Possible Explanation for the Large Difference in Recurrence Periods of Megathrust Earthquakes in Kamchatka on July 29, 2025 and in Japan on March 11, 2011

A high variability in recurrence periods of subduction megathrust earthquakes is studied using the 2025 Kamchatka event (Mw = 8.8) and the 2011 Tohoku earthquake (Mw = 9.0) as examples. A possible explanation is proposed under the key-block model that accounts for a fragmentation degree of the frontal wedge of the overlapping plate. Numerical modeling with FLAC3D is indicative of the fact that the critical Coulomb stress accumulates faster in monolithic wedge segments, whereas the partial stress releases periodically in wedges cut by longitudinal faults. The results suggest that the short-term recurrence period of Kamchatka megathrust earthquakes is related to a high consolidation of the frontal wedge, while the longer-term period in the Tohoku region is caused by a pronounced wedge segmentation.