Fault Line
A geological fracture in the earth's crust where two tectonic plates or rock masses meet, and where earthquakes are most likely to occur.
What is a Fault Line?
New Zealand sits on the boundary of the Pacific and Australian tectonic plates, making it one of the most seismically active countries in the world. Fault lines — fractures where the earth's crust moves — run through many populated areas. The Alpine Fault, Wellington Fault, and numerous smaller faults pose significant earthquake risk.
Properties located directly on or near an active fault line face a higher risk of ground rupture (the ground physically splitting apart along the fault), as well as stronger shaking during earthquakes. The Ministry for the Environment has published guidelines for building near active faults, and many councils have fault avoidance zones in their district plans.
Fault avoidance zones restrict or prohibit new buildings within a set distance of a known active fault trace. Existing buildings within these zones may face additional scrutiny from insurers and banks.
Why It Matters for Due Diligence
If a property sits on or near a known fault line, the risk isn't just shaking — it's potential ground rupture, where the land physically displaces. No building foundation can withstand this. Fault proximity also affects insurance terms and resale value.
Check the LIM report and council planning maps for fault hazard overlays. GNS Science maintains the Active Faults Database, which maps known fault traces across New Zealand. If the property is near a fault, understand any building restrictions and insurance implications before committing.
How to Check
The LIM report will typically note whether the property is within a fault hazard zone. Check your council's district plan maps for fault avoidance zones. The GNS Science Active Faults Database (available online) maps known active faults across New Zealand. For properties near known faults, a geotechnical report can provide more specific risk assessment.
Frequently Asked Questions
How close to a fault line is too close?
Council fault avoidance zones typically extend 20-50 metres either side of a known fault trace, but this varies by council and fault type. Even outside the avoidance zone, properties near faults will experience stronger shaking. There's no universal safe distance — it depends on the specific fault and soil conditions.
Are all fault lines equally dangerous?
No. Faults are classified by how recently they've moved and how frequently they move. 'Active' faults have moved in the last 125,000 years. Some faults move every few hundred years (like the Alpine Fault), while others have recurrence intervals of tens of thousands of years. GNS Science provides recurrence data for mapped faults.
Related Terms
Liquefaction
GlossaryA phenomenon where saturated, loose soil loses its strength during an earthquake and behaves like a liquid, causing the ground to shift, sink, or eject sand and water.
Earthquake-Prone Building
GlossaryA building assessed as having structural performance below 34% of the New Building Standard (NBS) for earthquake resistance, making it legally earthquake-prone under the Building Act 2004.
New Building Standard (NBS)
GlossaryA percentage rating that expresses an existing building's earthquake strength relative to the minimum standard required for a new building — 100% NBS means the building meets the current code for a new build.
LIM Report
GlossaryA Land Information Memorandum — an official council report summarising everything the council knows about a property.
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