Bay's quake risk

By Michele McPherson

An earthquake causing similar damage to the one that hit Christchurch on Saturday is likely to hit Tauranga once every 180 years.
A serious earthquake would affect Tauranga in a similar way to the Garden City, described by Bay of Plenty Civil Defence Emergency Management Group manager Greg Wilson as "fairly significant damage" to buildings and infrastructure.
The Bay of Plenty Civil Defence Emergency Management Group uses the Modified Mercalli Scale (MM) to measure the intensity of earthquake shaking that would be felt.
The MM scale goes from 1 to 12, with 12 being the most severe shaking.
MM8 shaking causes serious damage to poor-quality buildings and some damage to well-built constructions - and a shake of that magnitude can be expected in Tauranga once every 180 years.
Mr Wilson said there had been no earthquakes greater than MM8 since records began in 1840 and he was aware of none before that.
Damage from such a quake would be "pretty similar to what we have got down in Christchurch", although that quake would have been higher on the MM scale.
Mr Wilson said wastewater and freshwater pipes would likely crack, with electricity cut and mobile phone towers taken out.
GNS Science geologist Brad Scott said such a quake could cause significant damage, with the Bay particularly susceptible to landslides.
"MM8 is where you start to break windows and crack buildings.
"There are buildings in Christchurch that experienced MM 10, 11, 12. We wouldn't anticipate we would get that sort of shaking [in Tauranga] but the bottom line is we could still have a damaging earthquake."
Mr Scott said Tauranga would likely be hit with damage similar to that seen in the suburban areas of Christchurch.


"The houses are displaced, with all the broken pipes. The other thing in the Bay of Plenty area is, you would have a lot of landslides."
Parts of Tauranga could be subject to liquefaction - when sandy soil is shaken violently, causing water to rise through its pores.
Scientists have compared liquefaction in Christchurch to jumping on wet sand at the beach - it soon turns to a murky soup.
Mr Scott said coastal areas such as Mount Maunganui, Papamoa and low-lying areas near the harbour would be "quite susceptible".
Inland properties, which were 10 to 15m above sea level, would not be affected as badly as Canterbury.
The Bay of Plenty Civil Defence Emergency Management Group plan includes a "hazard scenario" of the effect of a magnitude 7.6 earthquake generated by abrupt movement of a fault in the North Island Shear Belt.
Typically these earthquakes occur 5 to 30km beneath the earth's surface.
Such an earthquake would see "extensive damage" in Whakatane and Opotiki, with Western Bay areas including Tauranga and Te Puke damaged to a lesser degree.
All lifeline infrastructure - generators, phone and power - would be disrupted to varying degrees.
Whakatane would be worst hit, with estimations of 30 deaths and many injuries in the commercial area.
Mr Wilson said the Christchurch quake was a reminder to be prepared.
"The better prepared a community is, the more resilient they will be, and the better able to withstand the impact of an event of this nature."
People should have a three-day kit of emergency supplies, a survival kit and an emergency communications plan.
"It might take up to three days for any organised help to get to you."
Tauranga City Council has rallied to offer "every assistance possible" to Christchurch Mayor Bob Parker.
Mayor Stuart Crosby said the best way for Tauranga people to help was to donate to the Mayoral Relief Fund.
The Bay of Plenty Civil Defence Group Emergency Management Office will coordinate any requests for assistance for specific staff such as engineers, surveyors, technical operations workers and building inspectors.
The services of the group's recovery manager Terry Wynyard have already been offered to Christchurch.
John Revington, regional manager of engineering consultants Beca, said three of the company's Tauranga-based structural engineers would head to Christchurch this week to join a team of workers.

- Bay of Plenty Times

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