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Earthquakes & Volcanoes BIG Ideas: 1. 2. 3. Most geologic activity occurs at the boundaries between plates. Earthquakes are natural vibrations of the ground, some of which are caused by movement along fractures in Earth’s crust. Volcanoes develop from magma moving upward from deep within Earth. I. Forces Within Earth Faults form when the forces acting on rock exceed the rock’s strength. Fault: a break or crack in Earth’s crust along which movement has occurred. Most active faults are located at or near plate boundaries. Earthquakes result when movement occurs along a fault. Locations of Earthquakes from 1980 to 1990 A. Stress and Strain Stress: the total force acting on crustal rocks per unit area. Strain: the deformation of materials in response to stress. Rocks that are strained past a certain point will fracture and spring back to original shape. Deformation: •a change in the shape or size of an object due to an applied force •misshapen •contort, twist and press out of shape Elastic Rebound Theory Three Types of Stress 1. 2. 3. compression: decreases volume of material tension: pulls material apart shear: causes material to twist B. Types of Faults Facts: •1000 km (621 miles) long •15-20 km (9-12 miles) deep Parts of an Earthquake Focus: spot within the Earth’s crust (lithosphere) where the origin of the Earthquake is located (where slippage along a fault occurs). Epicenter: spot on the surface of the Earth directly above the focus. C. Earthquake Waves Seismic Waves: vibrations of the ground produced during an earthquake. Every earthquake generates three (3) types of seismic waves… Types of Seismic Waves: 1. PRIMARY Waves: P-WAVES travel the fastest FIRST to be recorded travel through solid AND liquid compressional waves that push and pull Think Slinky! 2. SECONDARY Waves: S-WAVES second to be recorded only travel through solid material (NOT through liquid) shear waves that move side to side (like a rope) Which layer of Earth will S-Waves NOT travel through? 3. SURFACE (LAND) Waves: travel only along Earth’s surface slowest wave (last to be recorded) cause the surface of Earth to move sideways and up and down (like ocean waves) Which waves are the most destructive? Surface Waves (also known as L-WAVES) cause the greatest damage. II. Seismic Waves and Earth’s Interior A. Seismograph: instrument that detects and records seismic waves Seismogram: record produced by seismograph Analyzing a Seismogram: B. Clues to Earth’s Interior III. Measuring and Locating Earthquakes Scientists measure the strength and chart the location of earthquakes using seismic waves A. Earthquake Measurement magnitude: measure of energy released by an earthquake Richter Scale measures energy of the largest seismic waves (magnitude) produced during an earthquake Los Angeles New York City Which city would better withstand a catastrophic earthquake? WHY? B. Locating Earthquakes scientists graph the arrival times of the P and S waves the longer the S wave takes to arrive, the further away the quake THREE (3) seismic graph stations are required to locate the epicenter Finding the epicenter… Damage Ground Rupture: Damage due to ground motion will depend on Amplitude, Duration of vibrations, Nature of material building is built on, Design of structure Fire Landslides Tsunamis tidal (harbor) wave - vertical displacement at seafloor due to earthquake causes giant "ripple" in ocean Nimitz Freeway - Oakland, 1989 Loma Prieta - Ground Rupture Mexico City, 1985 After Before Tsunamis: Giant ocean wave or a series of waves usually associated with an undersea earthquake or landslide Formation of a tsunami IV. Volcanoes Opening where magma erupts onto Earth’s surface. MAGMA: molten (liquid) rock UNDERGROUND LAVA: molten rock that is ON THE SURFACE VENT: opening through which lava flows VOLCANO: the build up of material around the vent A. MAJOR VOLCANIC ZONES Most volcanic activity is associated with: subduction, rifting, or seafloor spreading 1. Pacific Ring of Fire 2. Mid-Ocean Ridges: rifting and seafloor spreading 3. Hot Spots: Volcanism within plates Hot Spot volcanic activity is exceptional because… this activity is NOT related to plate boundaries! B. TYPES OF VOLCANOES 1. SHIELD: LAYERS OF LAVA WIDE AND FLAT Hawaiian Islands 2. CINDER CONE: STEEP LAYERS OF PYROCLASTIC MATERIAL small, most common type of volcano 3. COMPOSITE: STEEP WITH LAYERS OF ALTERNATING LAVA AND PYROCLASTIC MATERIAL Mount Saint Helens SKYLIGHT – WINDOW INTO THE EARTH’S INTERIOR