Earthquakes Flashcards
Name five components of the anatomy of an earthquake
Fault, Hypocentre/ Focus, Epicentre, Plates and Seismic waves
Describe the fault
A fracture in rocks that make up the earth’s crust
Describe the epicentre
The point at the surface of the earth directly above the focus
Describe the hypocentre/ focus
The point within the earth where an earthquake rupture starts
Describe the plates
Massive rocks that make up the outer layer of the earth’s surface and whose movement along faults triggers earthquakes
Describe seismic waves
Waves that transmit the energy released by an earthquake
What two scales measure the magnitude of a tectonic event?
Richter scale and Moment Magnitude Scale
How does the richter scale measure magnitude?
Arrival times of P and S waves, amplitude of the S wave and distance from the epicentre
How does the Moment Magnitude scale measure magnitude?
Energy released by all shock waves and area and rupture of movement (more accurate)
What does logarithmic mean?
The scales go up with each level being ten times greater than the level below
What scale measures the intensity of an earthquake?
The Mercalli scale
What does the Mercalli scale use to measure intensity?
Amount of damage caused by seismic waves but local conditions can modify the correlation between intensity and damage
Describe scale 1,3,5,7,10 and 12
1 - Felt by almost no one
3 - Tremours noticed by many but not realised as an earthquake
5 - People awakened and trees/poles swaying
7 - Poorly built structures severely damaged
10 - Ground is badly cracked
12 - Total destruction
Describe scales 2.5, 4.5, 6 and 8+
2.5 - Generally not felt
4.5 - Some local damage
6 - Destructive
8+ Great
Describe primary waves
Vibrations caused by compression, they spread quickly from the fault at a rate of 8km/ second
Describe secondary waves
Move slowly at approx. 4km/ second and travel in right angles to the direction of travel but unlike P waves cannot move through liquids
What are body waves?
P and S waves
Describe love (Q) waves?
Waves that travel on the surface of the earth with vibrations in the horizontal plane with a high amplitude and moves from side to side
Describe rayleigh waves?
Vibrations that travel through the earth’s surface in a rolling motion that moves the ground up, down and side-to-side.
Name the primary hazards of an earthquake
Ground shaking and crust fractures
Name the secondary hazards of an earthquake
Liquefaction and landslides
Describe liquefaction
Shaking causes ground rocks to lose strength and become more liquid in composition so the subsoil loses the ability to support foundations of buildings and infrastructure which can disrupt gas pipes and cause fires
Describe landslides
Shaking places stress on slopes usually a magnitude over 4.0 will cause landslides and this risk is increased by liquefaction
Describe the 2003 Bam earthquake
- 7km hypocentre
- 5.26am local time
- Ancient buildings over 2000 years old
- 3 hospitals destroyed and 20% of professionals killed
- Winter so many trapped victims died of hypothermia
Describe the 2015 Nepal earthquake
- 7.8 magnitude
- 9000 died
- 22,000 injured
- Half a million houses collapsed
- Multiple hazard zone
Describe the 2010/11 New Zealand earthquakes
- Business activity rebounded rapidly after initial destruction
- Tourism decreased 40% in 2011/12
- Rebuild was largely insured
- Agriculture largely unaffected
