bars, respectively.

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