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Transcript
How and Where Earthquakes Happen Movement of ground caused by a sudden release of energy Movement along faults Rocks under stress suddenly shift along faults Stress caused faults to break Return of elasticity from deformed rock to original shape Rebound back into shape starting from weakest point Focus – point of 1st motion of a quake • 90% shallow Epicenter – point on surface above the focus • Most damage 0 km – 70 km are shallow • Most damage. WHY? 70km – 300 km are intermediate 300 km – 650 km are deep Travel in all directions Body wave – travel through the body of them medium Surface wave – Travel on surface of material NOT through the middle Vibrations are called seismic waves waves travel at different speeds P wave – Primary or compression • Fastest • Move through solids, liquids, & gases • The more ridged the material the faster they move S wave – Secondary • 2nd fastest • Side to side motion • Only travel in solids Shallow faults Slowest Cause Greatest Damage 2 types • Love – side to side • Rayleigh - rolling Useful in determining the Earth’s interior Tells about the makeup and structure of earth Crust Mantle • Lithosphere • Mesosphere • Asthenosphere core • Inner • outer What causes the speed of a seismic wave to change??? As it passes through Different layers of Earth Area where no direct seismic waves can be detected Earthquakes are the result of stresses in the lithosphere Most occur in 3 main tectonic environments Region of numerous faults Faults zones form at plate boundaries b/c of intense stress as the plates move New Madrid, Missouri 1811 and 1812 Felt in South Carolina Ancient fault deep in Earth Buried by sediment Seismology- study of earthquakes and seismic waves Seismograph-detects and records vibrations Vertical and horizontal motions recorded P- waves S-waves Surface waves • Love • Rayleigh Arrive last Scientist analyze the arrival times of the p & s waves A longer lag time between p & s waves means the further away the EQ occurred. Magnitude- strength of ground motion Richter scale- gives a strength reading Mercalli scale- effects of the earthquake The movement of the ground isn’t what causes injury –it’s the collapsing building Or other dangers • Fire • Down electric & gas • Explosion • Landslides • Etc. Earthquakes that occur in the water may cause tsunamis If you live in an area where EQ’s occur you should be prepared Areas where few EQ’s occur~ but have occurred in the past Where EQ are likely to occur in the future Small earthquakes that precede EQ Can be minutes before or weeks Looking for signals Hoping to detect EQ’s early or before they happen Water in cracks Natural gas seepage Magnetic properties Scientists keep looking for ways to improve May 2, 2015 in Battle Creek March 2015 in Portage Earthquakes occur in Mi. do