Complex rupture propagation in the august 2018 Kaktovik earthquake sequence constrained by sentinel-1 and ALOS-2 InSAR

Rupture propagation in the August 2018 Kaktovik earthquake sequence, which included Mw 6.4, Mw 5.3, and Mw 6.0 events near the Sadlerochit Mountains in northeastern Alaska, was constrained using three Sentinel-1 C-band interferometric synthetic aperture radar (InSAR) datasets acquired from different viewing geometries and one ALOS-2 L-band InSAR dataset. Line-of-sight (LOS) displacements measured from these datasets were used to derive east–west and vertical displacement components. The maximum displacements observed were 27.6 cm of westward motion near the Mw 5.3 epicenter and 20.9 cm of subsidence near the Mw 6.0 epicenter. The LOS displacements derived from all interferograms except one low-coherence descending Sentinel-1 interferogram were then jointly inverted to estimate the source parameters and distributed slip of the three faults responsible for the observed displacement. By integrating the distributed-slip models with Coulomb stress change analysis and aftershock patterns, we identified a fault network in which two intersecting faults interact with a main fault. In particular, the L-band InSAR observation clearly resolved a symmetric displacement pattern around the Mw 5.3 epicenter, and its integration with multi-track Sentinel-1 data in a joint inversion enabled estimation of a physically plausible geometry for the intersecting fault. These results are consistent with a rupture propagation scenario in which rupture may have initiated on the main fault and propagated eastward in a stepwise manner through interactions with the intersecting faults.