Geophysical processes and biosphere: article

Аnnotation: We have been considering some seismicity characteristics in the region of Southwestern Alaska. Aftershock zones of the Simeonof (Mw = 7.8) and Chignik (Mw = 8.2) earthquakes, occurred 22.07.2020 and 29.07.2021 respectively, were picked out. Characteristics of ring-shaped seismicity structures, being formed during a few decades prior to the Chignik earthquake, are described. Ear-lier prognosis of the place and magnitude of large event, which can be prepared to the east of the Simeonof earthquake rupture zone, was presented, based on parameters of these structures [Kopnichev, Sokolova, 2021a]. Predicted magnitude estimate (Mw = 8.2±0.2) was obtained using correlation dependences between ring-shaped structures parameters and magnitudes of large and great earthquakes for the eastern part of the Pacific. This prognosis, based on data, obtained prior to 21.10.2020, was presented in the paper, which was taken to publication before 29.07.2021. We consider possible change of ring-shaped structures parameters directly prior to the Chignik earthquake. We discuss geodynamic processes, which can lead to the ring structures formation.