Insights on the Source of the 28 September 2018 Sulawesi Tsunami, Indonesia Based on Spectral Analyses and Numerical Simulations

Mohammad Heidarzadeh, Abdul Muhari, Antonius B. Wijanarto

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140 Citations (SciVal)

Abstract

The 28 September 2018 Sulawesi tsunami has been a puzzle because extreme deadly tsunami waves were generated following an Mw 7.5 strike-slip earthquake, while such earthquakes are not usually considered to produce large tsunamis. Here, we obtained, processed and analyzed two sea level records of the tsunami in the near-field (Pantoloan located inside the Palu Bay) and far-field (Mamuju located outside the Palu Bay) and conducted numerical simulations to shed light on the tsunami source. The two tide gauges recorded maximum tsunami trough-to-crest heights of 380 and 24 cm, respectively, with respective dominating wave periods of 3.6−4.4 and 10 min, and respective high-energy wave duration of 5.5 and >14 h. The two observed waveforms were significantly different with wave amplitude and period ratios of ~16 and ~3, respectively. We infer tsunamigenic source dimensions of 3.4–4.1 km and 32.5 km, for inside and outside of the Palu Bay, respectively. Our numerical simulations fairly well reproduced both tsunami observations in Pantoloan and Mamuju; except for the arrival time in Mamuju. However, it was incapable of reproducing the maximum reported coastal amplitudes of 6–11 m. It is possible that these two sources are different parts of the same tectonic source. A bay oscillation mode of ~85 min was revealed for the Palu Bay through numerical modeling. Actual sea surface disturbances and landslide-generated waves were captured by two video recordings from inside the Palu Bay shortly after the earthquake. It is possible that a large submarine landslide contributed to and intensified the Sulawesi tsunami. We identify the southern part of the Palu Bay, around the latitude of -0.82 o S, as the most likely location of a potential landslide based on our backward tsunami ray tracing analysis. However, marine geological data from the Palu Bay are required to confirm such hypothesis.

Original languageEnglish
Pages (from-to)25-43
Number of pages19
JournalPure and Applied Geophysics
Volume176
Issue number1
DOIs
Publication statusPublished - 22 Jan 2019

Bibliographical note

Funding Information:
Two tide gauge records in Pantoloan and Mamuju were provided by the Agency for Geo-spatial Information, Indonesia (BIG) (http://tides.big.go.id). We sincerely thank scientists in BIG including Andi Eka Sakya, Hasanuddin Z Abidin and Mohamaad Arief Syafi’i for their efforts to provide the data in a timely manner. The Latu Datu tide gauge data were downloaded from the Intergovernmental Oceanographic Commission website (http://www. iocsealevelmonitoring.org/). The earthquake source model used in this study is based on that of USGS (https://earthquake.usgs.gov/earthquakes/eventpage/ us1000h3p4/finite-fault). We are grateful to scientists in the USGS Earthquake Hazards Programs for making the source model publically available. We used the GMT software by Wessel and Smith (1998) in this study. We sincerely thank Alexander Rabi-novich (Editor-in-Chief) for reading and commenting on the early version of this article and for producing Table 1. Results of spectral analyses were discussed with Alexander Rabinovich. We received help from Satoko Murotani (National Museum of Nature and Science, Tsukuba, Japan) for the analysis of vertical water displacement due to steep slopes. We sincerely thank two anonymous reviewers and Alexander Rabinovich (Editor-in-Chief) for their constructive review comments. MH is grateful to the Brunel University London for the funding provided through the Brunel Research Initiative and Enterprise Fund 2017/18 (BUL BRIEF).

Funding Information:
Two tide gauge records in Pantoloan and Mamuju were provided by the Agency for Geo-spatial Information, Indonesia (BIG) (http://tides.big.go.id). We sincerely thank scientists in BIG including Andi Eka Sakya, Hasanuddin Z Abidin and Mohamaad Arief Syafi’i for their efforts to provide the data in a timely manner. The Latu Datu tide gauge data were downloaded from the Intergovernmental Oceanographic Commission website (http://www.iocsealevelmonitoring.org/). The earthquake source model used in this study is based on that of USGS (https://earthquake.usgs.gov/earthquakes/eventpage/us1000h3p4/finite-fault). We are grateful to scientists in the USGS Earthquake Hazards Programs for making the source model publically available. We used the GMT software by Wessel and Smith (1998) in this study. We sincerely thank Alexander Rabinovich (Editor-in-Chief) for reading and commenting on the early version of this article and for producing Table 1. Results of spectral analyses were discussed with Alexander Rabinovich. We received help from Satoko Murotani (National Museum of Nature and Science, Tsukuba, Japan) for the analysis of vertical water displacement due to steep slopes. We sincerely thank two anonymous reviewers and Alexander Rabinovich (Editor-in-Chief) for their constructive review comments. MH is grateful to the Brunel University London for the funding provided through the Brunel Research Initiative and Enterprise Fund 2017/18 (BUL BRIEF).

Publisher Copyright:
© 2018, The Author(s).

Keywords

  • earthquake
  • Indonesia
  • numerical simulations
  • spectral analysis
  • Sulawesi earthquake
  • Tsunami

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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