GNS Science releases new liquefaction risk report for Hawke's Bay

Wednesday, 29 November 2017

GNS Science has released a report that has been in the making since 2013, detailing liquefaction risk levels for the Hawke's Bay region.

Hawke's Bay residents may feel safer after a new report shows liquefaction risk levels are largely unchanged and even lower in some areas compared with 18 years ago.

The 119-page report, compiled by GNS Science, was commissioned in 2013 by Hawke's Bay Civil Defence Emergency Management Group and the region's five councils to assess the region's risk for earthquake-induced liquefaction.

Pictured in pink are the areas which GNS Science said were at risk of potential liquefaction, however they could not determine the severity.

Civil Defence Hawke's Bay spokeswoman Lisa Pearse said the report was important as the Hawke's Bay region was more seismically active than Canterbury.

'What is important for people to remember is that earthquake-induced liquefaction, as seen in Canterbury, has been recorded in Hawke's Bay in the past, and is likely to happen here should a large (usually greater than magnitude-6) earthquake occur.'

An old map detailing liquefaction risk from 1999 has five risk levels of risk, ranging from very high to very low.

* Low interest in land repair for liquefaction risk, EQC says

*** Quake-hit homeowners face another year's wait for liquefaction risk compensation

Because Hawke's Bay sits above the subduction zone where the Pacific Plate is moving under the Australian Plate, locals should 'expect to experience shaking and liquefaction more often', she said.

The new report is the first of its kind since the original GNS liquefaction study in Hawke's Bay, which was released in 1999.

It found there was little change for liquefaction risk in the Wairoa, Napier and Hastings urban areas. However, parts of Taradale had a reduced risk of liquefaction.

Havelock North remained at a low risk, while Central Hawke's Bay also had a reduced risk.

GNS Science geologist Sally Dellow, who worked on both reports, said the new report was 'about making communities more resilient'.

'It's all about how you manage liquefaction, rather than how severe it might be. Thats the idea of it.'

Since the Canterbury earthquakes in 2010 and 2011, scientists had been able to improve risk maps using new technologies, including by using the cone penetrometer test (CPT), which Dellow described as the 'gold standard'.

CPT testing involves pushing a steel cone into the ground at a controlled rate, then measuring the cone tip's resistance, sleeve friction and pore water pressure to gather information on how weak the ground is.

Dellow said about 800 cones were used to compile the new data, and maps contained within the report would continue to be revised as more data was collected.

Pearse said not all areas within Hawke's Bay were able to be given a specific severity rating for liquefaction risk, hence the need for more data.

'The report is all about how we can mitigate the risks going forward, and how we can learn from situations like Canterbury and Kaikoura in the future.'

* From 10am on November 30, visit hbhazards.co.nz to discover the liquefaction risk for your property.