Source Model of the 2016 Kumamoto, Japan, Earthquake Constrained by InSAR, GPS, and Strong-Motion Data: Fault Slip under Extensional Stress

The 2016 Kumamoto earthquake is the largest event that ever happened since 1900 in the central part of Kyushu Island, Japan. It involves the Futagawa and Hinagu fault zones that contain some offsets and are controlled by extensional stress, providing a good opportunity to gain insights into rupture propagation under extensional stress. The coseismic deformation fields were derived from two types of Sentinel-1A imagery, Global Positioning System (GPS), and strong-motion data. A three-segment source model was constructed to fit the Interferometric Synthetic Aperture Radar (InSAR), GPS, and strong-motion data. The best-fitting model indicates that the rupture is dominated by right-lateral slip, with some normal component but at depth greater than 15 km, and a previously unmapped, high-dipping fault north of the Aso Volcano that ruptured during the 2016 Kumamoto earthquake. The source model yields a peak slip of 7.4 m, resulting in a geodetic moment of 4: 8 x 10(19) N . m, corresponding to M-w 7.0. We used the inferred source model to calculate the Coulomb stress change to discuss the triggering effects. The analysis of the finite-fault slip model and surface rupture trace suggests that, although the rupture can easily overcome a single bend or gap, the combination of bends and gaps put stronger constraint to inhibit rupture propagation. The analysis of the Kumamoto earthquake also reveals that the geologic structures play a critical role in arresting rupture propagation. In addition, the influence of fault geometry is important but not fully understood.