A century-long influence of large earthquakes on forthcoming earthquakes in active plate margins

Seismicity is associated with the stress field. Understanding the stress field changes in seismogenic zones is crucial for mitigation of seismic hazards. We investigate the stress-field perturbation by global large earthquakes. The static stress field perturbation is assessed by stacking the induced Coulomb stress changes by the large earthquakes. The Coulomb stress changes are calculated for 1588 earthquakes with magnitudes greater than or equal to 7.0 since 1900 in the circum-Pacific seismogenic zones. The cumulative Coulomb stress changes varied between -115.4 and 494.2 bar at convergent plate boundaries. Negative cumulative Coulomb stress changes were generally dominant, suggesting that loaded stresses were released after large earthquakes. The postseismic moderate-sized earthquakes in subduction zones was dominant in the regions of negative Coulomb stress changes. The number of moderate-seized earthquakes was generally proportional to the magnitude of the negative cumulative Coulomb stress change. This observation suggests that the postseismicity may be caused by the afterslip and viscoelastic relaxation of the medium after large earthquakes. We observed a large lateral variation in cumulative Coulomb stress changes in regions before megathrust earthquake occurrence. This observation suggests that the lateral heterogeneity of the static stress field may induce large earthquakes. The temporal changes in stress field may be crucial to understand the occurrence of great earthquakes.