| dc.description.abstract | Sulawesi Island in eastern Indonesia is situated at the triple junction of the Sunda, Australian, and Philippine Sea plates. The peculiar K-shape of Sulawesi, comprised of four arms (North, South, East, and Southeast), represented the complex geological and tectonic development at various phases in its evolution. As a result, each arm offered different seismotectonic characteristics. This study aims to analyze the seismotectonics of Sulawesi using the updated datasets for earthquake seismicity and focal mechanisms, as well as other related supporting data. We divided Sulawesi into two parts based on the depth distribution of earthquakes: shallow (60 km) and deep (60–400 km). Sulawesi’s shallow part was grouped into six regions. The distribution of seismicity and the types of focal mechanisms were then examined in the framework of Sulawesi’s tectonic configuration. We determined the Celebes Sea subduction zone in Region I and the Palu-Koro fault in Region II as the two most seismically active zones in Sulawesi’s shallow part. Nevertheless, despite geodetic studies indicating a high slip rate for these two structures, we found a lack of seismicity near the center of the North Sulawesi Trench and in the northern Palu-Koro fault. We suggested that the former might be due to a seismic gap or aseismic slip, while the latter was due to this part being beyond the high relative motion of the Makassar and North Sula Blocks. In Region III, we proposed that the Makassar Strait Thrust Somba segment is in a silent state, indicating the possibility of a large earthquake in the future. In Region IV, we found that the 2019 Tolo Bay earthquake sequence most likely originated from the offshore southwestern continuation of the Peleng fault that was previously unidentified. The largest earthquake in Region V was represented by the 2001 earthquake Mw 7.5 near the western segment of the Tamponas Fault Zone. However, the orientation of the focal mechanism was inconsistent with the western segment of the Tamponas Fault Zone. This earthquake might be triggered by an unidentified fault or the reactivation of the western segment of the Tamponas Fault Zone. For the deep part of Sulawesi, we primarily focus on the two opposite-polarity slabs in northern Sulawesi: the Celebes Sea slab and the Sula slab. We determined the geometry (strike and dip) of these two slabs based on the linear fitting method. We then projected P- and T-axes of earthquakes into the geographic and regional frames to study the stress states of the Celebes Sea and Sula slabs. Our results displayed that the Celebes Sea was subducted southward with an average strike of 920 and dip of 710, while the Sula slab shows steeper slab subduction dipping 730 to the north-northwestward with a 2530 strike angle. Moreover, we found an absence of earthquakes in the Sula slab’s western part at 60-230 km depth, which we interpreted as the upper slab detaching at the first stage of collision in the early Miocene. | en_US |