Analysis and interpretation of the heterogeneous rupture process: application of the empirical Green's function method and nonlinear inversion technique to large earthquakes

Abstract

Heterogeneous rupture processes were revealed using an empirical Green's function (EGF) method and a nonlinear inversion technique. Three events, the 1980 east Izu-Peninsula earthquake, the 1983 Japan Sea earthquake, and the 1987 east Chiba earthquake, are studied. Kernel events used as empirical Green's functions were selected among the foreshocks and aftershocks. The dimension and orientation of the fault plane were evaluated from the aftershock distribution and main shock fault plane solution. A moment ratio between the main shock and the kernel event was estimated in order to identify the number of subfaults. Strong motion waveforms recorded at near distances were inverted to estimate moment release, rupture time, and rise time at each subfault, with the stress drop calculated from the moment release and rise time. Distributions of these faulting parameters can be related to the aftershock distribution and geological structures. General features are that the moment release was large where the aftershock activity was low, that the irregular rupture propagations detected here were related to geological structures such as a ridge junction, seamount chains, and other tectonic plate boundaries, and that stress drop distributions show some relation to the pattern of aftershocks. An exception is the small moment release at the bending corner of the 1983 Japan Sea earthquake, where the aftershock activity was low. With this method, it is possible to extract not only the detailed source history but also information on geophysical structures.