EQ1:Earthquakes Flashcards
What is the global distribution of earthquakes?
The main earthquake zones are often found in clusters along plate boundaries - 90% of earthquakes are found at plate boundaries
How do earthquakes occur?
1.Earthquakes are caused by sudden movements near the Earth’s surface along a fault. Plate movement creates a build-up of tectonic strain and friction, which creates a store of energy.
2. When the pressure exceeds the strength of the fault, the crust fractures.
3. This sudden release of energy creates seismic waves which radiate outwards.
4. The crust rebounds near the fracture which causes the ground shaking felt on the surface.
What are the different seismic waves released from an earthquake?
-P waves (primary/pressure waves)
-S waves (secondary waves)
-L wave (love wave/surface level wave)
What are P waves?
-P waves are the first seismic waves that earthquakes generate
-They are the fastest waves and reach the surface first which allows them to arrive first at seismic recording stations
-they don’t cause any shaking and are the least damaging waves
What are S -waves?
-S waves are the second seismic waves generated by an earthquake
-they are slower than P waves and move the rock up and down
-they cause damage and shaking
What are L waves?
-these are the third seismic waves generated by earthquakes
-they are slowest waves and cause a side to side motion
-they are larger, most damaging and energy is most focused on the surface
What is a fault?
A fracture in the rocks that make up the earth’s crust
What is the epicentre of an earthquake?
The point of the surface of the earth directly above the focus
What is the focus of an earthquake?
The point within the earth where an earthquake rupture starts
What are seismic waves?
Waves that transmit the energy released by an earthquake
What factors can increase the severity of an earthquake?
human:
•population density- more likely to experience more significant damage due to the number of people and structures affected in the region
•corruption of government- authorising poorly built building
•level of education
•housing being built quickly with poor materials due to poverty
phyiscal:
•distance to epicentre- the closer a city is the more intense the shaking due to the direct transmission of energy
•magnitude
What is the primary hazard associated with earthquakes?
Ground shaking
What are the secondary hazards associated with earthquakes (4)?
1)Liquefaction- the process by which wet sediment behaves like a liquid e.g. Christ Church earthquake
2)crustal fracturing- facturing opens up on the crust
3)landslide- occurs in areas of steep relief and in areas that have unconsolidated sediment with wet condition)
4)tsunamis
