Postseismic processes in the region of the july 29, 2021 Chignik earthquake, Alaska. Part II: temporal evolution of displacements and correlation with aftershock activity

Abstract

Postseismic displacements in the source region of the July 29, 2021 Chignik M8.2 earthquake, Alaska, are analyzed based on the data from the GPS network sites. It is shown that these displacements have a nature of a postseismic creep (afterslip). The rate of postseismic displacements of the points on the Earth’s surface (GPS sites) decreases with time by the power law close to 1/t, where t is time after the earthquake. On the time interval of two years, the displacement magnitudes increase in time by the law of logarithmic creep. Using the regional catalog of the Alaska earthquakes, we have analyzed the aftershocks of the Chignik earthquake. The analysis has shown that the postseismic displacements at different GPS sites are proportional to the displacements in the seismotectonic flow of the rock mass caused by residual displacements in the aftershock sources. This allows the total displacements in the aftershock sources to be considered as produced by a single mechanism of postseismic creep deformation in the source region of the Chignik earthquake.