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EARTHQUAKES |
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Earthquakes
- Over 30,000 earthquakes occur worldwide each year. 75 of those are considered significant ones.
- The vibration of the Earth produced by the rapid release of energy
- focus - source point of the earthquake
- Earthquakes can be caused by explosions and volcanoes or by movement along fractures in the Earth's crust called faults
- What causes an earthquake?
- H.F. Reid studied the 1906 San Francisco earthquake to determine the cause of the earthquake.
At a fault, the plates are trying to move past each other causing forces to deform the rocks. The rocks bend and store elastic energy. Slippage causes the release of the stored energy allowing the deformed rock to spring back to its original shape. This is called elastic rebound. Once the strength of the rock has been exceeded, the rock breaks and causes the earthquake.
- Aftershocks are smaller, weaker earthquakes generated after a larger earthquake as the rock adjusts from displacement
- Foreshocks - small earthquakes that precede a major quake by days, weeks, or even years.
- Fault Creep - slow, gradual displacement along a fault
- Stick-slip motion - when segments are bound and storing energy for many years and then rupturing in great earthquakes