Abstract
The 220-km-long Palu–Koro Fault, Central Sulawesi, is a major fault with prominent expression in Eastern Indonesia. Many studies about the Palu–Koro Fault have shown its capability of generating large earthquakes, but how the Palu–Koro Fault has evolved remains enigmatic. This study is to investigate the geomorphology of NW Palu Valley based on DEMNAS (Digital Elevation Model of Indonesia) and field observations to understand the development of the Palu–Koro Fault. The study area comprises a high mountain in the west and a valley in the east. There are two major normal faults and a strike–slip fault observed in NW Palu Valley. The western normal fault is a basin-bounding fault, which marks the topographic break between mountain and valley. To the east, another normal fault is observed cutting the old alluvial fans and expressed by planar fault scarps. The strike–slip fault is observed within the basin and crosses the distal part alluvial fans. It is expressed by intra-basin ridges in places which are slightly uplifted from the adjacent surface. The surface rupture of the 2018 Mw 7.5 Palu earthquake in NW Palu Valley also shows left-lateral movement up to 4 m. We consider that the development of the Palu–Koro Fault in NW Palu Valley is characterized by toward-central-basin migration of faulting activity from basin-bounding fault to intra-basin fault.
Highlights
Sulawesi is located at the triple junction where the Pacific, Australian, and Eurasian plates converge, and it records a complex geological history of subduction, extension, obduction, and collision (e.g., Hamilton 1979; Silver et al 1983; Hall and Wilson 2000; Hinschberger et al 2005; Hall 2002, 2012, 2018; Nugraha and Hall 2018)
The convergence rate of the subduction increases toward west from 20 to 54 mm year−1, resulting from a clockwise rotation of North Sulawesi about a pole located at the NE Sulawesi (Silver et al 1983; Walpersdorf et al 1998; Stevens et al 1999; Rangin et al 1999; Bock et al 2003)
This study aims to interpret the tectonic geomorphology based on field investigation, including some recent surface rupture and digital elevation data of Indonesia (DEMNAS) along the NW Palu Valley that shows geomorphic evidence of faulting and its relative timing, we propose the evolutionary model of Palu–Koro Fault in NW Palu Valley
Summary
Sulawesi is located at the triple junction where the Pacific, Australian, and Eurasian plates converge, and it records a complex geological history of subduction, extension, obduction, and collision (e.g., Hamilton 1979; Silver et al 1983; Hall and Wilson 2000; Hinschberger et al 2005; Hall 2002, 2012, 2018; Nugraha and Hall 2018). The Palu–Koro Fault is the major active fault in Central Sulawesi with left-lateral movement and a NNW– SSE trend (Katili 1970; Tjia 1978; Hamilton 1979; Bellier et al 2001; Daryono 2016; Watkinson and Hall 2017). It can be recognized based on its prominent expression spanning from Palu to North Luwu Regency along. The Palu–Koro and Matano faults have been reactivated due to the Mid-Pliocene collision in an E–W direction between the East Sulawesi and the Banggai Sula Blocks in the eastern arm of Sulawesi (Villeneuve et al 2002; Bellier et al 2006) Both faults accommodate left-lateral slip transferred from the E–W convergence (Bock et al 2003; Socquet et al 2006). The convergence rate of the subduction increases toward west from 20 to 54 mm year−1, resulting from a clockwise rotation of North Sulawesi about a pole located at the NE Sulawesi (Silver et al 1983; Walpersdorf et al 1998; Stevens et al 1999; Rangin et al 1999; Bock et al 2003)
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