Coseismic deformation and multi-fault slip model of the 2019 Mindanao earthquake sequence derived from Sentinel-1 and ALOS-2 data

From October to December 2019, a sequence of four earthquakes of Mw > 6.0 occurred in southern Mindanao, the Philippines, and revealed complex tectonics in this region. We used Advanced Land Observing Satellite (ALOS)-2 and Sentinel-1A/B Synthetic Aperture Radar (SAR) data to map the coseismic deformation and to constrain both the fault geometry and kinematics of coseismic slip distributions during the four earthquakes. Our observed coseismic deformation field shows that these four earthquakes ruptured two intersected conjugate faults with NE and NW strikes. Based on ascending and descending Interferometric SAR (InSAR) data, we constructed elastic half-space models to search for the optimal fault dip angle and inverted the slip distributions of the four earthquakes. The results show that these four earthquakes were all dominated by left- and right-lateral strike-slip motion. The two conjugate faults clearly had significant differences in terms of slip behaviour and fault kinematics. The static Coulomb stress change indicates that earlier earthquakes had a significant triggering effect on subsequent earthquakes. The static Coulomb stress change induced by the four earthquakes suggests a significant stress loading effect on NW-trending faults. The results of this study show that the potential for future earthquakes on NW-trending faults cannot be ignored; however the magnitudes of future earthquakes should be limited by complex fault geometry and segmentation.