2007 年 59 巻 4 号 p. 309-324
A two-dimensional (2D) numerical simulation of seismic cycles on the plate boundary in a subduction zone is performed based on a rate- and state-dependent friction law to obtain insight into complicated cycle of interplate earthquakes off Miyagi Prefecture and to investigate possible precursory sliding behavior. Assuming that the complexity of seismic cycle such as the off Miyagi Prefecture Earthquake is mainly due to the heterogeneity of frictional properties, we divide the plate boundary into five segments along dip direction: three frictionally stable segments and two (shallower and deeper) seismogenic segments are placed alternately. From many trial simulation results, we find that the frictional parameters (b-a)and dc in the deeper seismogenic segment should be smaller than those in the shallower segment in order to generate earthquakes in the deeper segment more frequently than in the shallower segment. The simulation results show that preseismic, coseismic, and postseismic slip in a seismogenic segment tends to become larger when it occurs just after the earthquake in the other seismogenic segment, because the previous earthquake in the other seismogenic segment keeps on forward slip through the intermediate aseismic segment. We also find that the stress rate in the down-dip direction in the vicinity of the lower edge of the deeper seismogenic segment is compressional for the period of about one year prior to the occurrence of the earthquake in the segment while it is tensional prior to the event in the shallower segment. This result suggests that seismic activity change in a slab can be a clue to the intermediate-term prediction of large interplate earthquakes.