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Lecture 5

4 Pages

Environmental Science
Course Code
Nick Eyles

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Chapter 3 Earthquakes Earthquake is a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath the Earths surfacey Forces acting deep in the rock may place stress on it to bend or change its form y Seismic waves the waves of energy produced by the earthquake causing the ground to tremble y Fault break between two rock massesReasons for earthquake1 Elastic Rebound theory sudden release of progressively stored elastic strain energy in rocks causing movement along the fault y Internal forces tectonic forces act on a rock over decades making the rock bend stretch or lift but not break As bending becomes severe over buildup of stress the two rocks move past each other along the faulty Movement can be vertical horizontal or both y Energy is released creating seismic waves y Old idea exisiting faults are strong y New idea Existing faults are weak and need very little stress Evidence is suggestive but not conclusive2Volcanic eruption magma fills underground magma chambers before eruption May lead to noy fault movement y Rocks only near the surface of the earth have the brittle behavior of breaking At depth rocks are under increased temperature and pressurereduced brittleness Therefore they deform plastically ductile behavior rather than breaking y Because of this there is a limit to how deep a fault can occur y Forces acting deep in the rock may place stress on it to bend or change its formWhy do earthquakes cause so much damageFocus Hypocentre Point of earth where seismic waves first originate Point of initial breakage and movement of a fault Epicentre Point on earth surface directly above the focus2 types of seismic waves during an earth quakeseismic waves that travel outward from focus in the earths interior in all a Body wavesdirections Two types of body waves1 P primary wavefaster of the 2 waves travelling at near surface rocks at 4 to7 km per second compressional or longitudinal waveRock vibrates back and forth parallel to
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