Source model for buried thrust-dominated earthquakes using partial InSAR displacements: the 2018 Lombok, Indonesia, earthquake sequence

Abstract

SUMMARY A remarkable earthquake sequence struck the island of Lombok in Indonesia during the period from 2018 July 28 to August 19. In this study, we use Sentinel-1 and ALOS-2 radar images to investigate the deformation related to these events. The co-seismic surface deformation was pre-dominated by uplift without surface rupture. It is worth noting that some of the rupture of the Lombok sequence is offshore. For the thrust-dominated island earthquakes, whether the incomplete onshore deformation obtained by InSAR observation can well constrain the geometry of the underground faults is a question worthy of attention. Considering the positional relationship between the deformation and the island, we assumed two types of deformation distribution mode. Through simulation experiments, we found that when the major deformation for the second mode is less than about half, the nonlinear inversion results will be unstable. According to source models of each event, the Lombok sequence may have ruptured the Flores thrust. The peak magnitudes of slip for three events are 1.59, 1.93 and 2.87 m. The large magmatic plumbing systems of Rinjani volcano play a critical role during the cascading fault rupture of the Lombok event. Stress changing map indicates that the earlier events promote the later events. There is an obvious seismic gap in the northern part of the Sumbawa region and this region has the potential to form some moderate earthquakes in the future.