Multi-frequency Teleseismic P-wave Back-projection of the 2025 Mw 8.8 Kamchatka Peninsula Earthquake

Kotaro Tarumi , Kazunori Yoshizawa 

A great megathrust earthquake with moment magnitude Mw 8.8 struck off the Kamchatka Peninsula on July 29, 2025, generating a Pacific-wide tsunami and rupturing a segment of the Kuril–Kamchatka subduction zone that has repeatedly hosted M9-class earthquakes. We apply multi-frequency teleseismic P-wave back-projection (BP) analysis using six frequency bands spanning 0.003–2.0 Hz to investigate the frequency-dependent rupture process of this event. The BP images reveal four distinct radiation episodes (E0–E3) within 180 s, during which the main rupture propagated southwestward along the plate interface and produced two prominent shallow near-trench sources. Low-frequency (LF; 0.02–0.5 Hz) P-wave radiation highlights these shallow near-trench episodes, possibly reflecting dynamic overshoot similar to the 2011 Tohoku earthquake. In contrast, higher-frequency (HF: 0.1–2.0 Hz) radiation illuminates a patch at the downdip edge of the near-trench episode ( E3), as well as deeper sources in the initial and intermediate stages. The apparent migration speed of the radiating areas increases from about 1.0 to 2.0–2.5 km/s, and HF bursts coincide with rapid growth in the LF radiating area, suggesting abrupt changes in rupture and slip velocities. These findings further imply that the 2025 Kamchatka earthquake likely re-rupture source regions comparable to those of the 1952 Mw 9.0 event.