Abstract
A devastating Mw 7.5 earthquake and tsunami struck northwestern Sulawesi, Indonesia on 28 September 2018, causing over 4000 fatalities and severe damage to several areas in and around Palu City. Severe earthquake-induced soil liquefaction and landslides claimed hundreds of lives in three villages within Palu. The mainshock occurred at 18:03 local time at a depth of 10 km on a left-lateral strike-slip fault. The hypocenter was located 70 km north of Palu City and the rupture propagated south, under Palu Bay, passing on land on the west side of Palu City. The surface rupture of the earthquake has been mapped onshore along a 30 km stretch of the Palu-Koro fault. We present results of field surveys on the effects of the earthquake, tsunami and liquefaction conducted between 1–3 and 12–19 of October 2018. Seismic intensities on the Modified Mercalli Intensity (MMI) scale are reported for 375 sites and reach a maximum value of 10. We consolidate published tsunami runup heights from several field studies and discuss three possible interrelated tsunami sources to explain the variation in observed tsunami runup heights. Due to limited instrumentation, PGA and PGV values were recorded at only one of our field sites. To compensate, we use our seismic intensities and Ground Motion to Intensity Conversion Equations (GMICEs) and Ground Motion Prediction Equations (GMPEs) developed for similar tectonic regions. Our results indicate that the maximum predicted PGAs for Palu range from 1.1 g for GMICEs to 0.6 g for GMPEs.
Highlights
We present a summary of tsunami runup heights around the perimeter of Palu Bay from those published tsunami surveys and summarize three possible sources for the generation of the tsunami: (1) submarine landslides; (2) a submarine fault step-over accompanied by
We study areas that experienced extreme soil liquefaction and landslides, estimate expected Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) values at these sites based on existing Ground Motion to Intensity Conversion Equations (GMICEs) and Ground Motion Prediction Equations (GMPEs) developed for tectonic regions similar to Central Sulawesi
The southern portion of the earthquake surface rupture passed through the west side of Palu City (Fig. 3), along the Palu–Koro fault, and generated up to 4 m of left-lateral slip at a location 2 km south of Palu Bay (Fig. 5A)
Summary
The island of Sulawesi is located within a broader convergent zone where the Pacific-Philippine plate and the India– Australia plate subduct underneath the Sunda plate at rates of 90 mm and 75 mm/yr, respectively (Fig. 1; Socquet et al, 2006; Spencer, 2011). A prominent strike-slip fault in Sulawesi, the Palu-Koro fault (Fig. 1) passes directly through north-central Sulawesi and presents a high seismic hazard (Bellier et al, 2001; Socquet et al, 2006; Cipta et al, 2017; Watkinson and Hall, 2017). A devastating Mw 7.5 earthquake struck Sulawesi Island on 28 September 2018 at 18:03 local time (10:03 UTC), with an epicentre located 70 km north of Palu City (Fig. 2). The earthquake and tsunami destroyed large residential areas, damaging more than
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