| Abstrakt: |
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. Plain Language Summary: We propose a 3‐D‐hypocenter finite‐source Epidemic‐Type Aftershock Sequence model to improve the modeling and forecasting of aftershocks directly triggered by large earthquake. In this study, the rupture of the Kumamoto mainshock and the two large foreshocks, which are divided into small patches, are incorporated into the new model and estimated by early aftershocks. Each patch triggers its own aftershocks like a mainshock. Using a technique called "stochastic reconstruction", we have validated the model and found the following: (1) The spatial variations of aftershock productivity density along the rupture indicate that the postseismic relaxation process is complicated, and (2) large aftershocks are mostly located at the edge of asperities which are characterized by high productivity density values. Forecasting experiment shows that the new model has better performance in forecasting aftershock activity. This indicates that, with rupture geometry, early aftershock, and coseismic slip taken into consideration, this new model provides better short‐term aftershock forecasts. Key Points: The improved ETAS model incorporates earthquake focal depths and mainshock rupturesLarge aftershocks tend to nucleate at the edges of high aftershock productivity density areasThe new model has potential of improving short‐term aftershock forecasts [ABSTRACT FROM AUTHOR] |
Plný text