Earthquakes and Tectonics in New Zealand
Earthquakes and Tectonics: Understanding Our Shaky Isles
Our nation sits astride one of the world’s most active tectonic plate boundaries, making it a hotspot for seismic activity. This unique geological setting not only shapes our stunning landscapes but also presents significant challenges and risks to our communities. Understanding the relationship between earthquakes and tectonics is crucial for every Kiwi, as it informs our preparedness and resilience in the face of these natural hazards.
Our Tectonic Setting
Our islands are located on the boundary between the Pacific Plate and the Australian Plate. This boundary is complex and dynamic, with different types of plate interactions occurring along its length:
- In the North Island and upper South Island, the Pacific Plate is subducting beneath the Australian Plate along the Hikurangi Subduction Zone.
- In the central South Island, the plates are colliding, resulting in the uplift of the Southern Alps along the Alpine Fault.
- In the southwest of the South Island, the Australian Plate is subducting beneath the Pacific Plate.
This complex tectonic environment is responsible for the high frequency of earthquakes we experience, with GNS Science locating over 15,000 earthquakes in our region each year.
Major Fault Systems
Several major fault systems crisscross our landscape, each capable of generating significant earthquakes:
- The Alpine Fault: This 600km-long fault runs along the western edge of the South Island. It has a history of producing large earthquakes approximately every 300 years, with the last major rupture occurring in 1717.
- The Wellington Fault: Part of the North Island Fault System, this fault runs through the capital city and poses a significant risk to urban areas.
- The Hikurangi Subduction Zone: This offshore fault system extends along the east coast of the North Island and is capable of producing our largest earthquakes and tsunamis.
- The Marlborough Fault System: A series of large faults in the upper South Island that transfer motion between the Alpine Fault and the Hikurangi Subduction Zone.
Recent Significant Earthquakes
Our seismic history is punctuated by several major earthquakes that have shaped both our landscape and our approach to seismic resilience:
- 2016 Kaikōura Earthquake (Magnitude 7.8): This complex earthquake involved the rupture of multiple faults and caused significant damage to infrastructure.
- 2011 Christchurch Earthquake (Magnitude 6.3): Although not the largest in magnitude, this shallow earthquake caused extensive damage to Christchurch and resulted in 185 fatalities.
- 2010 Canterbury Earthquake (Magnitude 7.1): This event marked the beginning of the Canterbury earthquake sequence and highlighted the risk posed by previously unknown faults.
Earthquake Preparedness
Given our seismic setting, earthquake preparedness is a crucial aspect of life for all Kiwis. The National Emergency Management Agency recommends several key steps:
- Drop, Cover, and Hold: This is the recommended action during an earthquake. It protects you from falling objects and makes you a smaller target.
- Long or Strong, Get Gone: If you’re near the coast and experience long or strong shaking, move to higher ground immediately due to the risk of tsunami.
- Have an Emergency Plan: Prepare a household emergency plan and practice it regularly.
- Be Aware of Your Surroundings: Know the earthquake risks in your area and at your workplace.
Ongoing Research and Monitoring
Our scientific community is at the forefront of earthquake research globally. GNS Science, universities, and other research institutions are continuously working to improve our understanding of our seismic environment.
The GeoNet project, operated by GNS Science, maintains a network of seismometers across the country that monitor earthquake activity 24/7. This network not only helps in rapid earthquake detection and response but also contributes to long-term seismic hazard assessment.
Recent research has focused on slow-slip events, particularly along the Hikurangi Subduction Zone. These “silent earthquakes” release tectonic stress over days or weeks and may provide insights into the behaviour of the plate boundary.
Looking to the Future
As we continue to live with the reality of earthquakes, ongoing research, improved building standards, and public education remain crucial. The development of earthquake early warning systems, although challenging due to our proximity to major faults, is an area of active research.
Understanding our tectonic setting and the earthquakes it produces is not just a matter of scientific interest – it’s a fundamental aspect of life in our shaky isles. By combining scientific knowledge with practical preparedness, we can build a more resilient society capable of facing the challenges posed by our dynamic geological environment.