Surface creep rate distribution along the Philippine fault, Leyte Island, and possible repeating of M_w ~ 6.5 earthquakes on an isolated locked patch

Active faults commonly repeat cycles of sudden rupture and subsequent silence of hundreds to tens of thousands of years, but some parts of mature faults exhibit continuous creep accompanied by many small earthquakes. Discovery and detailed examination of creeping faults on land have been in a rapid progress with the advent of space-borne synthetic aperture radar interferometry. In this study, we measured the spatial variation of the creep rate along the Philippine fault on Leyte Island using ALOS/PALSAR data acquired between October 2006 and January 2011. Prominent creep of 33 ± 11 mm/year was estimated in northern and central parts of the island except for a locked portion around latitude 11.08–11.20^∘ N. We compared the creep rate distribution along the fault with the slip distribution of the 2017 M_w 6.5 Ormoc earthquake which occurred in northern Leyte, estimated from the displacements mapped by ALOS-2/PALSAR-2 interferometric data. The estimated slip of the 2017 earthquake amounted up to 2.5 m and to moment magnitude of 6.49, with the dominant rupture area coinciding with the locked portion identified from the interseismic coupling analysis. Teleseismic waveforms of the 2017 earthquake and another event that occurred in 1947 (M_s 6.9) exhibit close resemblance, indicating two ruptures of rather similar locations and magnitudes with a time interval of 70 years.[Figure not available: see fulltext.].