Hazard‐Consistent Aftershock Ground Motion Intensity Map and Arrival Time Sampling for Regional Seismic Risk Analysis

This article presents a method for sampling aftershock scenarios, ground motion intensity maps, and arrival times for evaluating aftershock risks shortly after major earthquakes. A catalog‐based regional aftershock probabilistic seismic hazard analysis is used as the backbone, where a full catalog of the first aftershock after a triggering major earthquake is generated using an earthquake rupture forecasting model and the modified epidemic‐type aftershock sequence model. The full aftershock catalog, consisting of both rupture scenarios and arrival times, may contain hundreds of thousands of aftershock scenarios, making seismic risk analysis computationally prohibitive. The proposed method selects a subset of aftershock rupture scenarios and samples ground motion intensity maps and arrival times that are consistent with the seismic hazard estimated from the full aftershock catalog. This approach minimizes the difference between the aftershock seismic hazard at various time points, as calculated using the sampled maps and arrival times, and that derived from the complete aftershock catalog. The method is demonstrated through a case study in Northern California. Results demonstrate that the proposed method efficiently samples aftershock ground motion fields and arrival times consistent with the full aftershock catalog, thereby enabling computationally tractable seismic risk assessment of spatially distributed infrastructure systems under aftershock effects, which would otherwise be prohibitively expensive using crude Monte Carlo simulation.