Dynamic analysis of geophysical characteristics of Una-Una Volcanic Island, Sulawesi, Indonesia

The Una-Una Volcanic Island is an active and isolated island, and its deep structure and dynamic causal mechanism have yet to be fully understood. The island is situated in Tomini Bay, between the north and east arms of Sulawesi Island in Indonesia. Around 5 Ma, the Sula Islands collided with the east arm of Sulawesi Island, which caused the subduction and retreat of the North Sulawesi Trench. Additionally, a sinistral strike-slip of roughly 4 cm/a initiated at the Palu-Koro fault on the western side of Sulawesi Island, ultimately leading to the formation of the isolated Una-Una Volcanic Island in Tomini Bay. Here, we utilized gravity, seismic, magnetic, and heat flow data to calculate the geophysical characteristics of three-dimensional temperature, velocity, and viscosity of the northern Sulawesi region. The results of our research showed that the crust in the northern region of Sulawesi Island is primarily characterized by brittle deformation. However, the presence of a southward-inclined weak layer in the crust, which resulted from the subduction of the North Sulawesi Trench, caused the region between the terrain and the Moho surface to exhibit a combination of brittle and ductile deformation. The weak zone in the crust in the northern region of Sulawesi Island is the primary controlling factor for the development of sinistral strike-slip. The uplift of the crustal weak area below the Una-Una Volcanic Island was caused by the southward subduction of the North Sulawesi Trench and the northward push of the Banggai-Sula microblock, ultimately leading to the formation of the Una-Una Volcanic Island in Tomini Bay.