Co‐Seismic Deformation and Local Stress Evolution of the Philippines Earthquakes in July and October 2022 Revealed by InSAR and GNSS Observations

Abstract On 27 July and 25 October 2022, an Mw 7.0 earthquake and an Mw 6.4 earthquake struck Abra, northwest of Luzon, Philippines, respectively, with a time interval of less than 3 months and a distance of about 16 km. In this research, interferometric synthetic aperture radar (InSAR) was utilized to retrieve the co‐seismic surface deformation field for each earthquake. Furthermore, leveraging the co‐seismic deformation data derived from both InSAR and Global Navigation Satellite System (GNSS) measurements, the source parameters of both events were determined based on dislocation models in an elastic half‐space. The results indicated that the July earthquake occurred on an east‐dipping and left‐lateral strike‐slip fault with a small thrust component, and the maximum slip reached 1.5 m. The October event occurred on an NNE‐dipping fault with a strike angle of 82° and a rake angle of 88°, signifying that this earthquake was a thrust event. The maximum fault slip of the October event was approximately 0.6 m, occurring at the depth of roughly 9.9 km. Neither the July nor the October events ruptured to the surface, but there was a clear triggering relationship between them, with the July earthquake likely promoting the rupture of the October fault, as suggested by the static Coulomb failure stress changes. The Vigan‐Aggao Fault, Abra River Fault, and Tubao Fault exhibit increased seismic hazards and warrant special attention in future studies.