Temporal and spatial correlations of the strain field in tectonic active region, southern Kyusyu, Japan

The southern Kyusyu district is one of the most characteristic subduction zones in Japan. In this region, large earthquakes occurred sequentially, although earthquake mechanisms are different and the distance between earthquakes is far. We investigate strain propagation caused by a strain fluctuation related to subducting plate velocity. For this purpose, we used the data obtained from extensometers installed in an observation network at Kyusyu district and applied the crosscorrelation function. If the strain associated with the subduction propagates in the crust, it is expected that the correlation around arrival of propagating signal varies from steady state. The results suggest existence of strain propagation in the overlying crust. Its velocity is estimated to be about 90–140 km/year with a direction from the subduction zone to inland.