Auckland Faultlines: Dozens of New Lines Discovered – Quake Risk Assessed

Auckland’s Hidden Faultlines: What the Latest Discoveries Mean

Dozens of previously unknown faultlines have been discovered beneath Auckland, prompting further investigation into the potential seismic risk to the city. Scientists are preparing to dig trenches across these newly identified lines to determine if they are active, a finding reported by Rowan Quinn of RNZ.co.nz. Currently, officials said the discovery has not increased the known risk to Auckland.

The research, which analyzed borehole samples taken around the city, has revealed a more complex geological landscape than previously understood. Auckland University senior lecturer James Muirhead explained that any fault which has moved in the past 125,000 years is considered active. Some of the discovered lines, however, may have remained still for as long as six million years, technically classifying them as inactive. Others are currently categorized as “suspected” faults requiring further analysis.

Unearthing the Past: How the Faultlines Were Found

The team’s work centered on analyzing borehole samples – holes drilled around Auckland to study subsurface movement over time. This process allowed researchers to identify potential faultlines based on patterns of ground displacement. The identified lines were then categorized into three groups: likely faults, possible faults, and possible structures. The “possible structures” designation indicates areas showing signs of ground movement, but where the cause remains unclear.

Key Faultlines Identified

Two of the most prominent probable faults run across Auckland, connecting the Waitematā and Manukau harbours. One traverses through Avondale, while the other extends from Glendowie to Blockhouse Bay. While these faults were previously suspected, the recent research has provided more accurate measurements and strengthened the evidence for their existence.

Additional possible faults have been identified around Northcote, Birkenhead, and Wiri. A larger number fall into the “possible structure” category, requiring more in-depth investigation in areas like Sandringham, Newmarket, and Ōtāhuhu. The research also suggests that intense urbanization may obscure the presence of faults, making detection more challenging.

Auckland’s Seismic History & Perception

Muirhead noted a common perception that Auckland is not particularly prone to seismic activity. He attributes this to comparisons with other regions of New Zealand, which experiences significantly higher levels of earthquake activity. However, Auckland has experienced notable seismic events, such as the 1891 Port Waikato earthquake, which was strong enough to shatter windows in the city.

The research also revealed that Auckland experiences more small earthquakes than previously thought, though Muirhead suggests This represents likely due to improved monitoring capabilities. This highlights the importance of ongoing seismic monitoring to accurately assess the region’s earthquake risk.

What Happens Next: Trenching and Analysis

The next phase of the research involves digging four-meter deep trenches across some of the identified faultlines, particularly in the rural south near Pukekohe and Drury. These trenches will be carefully analyzed to determine how recently the faults have moved, providing crucial data for assessing their activity level. Muirhead anticipates having a clearer understanding of the active faults and their potential seismic hazard within approximately two years.

Implications for Land Use and Future Development

The findings have been highlighted in the Natural Hazards Commission’s latest Resilience Highlights Report, which examines the impact of natural hazards. Even though major earthquakes are considered unlikely, the Commission believes the information could influence decisions regarding land use as Auckland continues to grow. Understanding the location and activity of faultlines is critical for informed urban planning and mitigating potential risks to infrastructure and communities.

Understanding Active Faults

An active fault is generally defined as one that has moved within the last 125,000 years. This timeframe is based on the understanding that faults are likely to move again in the future if they have been active in the recent geological past. Identifying and characterizing active faults is a key component of seismic hazard assessment. You can learn more about earthquake faults and their impact from the United States Geological Survey (USGS) here.

Reader FAQ

• Is Auckland at high risk of a major earthquake? While Auckland is located in a seismically active region, the risk of a major earthquake is considered relatively low compared to other parts of New Zealand. However, the discovery of these new faultlines underscores the need for ongoing research and monitoring.
• What does “active” mean when referring to a faultline? An active fault is one that has moved within the last 125,000 years and is therefore considered likely to move again in the future.
• How will this research impact Auckland residents? The research aims to provide a more accurate assessment of Auckland’s seismic hazard, which will inform land use planning and building codes to minimize potential risks.
• What is the Natural Hazards Commission’s role in this research? The Natural Hazards Commission provided funding for the research and is using the findings to inform its work on resilience to natural hazards.

This discovery serves as a reminder that understanding the geological landscape is crucial for ensuring the safety and resilience of growing urban areas like Auckland. The ongoing research promises to provide a more comprehensive picture of the city’s seismic risk and inform strategies for mitigating potential hazards. You can locate more information about New Zealand’s natural hazards and resilience efforts at the Resilience to Nature’s Challenges website.