Re-examination of fault model for the 1982 Urakawa-oki earthquake by analyses of seismic, geodetic, and Tsunami data.

Abstract

A fault model of the 1982 Urakawa-Oki earthquake is determined by analyzing seismic, geodetic, and tsunami data. Using Rayleigh waves with periods longer than 200s and P-wave first motions we obtain the source mechanism characterized by a reverse fault with the P-axis of the NE-SW direction. The seismic moment is 2.7×1026 dyn ·cm. The fault model is constrained but not uniquely determined by aftershock distribution and leveling data. Tsunami simulation for actual ocean bottom topography helps us infer the fault parameters. Comparison of tide gauge records and the simulated tsunamis shows that the fault model inclined from the Pacific Ocean to the inland of Hokkaido provides the best fit to the observation. The fault model has a dimension of 12×22 km2 on a plane dipping 39° toward N30°E. The average dislocation is estimated to be 2.5 m. The generation of the earthquake may be ascribed to the collision of the Kuril arc with the Tohoku arc.