Porirua Fault Trace Study
Search in document libraryPurpose of the report to update fault mapping and hazard classifications for Porirua District’s active faults to support risk-based land use planning and development decisions.
Geographic Area Covered:
Porirua District, including Porirua City centre, surrounding suburbs, and rural areas affected by the Ohariu, Pukerua, and Moonshine faults.
Summary of Key Findings:
This study was commissioned by Greater Wellington Regional Council and Porirua City Council to reassess fault rupture hazards in Porirua District. The district is crossed by three active faults: the Ohariu Fault (most active), the Pukerua Fault, and the Moonshine Fault. These faults are capable of producing significant ground surface rupture during earthquakes, posing risks to buildings and infrastructure.
Using high-resolution LiDAR data, recent aerial photography, and historical survey maps, the study re-mapped fault traces and identified a new active strand of the Ohariu Fault in Horokiri Valley. Fault Avoidance Zones were defined around each fault based on the location and complexity of surface rupture features. These zones range in width from 60 m (well-defined scarps) to over 800 m (poorly constrained areas such as beneath Porirua Harbour).
Each fault was assigned a Recurrence Interval Class based on estimated earthquake recurrence:
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Ohariu Fault: Class II (2,000–3,500 years)
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Pukerua Fault: Class III (3,500–5,000 years)
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Moonshine Fault: Class IV (5,000–10,000 years)
The Ohariu Fault runs through central Porirua City, but its traces have been obscured by urban development. Fault location estimates in this area relied on 1940s aerial photos and older survey plans. Two fault traces were mapped through the city centre, with the western trace considered more active.
The Pukerua Fault was mapped through hill country between Hongoeka Bay and Pukerua Bay. It shows clear fault features in some areas but is less well defined in others due to development and erosion. The Moonshine Fault, which passes through Judgeford, is the least studied and has the most uncertain location.
The report recommends:
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Improving recurrence interval estimates through further geological investigations.
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Refining Fault Avoidance Zones to reduce unnecessary constraints.
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Updating planning policies to reflect fault hazard classifications.
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Coordinating with neighbouring councils on hazard mitigation.
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Considering engineered solutions for critical infrastructure and existing developments over faults.
These findings support a risk-based approach to land use planning and development in Porirua District, consistent with national guidelines.