The 29 July 2021 MW 8.2 Chignik, Alaska Peninsula Earthquake Rupture Inferred From Seismic and Geodetic Observations: Re-Rupture of the Western 2/3 of the 1938 Rupture Zone

On 29 July 2021, an M_W 8.2 thrust-faulting earthquake ruptured offshore of the Alaska Peninsula within the rupture zone of the 1938 M_W 8.2 earthquake. The spatiotemporal distribution of megathrust slip is resolved by jointly inverting regional and teleseismic broadband waveforms along with co-seismic static and high-rate GNSS displacements. The primarily unilateral rupture expanded northeastward, away from the rupture zone of the 22 July 2020 M_W 7.8 Shumagin earthquake. Large slip extends along approximately 175 km, spanning about two third of the estimated 1938 aftershock zone, with well-bounded depth from 20 to 40 km, and up to 8.6 m slip near the hypocenter. The rupture terminated in the eastern portion of the 1938 aftershock zone in a region of very large geodetic slip deficit where peak slip appears to have occurred in the 1938 rupture. The 2021 and 1938 events do not have similar slip distributions and do not indicate persistent asperities.