InSAR-derived surface displacement gradients unveil subseismic faults of the 2022 Cianjur earthquake

Abstract The Cianjur in West Java, Indonesia, is characterized by high seismic susceptibility due to the presence of the prominent Cimandiri fault system and associated, often unmapped, sub-seismic fault structures. Accurate identification and characterization of these faults are paramount for robust seismic hazard assessment and effective disaster mitigation planning. This study investigates the complex fault system related to the Mw 5.6 earthquake of November 21, 2022, in Cianjur, by applying an analytical approach based on surface displacement gradients derived from Interferometric Synthetic Aperture Radar (InSAR) data. Our workflow integrates Differential InSAR (DInSAR) and Small Baseline Subset (SBAS) techniques to produce robust 1D Line-of-Sight and 2.5D (vertical and east–west) coseismic displacement models, revealing vertical subsidence near -14 cm and significant east–west motion. We demonstrate that the spatial gradients calculated from these displacement fields effectively illuminate linear zones of high strain. These zones correspond to previously unmapped or poorly resolved sub-seismic fault segments, particularly in the southern Rajamandala and Cugenang regions, with cross-sectional analysis confirming localized stress accumulation. Our findings reveal the detailed architecture of the Cianjur earthquake's faulting and establish a refined framework for using InSAR-derived displacement gradients to enhance fault characterization, directly informing seismic hazard models and land-use planning in vulnerable areas.