Fast report: performance of the ETAS model in forecasting aftershock occurrence and site-specific ground-shaking intensity for the 2025 Dapu, Taiwan, earthquake sequence

Abstract The 2025 Dapu, Taiwan, earthquake sequence highlights the need for real-time aftershock and ground-shaking forecasts to support disaster response and risk mitigation. This study applies the space–time epidemic-type aftershock-sequence (ETAS) model, integrated with a ground motion model, to simulate aftershock occurrence and site-specific ground-shaking intensity for the Dapu earthquake sequence. Using a real-time $${M}_{L}\ge 3.0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>M</mml:mi> <mml:mi>L</mml:mi> </mml:msub> <mml:mo>≥</mml:mo> <mml:mn>3.0</mml:mn> </mml:mrow> </mml:math> earthquake catalog, seismicity rates are estimated, and 1,000 sets of synthetic earthquake catalogs are generated for each forecast period. Results indicate that the workflow effectively forecasts aftershock activity and shaking intensity, with probabilities for $${M}_{L}\ge 5.0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>M</mml:mi> <mml:mi>L</mml:mi> </mml:msub> <mml:mo>≥</mml:mo> <mml:mn>5.0</mml:mn> </mml:mrow> </mml:math> events increasing from 30.5% within 1 day to 67.8% within 10 days, aligning with observed aftershocks. The probabilistic ground-shaking intensity forecasts for the Chiayi and Tainan stations demonstrate the model’s accuracy, capturing the spatiotemporal evolution of aftershocks. This approach enhances operational earthquake and aftershock forecasting, providing actionable insights for emergency preparedness in Taiwan.