Inferring rate and state friction parameters from a rupture model of the 1995 Hyogo-ken Nanbu (Kobe) Japan earthquake

We consider the applicability of laboratory-derived rate- and state-variabl e friction laws to the dynamic rupture of the 1995 Kobe earthquake. We anal yze the shear stress and slip evolution of Ide and Takeo's [1997] dislocati on model, fitting the inferred stress change time histories by calculating the dynamic load and the instantaneous friction at a series of points withi n the rupture area. For points exhibiting a fast-weakening behavior, the Di eterich-Ruina friction law, with values of d(c) = 0.01-0.05 m for critical slip, fits the stress change time series well. This range of d, is 10-20 ti mes smaller than the slip distance over which the stress is released, D-c, which previous studies have equated with the slip-weakening distance. The l imited resolution and low-pass character of the strong motion inversion deg rades the resolution of the frictional parameters and suggests that the act ual d, is less than this value. Stress time series at points characterized by a slow-weakening behavior are well fitted by the Dieterich-Ruina frictio n law with values of d(c) = 0.01-0.05 m. The apparent fracture energy G(c) can be estimated from waveform inversions more stably than the other fricti on parameters. We obtain a G(c) approximate to 1.5 x 10(6) J m(-2) for the 1995 Kobe earthquake, in agreement with estimates for previous earthquakes. From this estimate and a plausible upper bound for the local rock strength we infer a lower bound for D-c, of about 0.008 m.