What caused the Christchurch earthquake to happen?

Answer 1

he Earth's crust, or lithosphere (hard outer surface) is made up of "tectonic plates", or large plates. There are about 7 major plates and many smaller plates, around 100 km thick, which sit upon a lower soft layer (the asthenosphere). The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.

This accumulation of stress causes the rocks that make up the crust to deform elastically. This is very similar to what happens when you squash or stretch a spring and causes a form of energy to be stored in the rocks of the crust - technically described as elastic potential energy.

When this stress gets too large, it exceeds the strength of the rocks in the crust and causes a brittle failure. Brittle failures are failures where fractures form through the material. As these have been happening for a long time, the earth's lithosphere is already fractured. These fractures are known as faults and as these represent zones of weakness within the lithosphere, it is along faults where the majority of earthquake occur when they slip suddenly.

This sudden brittle failure causes all of the elastic potential energy to be released at one time in the form of seismic waves, just as if a spring or elastic band that was being stretched suddenly snapped.

These seismic waves cause the tremors that people feel on the surface and which can cause damage to buildings and other structures.

Answer 2

Plate boundaries, where one plate slides over another pushing it down into the mantle. This is called subduction zone or destructive plate boundaries. An earthquake is caused when the plate on top gets stuck on the one below (which is usually oceanic crust because it's heavier), immense pressure builds up and suddenly the pressure is too much and one plate gives way. Or, when the rock is being ground down into the mantle, it jolts causing earthquakes. The stored energy is released in seismic waves. These travel through the earth in all directions, shaking everything. Then you have after shocks, which are mini earthquakes as the rock settles into its new position.

Answer 3

The Indo-Australia plate subducted (slipped) underneath the Sunda Plate (A small plate trapped between the Eurasian and the Indo-Australian plates), displacing 1,600Km of plate boundary 15m vertically. This causes an underwater earthquake with magnitude 9.1 on the MMS (Moment Magnitude Scale). This caused 3 waves to be formed. Some of which travelled at 500mph.

Answer 4

This is still a mystery as it occurred well away from any known fault .

The region is an alluvial plain of silt washed down from the Southern Alps .

Christchurch has not had a strong quake since about 1888, and there are a lot of old buildings there.

It , and all the aftershocks have been very shallow. The 7M one was 5Km deep (per US Geological Survey) and the others have been around that also.

There is a subduction zone out to the east in the Tasman Sea where the Pacific Plate is going under the Australian Plate , but Christchurch is well away from this as well as from the Alpine fault which runs along the Southern Alps.

A lot of seismologists will be here or on their way to investigate and will eventually give us the answer.

Not an answer , but instant answers aren't always possible.

Bruce Sinton

of the Shaky Isles.

Answer 5

it was caused by moving plates beneath us

Answer 6

undersea subduction

Answer 7

9.3