Source: Environment Canterbury Regional Council – Fault-line building restrictions likely
Rural and residential development is unlikely to be restricted along the Ashley Fault Zone, north of Rangiora, as the result of a new report released today by Environment Canterbury.
“However it is ultimately up to the Waimakariri District Council and the community to decide what kind of development should be allowed or restricted,” said Environment Canterbury geological hazards analyst Marion Gadsby.
The Ashley Fault Zone can be seen at the ground surface as three overlapping fault scarps (steps in the ground surface. It crosses farmland and lifestyle blocks.
The report draws a “Fault Avoidance Zone” around the areas that could be affected by breaking and buckling of land immediately adjacent to the fault scarps from and earthquake on the Ashley Fault Zone.
“The Ashley Fault Zone is in an area with significant development growth, with more and more people moving into the area since the earthquakes, so it’s good to know that residential development there can continue,” Ms Gadsby said.
“Faults such as this can cause large earthquakes, when the ground on either side of the fault shift against one another. This fault-shifting causes severe shaking across a wide area and can also cause surface rupture and buckling of the ground surface by several metres at the fault,” she said.
“Buildings in the area are likely to suffer serious damage or even destruction, posing a significant threat of injury or even death to occupants of the buildings,” she said.
“Because of the risk to life and property, the approach under Ministry for the Environment guidelines would categorise the active fault area as a Fault Avoidance Zone, with only community facilities development and important infrastructure restricted in the immediate area.”
Marion Gadsby said that Environment Canterbury would work with the Waimakariri District Council to develop suitable rules for building near the Ashley Fault Zone.
The Ashley Fault Zone, which has an estimated recurrence of between 7000 and 15,000 years (although it could be as short as 5000 years), is made up of a broad upward bulge running east-west, with three overlapping fault strands each of up to 6 km in length. They are located between the Ashley River and Loburn, running as far upriver as the confluence with the Garry River and as far south as Boundary Road (see map).
The report, “Assessment of active fault ground deformation hazards associated with the Ashley Fault Zone, Loburn, North Canterbury” has been prepared by GNS scientists and is based on:
- Assessment of publicly available information of the Ashley Fault Zone, including aerial photography and satellite imagery
- Examination of a high resolution LiDAR dataset that provides a very precise picture of the height and shape of the ground surface
- An inspection of landforms near the Ashley Fault Zone
- Mapping of ground surface deformation of past earthquakes on the fault zone.
The fault zone was first mapped in 1973 and this latest report provides more detailed and up-to-date mapping of the fault zone.
The report can be downloaded from www.ecan.govt.nz/eqfaults and the attached GIS map is available on the Canterbury Maps website www.canterburymaps.govt.nz