Characteristics of Long-term Preseismic Sliding of a Large Interplate Earthquake: A Numerical Simulation

Abstract:

Various aseismic sliding processes preceding large earthquakes have been investigated observationally and theoretically. Especially, the slip nucleation process, in which accelerating aseismic slip is expected to occur immediately before earthquake occurrence, was extensively studied. On the other hand, numerical simulations of recurrent interplate earthquakes assuming rate- and state-dependent friction on a fault indicates that aseismic sliding progressively develops on a seismogenic part of the fault during an interseismic period. In the present study, aseismic sliding within a seismogenic region during an interseismic period of simulated cycles of large interplate earthquakes at a subduction zone is examined, and possible crustal deformation due to the aseismic sliding is discussed. A 2D uniform elastic half-space is considered, and friction on a shallower part of a plate boundary is assumed to obey a rate- and state-dependent friction law, while steady aseismic sliding is assumed on the deeper part. Shear stress is concentrated at the deeper edge of the seismogenic plate boundary due to deeper steady aseismic sliding, and aseismic sliding penetrates into the seismogenic part in an early phase of interseismic period. This aseismic sliding gradually propagates updip, and the aseismic slip rate is one order of magnitude smaller than the assumed relative plate velocity. This aseismic sliding is accelerated and an episodic aseismic slip event occurs even without heterogeneity of frictional property. The slip rate of the episodic slip event tends to be larger for a small characteristic slip distance of the friction law, and this event is possibly observable in the surface deformation. The average aseismic slip rate within the seismogenic part increases inversely proportional to the time to the earthquake occurrence and its amplitude is proportional to the characteristic slip distance and inversely proportional to the effective normal stress on the plate boundary.