EARTHQUAKES
Earthquake - the shaking or trembling caused by the sudden
release of energy, usually as a result of faulting,
which involves displacement of rocks along fractures
Aftershocks
- adjustments along a fault following a large
earthquake
- After a small earthquake, aftershocks usually cease
within a few days, but after a large earthquake, they
may continue for months.
Elastic Rebound Theory
- explains how energy is suddenly released during
earthquakes
- when rocks are deformed, they store energy and bend
- when the strength of the rocks is exceeded, they
rupture and release energy causing earthquakes
There are more than 150 000 earthquakes recorded each year.
There are 900 000 estimated earthquakes that are too small
to be recorded
Destructive effects of earthquakes:
- ground shaking
- fire
- tsunami
- ground failure
Factors effecting amount of destruction:
- time of day, day of week
- magnitude
- duration of shaking
- distance from epicentre
- geology of region
- type of structure
Ground shaking, collapsing buildings, falling building parts,
window glass and toppling monuments cause more damage and
result in the most loss of life and injuries than any other
earthquake hazard.
Earthquake Precursors (changes within the Earth that
precede most earthquakes)
- where earthquakes have occurred in the past but are
currently inactive (locked)
- changes in elevation and tilting of the land surface
- fluctuations in the water level of wells and local
changes in Earth’s magnetic field and the electrical
resistance of the ground are all due to changes due to
alterations in pore spaces in rocks as a result of
increased pressure
- change in animal behaviour prior to earthquakes
- dilatancy model (measures changes occurring in rocks
subjected to very high pressures)