Identification of Fault Structure in Lombok region, West Nusa Tenggara using Tomography Lombok Earthquake Data of July-August 2018

Lombok and Nusa Tenggara are one of the regions in Indonesia that have quite complex tectonic arrangements. With this order, not infrequently in the region there are often natural disaster phenomena. One of the most striking things is the occurrence of a series of earthquakes of magnitude Mw > 5.0 that rocked the northern region of the Island of Lombok on 29 July 2018 (Mw = 6.4), 5 August 2018 (Mw = 6.9), 9 August 2018 (Mw = 5.9), 19 August 2018 (M_w = 6.3 and 6.9) and 25 August 2018 (M_w = 5.5). This study aims to identify the condition of tectonic structures under the surface of the earthquake occurring region using the tomography method. This method utilizes earthquake travel time data recorded at 15 BMKG seismic stations. The tomogram results show the contrast of anomalous values in the Vp and Vs models. The contrast of the anomalous is associated with the presence of fault structures that have an allowance angle of about 20-30° and a thrust fault type, verified by focal mechanism ball data. This thrust fault is then indicated as the cause of the occurrence of earthquakes with magnitude Mw > 5.0, which shook the northern part of the island of Lombok in July-August 2018. According to the tomography result, the fault is located closer to the north side of Lombok Island than Flores Back arc Thrust.