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Using Cluster Analysis to Optimize Tsunami Evacuation Zones. William Power, Biljana Lukovi ć GNS Science, Lower Hutt, New Zealand. New Zealand tsunami sources. Distant/Regional Earthquakes. Local Earthquakes. Background Figures from: Integrated Tsunami Database for Pacific.
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Using Cluster Analysis to Optimize Tsunami Evacuation Zones William Power, Biljana Luković GNS Science, Lower Hutt, New Zealand
New Zealand tsunami sources Distant/Regional Earthquakes Local Earthquakes Background Figures from: Integrated Tsunami Database for Pacific
Source: Mw 9.1 Southern Peru (1868) Tsunami warnings • Divide the coast into zones • Assign a threat level for each zone, based on maximum predicted water level • Example is based on shipping forecast zones – not optimised for tsunami Tsunami threat levels
Source: Mw 9.1 Southern Peru (1868) Source: Mw 9.1 Southern Peru (1868) Tsunami threat levels Tsunami threat levels
The Basic idea Cluster 2 Cluster 1 Max water level Fault 2 Fault 2 Fault 1 Max water level Fault 1
Problem • The standard algorithms for computing clusters do not require the members of the cluster to be contiguous
No relationship between separated clusters of the same colour
Conclusions • New Zealand is exposed to tsunami from many directions • Different parts of the coast are more/less susceptible to different source regions • In a warning system based around zones it is beneficial if the coast within each zone has a similar pattern of susceptibility • Cluster Analysis is one route for classifying stretches of coast according to their susceptibility to different sources • A drawback of conventional cluster analysis is that it does not constrain the clusters to be contiguous around the coast • Approaches to adding the contiguity constraint are possible, but more work is required
Acknowledgments • NOAA – use of MOST and FACTS • Diana Greenslade (BOM) – discussions about warning zones • David Rhoades (GNS) – discussions about statistical analysis