Modeling Earthquake Catalog in Sumatra by Space–Time Epidemic-Type Aftershock Sequences Model: Combining Davidon–Fletcher–Powell and Stochastic Declustering Algorithms

Earthquake hazard mapping has an important role as a mitigation measure for earthquake disasters. In Indonesia, especially in the Sumatra, the risk of major earthquakes is high due to its geographical location. In this study, we conduct statistical analysis of earthquake catalog data (coordinates, time occurrences, and magnitudes) and develop earthquake hazard map in the Sumatra during 2005–2023 using the Space–Time Epidemic-Type Aftershock Sequences (Space–Time ETAS) model. We perform computationally feasible method for parameter estimation combining Davidon–Fletcher–Powell and stochastic declustering algorithms. To design the study and obtain the best model, we define four different models exploring the use of complementary events. Of the four designed models, we found that model with short period of complementary events performs best. In addition, we also found that aftershock generation mechanism in the Sumatra is mainly dominated by the magnitudes of mainshocks (rather than locations or time occurrences of mainshocks). The resulting hazard map also shows the mainshocks dominate the aftershocks, which is in accordance with Badan Meteorologi, Klimatologi, dan Geofisika (BMKG) records with respect to the earthquake-prone areas in Sumatra.