Co-seismic and post-seismic deformation associated with the 2018 Lombok, Indonesia, earthquake sequence, inferred from InSAR and seismic data analysis

In 2018, four deadly (Mw 6.2–6.9) earthquakes struck the north coast of Lombok Island on 28 July, 5 August, and 19 August. The slip distributions of the three mainshocks are modeled in this study by inverting the co-seismic deformation imaged using an interferometric analysis of Sentinel-1 synthetic aperture radar measurements (InSAR), based on rectangular dislocations embedded in a multi-layered elastic half-space. Our best-fit co-seismic slip model suggests the estimated maximum fault slips of 1.3 m, 2.2 m, and 2.5 m for the mainshocks from July to August, located at depths of 9.6 km, 13.6 km, and 22.2 km, respectively. We applied an unsupervised learning method (ST-DBSCAN) to cluster the relocated aftershocks so that we could identify the source of each aftershock. The clustered aftershocks are primarily distributed in the areas with increased Coulomb stress and are less abundant in the maximum slip patch on the three rupture faults, indicating consistency with our estimated co-seismic slip model. In addition, we use an InSAR time series, consisting of 337 descending and 177 ascending Sentinel-1 acquisitions to investigate the time-dependent, post-seismic deformation in the two years following the Lombok 2018 earthquake sequence, based on a pure afterslip model and a combined model that simulates viscoelastic relaxation and afterslip simultaneously. The best-fit combined model suggests a Maxwell viscosity of 1 × 1018 Pa s for both the lower crust and asthenosphere, and it reveals that the maximum of the cumulative afterslip within two years is ∼0.7 m, along the northwestward up-dip continuation of the co-seismic rupture area.