Formation of new ring-shaped seismicity structures in the region of South Kamchatka prior to great earthquake of July 29, 2025 (Mw=8.8)

We have been studying some seismicity characteristics in the region of South Kamchatka. It was shown that ring-shaped seismicity structures were formed in the South Kamchatka within three depth intervals: 0-33, 34-70 and 71-110 km. Similarly to the other subduction zones, the structures are characterized by threshold magnitude values (Mt1, Mt2 and Mt3 correspondingly) and also by big axis lengths (L1, L2 and L3). Epicenters of the large earthquake of August 17, 2024 and its biggest aftershocks lie on the shallow ring-shaped seismicity structure (Mt1=5.3). This effect confirms an assumption on a preparation of great earthquake in the region of the South Kamchatka. Earlier correlation dependences of Mt1 and Mt2 parameters on Mw values of major earthquakes for the west of Pacific were created. Using these dependences, we estimated magnitude of possible great earthquake in this area: Mw=8.7±0.2. The reasons for ring-shaped structures formation in different depth ranges of the subduction zones are discussed.