Source Mechanism Study of Quetta Earthquake of May 30, 1935.
Abstract
The source mechanism of the major destructive earthquake which occurred in the Quetta region on May 30, 1935 is determined using the P-wave first motions, S-wave polarization angles and surface waves spectral data. A thrust faulting is obtained along a plane with strike N 33"E, dip 68"NW, slip angle 124" and a focal depth of 20 km. A unilateral fault of about 106 km, rupturing with a velocity of 3.1 km/sec is obtained from the differential phase and the directivity function of G2 - G3 and R2 - R3 waves. The source parameters obtained from the surface waves spectra are: seismic moment = 1.75 x 1028 dyne-cm; dislocation = 32.81 meters; fault area = 1778 sq. km; apparent stress = 283 bars; stress drop = 567 bars; strain energy = 165 x 10 25 ergs and strain drop = 18.9 x 10-4. The high stress drop and apparent stress associated with this went suggest that high tectonic stresses are prevailing in this region. A major part of the stresses accumulated before the occurrence of this earthquake had been released through the main shock.
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