System to have false-alarm safeguard

A new tsunami-alert system in Christchurch will give officials a chance to back out before warning residents of a big wave heading their way.

The Christchurch City Council has been holding community meetings to discuss its plans to install 22 tsunami sirens on the coastline between Waimairi Beach and Sumner this month at a cost of $550,000. Concerns about the reliability of the systems have arisen after a Whitianga tsunami alert was accidentally triggered twice in just over a week, sending Coromandel residents into a panic over a non-existent tsunami.

City council civil defence emergency manager Murray Sinclair said the Christchurch system would be run through a computer panel and would be based on a ‘‘twoswitch’’ process, meaning an alert would not be sent out until it had been confirmed using the computer.

‘‘If someone accidentally touches the wrong part of the screen, an alert will come up saying, ‘Are you sure you want to do this?’’’

Sinclair said the community sessions had been wellattended, with about 185 people at one meeting.

Some residents were concerned about the possibility of a tsunami originating in Pegasus Bay, but a locally based tsunami was ‘‘pretty unlikely’’. ‘‘It would need a pretty significant earthquake to displace the sea floor, and even then the chance of it coming on to land and causing damage is very low.’’

He said the system would not be able to provide alerts about a ‘‘local’’ tsunami and would instead be used to warn of a distant tsunami triggered by a major offshore quake.

The system would be tested on July 22 at 11am so residents knew what it sounded like.