The Investigation of Viscoelastic Relaxation Following the 2018 Mw 6.2 Situbondo, Indonesia, Earthquake

The 2018 Mw 6.2 Situbondo earthquake occurred in an active fault where no earthquakes of magnitude 6 or higher have been recorded in the last decade. Since the fault geometry responsible of this earthquake is not well identified, we analyze the mainshock and aftershock of the 2018 earthquake. We conduct hypocenter relocation of earthquakes from 10 October 2018 to 25 December 2018. We find that the distribution of the relocated aftershocks forming a lineament to the northwest relative to the mainshock with an average depth of 12.6 km. This southeast-northwest pattern is in agreement with the previously-published coseismic fault model derived from GNSS (Global Navigation Satellite System) data. In this study, we investigate the deformation after earthquake associated with viscoelastic relaxation, using continuous GNSS data available in the region. During our investigation, we use a rheological structure with an elastic layer 50 km thick, along with Maxwell viscosity of 9.0.0 × 10¹⁷ Pa s. We compared the surface deformation obtained from our analysis with GNSS data. Our investigation presents evidence that viscoelastic relaxation responsible for less than 1 mm/yr during 1.5 years after the mainshock. By comparing the model and data velocities, it is found that the model velocities are only 0.02% compared to those of the data.