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What are Earthquakes? Earthquakes • Sudden release of energy in the crust – Tremors – small shaking of the crust Today’s earthquakes – About 2 Earthquakes occur every second. – But most are too small to be felt. – Most Earthquakes occur near plate boundaries – Deepest earthquakes occur on subduction zones (convergent boundaries) Where Does an Earthquake Start? EPICENTER – POINT DIRECTLY ABOVE THE FOCUS ON THE SURFACE FOCUS – STARTING POINT OF AN EARTHQUAKE BELOW THE SURFACE Damage Caused by Earthquakes • Faults • **** Most death’s and injuries are caused by falling buildings (Earthquakes don’t kill people buildings kill people). • Broken gas lines can lead to fires. • Broken water pipes compound the problem. because there is less available to put out the fires. • Landslides and mudflows • Liquefaction of soil (soil becomes so unstable that it moves like a fluid) • Tsunamis – extreme ocean waves caused by earthquakes • Tsunami detection system Damage is Amplified • Create Your Own Earthquake and Building Structures: compare damage • Damage will be more severe when building on loose sediments • The loose sediments will move more and result in liquefaction (soil acting as a fluid) – Houses could sink into the loose sediments Damage Prevention • Build on strong solid bedrock • Build Earthquake proof buildings – buildings that have internal gyroscopes which allows the building to move with the lithosphere. • Securely mount art to walls. • Avoid windows and move under a table to prevent being hit by falling objects Earthquake Preparedness • • • • Follow damage prevention plan Have a short food and water supply Evacuation Plan Move to higher ground to avoid Tsunami Measuring Seismic Waves • Seismograph – machine that measures seismic waves at a given location • Seismogram – record sheets of waves created by the seismograph Scales used to Report Earthquakes • Mercalli • Measures strength of an Earthquake according to the amount of damage done • Measures Intensity (by how intensely it was felt) • Scale ranging between I-XII • Not always accurate b/c some locations may incur severe dmg even when the EQ was not that strong (If buildings and structures are built on loose sediments then eqs are amplified • Intensity measurements of the 1906 San Francisco Earthquake • Richter • Measures MAGNITUDE of EQ based on Seismic waves Mercalli Scales Scales used to Measure E.Q’s • • • http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002pag e01.cfm?chapter_no=visualization ** p & s waves animations • http://www.classzone.com/books/earth_science/terc/content/visualizations/es1009/es1009pag e01.cfm Shadow zone • • http://www.thetech.org/exhibits_events/online/quakes/waves/p&s_waves.html Wave slinky and rope animation • • http://www.wwnorton.com/college/geo/egeo/flash/8_2.swf P and s waves http://www3.interscience.wiley.com:8100/legacy/college/skinner/0471152285/anim ations/animations/mod_5/seismic_waves.html Wave animations and shadow zone http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Shadow+Zone+ Flash+Animation&flash_file=shadowzone&flash_width=220&flash_height=300 Shadow zone