Deep-Learning-Based Catalog of Background Seismicity and Aftershocks of the 2020–2021 Large Earthquakes Along the Alaska Peninsula

Abstract The Alaska Peninsula section of the Alaska-Aleutian subduction zone shows significant along-strike variations in seismic activity and interseismic plate coupling. This region experienced the 2020 Mw 7.8 Simeonof megathrust, Mw 7.6 Sand Point strike-slip, and 2021 Mw 8.2 Chignik megathrust earthquakes. This study, utilizing deep learning techniques, presents a high-precision earthquake catalog, providing insights into background seismicity, aftershocks, and slab geometry. An abrupt change in the slab dip angle at 30–40 km depths in the Shumagin segment acted as a barrier to the Simeonof and Sand Point earthquake ruptures. The Simeonof event triggered more aftershocks in the overriding plate than the Chignik event, suggesting the overriding plate is more deformed and hydrated in the Shumagin segment. The Sand Point earthquake triggered numerous aftershocks in the overriding plate, delineating a fault in the overriding plate with similar geometry as the intraslab mainshock fault, but activated around seven days after the mainshock.