Transcript Earthquakes
Earthquakes What is an earthquake? What can we learn from earthquakes? How do we measure earthquakes? Can we predict earthquakes? What is an earthquake? An earthquake is a vibration of the earth due to a rapid release of energy. The energy travels out from the epicenter in waves. What can we learn from earthquakes? Origins of earthquakes were unknown until 1855 (faults) Mechanisms of earthquakes were unknown until H.F. Reid conducted a study following the 1906 San Francisco earthquake. Earthquakes happen after rock is bent and stretched to its limits due to tectonic plate movement. Faults Normal Reverse Strike-Slip San Francisco Earthquake of 1906 8.3 on Richter Scale 7.8 on Moment Magnitude Scale Major structural damage caused by earthquake Total destruction caused by fires after earthquake San Francisco 1906 http://findaid.oac.cdlib.org/findaid/ark:/13030/tf0q2nb1hm San Francisco 1906 http://findaid.oac.cdlib.org/findaid/ark:/13030/tf0q2nb1hm San Francisco 1906 http://findaid.oac.cdlib.org/findaid/ark:/13030/tf0q2nb1hm San Francisco 1906 http://findaid.oac.cdlib.org/findaid/ark:/13030/tf0q2nb1hm San Francisco 1906 http://findaid.oac.cdlib.org/findaid/ark:/13030/tf0q2nb1hm Other Large Earthquakes 1556 China (deadliest) 1886 South Carolina (Eastern USA largest) 1960 Chile 9.6 Magnitude (largest) 1964 Alaska 9.2 Magnitude (N.A. largest) 2006 Hawaii 6.7 (most recent significant earthquake in U.S.) http://earthquake.usgs.gov/ Measuring Earthquakes Seismographs use the property of inertia to measure the strength of earthquakes The recorded pattern of an earthquake is called a seismogram The seismograph records P waves first, then S waves, and finally Surface waves. Three seismographs can triangulate the epicenter of an earthquake Triangulate Epicenter 3 seismographs are used to pinpoint the epicenter which is directly above the focus of the earthquake http://www.calstatela.edu/faculty/acolvil/quakes/epi_location.jpg Body Waves Travel through the interior of the Earth http://www.bgr.bund.de/EN/Themen/Seismologie/Bilder/Sei__seis__ctbto__g,property=default.jpg P Waves Primary waves move faster Compression waves- the material travels parallel to the wave direction Travel through solids, liquids, and gasses http://www.geo.mtu.edu/UPSeis/waves.html S Waves Secondary waves move slower Transverse wave- the material moves perpendicular to the wave direction Travels through solids but not liquids or gasses http://www.geo.mtu.edu/UPSeis/waves.html Surface Waves Surface waves travel along the surface of the earth spreading out from the earthquakes epicenter Love- Side to side Rayleigh- elliptical motion similar to water waves http://www.geo.mtu.edu/UPSeis/waves.html http://www.geo.mtu.edu/UPSeis/waves.html Measuring Earthquakes Modified Mercalli Intensity Scale – Uses damage to determine strength I-XII Richter Scale (ML) – measures according to amplitude of vibration Moment Magnitude Scale (MW) – Measures displacement along a fault zone – Better for large earthquakes Earthquakes Most Earthquakes occur around the circumPacific belt. (Ring of Fire) Liquefaction may add to damage of earthquakes Liquefaction http://www.ce.washington.edu/~liquefaction/html/quakes/niigata/niigata.html Liquefaction http://www.ce.washington.edu/~liquefaction/html/quakes/niigata/niigata.html Triggered By Earthquakes Tsunamis – Tsunami Flash – Warning System Flash Landslides Fire Earth’s Layers Core – Iron Nickel Alloy Mantle – Solid Rocky Perdidotite Crust – Thin rocky layer of mostly Basalt Earth’s Layers Inner Core- solid metal alloy Outer Core- molten metal alloy Mesosphere- high pressure, gradual flow of solid rock Asthenosphere- high temp, soft weak layer Lithosphere- rigid structure, “floats” on upper asthenosphere Predicting Earthquakes Short Range (hours or days) – Efforts are made to monitor strain, uplifting, and subsidence in order to predict earthquakes. – Need more reliable means of prediction. Long Range (years or hundreds of years) – Probability based on past events – Helps in engineering buildings Earthquake Mitigation http://www.odditycentral.com/videos/world s-largest-earthquake-damper.html http://www.youtube.com/watch?v=NYSgd1 XSZXc&feature=related Resources www.sciencecourseware.org http://earthquake.usgs.gov/learning/ http://www.wwnorton.com/earth/egeo/index/animations.htm http://earthsci.org/education/teacher/basicgeol/earthq/earthq.h tml#Earthquakes