Dynamic fault rupture and stress recovery processes in continental crust under depth-dependent shear strength and frictional parameters

Abstract

Mikumo, T., 1992. Dynamic fault rupture and stress recovery processes in continental crust under depth-dependent shear strength and frictional parameters. In: T. Mikumo, K. Aki, M. Ohnaka, L.J. Ruff and P.K.P. Spudich (Editors), Earthquake Source Physics and Earthquake Precursors. Tectonophysics, 211: 201–222. The dynamic rupture process of large earthquakes in continental crust and the post-seismic stress recovery process due to visco-plastic behaviour are investigated by three- and two-dimensional numerical modelling, taking into account the possible depth variations of the shear strength, tectonic stress, expected stress drop and of the critical weakening slip, which are suggested by recent laboratory experiments on frictional parameters. It was found that dynamic rupture can initiate at any depth in a brittle zone if high stress is concentrated with a dimensionless stress ratio S less than a certain limit, but that the rupture cannot nucleate in a semi-brittle zone with negative stress drop. This suggests that the boundary between the fully brittle and semi-brittle zones delineates the base of the seismogenic zone of background seismicity and aftershock distribution. However, the dynamic rupture of large earthquakes originating from the brittle zone can propagate into the semi-brittle zone after some temporary arrest or with decelerated velocities, which could generate low-frequency seismic waves. The depth extent of dynamic faulting and the maximum fault displacement are affected by the depth to the brittle/semi-brittle boundary and hence by the geothermal state within the crust. The stress recovery due to visco-plastic behaviour in the semi-brittle and plastic regimes suggests that the rupture for eventual earthquakes tends to be nucleated near the upper boundary of the semi-brittle zone.