Complementary Occurrence of Fault Creep and an MW 6.5 Earthquake Along the Philippine Fault on Leyte Island Revealed by ALOS and ALOS-2 Sar Interferometry

It has been inferred that the Philippine fault on Leyte Island has been creeping. On 6 July 2017, an Mw 6.5 earthquake struck northern Leyte, suggesting that not all parts along the fault have been creeping. We conducted InSAR time-series analyses using ALOS/PALSAR data (2006-2011) to estimate the spatial variation of the fault creep rate, and fault slip modeling of the 2017 earthquake using the displacements obtained from ALOS-2/PALSAR-2 interferometry. We found that the section ruptured by the 2017 earthquake had been locked (lack of fault creep) while the neighboring sections, in northernmost and central areas of the island, have been creeping with rates of up to 30 mm/year. We speculate from the creep analysis that the size of the 2017 earthquake would be the maximum-class earthquake along the Philippine fault in the northern half of Leyte. Considering the similarity in size and location, we infer that the 1947 earthquake also ruptured the same locked portion as the 2017 earthquake. Our findings demonstrate the usefulness of InSAR time-series analysis to identify future earthquake-prone sections along active faults.