Analysis of Deformation Along the Flores Back-Arc Thrust Using GPS Observation Data

Abstract Indonesia is located on the World Plate and composed of several microblocks. One of the microblocks in Indonesia is along the Back-Arc Thrust of Flores, which is suspected to cause many earthquakes throughout 2022 in Bali and Nusa Tenggara. The high activity of earthquakes encourages the need for deformation monitoring as a mitigation effort. This study aims to analyse the movement and strain patterns that occur in the Flores Back-arc as an effort to see the deformation that occurs. This research uses BIG GPS CORS observation data from 2019-2023 and processed using GAMIT/GLOBK software. The results then will be estimated to obtain velocities, strains, and compare them with the earthquake occurrence. This study shows that the horizontal displacement is dominantly towards the northeast within 20-57 mm/year and dominantly subsidence for vertical displacement with the largest value of −62 mm/year. The high velocity is related to several large earthquakes, one of which is the Flores earthquake in 2021 which caused a offset of up to 19 mm at CBJW, CRTG, CREO, and CLBJ stations. In addition, the strain pattern shows that compression is dominant in the study area with a value range of to 29.3 to 55.7 nstrain/year. While the extension value has a range of 2.7 to 16.9 nstrain/year. The results show that the Southeast region has a high level of energy accumulation as seen from the high values of compression and extension that occur. While the Northwest region shows high energy accumulation indicated by the dominance of compression values due to Flores back-arc thrust in the north.