Interactions of aseismic and seismic slips of the Philippine Fault on Leyte Island revealed by InSAR and GNSS time-series

Abstract Slip behavior on active faults exhibits spatial heterogeneity, with varying characteristics observed across different fault segments. Certain fault sections may be locked seismically, while others undergo aseismic creep with different rates. These variations influence the seismic hazard profile across the fault system, resulting in regionally distinct earthquake risks. Therefore, analyzing slip rate distributions along fault systems is essential for refining fault models and improving earthquake hazard assessment and disaster mitigation strategies. In this study, we determined the spatiotemporal slip rate distribution along the Philippine Fault on Leyte Island from March 2016 to July 2023 using a combination of synthetic aperture radar interferometry (InSAR) time-series analysis with ALOS-2/PALSAR-2 data and Global Navigation Satellite System (GNSS) displacement time-series. We obtained (1) the coseismic step and postseismic decaying displacements due to the 6 July 2017 earthquake, and (2) variable surface creep rates ranging from 35 to 55 mm/yr along the fault. In particular, creep rates in the northern part were significantly higher than the estimates before March 2013, as measured both by InSAR and in situ observations, suggesting decadal-scale temporal variations in the creep rates. In addition, we identified two fault sections with shallow slip deficits in the northernmost and central parts of Leyte Island. Along the northernmost section, a shallow (1 km depth) Mw 4.7 earthquake occurred on 15 January 2023, producing ~ 8-km-long surface rupture with displacement up to 2 cm precisely along the surface trace of the Philippine fault. The shallow slip deficit detected in our analysis may have contributed to this earthquake.