Seismotectonic modeling of the 2017 Hojedk (Kerman) earthquake sequence from joint inversion of InSAR and offset tracking techniques

We investigate the geometric/kinematic characteristics of faulting a triplet of Mw ∼ 6 earthquakes (E1, E2, and E3) in Kerman province, Central Iran, over twelve days in December 2017. A geodetic framework is implemented and combined with seismic and geological methods to provide an integrated model of faulting within the sequence. To retrieve coseismic displacements in the complex and high-gradient near-field area, an adaptive method is proposed based on image-alignment techniques applied to both SAR (Sentinel-1) and optical data (PlanetScope). A continuous deformation map is created by combining interferometric and pixel offset tracking results through principal component analysis. We jointly invert the geodetic data, including along- and across-track displacement maps, through a constraint-based Bayesian inversion process to optimize the source parameters of the causative faults. The results reveal that the NE-dipping nodal planes, with variable slip peaks of 63 and 17.5 cm at depths of 5.5 and 9.1 km, best fit the data for the E1 and E2 events, respectively, whereas the E3 event was on a SW-dipping fault plane including ∼E- and NW-striking segments. The E3 plane was shallow with maximum slip of 1.2 m at a depth of 2.2 km. We relocate 93 events and use the InSAR slip distributions as constraints to indirectly calibrate the epicenter of the earthquake cluster, and obtain the local stress state from the inversion of the focal mechanism solutions of the ten largest events of the Hojedk cluster. The resultant compressional stress explains the dextral and sinistral components found on the western and eastern segments of the E3 rupture, respectively. All together suggest a NW-striking pop-up structure in a restraining stepover between the ∼N-striking dextral Lakarkuh and Golbaf-Sirch-Gowk fault systems. This structural model highlights the interaction between thick-skinned and thin-skinned seismic deformation within Iran.