3. Earthquakes Flashcards
What are earthquakes?
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)
Where do the most severe earthquakes occur?
Transform and Convergent boundaries
What are seismic waves?
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
What are foreshocks?
Smaller earthquakes that precede major earthquakes
What are aftershocks?
Smaller earthquakes that follow the main one
What is the focus/ hypocentre of an earthquake?
The origin of the earthquake deep within the crust. From here the seismic waves radiate outwards
What is the epicentre of an earthquake?
The point on the earths surface directly above the focus. Areas closest to the epicentre experience the most damage
What is a fault?
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
What is a fault scarp?
The fault scarp is the feature on the surface if the earth that looks like a step causes by a slip in the fault
What are the causes of earthquakes?
Slipping Plates, Sinking Plates, Ice Age and Ancient Faults
What are slipping plates?
- 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
What are sinking plates?
- 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
How does an ice age cause earthquakes?
- 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
How do ancient faults cause earthquakes?
- When cracks open again in areas where fault lines used to exist
- Accounts for only 1.1% of earthquakes
What is a shallow focus earthquake?
- 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