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earthquake: shaking and trembling that results from sudden movement of part of the Earth’s crust Caused by release of energy (lithospheric plates) OCCURS FOR MANY REASONS: •ground shakes from erupting volcano •collapse of a cavern •impact of meteor •major cause- stress that builds up and causes faulting Elastic rebound theory: rocks that are strained past a certain point will fracture and spring back to their original shape Depth inside the Earth at which an earthquake occurs depends upon the kind of plate boundary focus: point beneath the Earth’s surface where the rocks break or move apart •Point on fault plane where 1st movement occurs 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 L waves (surface): •move slowest •move like ripples on a pond 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. Seismograph: instrument that detects and measures seismic waves Seismogram:seismograph’s record of waves; has wavy lines recorded on paper Seismogram Seismologist: scientists who study earthquakes 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 seismograms can be used to determine strength or magnitude of energy produced by an earthquake Richter scale: measures how much energy an earthquake releases by assigning a number from 1 to 10each is 10x’s higher Pacific Ring of Fire: major earthquake zone that forms a ring around the Pacific Ocean Successful earthquake prediction must correctly forecast: •where it will occur •when it will occur •what magnitude it will be Possible methods for prediction: •detect slight tilting of ground before an earthquake •natural gas seepage •Microquakes (foreshocks) Foreshocks & Aftershocks • Foreshock: small earthquakes that occur prior to a major quake • Aftershock: small earthquakes generated by adjustments of materials that follow a major quake. Animal Behavior • Unusual behavior prior to an earthquake event • behavior of animals • 2004 Indonesia Tsunami – In Thailand, elephants broke their chains and ran to a mountaintop – People survived by following animals (monkeys, elephants, dolphins) fleeing from the coast. – Very few animal corpses were found Fault • Fractures in the Earth where movement has occurred. • Causes by stress • faulted rocks have two blocks: – hanging wall: block of rock above fault – foot wall: block of rock below fault Types of Faults • normal fault: formed when hanging wall moves down relative to the foot wall • reverse fault: formed when hanging wall moves up relative to the foot wall • strike-slip fault: rocks on either side of fault are moving past each other • fold: bend in the rock (rock deformed but doesn’t break) •anticline: upward fold in the rock (forms ridges) •syncline: downward fold in the rock (forms valleys)