Limited Shallow Slip in the 1938 <i>M</i> _<i>S</i> 8.3 Alaska Peninsula Earthquake Rupture

Abstract The 1938 M S 8.3 and 2021 M W 8.2 earthquakes both ruptured within the Semidi segment of the Aleutian‐Alaska subduction zone. The large‐slip distribution of the 2021 event is well constrained within the depth range 25–45 km, with seaward tsunami observations excluding significant shallower coseismic slip. The 1938 event slip distribution is more uncertain. Regional and far‐field tide gauge observations for the 1938 event are modeled to constrain the location of large coseismic slip. The largest slip (2.0 m) is located below the continental shelf on a 180‐km‐long portion of the rupture extending further northeast than the 2021 rupture, to near Sitkinak Island. Minor slip (1.0 m) extends seaward under the continental slope to 8 km deep, where large slip may have occurred in 1788. The megathrust shallower than 25 km depth to the southwest experienced many small aftershocks and aseismic slip following the 2021 event, and has limited slip deficit.