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Processes causing earthquakes

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Page 1: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Processes causing earthquakes

Page 2: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

What causes earthquakes?

The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are caused when stress, building up within rocks of the earth's crust, is released in a sudden jolt. Rocks crack and slip past each other causing the ground to vibrate.

Cracks along which rocks slip are called faults. They may break through the ground surface, or be deep within the earth. The location on a fault where slip first occurs is called the focus, whereas the position directly above it on the ground surface is called the epicentre.

Page 3: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

The plates move…

The convection currents have caused the earth’s outer layer to move and break – this has resulted in a number of different plates around the world.

Page 4: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

There are many different types of plates on the earth’s surface.

Page 5: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

When the plates collide it results in sub-duction. As the oceanic plates are heavier they are forced under the continental plate.

Page 6: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Transform faults

Sometimes the plates slide past each other. When plates move in exactly opposite directions on either side of a fault (fracture) in the crust, the friction between them can cause severe earthquakes.

Page 7: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Plates may move apart

When plates move apart magma from the earth’s surface forces its way up through cracks in the surface forming ocean ridges or volcanic islands.

Sometimes this process causes earthquakes to occur.

Page 8: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Fold mountains

Page 9: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

New Zealand fault lines

These run on a NE/SE direction due to the alignment and moving together of the Indo-Australian and the Pacific plate.

This instability has resulted in faulting, causing block mountains of the Southern Alps.

Page 10: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Fault movement

Fault lines move horizontally or vertically. If a fault movement is sudden it will generate

an earthquake. The point at which layers of rock shift underground and reposition themselves is the focus.

Directly above this at ground level is the epi- centre where shock waves cause severe vibrations on the earth’s surface.

Page 11: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

The location on a fault where slip first occurs is called the focus, whereas the position directly above it on the ground surface is called the epicentre.

Page 12: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Summary then ..

Page 13: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Where do earthquakes occur? Stress that causes earthquakes is created by movement of

almost rigid plates that fit together and make up the outer shell of the Earth. These plates "float" on a dense, more fluid layer just beneath them. The plates move at such a slow rate, about the same as a fingernail grows, that we do not notice it in our everyday lives.

For instance, the Juan de Fuca plate off the coast of B.C. moves only about 4-5 cm/year relative to the North American plate. Over time, however, this small movement can build up enough stress to produce significant earthquakes.

Earthquakes occur most frequently on, or near, the edges of plates where stress is most concentrated.

Page 14: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Location of world earthquakes…

Page 15: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

New Zealand’s main faultlines

Page 16: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

Likelihood of an earthquake occurring

Page 17: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

New Zealand’s recent large earthquakes.

Page 18: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

New Zealand’s shallow earthquakes…

What patterns can be seen?

Write a generalisation on where the shallow earthquakes have occurred in NZ in recent years.

Page 19: Processes causing earthquakes. What causes earthquakes? The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are

New Zealand’s deep earthquakes… What patterns can be

seen? Write a generalisation

on where the shallow earthquakes have occurred in NZ in recent years.

How does this compare to the shallow earthquakes?