Source Characteristics of the 28 September 2018 Mw 7.4 Palu, Indonesia, Earthquake Derived from the Advanced Land Observation Satellite 2 Data

Abstract

On 28 September 2018, an Mw 7.4 earthquake, followed by a tsunami, struck central Sulawesi, Indonesia. It resulted in serious damage to central Sulawesi, especially in the Palu area. Two descending paths of the Advanced Land Observation Satellite 2 (ALOS-2) synthetic aperture radar (SAR) data were processed with interferometric synthetic aperture radar (InSAR) and pixel tracking techniques to image the coseismic deformation produced by the earthquake. The deformation measurement was used to determine the fault geometry and the coseismic distributed slip model with a constrained least square algorithm based on the homogeneous elastic half-space model. We divided the fault into four segments (named AS, BS, CS and DS, from the north to the south) in the inversion. The BS segment was almost parallel to the DS segment, the CS segment linked the BS and DS segments, and these three fault segments formed a fault step-over system. The Coulomb failure stress (CFS) change on the causative fault was also calculated. Results show that the maximum SAR line-of-sight (LOS) and horizontal deformation were −1.8 m and 3.6 m, respectively. The earthquake ruptured a 210-km-long fault with variable strike angles. The ruptured pattern of the causative fault is mainly a sinistral slip. Almost-pure normal characteristics could be identified along the fault segment across the Palu bay, which could be one of the factors resulting in the tsunami. The main slip area was concentrated at the depths of 0–20 km, and the maximum slip was 3.9 m. The estimated geodetic moment of the earthquake was 1.4 × 1020 Nm, equivalent to an earthquake of Mw 7.4. The CFS results demonstrate that the fault step-over of 5.3 km width did not terminate the rupture propagation of the main shock to the south. Two M>6 earthquakes (the 23 January 2005 and the 18 August 2012) decreased CFS along CS segment and the middle part of DS segment of the 2018 main shock. This implies that the stress release during the previous two earthquakes may have played a vital role in controlling the coseismic slip pattern of the 2018 earthquake.

Space‐Time Stress Variations on the Palu‐Koro Fault Impacting the 2018 Mw 7.5 Palu Earthquake and Its Seismic Hazards

“…In the first year following the shock, many researchers explored the earthquake rupture process through geodetic and seismic data inversion. The earthquake is suspected to involve predominantly unilateral southward rupture propagation (Bao et al., 2019; Cevikbilen & Taymaz, 2019; Fang et al., 2019; Hayes, 2018a, 2018b; Socquet et al., 2019; Song et al., 2019; Ulrich et al., 2019; Y. Wang et al., 2019). The rupture on the Palu‐Koro fault propagated southward for about 130 –140 km from the hypocenter.…”

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

Review of Regional Geological Structures on the Appearance of Geothermal Manifestations in the “Neck” Region of Western Sulawesi Island

“…The maximum shift at that time was 6 ± 0.5 m in the vicinity of Palu City, and on average between 1.9 m and 4.7 m in the northern and southern regions of Palu City [31]. After the incident, many researchers studied or mapped surface rupture path of Palu-Koro fault which was investigated using various sources of the data and methods, both by field surveys and utilizing digital or satellite data [21,[31][32][33][34][35][36][37]. The results show that rupture of Palu-Koro fault length > 150 km starting from the Palu Valley (south) to the western neck of Sulawesi Island (north).…”

On Analysis of Seismic Vibrations Data Applying Doppler Effect Expression

“…Various data sources were applied to investigate the phenomena of eruptions [28][29][30]. Great achievements are done using modern techniques like InSAR interferometry [31][32][33][34], GNSS [35][36][37][38], and satellite imagery [39][40][41][42]. Several studies are dedicated to one of the most destructive eruptions-the 2018 Indonesia Sulawesi magnitude 7.5 Palu earthquake [34,37,41,42].…”

“…What deals with scientific techniques and methods to investigate earthquakes application has InSAR technology, which enables detecting surface slips and Earth surface deformations [34,37,41]. For example, the 4-7 m surface slip in the area of Palu earthquake was detected [37] and the maximum horizontal deformation was from 1.8 m till 3.6 m [41], when ALOS-2 interferogram showed a peak slip of 6.5 m located at the south of Palu city [34]. GNSS plays a great role in the research of earthquakes giving very precise metrical parameters to improve the crustal deformation field and 3D geometric complexities of the faults in total [38,53,60,65,68].…”