Earthquakes

What is a tectonic plate?

Large moving slab of Earth's lithosphere.

What is the lithosphere?

Rigid crust and uppermost mantle.

What drives plate movement?

Mantle convection and forces such as slab pull.

Where are most earthquakes and volcanoes?

Along tectonic plate boundaries.

What is a destructive plate boundary?

Plates converge, often with one subducting.

What is subduction?

One plate sinks beneath another into the mantle.

Why can subduction create earthquakes?

Stress builds and releases as plates lock and slip.

What is a collision boundary?

Two continental plates converge and crumple.

What forms at continental collision zones?

Fold mountains and earthquakes, usually few volcanoes.

What is a conservative boundary?

Plates slide past each other.

What is an earthquake?

Sudden ground shaking from released energy in rocks.

What is the focus of an earthquake?

Point inside Earth where rupture starts.

What is the epicentre?

Point on the surface directly above the focus.

What is earthquake magnitude?

Measure of energy released by an earthquake.

What is earthquake intensity?

Severity of shaking and effects at a location.

What is a tsunami?

Large sea wave generated by sudden water displacement.

How can undersea earthquakes cause tsunamis?

Seafloor movement displaces a large volume of water.

What is a primary earthquake hazard?

Direct shaking or ground rupture.

What is a secondary earthquake hazard?

Consequent landslide, fire or tsunami.

Why are shallow earthquakes often damaging?

Shaking reaches the surface with less energy loss.

Why can soft ground increase earthquake damage?

Loose sediment amplifies shaking or liquefies.

What is liquefaction?

Saturated loose soil temporarily loses strength during shaking.

How can earthquake deaths be reduced?

Stronger buildings, drills, warnings and emergency planning.

Why can earthquake prediction be difficult?

Exact timing, place and magnitude cannot be reliably forecast.

Why may richer countries suffer fewer deaths?

Stronger buildings, monitoring and emergency services.

When did the Christchurch earthquake occur?

22 February 2011.

Where was the Christchurch earthquake?

Near Christchurch, Canterbury, New Zealand.

What was the magnitude of the 2011 Christchurch earthquake?

Magnitude 6.2–6.3, depending on scale used.

Why was Christchurch badly affected?

Shallow earthquake close to the city caused strong shaking and liquefaction.

How many people died in the Christchurch earthquake?

185 people.

What were two Christchurch earthquake impacts?

Building collapse and damaged roads, water pipes and sewers.

What were immediate responses in Christchurch?

Search and rescue, emergency shelters and restoration of services.

What were long-term responses in Christchurch?

Rebuilding infrastructure and strengthening building standards.

What happens at a conservative plate boundary?

Plates slide past; friction causes stress and earthquakes.

What happens at a collision plate boundary?

Continental plates collide, causing earthquakes and fold mountains.

What happens at a constructive plate boundary?

Plates separate; shallow earthquakes can occur.

What are seismic waves?

Energy waves travelling through Earth after an earthquake.

What is a foreshock?

A smaller earthquake before a larger mainshock.

What is an aftershock?

A smaller earthquake following the mainshock.

Why can earthquakes trigger landslides?

Shaking destabilises steep slopes.

How do earthquake-resistant buildings reduce damage?

Flexible structures and reinforced frames withstand shaking.

What is an earthquake early-warning system?

Sensors detect initial waves and alert people before stronger shaking.

Why can tsunamis affect distant coasts?

Waves travel long distances across the ocean.