Tsunami hazard in New Zealand due to South American

earthquakesWilliam Power, Gaye Downes, Mark StirlingWilliam Power, Gaye Downes, Mark StirlingInstitute of Geological and Nuclear SciencesInstitute of Geological and Nuclear Sciences

Napier, New Zealand, 1960

New Zealand tsunami sourcesNew Zealand tsunami sources

Figures from: Integrated Tsunami Database for Pacific

Magnitude/frequency of NZ Magnitude/frequency of NZ tsunami sources tsunami sources (approximate)(approximate)

Size of Tsunami (m)

Rec

urre

nce

Inte

rval

(yr

)

(ann

ual p

roba

bilit

y of

exc

eede

nce)

-1

1

10

100

1000

10000

1

10 100 1000

Distant Earthquakes

Local Earthquakes

Landslides

Asteroid Impact

Volcanoes

1933M8.3

1957M8.1

Which distant earthquakes caused tsunami which were damaging in New Zealand?Which distant earthquakes caused tsunami which were damaging in New Zealand?

Figures from: Integrated Tsunami Database for Pacific

1960M9.5

1877M9.0

1868M9.1

1906M8.6

1964M9.21952

M8.5

1919M8.3

?

?

1946M8?

?

?

?

?

19601960

Figure from: Integrated Tsunami Database for Pacific

South American subduction South American subduction zone earthquake sourceszone earthquake sources

Discretise by location and magnitudeDiscretise by location and magnitude

Ignore smaller earthquakes Mw < 8.5Ignore smaller earthquakes Mw < 8.5

Estimate typical uplift distribution for each Estimate typical uplift distribution for each location and magnitude combinationlocation and magnitude combination

Model tsunami propagation for each uplift Model tsunami propagation for each uplift distributiondistribution

Source ParametersSource Parameters

20º

2 km

130 km

Plate Boundary

Fault Plane

Refs: Abe (1975), Scholz (1982), Barrientos and Ward (1990) Refs: Abe (1975), Scholz (1982), Barrientos and Ward (1990)

Propagation modelPropagation model

Maximum heightsMaximum 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

Monte-CarloMonte-Carlo

Generate a synthetic catalogue of eventsGenerate a synthetic catalogue of events

For each source location:For each source location:

Select the number of earthquakes (Poisson)Select the number of earthquakes (Poisson)

For each earthquake:For each earthquake:

Select the magnitude (Gutenberg-Richter)Select the magnitude (Gutenberg-Richter)

For each point on the New Zealand grid:For each point on the New Zealand grid:

Accumulate exceedence countsAccumulate exceedence counts

End loop of pointsEnd loop of points

End loop of earthquakesEnd loop of earthquakes

End loop of sources End loop of sources

124 6 1082 14

2500 year return time peak-to-trough waveheights (metres)

124 6 1082 14

Gisborne

Napier

Wellington

AucklandChristchurch

Dunedin

Preliminary resultsPreliminary results. South American sources only.

500 year return time peak-to-trough waveheights (metres)

Gisborne

Napier

Wellington

Auckland

Christchurch

Dunedin

62 3 541 7 62 3 541 7Preliminary results. South American sources only.

DisaggregationDisaggregation

1

32

16

8

24

.

Improve geometrical and statistical modelsImprove geometrical and statistical models

Use further levels of nested grid, and model inundationUse further levels of nested grid, and model inundation

Study effects of non-uniform slip distributionStudy effects of non-uniform slip distribution

Consider other distant source regions, then local sourcesConsider other distant source regions, then local sources

What next?What next?

ConclusionsConclusions

South American earthquakes pose one of the South American earthquakes pose one of the most significant distant-source tsunami hazards most significant distant-source tsunami hazards for New Zealand.for New Zealand.

The hazard can be estimated using techniques The hazard can be estimated using techniques similar to seismic hazard modelling.similar to seismic hazard modelling.

A Monte-Carlo approach is a practical approach A Monte-Carlo approach is a practical approach to use for estimating tsunami hazard.to use for estimating tsunami hazard.

AcknowledgementsAcknowledgements

NOAA: Vasily Titov, Frank Gonzalez, Hal Mofjeld – MOST NOAA: Vasily Titov, Frank Gonzalez, Hal Mofjeld – MOST propagation model, many useful discussionspropagation model, many useful discussions

USC: Jose Borrero – general tsunami modelling adviceUSC: Jose Borrero – general tsunami modelling advice

GNS: John Beavan, Laura Wallace, Mauri McSaveney, GNS: John Beavan, Laura Wallace, Mauri McSaveney, Rafael Benites, Russell Robinson, Martin Reyners, Rafael Benites, Russell Robinson, Martin Reyners, Vaughan Stagpoole, Biljana Lukovic, Carolyn HumeVaughan Stagpoole, Biljana Lukovic, Carolyn Hume

Bathymetry: Smith & Sandwell, GEBCO, Seabed MappingBathymetry: Smith & Sandwell, GEBCO, Seabed Mapping(NZ contribution to GEBCO: NIWA)(NZ contribution to GEBCO: NIWA)

Tsunami hazard in New Zealand due to South American

earthquakes

William Power, Gaye Downes, Mark StirlingWilliam Power, Gaye Downes, Mark StirlingInstitute of Geological and Nuclear SciencesInstitute of Geological and Nuclear Sciences

Email: w.power@gns.cri.nz