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Examining the impact of the Great Barrier Reef on tsunami propagation using numerical simulations

Abstract

Coral reefs may provide a beneficial first line of defence against tsunami hazards, though this is currently debated. Using a fully nonlinear, Boussinesq propagation model, we examine the buffering capacity of the Great Barrier Reef against tsunamis triggered by several hypothetical sources: a series of far-field, Solomon Islands earthquake sources of various magnitudes (Mw 8.0, Mw 8.5, and Mw 9.0), a submarine landslide source that has previously been documented in the offshore geological record (the “Gloria Knolls Slide”), and a potential future landslide source (the “Noggin Block”). We show that overall, the Great Barrier Reef acts as a large-scale regional buffer due to the roughness of coral cover and the complex bathymetric features (i.e. platforms, shoals, terraces, etc.) that corals construct over thousands of years. However, the buffering effect of coral cover is much stronger for tsunamis that are higher in amplitude. When coral cover is removed, the largest earthquake scenario (Mw 9.0) exhibits up to a 31% increase in offshore wave amplitude and estimated run-up. These metrics increase even more for the higher-amplitude landslide scenarios, where they tend to double. These discrepancies can be explained by the higher bed particle velocities incited by higher-amplitude waves, which leads to greater frictional dissipation at a seabed covered by coral. At a site-specific level, shoreline orientation relative to the reef platforms also determines the degree of protectiveness against both types of tsunamis, where areas situated behind broad, shallow, coral-covered platforms benefit the most. Additionally, we find that the platforms, rather than gaps in the offshore reef structure, tend to amplify wave trains through wave focussing when coral cover is removed from simulations. Our findings have implications for future tsunami hazards along the northeastern Australian coastline, particularly as the physiological stressors imposed by anthropogenic climate change further exacerbate coral die-off and reductions in ecosystem complexity. Therefore, areas that experience a protective benefit by the Great Barrier Reef’s platforms could be disproportionately more vulnerable in the future.

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Fig. 1

source zones of major tsunamigenic earthquakes. Landslides are plotted as red circles sized proportionally to the natural log of a given landslide’s volume. This compilation is based on several reviews (Hampton et al. 1996; Elverhøi et al. 2002; Owen et al. 2007; Lee 2009; Urlaub et al. 2013; Harbitz et al. 2014; Papadopoulos et al. 2014; Moscardelli and Wood 2016), where landslides with estimated volumes of 1 km3 were excluded. All original references documenting each of the plotted slides are provided in the reference list of this study. Landmasses are overlaid with gridded UN-adjusted population density for 2020 (CIESIN 2018), with ETOPO1 as the base map (Amante and Eakins 2009)

Fig. 2

source zone, the Coral Sea, and the northeastern Australian margin, which includes the GBR (orange). Also plotted are the locations along the Australian coastline where historical tsunamis that exceeded maximum water heights of 10 cm have been observed using tide gauges (triangles; NGDC/WDS 2020). The red line indicates the subduction zones that traverse the Solomon Islands source zone

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source are 0.32 m, 1.7 m, and 9.7 m, respectively. The simulated propagation time represented here is ~ 8 h to allow waves to reach all parts of the bathymetric domain

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Data availability

The bathymetry of the Great Barrier Reef region can be found here: http://eatlas.org.au/data/uuid/200aba6b-6fb6-443e-b84b-86b0bbdb53ac. The Great Barrier Reef Banks shapefile can be obtained here: https://data.gov.au/dataset/ds-ga-c00ab093-f02d-5b03-e044-00144fdd4fa6/details?q=great%20barrier%20reef%20banks. The global reef dataset can be downloaded here: www.wri.org/resources/data-sets/reefs-risk-revisited.

Code availability

The code Geowave can be downloaded here: http://www.appliedfluids.com/geowave.html. The codes NHWAVE and FUNWAVE-TVD can be downloaded from GitHub (github.com/JimKirby/NHWAVE; fengyanshi.github.io/build/html/index.html).

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Acknowledgements

We extend our sincere gratitude to Fengyan Shi for his assistance with model set-up and troubleshooting. We also thank Lorena Moscardelli for allowing us to reproduce a significant portion of her submarine landslide database for this work. We are grateful to Tristan Salles, Jon Hill, and Greg Houseman for their constructive and insightful comments. Stewart Allen and Diana Greensdale from the Australian Bureau of Meteorology provided earthquake source parameters. Computational resources were provided by the National Computational Infrastructure (NCI) in Canberra, Australia, which is supported by the Australian Commonwealth Government. We also thank the Sydney Informatics Hub at the University of Sydney for the provisioning of both expertise and computing power by their high-performance computing facility (Artemis).

Funding

A. T. was supported by the University of Sydney DBH Scholarship, and S. B. was supported through the Helmholtz Young Investigators Group CRYSTALS (VH-NG-1132).

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Correspondence to Mandi C. Thran.

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Thran, M.C., Brune, S., Webster, J.M. et al. Examining the impact of the Great Barrier Reef on tsunami propagation using numerical simulations. Nat Hazards 108, 347–388 (2021). https://doi.org/10.1007/s11069-021-04686-w

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  • DOI: https://doi.org/10.1007/s11069-021-04686-w

Keywords

  • Coral reef
  • Tsunami
  • Great Barrier Reef
  • Submarine landslide
  • Earthquake
  • Numerical simulation