Geodetic constraints of the 2015 Mw6.5 Alor, East Indonesia earthquake: a strike-slip faulting in the convergent boundary

On 2015 November 4, an M-w 6.5 earthquake struck the east region of Alor Island, eastern Indonesia. Here, we use Sentinel-1 and ALOS-2 data to explore the coseismic surface displacement of this earthquake. Based on the ALOS-2 coseismic interferograms, the first fault model and coseismic slip distribution of the 2015 Alor earthquake are presented in this study. The preferred slip model links to a blind south-southeast striking, south-southwest dipping strike-slip fault with amount of normal slip component and a peak slip of 2.09 m at 2.34 km of depth. Considering the fact that the ascending and descending InSAR prediction of the distributed slip model does not fit the InSAR observations at the northwest and southeast tips with the simple planar fault model. We tried to construct a strike-variable fault model to further improve data fit. The results of the calculated Coulomb stress change imply that the regions with positive CFS changes mainly located at the northwest and southeast extremities of the rupture of the Alor earthquake, and in the lobes north and south of the rupture. The most striking discovery from the InSAR observations of the Alor earthquake is that most of the displacements occurred on a fault whose existence was unknown before the earthquake.

Automated summary

On November 4, 2015, a M-w 6.5 earthquake occurred in the eastern region of Alor Island, eastern Indonesia. In this study, Sentinel-1 and ALOS-2 data were used to analyze the coseismic surface displacement of the earthquake. The findings revealed a previously unknown fault and provided the fault model and coseismic slip distribution of the 2015 Alor earthquake, indicating a south-southeast striking, south-southwest dipping strike-slip fault with a normal slip component and a peak slip of 2.09 m at a depth of 2.34 km.