Rupture Model for the 29 July 2021 <i>M</i> _<i>W</i> 8.2 Chignik, Alaska Earthquake Constrained by Seismic, Geodetic, and Tsunami Observations

A great earthquake struck the Semidi segment of plate boundary along Alaska Peninsula on 29 July 2021, re-rupturing part 1938 rupture zone. The 2021 MW 8.2 Chignik occurred just northeast 22 2020 7.8 Simeonof earthquake, with little slip overlap. Analysis teleseismic P and SH waves, regional Global Navigation Satellite System (GNSS) displacements, near-field far-field tsunami observations provides a good resolution process. During ?60-s long faulting, was nonuniformly distributed megathrust over depths from 32 to 40 km, up ?12.9-m in an ?170-km-long patch. 40–45 km down-dip limit is well constrained by GNSS Peninsula. Tsunami preclude significant extending <25 confining all coseismic beneath shallow continental shelf. Most aftershocks locate seaward large-slip zones, concentration activity up-dip deeper southwestern Some localized aftershock patches slope. surface-wave magnitude MS 8.1 for smaller than = 8.3–8.4 event. Seismic data indicate that concentrated eastern region its zone, beyond Islands, where event did not rupture.