Geodetic Observations of the 2018 Mw 7.5 Sulawesi Earthquake and Its Implications for the Kinematics of the Palu Fault

Abstract

The ascending and descending interferometric synthetic aperture radar data are used to investigate the fault rupture and slip model of the 2018 Mw 7.5 Sulawesi, Indonesia, earthquake. The best fitting slip model indicates that this earthquake ruptured not only a segment extending the Palu fault to the north but also a northwestern segment offshore. The slip on the onshore fault is predominant left‐lateral strike slip. The slip on the offshore fault is dominated by normal faulting with a maximum slip of ~6.3 m. The newly discovered offshore normal faulting is likely to be the cause of the tsunami after the shock. Combined with previous geomorphic, tectonic, geodetic, and modeling studies, we suggest that the kinematics of the Palu fault maintained the same style of faulting from north to south, which resulted from an oblique extension occurred on an east dipping fault at depths. The deformation pattern of NW Sulawesi is dominated by this slip mechanism.

Stress partition on the Palu-Koro fault controlling the 2018 Mw 7.5 Palu earthquake and its seismic hazards

“…This value was subsequently modified to assess its effect on the calculated ΔCFS. Previous studies reported the 2018 Palu Mw 7.5 earthquake fault parameters using seismic wave, GPS, and INSAR data inversions (Bao et al, 2019;Fang et al, 2019;Socquet et al, 2019;Song et al, 2019;Ulrich et al, 2019;Wang et al, 2019aWang et al, , 2019bCevikbilen et al, 2019;USGS). The employed fault-plane segments, fault geometries, and slip distributions differed due to inversion differences in the modelling techniques and data sets.…”

“…Previous studies have revealed the fault rupture process of the 2018 Palu Mw 7.5 earthquake using seismic wave, GPS, and InSAR data inversions (Bao et al, 2019;Fang et al, 2019;Socquet et al, 2019;Song et al, 2019;Ulrich et al, 2019;Wang et al, 2019aWang et al, , 2019bCevikbilen et al, 2019;USGS). The present study used the fault slip model developed by Song (2019) as it exhibited a geometrical simplicity and comparable slip distribution as compared to the other models (Bao et al, 2019;Socquet et al, 2019;Song et al, 2019;Wang et al, 2019).…”

“…Following the first year of the shock, many researchers explored the earthquake rupture process through geodetic and seismic data inversion. The earthquake rupture is highly suspected to present predominantly unilateral southward propagation (Bao et al, 2019;Fang et al, 2019;Socquet et al, 2019;Song et al, 2019;Ulrich et al, 2019;Wang et al, 2019;Cevikbilen et al, 2019;USGS). The along strike rupture on the Palu-Koro fault propagated southward for about 130 km to 140 km.…”

“…The along strike rupture on the Palu-Koro fault propagated southward for about 130 km to 140 km. In comparison, northward propagation was observed for only about 20 km to 30 km (Socquet et al, 2019;Song et al, 2019). Significant attention was focused towards the 2018 Palu earthquake rupture's southward unilateral propagation and termination during the past one year.…”

“…The Palu-Koro fault extends around 460 km N-S from the west of Minahassa trench to the north of Matano fault. The 2018 Palu earthquake only ruptured the central part (about 160 km) of the Palu-Koro fault (Bao et al, 2019;Fang et al, 2019;Socquet et al, 2019;Song et al, 2019;Ulrich et al, 2019;Wang et al, 2019;Cevikbilen et al, 2019;USGS). Two seismic gaps were left to the north offshore and the south on shore of the Palu-Koro fault with the length of about 180 km and 120 km, respectively (Figure 1).…”