Abstract
The source process of a deep-focus earthquake (h=544km) of January 29, 1971 in the Sea of Okhatsk is investigated on the basis of the primary P and SH pulses, which are deduced from the WWSSN long-period seismic signals after eliminating the influence of the seismograph, crust and mantle by the deconvolution technique. The shape of the primary P and SH pulses is characterized by a uni-directional, single pulse. The pulse widths of these primary pulses vary depending on the location of stations. The pulse width of the primary SH pulses is comparable to that of the primary P pulses at stations placed in nearly the same azimuth and having nearly the same epicentral distance. These results strongly suggest that the earthquake occurred in the form of shear faulting, the model of which was inferred to be a uni-lateral propagating fault. In the deduction of this inference, the primary SH pulses especially played an important role. Source parameters for the present earthquake are determined by comparing the theoretical P and SH wave displacements directly with the primary P and SH pulses. Seismic moment Mo, rupture velocity υ, fault length L, fault width W, displacement discontinuity D and stress drop Δσ determined are as follows: Mo=2.8×1026dyne·cm, υ=4.5km/sec, L=20km, W=10km, D=1.2m and Δσ=240 bars.
