On 28 September 2018, a shallow, large earthquake struck in the neck of the Minahasa Peninsula, Indonesia, with its epicentre located in the mountainous Donggala Regency, Central Sulawesi. The magnitude 7.5 quake was located away from the provincial capital Palu and was felt as far away as Samarinda on East Kalimantan and also in Tawau, Malaysia. This event was preceded by a sequence of foreshocks, the largest of which was a magnitude 6.1 tremor that occurred earlier that day. Following the mainshock, a tsunami alert was issued for the nearby Makassar Strait. A localised tsunami struck Palu, sweeping shore-lying houses and buildings on its way. The combined effects of the earthquake and tsunami led to the deaths of an estimated 4,340 people. This makes it the deadliest earthquake to strike the country since the 2006 Yogyakarta earthquake, as well as the deadliest earthquake worldwide in 2018, surpassing the previous earthquake that struck Lombok nearly 2 months earlier, killing more than 500. The Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) confirmed that a tsunami had been triggered, with its height reaching an estimated maximum of , striking the settlements of Palu, Donggala and Mamuju along its path. The earthquake caused major soil liquefaction in areas in and around Palu. In two locations this led to mudflows in which many buildings became submerged causing hundreds of deaths with many more missing. The liquefaction was considered to be the largest in the world and was deemed as rare. Tectonic setting Sulawesi lies within the complex zone of interaction between the Australian, Pacific, Philippine and Sunda Plates in which many small microplates are developed. The main active structure onshore in the western part of Central Sulawesi is the left-lateral NNW-SSE trending Palu-Koro strike-slip fault that forms the boundary between the North Sula and Makassar blocks. The rate of slip along this fault is estimated to be in the range 30–40 mm per year. 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. 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. In 2017 a study recognised this fault as representing the greatest seismic risk in eastern Indonesia. Earthquake Foreshocks The mainshock was preceded by a