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

Creators: Amlani, Faisal; Bhat, Harsha S.; Simons, Wim J. F.; Schubnel, Alexandre; Vigny, Christophe; Rosakis, Ares J.; Efendi, Joni; Elbanna, Ahmed E.; Dubernet, Pierpaolo; Abidin, Hasanuddin Z.

Abstract

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.

Additional Information

© The Author(s) 2022. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Received: 10 January 2022. Revision received: 01 March 2022. Accepted: 15 April 2022. Published: 08 June 2022. FA would like to thank N.M. Pahlevan at USC for encouraging this work. HSB acknowledges the European Research Council grant PERSISMO (grant 865411) for partial support of this work. AS would like to acknowledge the European Research Council grant REALISM (2016-grant 681346). AJR was supported by the Caltech/MCE Big Ideas Fund (BIF). AE acknowledges support by the National Science Foundation (CAREER Award Number 1753249). The continued (long-term) operation of the GPS stations in Central Sulawesi, Indonesia data has been co-facilitated by the EU-ASEAN SEAMERGES (2004-2006) and GEO2TECDI-1/2 projects (2009-2013) in cooperation with the Geospatial Information Agency of Indonesia (BIG). GPS data acquisition and research was partly funded by grants from the Dutch NWO User Support Programme Space Research (2007-2018). We would like to express our special thanks to the local staff of the Indonesian Meteorology, Climatology, and Geophysical Agency (BMKG) offices in Palu for hosting the GPS station and for being available 24/7 to assist us with optimal operation of the equipment. A special thanks to our local survey staff, B.R. Umar and A. Urif, for their continued support (including directly after the earthquake) in inspecting the GPS stations. DATA AVAILABILITY. All codes are available upon reasonable request to the corresponding author. All relevant data relating to the tsunami modelling and the PALP GPS are available on Zenodo: https://doi.org/10.5281/zenodo.5018003

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