Earthquakes and Earthquakes in New Zealand
New Zealand is located on the boundary of two moving plates and sits in the seismically active “Ring of Fire”. Earthquakes occur when stresses cause rocks to break suddenly. When the resulting crack or fracture reaches the surface it is known as a fault line.
The 2010 earthquake that killed 185 people in Christchurch involved multiple faults and was a complex event. AIR’s New Zealand risk model simulates the site-specific peak ground acceleration (PGA) and associated damage from such events.
Why do we have earthquakes?
Earthquakes happen all over the world, but they are most frequent in regions where two tectonic plates grind against each other. This produces tension that can be released in earthquakes.
In New Zealand, these quakes usually happen near the margins of the Pacific and Australian plates. They can be very powerful and cause widespread damage.
The type of ground beneath buildings can make a big difference to how they shake. Bedrock shakes the least, while soft sediment or even artificial fill can amplify shaking and cause structures to slip, shift or liquefy. Liquefaction was a major cause of the widespread damage caused in Christchurch in 2010-11.
The magnitude 7.8 quake that hit Kaikoura was different from many other New Zealand quakes in that it involved the slow-slip movement of multiple faults. This has implications for how geologists model the likelihood of a quake in specific regions. Currently, seismic-hazard models typically only consider the movement of one fault at a time.
What causes earthquakes?
Earthquakes happen when the tectonic plates that make up the planet’s crust slip past each other. The more they scrape, the more tension builds up until a sudden release of that energy causes an earthquake. It’s not a good idea to live in the path of an earthquake, because it can knock down buildings and cause other damage. Earthquake-resistant building codes help reduce loss of life, but it’s not possible to stop every quake.
Every year, thousands of earthquakes shake New Zealand. Most are too small to be felt, but some generate strong shaking that can cause serious damage.
Earthquakes are most frequent in regions that sit on the boundary of two moving plates. This is the case for New Zealand, which straddles the Pacific and Australian tectonic plates in the ‘Ring of Fire’, a circle around the Pacific Ocean where many volcanoes and earthquakes occur.
Where do earthquakes happen?
The Earth’s seemingly solid outer surface is actually divided like a jigsaw puzzle into huge sections called tectonic plates. These plates rub together, and when they do an earthquake happens.
Earthquakes occur everywhere on the planet, but New Zealand is especially prone to them because it sits on a boundary between two plates. Those plates – the Australian and Pacific plates – are constantly grinding into each other. The movement causes stresses to build up in the brittle upper layers of the plates. Eventually, those stresses are abruptly released along a fault, which ruptures and produces the shaking we feel.
This activity is happening all the time, and most quakes are too small to be felt. However, large quakes can cause damage and even kill people. The earthquakes that hit Christchurch in September were very damaging because they occurred on a soft, wet part of the Canterbury Plains. This type of ground is prone to a process called liquefaction, where water seeps through the soil and makes it lose its strength.
What can we do to prepare for an earthquake?
Earthquake-safe homes and workplaces can reduce the risk of injury during an earthquake. It is important to practice Drop, Cover and Hold so that you know what to do in an earthquake. It is also a good idea to make an emergency plan with your family and have a kit prepared.
When an earthquake happens, you should drop to the ground and stay there until the shaking stops. This is the safest place to be. If you are in a vehicle it is a good idea to stop in a clear area away from overpasses, power lines, trees and street signs. It is also a good idea to keep your seatbelt fastened.
If you are near the ocean and feel a long and strong earthquake, move away from the coast as tsunami can follow. This is because earthquakes can cause landslides which can cause waves to break over the shore. Also, earthquakes can change the water level in lakes and this can create rockfall tsunami which can occur on the lake edge.