2D and 3D modelling of Molucca Sea double subduction zone based on primary waves travel time seismic tomography inversion

Abstract

Molucca Sea is one of the areas with a high level of seismicity in Indonesia due to its location between three plates. The activities of them forming a quite unique subduction zone. The Eurasian Plate (Sangihe Microplate) move to the East and The Philippine Sea Plate (Halmahera Microplate) continues to Westward caused The Molucca Sea Microplate to be pressed, and subducts in two opposite directions modelat the same time forming an inverted “U”. This research used 3663 hypocenters and 9 BMKG stations in the last 5 years (2016 - 2021) with a magnitude of 3 - 8 Mw and a depth of 3 - 630 kilometers. Seismic inversion of travel time tomography is used to produce 2D models of the subduction zone around The Molucca Sea. The distribution of high ΔVp values is ranging from 3.5% to 4% is associated with a solid medium, like The Sangihe Plate, Halmahera Plate, and The Molucca Sea Plate subduction slab. While the low ΔVp is ranging from 1.8% to 2% is associated with the destruction zone and the presence of thermal fluids such as magma or partial melting (the presence of volcanoes). The 3D model is based on the Gaussian Process Regression principle using magnitude and depth data as initial model parameters. Plotting of the thrust faults at the front of the two arcs, namely The West Sangihe Thrust Fault and The East Halmahera Thrust Fault. It can be seen that the subduction under The Sangihe Microplate is deeper (627.2 kilometers) has the average subduction angle of 45.3° compared to the subduction under The Halmahera Microplate (280.0 kilometers) has the average subduction angle of 35.8°