3.1. Hazardous environments resulting from tectonic movement Flashcards Preview

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Define earthquakes

  • the shaking/trembing caused by the sudden release of energy
  • usually associated with faulting/breaking of rocks
  • continuing adjustments of position results in aftershocsk


Define focus/hypocenter

The point within the earth where faulting begins


Define epicentre

The point directly above the focus on the surface


Why do earthquakes occur?

  • Occur along plate margins
  • Plates move at a rate between 1.5cm and 7.5cm per year
  • When plates move past/towards/away from each other, the movement is not smooth as friction causes the plate to get stuck => causes pressure to build up
  • Energy waves then race rapidly from the focus causing commotion on the ground


Elastic Rebound Theory

Explains how energy is stored in rocks:

  • Rocks bend until the strength of the rock is exceeded
  • Rupture occurs and the rocks quickly rebound to an undeformed shape
  • Energy is released in waves that radiate outward from the fault


2 types of body waves (wave that travel within earth's interior)

  • P Wave/Pressure wave/Primary wave
  • S wave/Sheer wave/Secondary wave


P Waves

  • The fastest body waves
  • These are compressional waves where the material movement is in the same direction as wave movement
  • They travel through solids and liquids


S Waves

  • Slower than P-waves
  • Travel with a sideway motion and move material perpendicular to wave movement thus making the ground move horizontally
  • Travel through solids only
  • Cause a lot of damage


Mohorovicic Discontinuity - Moho

  • Seismographs close to epicentre showed slow travelling P-waves and S-waves which contrasted with the faster moving P-waves and S-waes further away from the shock
  • If the shock waves pass through the denser rocks, they speed up and vice versa
  • S-waves don't go through solid so stop at outer core
  • Whereas, P-waves are refracted


Types of seismic waves/surface waves (travels through crust)

  • Slower than body waves
  • Long/love waves (cause ground to move sideways)
  • Rayleigh waves (cause ground to move up and down


Impact of P-waves

Can turn solid sediments into fluids like quicksand by disrupting sub-surface water conditions. This is known as liquefaction or fluidisation


Different types of fault

  • Normal dip-slip faults: results from tension in crustal rocks pulling apart
  • Reverse dip-slip faults: results from compression in the crust collision
  • Strike-slip faults: results from crustal blocks sliding past each other


Richter scale

  • Measures magnitude of a tremor using seismometer which records data on seismograph
  • Logarithmic scale (a size 2 s 10 times larger than 1)
  • Less than 3: not felt
  • 3-3.9: felt, little damage
  • 4-4.9: some structural damage
  • 5-5.9: losses in populated areas
  • 6-6.9: large losses in urban area
  • 7-7.9: serious building damage, major loss of life
  • >8: total destruction


Mercalli scale

  • measures how much damage is caused by the earthquake based on observations (a result of surface shaking)
  • measures intensity of earthquake by indicating the violence of the earth motion
  • scale between 1 and 12


Differences between Richter and Mercalli

  • Richter measures strengths, Mercalli measures damage/effects
  • Richter scale is based on scientific data, Mercalli is based on people's observations
  • Richter measured by seismometers, Mercalli measured by people
  • Mercalli uses whole number, Richter uses numbers to one decimal place


Physical factors affecting earthquake

  • Magnitude of earthquake
  • Time of the day - occur during rush hour can be more damaging
  • Distance from epicentre - shorter => less energy is disspated
  • Depth of focus (same as above)
  • Type of rock and sediments - loose materials are more vulnerable to liquefaction
  • Coastal locations are more vulnerable to tsunami


Human factors affecting earthquake damage

  • Population/population density
  • Type of buildings
  • Level of economic development for prediction and preparation


Impacts of earthquakes

Primary hazard (ground shaking, surface faulting)

  • loss of life
  • total/partial destruction of infrastructure
  • communications cut off
  • economic depression
  • blocked transport routes

Secondary hazard (liquefaction, landslides, rockfalls, tsunamis, debris mudflow)

  • same as above


Define tsunami

harbour wave in Japanese


Causes of tsunami

  • Sudden motion on the ocean floor.
  • This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami.


Types of volcanic eruptions

  • Icelandic lava
  • Hawaiian
  • Strombolian
  • Vulcanian
  • Vesuvian
  • Plinian


Iceland lava eruptions

  • persistent fissure eruptions
  • large quantities of basaltic lava build up vast horizontal plains
  • formed Deccan Plateau and Columbia Plateau


Hawaiian eruptions

  • central activity
  • runny,basaltic lava travels down the sides of the volcano in lave flows
  • gases escape easily
  • occasional pyroclastic activity


Stombolian eruptions

  • frequent gas explosions
  • blast fragments of runny lava into air to form cones
  • large quantities of pyroclastic rock
  • white cloud of steam emitted from crater


Vulcanian eruptions

  • violent gas explosions blast out plugs of sticky or cooled lava
  • fragments build up into cones of ash and pumice
  • occurs when there is very viscous lava which solidifies rapidly after an explosion
  • clears blocked vent ad spews large quantities of volcanic ash into atmosphere


Versuvian eruptions

  • powerful blast of gas pushing ash clouds
  • more violent
  • lava flows
  • ash falls


Plinian eruptions

  • gas rushes up through sticky lava
  • blasts ash and fragments into sky in a huge explosion
  • immense clouds of gas and volcanic debris several km thick
  • parts of volcano may be blasted away during the eruption


Define pyroclastic flows

a fast moving current of high-density mix of hot lava blocks, pumice, ash and volcanic gas


Define lava flows/bombs

streams of molten rock that pour or ooze from an erupting vent


Define fire fountains

a continuous spray of disrupting magma through a vent to form a persistent fountain of magma above the vent