Spatial Heterogeneity of the Aftershock Productivity of the Kumamoto Earthquake Modeled by the Finite Source ETAS model

We implemented an extended version of the space-time Epidemic-Type Aftershock Sequence (ETAS ) model, which simultaneously incorporates earthquake focal depths and rupture geometries of large earthquakes, and applied it to the 2016 Kumamoto earthquake sequence. Results show that the new model corrects the estimation biases of model parameters due to the isotropic response function of aftershock locations adopted in the point source ETAS model. The reconstructed patterns of density of aftershock productivity, along the mainshock rupture plane, show significant migrations in space and time. Another interesting phenomenon is that large aftershocks tend to nucleate at the edges of high productivity areas. The decay of direct aftershocks near the mainshock rupture is consistent with static stress changes caused by the mainshock. In simulations, the incorporation of focal depths improves the forecasting resolution. By comparing aftershock productivity with the slip distribution of the mainshock, we find that high aftershock productivity forms complementary patterns for coseismic slips in space. This indicates that aftershocks play a role in the postseismic relaxation process.