Ring-Shaped Seismicity Structures in South Kamchatka: Probable Preparation of a Great Earthquake

Abstract—Some characteristics of seismicity in South Kamchatka are discussed. Parameters of the aftershock cloud of the August 17, 2024 large earthquake (M_w = 7.0) are studied. It is shown that ring-shaped seismicity structures in South Kamchatka have been formed in three depth ranges: 0–33, 34–70, and 71–110 km. As in other subduction zones, the structures are characterized in terms of limiting magnitude values—threshold magnitudes Mt1, Mt2, and Mt3, respectively, and lengths of major axes L1, L2, and L3. The epicenters of the August 17, 2024 earthquake and its strongest aftershocks fall in a shallow ring-shaped structure (Mt1 = 5.3), which supports the hypothesis of a preparation of a great earthquake in the South Kamchatka region. In the previous works, the correlation dependences of parameters Mt1 and Mt2 on the magnitudes M_w of large earthquakes have been constructed for the western Pacific (in the range M_w = 7.0–9.0). Using these dependencies, we estimated the magnitude of the great possible event in this region at M_w = 8.6 ± 0.2. The factors responsible for the formation of ring-shaped seismicity structures at different depths in the subduction zones are discussed.