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Geological Disasters and Society Study Guide Exam 1 - 4.0ed the exam

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University of Arizona
GEOS 218

Geos 218 Introduction natural disaster: an event that causes catastrophic damage or catastrophic loss of life EX: earthquake, volcano, etc. natural hazard: the setting for a natural disaster to take place EX: living near a fault zone or a known active volcano -natural disasters are different from dangerous ones than non-dangerous ones because there could be a 9.5 magnitude earthquake and not be as dangerous because it could be in the middle of the ocean where here are no humans, rather than living near a fault zone where you can have only 6.5 earthquakes and it be more dangerous because it can cause massive damage. -rare but bigger earthquakes have a longer return rate and cause more damage -frequent but smaller earthquakes have a short return period and cause less damage -average death per year from natural disasters=30,000 ppl -”good year”=10,000 ppl -”bad year”=100,000 ppl -people die about the same in motor related accidents (30,000 ppl) -natural disasters result from rapid release of concentrated energy Plate Tectonics accretion heat: energy of incoming stuff converted to heat on collision gravitational heat: converted to heart when heavy iron melted and sank to make the core radioactive heat: from slow decay of radioactive substances in the Earth -***MAIN SOURCE OF HEAT -***MAIN CAUSE FOR EARTHQUAKES, TSUNAMIS, ETC. -Earth was much hotter when it first started to form core: ½ Earth's radius -mostly iron mantle: solid rock but can flow -also ½ of Earth's radius -about 2,900 km thick crust: solid rock -very thin -about 0-100 km lithosphere; crust and upper most mantle of the Earth (plates) -very strong aesthenosphere: weak -solid NOT molten, can flow -right under the lithosphere, not apart of the plate -***more important than lithosphere bc it helps the plates move around and flow better ***STRENGTH LAYERING CONTROLS PLATES -the Himalayas are the strongest on Earth Common Mistakes -plates are NOT continents -plates are created at the spreading centers of divergent boundaries -few inches a year -plates are destroyed at subduction zones ***There are more spreading centers because subduction zones are destroyed twice as fast -there are about 15 MAJOR PLATES oceanic crust: less than 10 km thick -dense continental crust: less dense than oceanic crust but thicker and higher elevation Plate Tectonics and Earthquakes ***EARTHQUAKES HAPPENAT PLATE BOUNDARIES MOSTLY divergent boundary: mostly found in the ocean -EX: The mid-Atlantic Ridge -can cause big earthquakes but mostly in the middle of the ocean convergent boundary: when two plates collide -form mountains -too light for either one to subduct -EX: The Himalayas, the Eurasian Plate collides with the IndianPlate subduction boundary: when one denser plate (an oceanic plate) subducts under the continental plate -EX: the Juan de Fuca Plate subducts under the North American Plate in Washington state -these cause the biggest earthquakes -mostly found on the Ring of Fire transform boundary: plates slide past each other, neither destructive or constructive -EX: the SanAndreas Fault in California -can cause big earthquakes Earthquakes and Faults 3 Types of Stress Faults: 1. Compressional -thrust and reverse fault -block above the fault moves up, EX: Rocky Mountains and Northridge EQ -tectonic setting: convergent -largest EQs 2. Extensional -normal fault -block above the fault moves down EX: Wasatch Fault in Utah -tectonic settings: spreading centers -frequent EQs, small and non-dangerous 3. Shear Stress -strike-slip fault -horizontal motions on a vertical fault EX: SanAndreas -tectonic settings: transform fault -frequent and can be big strike-slip faults: when straddling a fault, if right side moves toward you then it is a right lateral fa
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