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Transcript
EARTHQUAKES • An earthquake is the shaking and trembling that results from the movement of rock beneath the Earth’s surface • There are about 1,000,000 earthquakes a year; ONLY about 20 are considered severe Seismology à study of earthquakes Seismologist à scientist who studies earthquakes and seismic waves Keep in mind: Seismologists don’t have to be right near an earthquake to study it. Why is this? Fault à a break in the crust along which plates shift and slip past each other • Where are faults found? Plate boundaries & inside plates What plate is surrounded by earthquakes? PACIFIC PLATE! PLATE BOUNDARY FEATURES Focus à Actual point of the shift along the fault where the rock breaks Usually miles underground Epicenter à Closest point to the focus on the earth’s surface Always directly above the focus Deformation à rocks changing shape due to stress from tectonic motion Plastic Deformation Elastic Deformation Plastic Deformation Stress causing a fold Elastic Deformation Stress causing a fold then a break Elastic deformation causes earthquakes because of the elastic rebound! Elastic rebound à stress builds up to the point where the rock breaks and snaps back ELASTIC REBOUND Seismic waves à • During an earthquake seismic waves race out from the focus in all directions • Can you label them on your notes? • Carry waves of energy from an earthquake away from the focus through Earth’s interior and across the surface Different types of seismic waves travel through the Earth’s layers at different speeds. Body Waves à Seismic waves that move through Earth (P and S waves) • Primary or pressure waves • Travel through solid and liquid (entire Earth) • fastest wave • particles move in a back & forth direction the same direction as the wave (longitudinal) In one direction Radiating out from epicenter • Secondary or shear wave • Travel only through solid (not liquid) • Move slower than Pwaves • Particles move in an up and down motion perpendicular to the direction of the wave (transverse) In one direction Radiating out from epicenter Both can be easily demonstrated with a Slinky! Surface Waves à Seismic waves that travel on the surface of Earth (L L-waves • Love wave (surface) waves) • Travel only on the surface • Slowest but most destructive • Moves like an ocean wave – up, down, and around Surface wave SEISMIC WAVE MOTION SEISMIC WAVE MOTION WITH SURFACE EFFECTS P-waves (Pressure waves) S-waves (Shear waves) Relative Speed: Relative Speed: fastest slower back and forth Up and down Where they travel: Where they travel: through the entire earth only through solid Surface waves Relative Speed: slowest, but most damaging up, down, and around Where they travel: on the earth’s surface