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) Size of Tsunami (m) Recurrence Interval (yr)  (annual probability of exceedence) -1 1 10 100 1000 10000 1 101001000 Distant Earthquakes Local Earthquakes Landslides Asteroid Impact Volcanoes

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

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

8. Propagation model

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

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. 1246108214 2500 year return time peak-to-trough waveheights (metres) 1246108214 Gisborne Napier Wellington Auckland Christchurch Dunedin Preliminary results Preliminary results. South American sources only.

12. 500 year return time peak-to-trough waveheights (metres) Gisborne Napier Wellington Auckland Christchurch Dunedin 6235417 6235417 Preliminary results. South American sources only.

13. Disaggregation 1 32 16 8 24.

14. 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 What next?

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 William Power, Gaye Downes, Mark Stirling Institute of Geological and Nuclear Sciences Email: w.power@gns.cri.nzw.power@gns.cri.nz