Coupled, Physics-based Modelling Reveals Earthquake Displacements are Critical to the 2018 Palu, Sulawesi Tsunami

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. Our 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. In our model, a straight fault segment dipping 65 degree East beneath Palu Bay hosts a combination of up to 6 m left-lateral slip and up to 2 m normal slip determined by a regional transtensional stress regime. 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. Our results have important implications for submarine strike-slip fault systems worldwide. Physics-based modeling offers rapid response specifically in tectonic settings which are currently underrepresented in operational tsunami hazard assessment.

@article{id2448,
  author = {Ulrich, Thomas and Vater, Stefan and Madden, Elizabeth H. and Behrens, Joern and van Dinther, Ylona and van Zelst, Iris and Fielding, Eric J.  and Liang, Cunren and Gabriel, Alice-Agnes},
  doi = {10.31223/osf.io/3bwqa},
  journal = {Pure and Applied Geophysics},
  language = {en},
  title = {Coupled, Physics-based Modelling Reveals Earthquake Displacements are Critical to the 2018 Palu, Sulawesi Tsunami},
  url = {https://eartharxiv.org/3bwqa/},
  year = {2019},
}

%O Journal Article
%A Ulrich, Thomas
%A Vater, Stefan
%A Madden, Elizabeth H.
%A Behrens, Joern
%A van Dinther, Ylona
%A van Zelst, Iris
%A Fielding, Eric J. 
%A Liang, Cunren
%A Gabriel, Alice-Agnes
%R 10.31223/osf.io/3bwqa
%J Pure and Applied Geophysics
%G en
%T Coupled, Physics-based Modelling Reveals Earthquake Displacements are Critical to the 2018 Palu, Sulawesi Tsunami
%U https://eartharxiv.org/3bwqa/
%D 2019