Abstract
The source process of a large deep-focus earthquake (h=643 kin) which occurred in the Sea of Okhotsk in 1970 is studied on the basis of the seismic body waves recorded on the WWSSN long-period seismograms. The P-wave source functions are obtained from the long-period P-wave signals by eliminating the effects of the seismograph, crust and mantle. The interpretation of the source functions yields the following results: this shock is a triplet and three events are located at nearly the same hypocenter; the rupture corresponding to each event spreads out separately but finally covers a more or less fan-shaped surface. The source parameters are estimated from the comparison of the P-wave source functions with the calculated P-wave displacements. Seismic moment Mo, rupture velocity c, fault area S, displacement discontinuity D and stress drop da are estimated as follows: M0=1.1×1027 dyne ·cm, c-4.0 km/sec, S=420 km2, D=1.9 m and Δσ= 320 bars. The tectonic implications of the source parameters and the orientation of the earthquake-generating stress are discussed.
