earthquakes

what is an earthquake?

release of stress from the earth's crust
series of shock waves originate from the earthquake focus - the location where the stress is released - and where this is located is known as an 'epicentre'
main locations for earthquakes
- mid-ocean ridges
- ocean trenches
- island arcs
- collision zones
- conservative plate margins

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shallow:
- surface of crust down to approximately 70 km
- often occurs in brittle rocks
- generally release low levels of energy but can cause severe impacts
deep
- 70-700 km
- increasing depth leads to high pressure and temperature
- less frequent but very poweful

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richter scale: developed in 1935; uses the amplitude of seismic waves to measure magnitude. scale of 1-9, each whole number is a ten-fold increase
moment magnitude scale: scale of 1.0-9.0 measuring energy release related to geology, the area of the fault surface and the amount of movement at the fault. used only for large earthquake as it looks at the physical movements
modified mercalli scale: measures earthquake intensity and impact. relates to impacts felt and seen by those affected - qualitative and not quantative

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groundshaking and ground displacement: vertical and horizontal movement of ground. severity depends on distance from the epicentre and geology
liquidefaction: when violently shaken, soils with high water content lose their mechanical strength and become fluid
landslides and avalanches: slope failure results in ground shaking
tsunamis: giant sea wave generated by shallow focus underwater earthquakes, volcanic eruptions and landslides falling into the sea. tsunamis have a long wavelength and low wave height
flooding: indirect cause of a quake. caused by a tsunami, destabilising/destroying dams

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