Earthquakes

Earthquakes

Facts
1. result of the release of pressure built up in tn the rocks of the Earth's crust
  1. Landwaves may trigger mass movements and avalanches
2. energy release as seismic waves
  1. lose energy as the radiate outwards from the focus
3. The epicentre suffers the greatest intensity of seismic waves
4. Modified Mercalli scale - measures intensity, the effects
  1. semi-quantitative linear scale
5. Richter scale - measures magnitude
  1. Quantitative logarithmic scale
  2. Improved as moment magnitude scale as was hard to differentiate between intensity
    1. E.g. 1964 - Prince William Sound in Alaska - amplitude magnitude of increased to 9.2
Shockwave types (3)
1. Primary - Longitudinal
  1. Fastest waves average 5 km per second
  2. go through solids and liquids
  3. expand and contract
2. The nature of wave determines how it travels through the Earth
3. Secondary - Transverse
  1. slower 3 km per second
  2. cannot travel through liquids
  3. side to side
4. Surface/long - Transverse
  1. Slowest - greatest wave length
  2. carry most of the eq's energy
  3. travel around the surface of the Earth
    1. E.g. 1960 - Chilean Eq surface waves travelled around the Earth 20 times and still registering on seismometers 60 hours after the main shock
  4. up and down
Features (3)
1. Foreshock
  1. Initial shattering of obstructions or bonds along the failure planes
2. Principal shock
  1. most severe
3. Aftershocks
  1. recur as shockwaves travel around the Earth
    1. decrease in frequency and intensity overtime

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