Earthquake Study Guide:
*Stress: Movement of the Earth's plates creates great forces that squeeze and pull the rock in the crust. A force that acts on an area of rock to change its shape or volume.
*Tension: Type of stress called tension pulls on the crust, stretching rock so that it becomes thinner in the middle (Landform result-Valley)
*Compression: Type of stress called compression squeezes rock until it folds or breaks (Landform result- Mountains)
*Shearing: Stress that pushes a mass of rock in two opposite directions
(Landform result- Faults & Earthquakes)
*Faults: A break or crack in Earth's lithosphere, along which the rock moves. Breaks in the Earth's crust where rocks have slipped past each other.
*Folding: bends in rock that form when compression shortens and thickens part of the Earth's crust.
*Anticline: A fold in rock that bends upward into an arch(picture#178)
*Syncline: A fold in rock that bends downward to form a valley (picture #178)
*Normal Fault: Tension in Earth's crust pulls rock apart. The fault is at an angle, so one block of rock lies above the other block of rock. (picture #176)
*Hanging Wall: The block that lies above is called the hanging wall.
*Footwall: The rock that lies below is called the footwall.
*Reverse Fault: In places where the rock of the crust is pushed together, compression causes reverse faults to form. It has the same structure as the normal fault, but the blocks of rocks move in the opposite direction (picture # 177)
*Strike-Slip Fault: In places where the plates move past each other, shearing creates strike slip faults. The rocks on either side of the fault slip past each other sideways, with little up or down motion.
*Plateau: Large area of flat land elevated high above sea level. Some form when forces in the Earth's crust push up a large, flat block of rock. It is wider then it is tall.
*Earthquake: Is the shaking that results from the sudden movement of rock along a fault. Most earthquakes begin in the lithosphere.
*Focus: Is the area 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 Wave: Vibrations that travel through Earth carrying the energy released during an earthquake. They carry energy from an earthquake away from the focus, through the Earth's interior and across the surface.
*P Wave: The first waves to arrive from the earthquake are "Primary Waves", They are seismic waves that compress and expand the ground like an accordion. Can move through solids & liquids.
*S Waves: After P Waves come the "Secondary Waves." They are seismic waves that vibrate from side to side as well as up and down. They shake the ground back and forth. They can't move through liquids, just solids.
* Surface Waves: When P and S waves reach the surface, some become surface waves. They move more slowly then P & S waves, but produce severe ground movements, Moves ground like ocean waves and shakes buildings side to side.
*Mercalli Scale: was developed to rate earthquakes according to their intensity or strength at a given place- 12 step scale- the same earthquake can have different Mercalli ratings because it's intensity varies depending on locations.
*Richer Scale: assigns a magnitude number to an earthquake based on the size of seismic waves.
*Moment Magnitude Scale: Rating system that estimates the total energy released by an earthquake. Can be used to rate earthquakes of all sizes, near or far away. The geologists use the data on how much movement occurred along the fault and the strength of the rocks that broke when the fault slipped. Used now by most geologists.
*Magnitude: a number that geologists assign to an earthquake based on the earthquake size. The geologists determine the magnitude by measuring the seismic waves and fault movement during earthquakes.
*Seismograph: The seismic waves are measured by the seismograph. An instrument that records and measures seismic waves.
*Seismogram: The record of an earthquakes seismic waves produced by a seismograph. Zigzag pattern of lines that represent the earthquake.
*Liquefaction: occurs when an earthquakes violent shaking suddenly turns loose, soft soil into liquid mud. Is likely where the soil is full of moisture. As the ground gives way, buildings sink and pull apart.
*Aftershock: Is an earthquake that occurs after a larger earthquake in the same area. May strike hours, days or months later.
*Tsunami: When an earthquake jolts the ocean floor, plate movement causes the ocean floor to rise slightly and push water out of its way. The water displaced by the earthquake may form a large wave called a tsunami. As it approaches shallow water, the wave grows into a mountain of water.
*Base isolator: designed to reduce the amount of energy that reaches the building during an earthquake. Base isolator buildings rest on shock absorbing rubber pods or springs.
*Mass Damper: Dampers work like the shock absorbers in a car to absorb some of the energy of seismic waves.
*Flexible pipes: Water and gas pipes have flexible joints that bend when energy passes through them, reducing damage.
*Active tendon system: Sensors notify a computer that the building is moving. Then, the computer activates devices to shift a large weight to counteract the movement.
*Steel cross braces: are placed between stories of a building to stiffen a buildings frame and absorb energy during an earthquake.