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Earthquakes
Term | Definition |
---|---|
Stress | force that acts on rock to change its shape or volume |
Tension | pulls on the crust, stretches rock causing it to become thinner in the middle |
Compression | squeezes and pushes rock together until it folds or breaks |
Shearing | pushes two masses of rock in two opposite directions, can cause masses of |
Faults | most faults occur along boundaries, where the forces of the plate motion push or pull the crust so much that the crust breaks |
Hanging Wall | rock that lies above the fault |
Footwall | rock that lies below the fault |
Normal Faults | fault is at an angle, so one block of rock lies above the fault (hanging wall) while the other block lies below the fault (footwall) |
Reverse Faults | compression causes reverse faults. They have the same structure as a normal fault, but the blocks move in the opposite direction |
Strike-slip Faults | rocks on either side of the fault slip past each other sideways, with little up or down motion |
Anticline | a fold in rock that bends upward into an arch |
Syncline | a fold in rock that bends downward to form a valley |
Folded Mountains | mountain created from bends in the rock that create anticlines and synclines |
Fault Block Mountain | mountain created when two normal faults cut through rock. |
Plateau | large area of flat land high above sea level |
Earthquake | shaking and trembling that results from movement of rock beneath Earth’s surface |
Focus | area beneath Earth’s surface where rock that is under stress breaks, triggering and earthquake |
Epicenter | point on the surface directly above the focus |
P Waves | first waves to appear are primary waves that compress and expand like an accordion |
S Waves | secondary waves that vibrate from side to side as well as up and down |
Surface Waves | move more slowly and can produce more ground movement |
Merchalli Scale | rates earthquakes according to level of damage. |
Richter Scale | rating of earthquakes magnitude based on the size of the earthquake’s seismic waves |
Moment Magnitude Scale | rating system that estimates the total energy released by an earthquake |
Seismograph | device that records ground movement caused by seismic waves as they move through Earth |
Tiltmeters | measures tilting or rising of the ground. It is similar to a carpenter’s level |
Creep Meter | uses a wire stretched across a fault to measure horizontal movement of the ground |
Laser-ranging Devices | uses a laser beam to detect horizontal fault movement |
GPS Satellites | can monitor changes in vertical as well as horizontal movement along faults using Earth-orbiting satellites called Global Positioning System |
Liquefaction | occurs when an earthquake’s violent shaking suddenly turns loose, soft soil into mud |
Aftershocks | an earthquake that occurs after a large earthquake in the same area. They can strike hours, days, even months later |
Tsunamis | water displaced by the earthquake may form a large wave |