Imagine a scene straight out of the movie “San Andreas,” where Dwayne “The Rock” Johnson is racing against time to save his family from a massive earthquake. While the movie is set in California, the real-life potential for such a catastrophic event exists right here in New Zealand, centred around the Hikurangi Subduction Zone (running up the east coast of the North Island - basically Wellington to Gisborne).
Hollywood aside, I have been asked by some of our Wellington-based customers what a megathrust Hikurangi earthquake would look like? This is a great question and so we will try and unpack this scenario in this short blog.
The Hikurangi Subduction Zone is where the Pacific Plate subducts beneath the Australian Plate, located off the east coast of New Zealand’s North Island. This zone extends directly beneath the North Island, making it directly relevant for residents of Wellington and Napier. According to GeoNet, the Hikurangi Subduction Zone lies about 25 km below Wellington and 15 km below Napier.
In Wellington, the shallower depth of the subduction zone is particularly important for earthquake risk assessment. In Napier, the deeper offshore positioning also poses significant tsunami hazards. The movement between these plates can cause large earthquakes, similar to the 2011 Tohoku earthquake in Japan, as well as smaller quakes along the coastline.
Much like the unexpected quakes in the movie "San Andreas," the Hikurangi Subduction Zone has a history of both large earthquakes and slow slip events.
A major earthquake in the Hikurangi Subduction Zone could cause severe shaking across the North Island and the top of the South Island, along with a large tsunami. The odds are quite terrifying, with scientists estimating a 25% chance of a magnitude 8 or larger quake striking the southern section of the Hikurangi Subduction Zone (beneath Wellington, Marlborough, and Wairarapa) within the next 50 years.
GNS Science has developed a credible scenario exploring the impact of an 8.9 magnitude Hikurangi earthquake, which would release 45 times more energy than the M7.8 Kaikoura earthquake. This event would result in significant human and economic toll. Coastal communities, particularly those in Gisborne, Napier, Hawkes Bay, and Wellington, would be at high risk.
In populated areas like Wellington, we can anticipate significant damage to property and assets. Even the Auckland region is likely to experience severe shaking lasting up to 30 seconds. Infrastructure such as roads, rail, water, and electricity would be significantly damaged. Similar to the Tohoku Earthquake, we can also expect additional damage from a massive tsunami wave overwhelming the shaken landscape.
For a detailed explanation, you can watch a GNS Science YouTube video that explores this scenario.
A good place to start is to explore the impact of similar megathrust earthquake events. We don't have to look far to get a sense of the potential impact of a Hikurangi rupture than by examining the Tohoku M9.0 Earthquake in 2011. The earthquake occurred where the Pacific Plate is subducting beneath the North American Plate in an area known as the Japan Trench. This earthquake triggered a massive tsunami with waves reaching heights of up to 40 meters, inundating coastal areas and causing significant loss of life and property. It led to the Fukushima Daiichi nuclear disaster and resulted in economic damage upwards of $200 billion. The tsunami also resulted in a death toll of approximately 19,700, with thousands more injured and missing.
Following some good information sessions by the National Hazards Commission (NHC), there is a growing awareness surrounding the earthquake and tsunami risks relating to the Hikurangi Subduction zone. Prepare and make your home safer and stronger for earthquakes. Talk with whānau and make a plan. Be familiar with your local civil defence emergency management group.
Most importantly, if you live near the coast and you experience a quake that is Long or Strong, Get Gone. If you’re near the coast, or a lake, and an earthquake of any size is long (shaking lasts more than a minute), or strong (it’s hard to stand up), then get gone to higher ground or inland immediately. Don't wait for any official announcement, just get moving. For more information, refer to the GeoNet site.
GNS Science and the National Hazards Commission are focused on better understanding these types of events. Please click here to learn more about the Hikurangi subduction zone and related earthquakes.
The Hikurangi Subduction Zone represents a significant earthquake and tsunami risk for New Zealand, comparable to the Tohoku experience in Japan. While each region has unique characteristics and challenges, the potential for devastating earthquakes and tsunamis is a common thread.
Ongoing research, improved preparedness, and resilient infrastructure are crucial to mitigating the devastating effects of these natural disasters. For New Zealand, understanding and preparing for the risks associated with the Hikurangi Subduction Zone is essential for safeguarding communities and ensuring a resilient future. And while we may not have "The Rock" to save the day, our forward planning and collective efforts can make a world of difference.
