Like waves in a bathtub – the Chile tsunami reverberated around and around bays in New Zealand

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The results from 19 sea-level gauges around New Zealand reveal that six locations had peak wave heights of over one metre generated by a magnitude 8.8 earthquake off Chile on 27 February.

At most locations the highest waves didn’t occur for some time, ranging from 1.2 hours to 26 hours after the first wave arrived. In all cases in New Zealand, the first wave to arrive was an upwards rise rather than a drawdown of the water level.

Tsunami waves arrived first at Scott Base, although the waves were small, then reached the Chatham Islands (Kaingaroa) about 11.6 hours after the earthquake in Chile. It touched down on the North Island at East Cape nearly an hour later. Lyttelton experienced the largest waves, with a peak wave of 1.9 metres (crest-to-trough) in mid-afternoon arriving six hours after the first wave. Other peak wave heights over a metre were measured in Chatham Islands, Gisborne, Sumner, Timaru and Whitianga.

“The tsunami was measured all along the west coast as well, but peak wave heights were much smaller (0.3–0.5 metres),” says NIWA Principal Scientist, Dr Rob Bell.

The delay in arrival of the largest waves from a distant tsunami source is due to waves bouncing off continental shelves, coastal headlands, and from much slower-travelling waves that get trapped on the coast and spread along the coastline, diminishing slowly.

These findings provide important feedback to civil defence and emergency management agencies as they refine tsunami warnings and when to scale down to a tsunami advisory.

Sea-level gauges around New Zealand are operated by various agencies including NIWA, port companies, regional and district councils operate various sea-level gauges which complement the operational real-time monitoring undertaken by GNS Science through GeoNet (New Zealand’s geological hazard monitoring system).

NIWA and GNS are anchor partners in the new Natural Hazards Research Platform, and undertake research that focuses on understanding the impact of Tsunami on New Zealand.

For more information, including plots and summary data, see Rob Bell’s analysis.

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Principal Scientist - Coastal and Estuarine Physical Processes