Investigating earthquakes – introduction

Shaky New Zealand

About 14,000 earthquakes are recorded in and around New Zealand every year. Fortunately, most of them are too small for us to feel at the surface. However, many of us have felt the shake of an earthquake, and there are some big ones that have become part of New Zealand history. The earthquakes in and around Christchurch in February 2011 and Kaikōura in 2016 were devastating, and reminded people around the country that they too must be prepared for ‘the big one’.

(Earthquakes are measured on the Richter scale.)

When?	Where?	How big?	What happened?
23 January 1855	Wairarapa	8.2	Land raised in Wellington region
17 June 1929	Buller, South Island	7.8	Much destruction in Murchison area
3 February 1931	Hawkes Bay	7.8	Napier and Hastings badly damaged, land uplifted, 256 people killed
2 March 1987	Edgecumbe	6.6	Much faulting and land sinking
4 September 2010	Christchurch and surrounds	7.1	Many buildings damaged, land shifted, but few people injured
22 February 2011	Christchurch and surrounds	6.3	Widespread destruction of buildings and services, hundreds of people injured or killed.
14 November 2016	Kaikoura and further	7.8	Extensive destruction of buildings and services, land uplifted, widly felt, 2 deaths

Why does New Zealand get earthquakes?

Earthquakes and volcanoes are common around the world where one tectonic plate is sinking under another at a subduction zone. Look for New Zealand on a world map of tectonic plates. It is right at the junction of the Australian and Pacific plates – a shaky place! There is a lot of geological activity here, including earthquakes, volcanoes, mountain building, faulting and erosion. Find out more in the article Plate tectonics.

Discover the two violent tectonic events that shaped the continent Zealandia and what makes this submerged continent so different to others.

What causes earthquakes?

At a subduction zone, two tectonic plates try to pass each other. Along faults, rocks grind past each other, some more easily than others. Instead of sliding, some rocks lock together – but they are still being pushed, so they bend and distort, and stresses build up. Eventually, the pressure becomes too much, and the two sides of a fault jerk past each other. This releases stored energy as shock waves (called seismic waves) that travel out from the focus through the surrounding rock, sometimes to the other side of the world. The articles Moulding the Earth and Liquefaction disucss what happens as a result of these stresses and pressures.

The seismic waves travel at different speeds. The faster P-waves reach the surface first, followed by the slower S-waves, which can cause the ground to shudder backwards and forwards. Both types of waves set off new waves at the surface, around the epicentre, which cause most of any damage.

Scientists use seismographs to measure when the seismic waves reach three different points, and they can work out where the focus and epicenter are. They also use the waves to work out the magnitude of the earthquake, normally measured on the Richter scale.

Earthquake research

Earthquakes are important in the geology of New Zealand, and they have the potential to cause damage and affect people’s lives. Because of this, there is a lot of research going on to try and understand them more. Some of the research focuses on the Alpine Fault – and the squishy zone below it. Scientists from other countries come to New Zealand to help build up a world picture of tectonic activity. Find out how teaching fellow Keith Machin lent them a hand.

Research includes trying to:

• understand what happens inside the Earth
• understand the details of how earthquakes are caused
• increase the accuracy of measurements and forecasting
• monitor earthquake activity to help emergency and long-term planning
• understand seismic waves and surface effects so that buildings can be made safer
• find out more about the forces shaping New Zealand
• explain newly recorded events, such as slow slips, about which Dr Laura Wallace is an expert.

Take up the challenge

Use the teaching resource Earthquakes New Zealand to learn about seven activities designed to help students develop an understanding about earthquakes in New Zealand, including why we get them and how we measure them. Something creepy is happening explores tectonic movements called slow slips. The Best base isolator uses a physical model to investigate the effectiveness of different properties for base isolators. There is even a unit plan to help middle and upper primary classrooms get started.

Explore this resource for teachers from Te Papa and EQC Building an earthquake-ready future. It is aimed at curriculum levels 2–5 covering science, social studies and literacy.

Question bank

The Investigating earthquakes – question bank provides a list of questions about earthquakes and places where their answers can be found. The questions support an inquiry approach.

Key terms

For explanations of key concepts, see Investigating earthquakes – key terms.

Timeline

Explore the timeline to look at some of the historical aspects of earthquakes. Find out how our understanding of what causes earthquakes has changed.

Planning pathways

Realistic contexts connect students to authentic scientific processes and purposes. It’s all explained in Earthquakes resources – planning pathways.