Supershear shock front contribution to the tsunami from the 2018 Mw 7.5 Palu, Indonesia earthquake

Faisal Amlani (1) , Harsha S Bhat (2) , Wim J F Simons (3) , Alexandre Schubnel (2) , Christophe Vigny (2) , Ares J Rosakis (4) , Joni Efendi (4) , Ahmed E Elbanna (5) , Pierpaolo Dubernet (2) , Hasanuddin Z Abidin (6)

1 USC - University of Southern California
2 LGENS - Laboratoire de géologie de l'ENS
3 TU Delft - Delft University of Technology
4 CALTECH - California Institute of Technology
5 UIUC - University of Illinois at Urbana-Champaign [Urbana]
6 ITB - Institut Teknologi Bandung

Hazardous tsunamis are known to be generated predominantly at subduction zones. However, the 2018 M w 7.5 Palu (Indonesia) earthquake on a strike-slip fault generated a tsunami that devastated the city of Palu. The mechanism by which this tsunami originated from such an earthquake is being debated. Here we present near-field ground motion (GPS) data confirming that the earthquake attained supershear speed, i.e. a rupture speed greater than the shear wave speed of the host medium. We subsequently study the effect of this supershear rupture on tsunami generation by coupling the ground motion to a 1-D non-linear shallow-water wave model accounting for both time-dependent bathymetric displacement and velocity. With the local bathymetric profile of Palu bay around a tidal station, our simulations reproduce the tsunami arrival and motions observed by CCTV cameras. We conclude that Mach (shock) fronts, generated by the supershear speed, interacted with the bathymetry and contributed to the tsunami.

Mots clés: Earthquake dynamics; Geodetic instrumentation; Tsunamis; Numerical modelling; Numerical approximations and analysis

Domaines: Sciences de la Terre

Faisal Amlani, Harsha S Bhat, Wim J F Simons, Alexandre Schubnel, Christophe Vigny, et al.. Supershear shock front contribution to the tsunami from the 2018 Mw 7.5 Palu, Indonesia earthquake. Geophysical Journal International, 2022, 230, pp.2089 - 2097. ⟨10.1093/gji/ggac162⟩. ⟨hal-03869566⟩