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Tsunami hazard in New Zealand due to South American earthquakes

Tsunami hazard in New Zealand due to South American earthquakes. William Power, Gaye Downes, Mark Stirling Institute of Geological and Nuclear Sciences. Napier, New Zealand, 1960. New Zealand tsunami sources. Figures from: Integrated Tsunami Database for Pacific.

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Tsunami hazard in New Zealand due to South American earthquakes

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  1. Tsunami hazard in New Zealand due to South American earthquakes William Power, Gaye Downes, Mark Stirling Institute of Geological and Nuclear Sciences Napier, New Zealand, 1960

  2. New Zealand tsunami sources Figures from: Integrated Tsunami Database for Pacific

  3. Magnitude/frequency of NZ tsunami sources (approximate) 1 Distant Earthquakes 10 100 Recurrence Interval (yr) (annual probability of exceedence)-1 Local Earthquakes 1000 Volcanoes Landslides 10000 Asteroid Impact 1 10 100 1000 Size of Tsunami (m)

  4. Which distant earthquakes caused tsunami which were damaging in New Zealand? 1964 M9.2 1946 M8? 1957 M8.1 1952 M8.5 ? 1933 M8.3 ? ? 1906 M8.6 ? 1868 M9.1 1919 M8.3 1877 M9.0 ? ? 1960 M9.5 Figures from: Integrated Tsunami Database for Pacific

  5. 1960 Figure from: Integrated Tsunami Database for Pacific

  6. South American subduction zone earthquake sources • Discretise by location and magnitude • Ignore smaller earthquakes Mw < 8.5 • Estimate typical uplift distribution for each location and magnitude combination • Model tsunami propagation for each uplift distribution

  7. Plate Boundary 2 km 20º 130 km Fault Plane Source Parameters Refs: Abe (1975), Scholz (1982), Barrientos and Ward (1990)

  8. Propagation model

  9. Maximum heights Maximum wave height estimates, source 19, Mw 8.8 Maximum wave height estimates, source 19, Mw 8.8 1m+ 1 m 10 cm 10 cm 1 cm 1 cm

  10. Monte-Carlo • Generate a synthetic catalogue of events For each source location: Select the number of earthquakes (Poisson) For each earthquake: Select the magnitude (Gutenberg-Richter) For each point on the New Zealand grid: Accumulate exceedence counts End loop of points End loop of earthquakes End loop of sources

  11. 2 2 4 4 6 6 8 8 10 10 12 12 14 14 2500 year return time peak-to-trough waveheights (metres) Christchurch Auckland Gisborne Napier Dunedin Wellington Preliminary results Preliminary results. South American sources only.

  12. 1 1 2 2 3 3 4 4 5 5 6 6 7 7 500 year return time peak-to-trough waveheights (metres) Christchurch Auckland Gisborne Napier Dunedin Wellington Preliminary results. South American sources only.

  13. Disaggregation . 32 24 16 8 1

  14. What next? • Improve geometrical and statistical models • Use further levels of nested grid, and model inundation • Study effects of non-uniform slip distribution • Consider other distant source regions, then local sources

  15. Conclusions • South American earthquakes pose one of the most significant distant-source tsunami hazards for New Zealand. • The hazard can be estimated using techniques similar to seismic hazard modelling. • A Monte-Carlo approach is a practical approach to use for estimating tsunami hazard.

  16. Acknowledgements • NOAA: Vasily Titov, Frank Gonzalez, Hal Mofjeld – MOST propagation model, many useful discussions • USC: Jose Borrero – general tsunami modelling advice • GNS: John Beavan, Laura Wallace, Mauri McSaveney, Rafael Benites, Russell Robinson, Martin Reyners, Vaughan Stagpoole, Biljana Lukovic, Carolyn Hume • Bathymetry: Smith & Sandwell, GEBCO, Seabed Mapping (NZ contribution to GEBCO: NIWA)

  17. Tsunami hazard in New Zealand due to South American earthquakes Email: w.power@gns.cri.nz William Power, Gaye Downes, Mark Stirling Institute of Geological and Nuclear Sciences

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