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Bell Ringer Monday 11/30/09 Where do most volcanoes tend to form? a. convergent plate boundaries b. divergent plate boundaries c. hot spots d. all of the above EARTHQUAKES • Earthquakes – vibrations of the Earth’s crust • Elastic Rebound Theory – theory that rocks that are strained past a certain point will fracture and spring back to their original shape • Seismic Waves – energy released as vibrations when rocks fracture; these vibrations travel through the Earth • Aftershocks – a tremor that follows and is smaller than a major earthquake • Focus – the area along a fault where slippage first occurs (see Figure 2-p 739- copy it into your notes) • Epicenter – the point on Earth’s surface directly above the focus • Earthquakes that cause the most damage usually have a shallow focus (a depth in the Earth of less than 70 km) • Earthquakes with a deep focus cause less damage because much of their energy has been used up before the seismic wave reaches the surface • 3 Major Earthquake Zones • Pacific Ring of Fire • Mid-ocean ridges • Eurasian-Melanesian belt • Fault Zone – group of interconnected faults (example – San Andreas Fault in CA) • Seismograph – instrument used to detect seismic waves • 3 types of waves • P waves – primary waves •Fastest waves •Move through solid and liquid material • S waves – secondary waves •Move through solid material only • L waves – long waves •Slowest waves •Also called surface waves •Occur when P waves and S waves reach the surface •Destructive to Earth’s surface • Locating the epicenter of an Earthquake • Use a time-distance graph to plot arrival times of P waves, S waves and L waves • Need three locations to determine the epicenter of earthquake • Richter scale – used to express the magnitude of an earthquake • Magnitude – is a measure of the energy released by an earthquake • Largest recorded earthquake measured 9.6 on the Richter scale • Microquakes – have magnitudes of less than 2.5 on the Richter scale • Earthquake Dangers • Building collapse • Landslides • Fires • Falling objects • Flying glass • Explosions from broken gas and electric lines • Flooding from broken dams • To withstand an earthquake, buildings should: • Have strong walls • Be built on soil or rock that is firm • Tsunami – a giant ocean wave caused by an earthquake with an epicenter on the ocean floor • An earthquake may also trigger underwater landslides – which may cause a series of tsunamis • Earthquake safety • Before an earthquake, be prepared •make a plan •have emergency supplies –Canned food & bottled water –Flashlight, portable radio, & batteries •Learn how to turn off the gas, water, and electricity in your home. • During an earthquake, stay calm • Get under a desk or table or stand in a doorway • Stay away from windows and heavy furniture • If in a car, stop in a place away from tall buildings, tunnels, power lines, and bridges; stay in the car until the tremors stop • After an earthquake, be cautious • Check for fire and fire hazards • Wear shoes when walking in broken glass • Avoid downed powerlines and objects touched by downed wires • Earthquake warnings & predictions • Strange animal behavior • Seismic gaps – a place where the fault is locked and unable to move; likely place for future earthquake • Scientists detect: •Slight ground tilting •A decrease in local P waves Giant Earthquake Hits Shelby County!! • Write a brief newspaper article detailing the events that occurred before, during, and after an earthquake. Be as creative as you can be. However, your article must include a picture and the scientific words that we have been studying in class.