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 movements in the source region of the July 29, 2021 Chignik M8.2 earthquake, Alaska, are analyzed using observations from GPS sites. It is shown that the displacements are have a nature of a postseismic sliding (afterslip). The velocity 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. Over an interval of two years, the magnitudes of displacements increase in time by the law of logarithmic creep. Based on 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 various GPS sites are proportional to the displacements in the seismotectonic flow caused by residual displacements in the sources of aftershocks. This allows us to consider total displacements in the aftershock sources as a universal mechanism of the postseismic afterslip deformation in the source region of the Chignik earthquake.