Unit One: natural Environments
Earthquakes
Class notes:
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collision and grinding of plates create stresses that rigger earthquakes along
plate boundaries
strong spatial association between earthquakes and folding and faulting of
rocks
earthquakes are tremors / ground movements caused by shock waves
they occur in the outer most layer of the earth’s crust
95% of earthquakes occur on plate boundaries
the depth of earthquakes varies considerably
some earthquakes occur away from plate boundaries – intra plate earthquakes
intra plate earth quakes
* along fault lines
* lines of weakness
* tend to be smaller in magnitude and shallower
m’ment of crust into subduction zone – deepest earthquakes – 700 km
focus – point of origin of the earthquake
epicentre
* point directly above focus at earth’s surface
* first impact occurs
* most damage occurs
seismic waves / shock waves spread our from focus
after a major earthquake – region experiences aftershocks
epicentre – beneath an ocean – generate tsunamis
strength of earthquake – 2 scales:
o Richter Scale – measure of magnitude of the event
o Mercalli Scale – measure of intensity of effects actually experienced at
the location
nature of rock can influence pattern of shocks and vibrations
Impacts:
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cannot predict when earthquakes will occur
can id. regions where they are likely to occur
thousands occur each year
o not near populated regions
o not strong enough to cause loss of life
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extend to damage to structure and loss of life depends on a combination of:
o magnitude of quake
o population density
o building density
o nature of buildings
o nature of bedrock
o accessibility / isolation of region
o time of day earthquake occurred
Source: Place and Change, pg 264 - 265
Earthquakes Notes