Modeling of seismic activity modulated by stress changes during the interplate earthquake cycle along the Sagami Trough, central Japan

The Kanto region of central Japan has experienced temporal clustering of M7-class earthquakes, particularly during the later stages of the large interplate earthquake cycle along the Sagami Trough. However, the role of static stress changes in driving this pattern remains poorly understood. Therefore, to examine whether static stress changes from the Sagami Trough earthquake cycle could be responsible for this pattern, we simulated stress evolution using a layered elastic-viscoelastic model. The receiver faults were defined based on the focal mechanisms of earthquakes observed between 1997 and 2023. Additional intrinsic stress loading was also applied with a CFS accumulation rate of 1.0 kPa per year to all receiver faults for permanent stress accumulation. We assumed the earthquake occurrence rate at each receiver fault to be proportional to the increase in the Coulomb failure stress (CFS) from its previous maximum value, and set it to zero when CFS decreased. The spatial and temporal distributions of earthquake occurrence rates were then assessed by aggregating them across the study region. The spatial distribution of earthquake occurrence rates calculated by our optimal model closely matches the distribution of earthquakes observed between 1997 and 2023, supporting the validity of our modeling approach. Although our model could not fully explain the locations of several M7-class earthquakes that occurred before the 1923 Kanto earthquake, we found that these events tended to occur during periods when the modeled earthquake occurrence rate at each location was estimated to be high within the earthquake cycle. We discovered that interplate earthquakes in the transition zone from full coupling to no coupling are likely to increase as the next M8-class interplate earthquake along the Sagami Trough approaches. The results suggest that a physics-based framework for constructing earthquake activity scenarios in the Kanto region can improve seismic hazard assessments and contribute to disaster risk reduction.