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EQ notes 25.2 Earthquake -A sudden movement or vibration of the ground that occurs when rocks slip or slide along cracks in the Earth - corresponds closely with plate boundaries -usually shallow EQ’s (70km or lower) occur at divergent boundaries -deep EQ’s (70km or more) occur at convergent boundaries FAULTS -crack in the Earth’s crust where rock has moved CAUSES -Energy is released along a fault -caused by forces applied to rocks along plate boundaries DEFORMATION -Caused by forces applied to objects -Stress on a object is the force/unit area that acts on that object 4 types of STRESS 1- compression (comes together) 2- tension (pulls apart) 3- shearing (moves opposite ways) 4- torsion (twists) Types of deformation Elastic deformation occurs when stress is applied and the object snaps back to its original shape. Plastic or Inelastic deformation occurs when stress is applied and the object DOES NOT snap back to original position ENERGY RELEASE Elastic Rebound- EQ occur when a rock that has been stressed releases strain energy and moves along the fault. SEISMIC WAVES - Point of ORIGIN from an EQ is called the FOCUS - Point on SURFACE above focus is the EPICENTER SEISMIC WAVES CONT. P-waves (primary)- Compressional waves that, move through material by squeezing and stretching in the same direction as the wave is moving. EX- a spring S-waves (secondary)- Transverse waves move materials at right angles to the wave direction. EX- a rope Surface waves- move on the surface like ocean waves move vertically and horizontally http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es 1002page01.cfm EQ MEASUREMENT Richter Scale- magnitude scale, measures the energy released during an EQ Mercalli Scalemeasures EQ intensity Seismograph- records ground vibration during an EQ EQ DAMAGE • Nearly all EQ damage comes from buildings and human made objects. • Can cause tsumanis • In the middle of nowhere an EQ does not cause much damage at all