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What is an earthquake? shaking and trembling that results from sudden movement of part of the Earth’s crust Caused by release of energy (lithospheric plates) What are the causes of Earthquakes? •ground shakes from erupting volcano •collapse of a cavern •impact of meteor •major cause- stress that builds up and causes faulting What is the theory of Elastic rebound? Elastic rebound theory: rocks that are strained past a certain point will fracture and spring back to their original shape What is the focus? focus: point beneath the Earth’s surface where the rocks break or move apart •Point on fault plane where 1st movement occurs What is the epicenter? epicenter: point on Earth’s surface directly above the focus •site of most violent shaking focus P waves (primary): •move fastest •back and forth waves •move through solid, liquid or gas •push-pull waves S waves (secondary): •travel slower •move side to side •travel through solids only L waves (surface): •move slowest •move like ripples on a pond •only travel along the surface Blue primary waves followed by red secondary waves move outward in concentric circles from the epicenter of an earthquake off British Columbia and Washington State. What is a Seismograph? instrument that detects and measures seismic waves Seismogram:seismograph’s record of waves; has wavy lines recorded on paper Seismologist: scientists who study earthquakes How are Earthquakes measured? Locating an Earthquake Earthquake • Distance The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance. Earthquake Direction Tracing made by a seismograph can be used to tell how far away an earthquake’s epicenter is from the station that recorded it: •Need distance from 3 different stations in order to determine location •Point where all 3 circles meet is location of epicenter Locating an Earthquake How is Earthquake strength determined? seismograms can be used to determine strength or magnitude of energy produced by an earthquake Richter scale: measures how much energy an earthquake releases (magnitude)by assigning a number from 1 to 10 Earthquake Magnitudes Some Notable Earthquakes What is the Pacific Ring of Fire? major earthquake zone that forms a ring around the Pacific Ocean What damage occurs from Earthquakes? • • • • • Building collapse Liquefaction Tsunamis Landslides Fire Successful earthquake prediction must correctly forecast: •where it will occur •when it will occur •what magnitude it will be What are possible methods for predicting Earthquakes? •microquakes •behavior of animals •detect slight tilting of ground before an earthquake •natural gas seepage