Fig. 1

a Tectonic map of Sulawesi showing major structures in the region (compiled from Hamilton 1979; Hall and Wilson 2000; Hinschberger et al. 2005; Hall 2012). Red dots indicate earthquake hypocenters with a magnitude greater than 4.5 and a depth less than 30 km between 1980 and 2016. Moment tensor of the Mw 7.5 2018 earthquake and earthquake hypocenters are from the USGS Earthquake Catalog. b DEM map showing morpho-structural elements of Palu Basin. Palu Valley is bounded by two mountains in the East and West. Structural elements in Palu Valley are compiled from previous authors (e.g., Bellier et al. 2001; Watkinson and Hall 2017; Socquet et al. 2019)