Friday delivered a big test for NZ’s tsunami response. How did we do?
By Ursula Cochran
It was an exceptional morning: three large earthquakes within six hours, and an unfolding of events that put our emergency preparedness to the test. On this question, that the tsunamis that materialised on Friday March 5 ended up being relatively small is not what matters; what matters is the way we responded.
A regional tsunami is triggered a bit further away, and will arrive at the coast within one to three hours. It is not as far away as a distant tsunami, which offers more time to prepare, but far enough that we rely on an official warning for evacuation because the triggering earthquake is unlikely to have been felt for very long or strongly, if at all. There will be no self-evacuation underway. That creates a high-pressure situation for those involved in producing official tsunami warnings. On Friday we had two such events.
How do we know whether a tsunami is coming? Earthquake location, magnitude, depth, and style of movement are important clues in determining whether the sea floor has moved and displaced seawater. Once seawater is on the move as a tsunami, it can be detected in the open ocean with technology such as DART buoys (pressure recorders on the seafloor connected to a buoy at the surface which sends data back to land), or on tide and sea-level gauges around coastlines. If you have time and a good handle on the earthquake, near real-time modelling of the tsunami can provide detailed estimates of tsunami characteristics.
March 5 2021 saw many years’ of tsunami response coalesce in one day. It provided an illustration of how a wide range of tactics, at every level from personal to political, are required in responding. The science continues to be developed to speed up characterisation of earthquakes, near-real-time tsunami modelling, and to improve offshore monitoring capability. But Friday showed how far we have come already. It showed that New Zealanders are prepared to evacuate quickly for both natural and official tsunami warnings. We saw people taking responsibility for their own and their neighbours’ safety – driving, cycling and walking out of a danger zone. We saw scenes of care and preparedness – marae taking in strangers, mayors knocking on doors, parents trusting schools to look after children. And we saw that New Zealanders understand, critically, that high ground is a saviour.