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 BACK VARIOUS NOTES: EARTHQUAKES AND FAULTS EARTH: CHAPTER 2 STUDY GUIDE  CHAPTER 2 EARTH NOTES Section 1 Earthquake-the shaking and trembling that results from the movement of rock beneath Earth's surface. Stress-a force that acts on rock to change its shape or volume. Volume is the amount of space an object takes up. Shearing, tension, and compression work over millions of years to change the shape and volume of rock. Shearing-the stress that pushes a mass of rock in two opposite directions. Tension-the stress force that pulls the crust, stretching rock so that it becomes thinner in the middle. Compression-the stress force that squeezes rock until it folds or breaks. Deformation-any change in the volume or shape of Earth's crust. Fault-a break in Earth's crust where slabs of crust slip past each other. Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the curst so much that the crust breaks. Strike-slip fault-the rocks on either side of the fault slip past each other sideways with little up-or-down motion. Normal Fault-The fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault. Hanging wall-The half of the fault that lies above. Footwall-The half of the fault that lies below. Reverse Fault-Has the same structure as a normal fault, but the blocks move in opposite direction. Over millions of years, fault movement can change a flat plain into a towering mountain range. Fault-block mountain- these form when normal faults uplift a block of rock. Folds-bends in rock that form when compression shortens and thickens part of Earth's crust. Anticline-a fold in rock that bends upward into an arch. Syncline- a fold in rock that bends downward in the middle to form a bowl. Plateau- a large area of flat land elevated high above sea level. Section 2:  Focus-The point beneath Earth's surface where rock that is under stress breaks, triggering an earthquake.  Epicenter-The point on the surface directly above the focus. Seismic waves carry the energy of an earthquake away from the focus, through Earth's interior, and across the surface. There are three categories of seismic waves: P waves, S waves, and surfaces waves. P waves-Earthquake waves that compress and expand the ground like an accordion. S waves- Earthquake waves that vibrate from side to side as well as up and down. Surface waves-When P waves and S waves reach the surface, some of them are transformed to surface waves. These move more slowly than P waves and S waves, but they produce the most severe ground movements.  Seismograph- records the ground movements caused by seismic waves as they move through the Earth.  Magnitude- a measurement of earthquake strength based on seismic waves and movement along faults.  Mercalli scale- was developed in the 20th century to rate earthquakes according to their intensity. Section 3:  The severe shaking produced by seismic waves can damage buildings and bridges, topple utility polls, and fracture gas and water mains. Liquefaction- created by cracks. Occurs when earthquakes violent shaking suddenly turns loose into liquid mud. Aftershock- An earthquake that occurs after a larger earthquake in the same area. Tsunamis- Water displaced by the quake that forms large waves. To reduce earthquake damage, new buildings must be made stronger and more flexible. Older buildings must be modified to withstand stronger quakes. Base-isolated buildings- A building designed to reduce the amount of energy that reaches the building during an earthquake.  During an earthquake- The best way to protect yourself is to drop, cover, and hold. Section 4:  To observe these changes, geologists put in place instruments that measures stress deformation in the crust Geologists can determine earthquakes risk by locating where faults are active and where past earthquakes have occurred.
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