Model of the Seismic Rupture Surface of the Chignik Earthquake (Alaska, USA) 07.29.2021 Based on SAR Interferometry and GNSS Data

Abstract

The paper presents a new rupture model for the Mw = 8.2 “Chignik” earthquake, which occurred off the coast of the Alaska Peninsula on 29.07.2021. The model is based on the Earth’s surface displacement fields obtained by InSAR (Interferometric synthetic aperture radar) method using images of the ESA Sentinel-1 satellites from 17.07 to 10.08.2021 and data on horizontal displacements at nearest permanent GPS sites from 18.07 to 08.08.2021. Obtained displacement fields include both coseismic and part of postseismic displacements. When constructing a model of the seismic rupture surface, we used F. Pollitz’s solution of the problem of the displacement fields at the surface of a spherical radially stratified planet caused by displacements on a rectangular discontinuity located inside it. For the regularization of the inverse problem, we added the condition that the direction of slip on each element of the fault plane is close to the rake angle, determined from seismological data. In the constructed model, the seismic rupture area was approximated by a single plane with a length of 225 km along the strike, 126 km along the dip, divided into 48 identical rectangles. According to the constructed model, the type of displacements is almost pure thrust, and displacements, in general, occurred throughout all the source area. The maximum displacement was 5.7 m, with an average displacement over the entire plane of 2.2 m, which is close to the USGS and GCMT estimates derived from seismological data.