Focal mechanism along the subduction zone, Indonesian archipelago

Abstract

From the collision and subduction between Indo-Australian and Eurasian tectonic plates, the Indonesian Archipelago is exposed to high earthquake and tsunami hazards. Theoretically, tsunamis are formed when an earthquake causes vertical displacement at the seafloor. The main aims of this study are i) to evaluate tsunami risks along the Indonesian Archipelago and ii) to determine the stress states in the subducting slabs. In this study, a total of 2,998 focal mechanism solutions were obtained from the Global CMT project. The data contain information of fault plane orientation and fault movement. Seismotectonically, the data were divided into 2 settings, interplate earthquakes (focal depth between 0-50 km) and intraslab earthquakes (focal depth more than 50 km). The result suggested that, in case of interplate earthquakes, Java-Sumba Outer-rise segment and Aru Trough segment, both of which are defined as normal faulting regions, are able to generate relatively high initial tsunamis (0.65-0.73 m from a Mw 7.6 earthquake). In addition, a new seismogenic fault zone has been found in the South Banda Sea. From the consistency of the focal mechanism solutions and the trend of the earthquakes, this fault zone is NE-SW left-lateral strike-slip fault. In case of intraslab earthquakes, the result showed that the slabs are experiencing down-dip compression between the depths of 300-700 km, while at intermediate depths (50-300 km) the stress states are variable in different slabs due to heterogeneous slab compositions and other stress sources. Hence, apart from earthquake, a tsunami mitigation should be conducted along Java-Sumba Outer-rise and Aru Trough. Also, more research is needed to study the newly found fault zone in the South Banda Sea.