3. Earthquakes

Question 1

What are earthquakes?

Answer 1

Earthquakes are sudden vibrations or shaking of the Earth’s crust caused by movements at plate boundaries and at major fault lines (cracks in the earth’s surface)

Question 2

Where do the most severe earthquakes occur?

Answer 2

Transform and Convergent boundaries

Question 3

What are seismic waves?

Answer 3

The energy released by an earthquake is in the form of seismic waves. The waves travel through the crust giving off a series of shocks called tremors

Question 4

What are foreshocks?

Answer 4

Smaller earthquakes that precede major earthquakes

Question 5

What are aftershocks?

Answer 5

Smaller earthquakes that follow the main one

Question 6

What is the focus/ hypocentre of an earthquake?

Answer 6

The origin of the earthquake deep within the crust. From here the seismic waves radiate outwards

Question 7

What is the epicentre of an earthquake?

Answer 7

The point on the earths surface directly above the focus. Areas closest to the epicentre experience the most damage

Question 8

What is a fault?

Answer 8

A fault is a break in the rocks that make up the earths crust, along which rocks on both sides have moved past each other. Not every crack in the ground is a fault. What defines a fault is the movement of the rock on both sides

Question 9

What is a fault scarp?

Answer 9

The fault scarp is the feature on the surface if the earth that looks like a step causes by a slip in the fault

Question 10

What are the causes of earthquakes?

Answer 10

Slipping Plates, Sinking Plates, Ice Age and Ancient Faults

Question 11

What are slipping plates?

Answer 11

• As plates move slowly, rocks sometimes become deformed on both sides of the fault line
• The rocks bend and store elastic energy
• Eventually, the plate slips at the weakest point called the focus

Question 12

What are sinking plates?

Answer 12

• The melting of plates as they slip into the mantle can cause earthquakes
• Sudden large volcanic eruptions can also cause earthquakes as the movement of magma changes the pressure in rocks

Question 13

How does an ice age cause earthquakes?

Answer 13

• Huge ice sheets on Europe, Asia and N.America weighed heavily on the crust
• When this ice melted the weight was eased and the crust started to lift, causing earthquakes along fault lines

Question 14

How do ancient faults cause earthquakes?

Answer 14

• When cracks open again in areas where fault lines used to exist
• Accounts for only 1.1% of earthquakes

Question 15

What is a shallow focus earthquake?

Answer 15

• Occur at all types of plate boundaries
• Means the focus is less than 80km below the surface
• The most common and destructive type of earthquake

Question 16

What is an intermediate focus earthquake?

Answer 16

• Focus is 80-300km below the surface
• Usually associated with oceanic-continental plate subduction

Question 17

What is a deep focus earthquake?

Answer 17

• Focus is deeper than 300km below the surface
• Usually associated with Oceanic-Oceanic subduction
• Occur so deep in the crust, they rare,y cause damage on the surface

Question 18

What are Benioff Zones?

Answer 18

Dipping, roughly flat zones of increased earthquake activity produced by the interaction of a sinking oceanic plate with an overriding continental or oceanic plate. Usually associated with deep focus earthquakes