GNSS imaging coseismic and postseismic slip associated with the 2021 M 8.2 Chignik, Alaska earthquake

Abstract

The coseismic and postseismic slip associated with the 2021 M 8.2 Chignik, Alaska earthquake is imaged using the geodetic modeling method. Further, the spatio-temporal evolution of afterslip and aftershocks (0–60 days) is also investigated based on the postseismic deformations captured by Global Navigation Satellite System (GNSS) sites in this study. The coseismic slip is mainly concentrated at depths of 20–50 km with a maximum of 3.92 m. After this earthquake, a significant afterslip can be observed in the shallow region, which is distributed around the coseismic rupture region. Afterslip is primarily accumulated at depths of 10–30 km, and the maximum reaches 1.29 m, which is located at a longitude of 157.19°W, latitude of 55.09°N, and depth of 21.80 km. The spatio-temporal properties of afterslip indicate that the spatial extent and magnitude of afterslip continuously increase during the 60 days after the earthquake, and the fault activity in the first seven days is significantly strong. Meanwhile, the fault slip rate during the time span of 0–7 days is the largest with a maximum of 0.054 m/day. The fault slip rate gradually decreases with time, implying that the fault activity is slowly weakening. The Coulomb Failure Stress (CFS) distribution suggests that afterslip and most aftershocks are located at the southeastern region of the hypocenter, which is covered by positive CFS. Moreover, in addition to coseismic rupture effects, afterslip may be a possible triggering mechanism of early aftershocks as evidenced by the fact that the spatial distributions of afterslip and aftershocks are highly consistent.