The Geometry and Thermal Models of the Flores Thrust Harisma Andikagumi, Kyle Bradley
Earth Observatory of Singapore, Nanyang Technological University, Singapore-
Asian School of Environment, Nanyang Technological University, Singapore
Abstract
The 2018 Lombok earthquake demonstrated the hazard that the Flores Thrust possess and highlighted our lack of knowledge on this crustal scale back thrust. The Flores Thrust extends from west to east, located at the backarc of the Lesser Sunda Islands, Indonesia. Here we construct the geometry model of the Flores Thrust by fitting the best surface on the relocated earthquake catalogues using simulated annealing and interpolating using FastRBFTM algorithm. The thrust has a flat and a ramp component, where the flat is generally constant, inclined ~5˚- southward, but limited between eastern Bali and western Sumbawa formed due to the sediment-filled North Bali-Lombok basin. The ramp of the thrust is dipping southward with 38˚- average dip, where the dip increases eastward from Bali (27˚--37˚-) to Lombok (28˚--38˚-), Sumbawa (30˚--50˚-), and western Flores (40˚--58˚-), but then shallower in central Flores (29˚--39˚-). Based on our analysis of volcano distribution, the seismogenic zone of Flores Thrust is constrained by arc volcano distribution- bounded by volcanoes at the eastern and the western tips while the deeper part is terminated by the along-arc distribution of volcanoes or where the temperature exceeds 450˚-C. The interaction between fault propagation and arc volcanism possibly influences the geometry of Flores Thrust and perhaps affecting the arc by migrating the active volcanism northward in Sumbawa, leaving extinct edifices in its south while forming the highly potassic rear-arc volcanoes, Tambora and Sangeang Api, in the north. The other alternative to explain the segmented geometry of the thrust is that the thrust was initiated from multiple isolated faults that interconnected in the later stage of fault development. Therefore, the complexity of the Flores Thrust geometry and its interplay with the volcanism should be investigated further, to mitigate the greater effects of any geohazards in the region.
Keywords: Flores Thrust, Volcano, Fault Model, Thermal Model
