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Summary Earthquakes and Volcanoes
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A comprehensive and detailed summary of what volcanoes and earthquakes. Includes definitions and primary/secondary impacts that you may not initially think of.
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Earthquake: seismic (tension in rock) events which include the movement/shaking of theground as a result of shifting tectonic plates. Or volcanoes which last just a few seconds.
Shockwaves: Invisible waves of energy sent out from the focus and epicentre of an
earthquake which cause destruction can be P/S/Rayleigh/Love. Which decreases in energy
as they spread outwards.
Focus: the exact location of where the earthquake originates (the centre) from where tension
is released often deep within the plates and below the Earth’s surface. Shallow focus EQs
cause the greatest damage (0-70km deep)
Aftershocks: settling back into place
Epicentre: location on the surface of the crust, directly above the focus where energy is sent
from
Nature and distribution: found most frequently along tectonic boundaries where there is
movement which causes the built up of tensions and therefore distortion of the plates. When
there is enough energy built up then the friction will be overcome and the plates will move
over or past each other causing them to snap back into a new position releasing huge
amounts of energy and sending out shockwaves.
Waves: P waves are the first to be released and travel the quickest, through any surface (go
thru mantel and core, up and down). Can be used to predict when the most destructive will
arrive and can act as a warning.
S waves: secondary, half as fast but much more destructive.
Love waves= Most destructive and slowest
Primary effects:
Ground rupturing: visible breaking of the Earth’s surface. Bad for nuclear power point.
Ground shaking: the movement of the Earth’s crust as a result of shockwaves.
Secondary effects:
Liquefaction: when the ground has been shaken so violently by S waves that the particles
are disturbed and break apart to the extent that solid surfaces e.g. tarmac turn to a liquid
state so any building on top loose their foundation and fall. Also a result of the build up of
pore pressure which reduces the shear strength of the soil.
Tsunamis: the sudden movement of a plate e.g. it’s subduction means that huge volumes of
water a displaced from the sea beds. There is an instant rush of water to fill a gap where the
plate used to be, therefore when the water retreats back to try and restore an equilibrium a
wave begins to form. Initially tsunamis are less than 1m and can travel up to 800km/h but as
they approach a coastline, the friction causes them to slow. As the water slows there
become a build up of water and so the wave crest grows and can be up to 30m tall. Caused
by energy from the EQ forcing masses of wate out
Deaths: Can be the result of falling buildings, hypothermia from being outside, fires breaking
out or other loose items that hadn’t been secured.
Damage to infrastructure: ground shaking and shockwaves can cause buildings to collapse.
Including: hospitals, schools and homes
Fires: Gas pipes can become damaged/broken from abrupt movement therefore sparking
fires throughout cities.
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