The September 2018, Mw 7.5 Sulawesi earthquake occurring on the Palu-Koro strike-slip fault system was followed by an unexpected localized tsunami. We show that direct earthquake-induced uplift and subsidence could have sourced the observed tsunami within Palu Bay. To this end, we use a physics-based, coupled earthquake–tsunami modeling framework tightly constrained by observations. The model combines rupture dynamics, seismic wave propagation, tsunami propagation and inundation. The earthquake scenario, featuring sustained supershear rupture propagation, matches key observed earthquake characteristics, including the moment magnitude, rupture duration, fault plane solution, teleseismic waveforms and inferred horizontal ground displacements. The remote stress regime reflecting regional transtension applied in the model produces a combination of up to 6 m left-lateral slip and up to 2 m normal slip on the straight fault segment dipping 65 ∘ East beneath Palu Bay. The time-dependent, 3D seafloor displacements are translated into bathymetry perturbations with a mean vertical offset of 1.5 m across the submarine fault segment. This sources a tsunami with wave amplitudes and periods that match those measured at the Pantoloan wave gauge and inundation that reproduces observations from field surveys. We conclude that a source related to earthquake displacements is probable and that landsliding may not have been the primary source of the tsunami. These results have important implications for submarine strike-slip fault systems worldwide. Physics-based modeling offers rapid response specifically in tectonic settings that are currently underrepresented in operational tsunami hazard assessment.
Bibliographical noteKAUST Repository Item: Exported on 2021-04-13
Acknowledged KAUST grant number(s): ORS-2016-CRG5-3027, ORS-2017-CRG6 3389.02
Acknowledgements: We thank Taufiqurrahman for helping us accessing data on Indonesian websites, and for putting us in contact with Indonesian researchers. We thank Dr. T. Yudistira for providing their crustal velocity model of Sulawesi and Dr. Andreas Fichtner for providing us part of the ‘Collaborative Seismic Earth Model’. We thank Dr. Marcello de Michele for providing his inferred ground-deformation data and for fruitful discussions. The ALOS-2 original data are copyright JAXA and provided under JAXA RA6 PI projects P3278 and P3360. Dr. Widodo S. Pranowo provided access to very early field survey observations. Furthermore, Dr. Abdul Muhari supported this work by providing 1-min tide gauge data for the Pantoloan tide gauge. We thank two anonymous reviewers and the editor-in-chief Alexander Rabinovich for their constructive comments. Finally, we thank the #geotweeps twitter community and the participants of the AGU special session about the Palu earthquake and tsunami for stimulating discussions. The work presented in this paper was enabled by the Volkswagen Foundation (project “ASCETE”, Grant no. 88479). Computing resources were provided by the Institute of Geophysics of LMU Munich (Oeser et al. 2006), the Leibniz Supercomputing Centre (LRZ, Projects no. h019z, pr63qo and pr45fi on SuperMUC), and the Center for Earth System Research and Sustainability (CEN) at University of Hamburg. T.U., E. H. M. and A.-A. G. acknowledge support by the German Research Foundation (DFG) (projects no. KA 2281/4-1, GA 2465/2-1, GA 2465/3-1), by BaCaTec (Project no. A4) and BayLat, by KONWIHR—the Bavarian Competence Network for Technical and Scientific High Performance Computing (Project NewWave), by KAUST-CRG (GAST, Grant no. ORS-2016-CRG5-3027 and FRAGEN, Grant no. ORS-2017-CRG6 3389.02), by the European Union’s Horizon 2020 research and innovation program (ExaHyPE, Grant no. 671698 and ChEESE, grant no. 823844). S. V. acknowledges support by Einstein Stiftung Berlin through Grant EVF-2017-358(FU). Part of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration (NASA) by Earth Surface and Interior focus area and NISAR Science Team.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.
ASJC Scopus subject areas
- Geochemistry and Petrology