Modeling and Forecasting Aftershocks Can Be Improved by Incorporating Rupture Geometry in the 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 in the point source ETAS model. The reconstructed patterns of productivity density of aftershocks, along the mainshock rupture plane, form complementary patterns for coseismic slip in space and show significant spatiotemporal migrations. Large aftershocks tend to nucleate at the edges of high productivity density areas. The decay of direct aftershocks near the mainshock rupture is consistent with static stress changes caused by the mainshock. The forecasting capability of the ETAS model can be enhanced by considering the rupture geometries of mainshocks, especially for forecasting aftershocks in the first 1-2 days. In the simulation test, the incorporation of focal depths improves the forecasting resolution.