Sulawesi lies within the complex zone of interaction between the Australian, Pacific, Philippine and Sunda Plates in which many small microplates are developed.[4] The main active structure onshore in the western part of Central Sulawesi is the left-lateral NNW-SSE Palu-Koro strike-slip fault that forms the boundary between the North Sula and Makassar blocks.[5] The rate of slip along this fault is estimated to be in the range 30–40 mm per year.[6] At Palu, there are several parallel fault strands defining the margins of a pull-apart basin, each of which take up some of the overall slip.[5] Several major earthquakes have been attributed to movement on this fault since 1900 and three larger events in the last 2,000 years have been deduced from studies of the fault zone.