Research on the variety of seismicity caused by mechanical interaction between fault systems

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In order to understand the cause of complex phenomena such as long range correlation, migration etc. that are observed in seismicity in and around the Japanese islands, we conducted a simulation study with a fault system model which was derived from geodetic data for 100 years incorporating interaction between faults.First, we constructed a code on PC, performed a simulation with the original model whose fault elements are 104 and observed that interaction between faults may cause simultaneous rupture on neighboring faults and migration of seismicity.Second, we transferred this code to a supercomputer of the Data Processing Center, Kyoto University, so that we could deal with a model with many fault elements. We divided the original faults into 5 x 5 elements in both the strike and dip directions of each fault. In total, the model has 2600 elements. This model can simulate as small earthquakes as M5. We also examined the effect of variation in rupture strength by changing them. The main results obtained in the above simulation are as follows.(1) Events that simultaneously rupture the entire fault rarely occur.(2) Since the frequencies of medium-size events are relatively high, simulated seismicity does not necessarily fit the Guternberg-Richter's law.(3) A complementary relationship between large earthquakes along the Suruga-Nankai troughs and inland events in southwest Japan is recognized.(4) Migration of source regions of large events along the Suruga-Nankai troughs is observed, but its *rection differs from time to time.Furthermore we estimated fault motions using recent continuous GPS data and calculated horizontal strain rates with new trilateration data in order to examine the validity of the above fault system model.