Source rupture model of the 2018 M_W6.7 Iburi, Hokkaido earthquake from joint inversion of strong motion and InSAR observations

The 2018 M_W6.7 Iburi earthquake shocked the eastern Iburi region to the west of the Hidaka Collision Zone in Hokkaido, which is a destructive inland earthquake. We resolved the kinematic rupture process of the event by combining strong motions (SM) and synthetic aperture radar (SAR) images in a joint inversion. The results reveal that the duration of the whole rupture is about 17s, yielding a total seismic moment of 1.4×10¹⁹ N·m (M_W=6.7). The main slip area is located at a depth of approximately 24 km with a peak slip of ~0.8m above the hypocenter. The comparison with the regional velocity model shows the earthquake was initiated in the upper mantle, while the majority of slips are located in the lower crust, which is an “aseismic” domain in the typical sandwich model. The location of the major slip area is consistent with a high-conductivity volume. We proposed a mechanism of low frictional property (<0.3) produced by high pore pressure to explain the abnormal high dip angle and centroid depth located in the ductile lower-crust. Aftershocks are distributed in areas where the Coulomb frictional stress increases due to co-seismic displacement with a mechanism conjugating to the mainshock.