Earthquakes
• Vibrations caused by the sudden movement of surface rocks.
• These vibrations, called seismic waves, result when rock suddenly breaks and moves, releasing large amounts of energy.
Where Do Earthquakes Occur ?
• 80% of all earthquakes occur in the circum-Pacific belt
• Other belts of activity runs through central Asia, Mediterranean Sea and Caribbean Sea.
Forces within Earth
• Compression- pushes against a body from directly opposite sides
• Tension- stretching or “pulling apart” force
• Shearing- pushes against a body from different sides, producing twisting and tearing
Fractures and Joint System
• Break in the rocks are called fractures.
• Joint system are fracture pattern which covers a large area.
- joints are important to weathering because they increase the surface area of the rock mass.
What is the Elastic Rebound Theory?
• Solids with elastic properties recover their original shape and size unless the force is too great. Then the solid passes its elastic limit and breaks.
• Rocks also show elastic properties, when forces on rock passes its elastic limit, it breaks and stored energy is released as seismic waves.
What is Fault ?
• Fracture along which movement takes place.
• Earthquakes occur when two plates rub together, they are often said to occur on fault lines.
Types of Faults
Normal faults
• Produced by tensional forces.
• The upper block (hanging wall) moves down relative to the lower block (foot wall).
Reverse faults
• Produced by compressive forces.
• The upper block (hanging wall) moves up relative to the lower block (foot wall).
Transform faults
• Move horizontally in response to shearing stresses. They are also called strike-slip faults because the movement is along strike.
• A fracture zone that is composed of many faults that are more or less parallel because of this it has been the site of several...