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EARTHQUAKES 1988 Armenian Earthquake – Spitak Communications Building USGS EARTHQUAKES Occur in all plate boundaries Diverging Converging Continent/ocean (Subduction) Ocean/ocean (Subduction) Continent/continent (Collision) Transform PLATE BOUNDARIES WORLD WIDE DISTRIBUTION OF EARTHQUAKES Earthquakes Terms Focus – point within the earth where initial slip is generated Epicenter – point on the earth’s surface directly above the focus Seismic waves move outward from focus SEISMIC WAVES P-WAVE (Primary) Fastest seismic Travels through liquids and solids inside the Earth Compresses and expands in the direction of wave movement. Tasa S-WAVE (Secondary) 2nd fastest Travels through solids inside the earth Moves with a shearing motion perpendicular to wave travel TASA SURFACE WAVES Slowest wave Travels on the earth’s surface Moves with an elliptical motion or shearing Potentially most destructive TASA Earthquake Waves MEASURING EARTHQUAKES TASA Seismograph SEISMIC WAVE – TRAVEL TIME Amount of time between P and S waves are directly related to distance to the epicenter Tarbuck &Lutgens LOCATING AN EARTHQUAKE 3 Seismic Stations Required Press & Siever MEASURING EARTHQUAKES INTENSITY (EFFECTS) Modified Mercalli Intensity Scale Measures damage produced by an earthquake Useful for: historic quakes earthquake engineering pin-pointing damaged localities Guiseppe Mercalli 1850-1914 What affects intensity? Amount of energy released in the earthquake Distance from the epicenter Type of bedrock Population density Building construction 1989 Loma Prieta Earthquake USGS MEASURING EARTHQUAKES MAGNITUDE (Wave Amplitude) Richter Scale – based on largest amplitude of a seismic wave from seismograph during an earthquake An increase by 1 in magnitude equals 10x increase in amplitude Measure of the amount of energy released Energy released increases 32 x’s for each unit Charles Richter 1900-1985 Earthquake Energy Equivalents Education and Outreach IRIS Consortium: www.iris.edu MEASURING EARTHQUAKES MOMENT MAGNITUDE More accurate than Richter Scale Estimates total amount of energy released Takes into account several factors Displacement along fault Area of ruptured surface Strength of underlying rock More precisely measures large earthquakes, similar magnitudes as Richter for smaller quakes Can be verified by field studies of fault displacement measurements EARTHQUAKE HAZARDS Ground shaking Liquefaction Fire Subsidence & uplift Landslides & avalanches Tsunamis Mexico City Earthquake, September 19, 1985 USGS Earthquake Hazard GROUNDSHAKING Strain accumulation One side of the fault is moving in opposition to the other side of the fault Result: ground cracks and structures collapse Mexico City Earthquake, 1985 Oklahoma University Ground Shaking and Cracking San Francisco Earthquake 1906 G.K. Gilbert 1992 - Landers, CA - 7.5 M Earthquake Kobe, Japan January 17, 1995 6.9M Press & Siever Kobe, Japan Expressway fell on it’s side 6308 killed Press & Siever Tohoku, Japan March 11,2011 Magnitude 9.0 401 aftershocks 4 foreshocks 18,000+ killed Ground Shaking Material Amplification Surface waves are relatively small in solid crystalline bedrock Surface waves amplify (increase) in poorly consolidated sediments Prentice Hall Mexico City Earthquake, 1985 City built on lake sediments that amplified seismic waves 1985 Mexico City Earthquake - M 8.1 Earthquake Hazard LIQUEFACTION Sand grains saturated with water shake Sand grains are detached Sand is unable to support overlying weight of buildings Niigata, Japan 1964 Karl V. Steinbrugge LIQUEFACTION Marina District in San Francisco Loma Prieta Earthquake – 1989 M 7.1 Nimitz Freeway 1989 Loma Prieta Earthquake – M 7.1 Dennis Laduzinski Earthquake Hazard FIRE San Franscico, 1906 Kobe, Japan 1995 Causes: Gas mains break Gas stoves, water heaters, etc. in homes Inadequate water supply Firefighters can’t reach fire Blasting sometimes used to create a fire break Fire San Francisco Earthquake 1906 April 18, 1906 5:15 am Shaking lasted about 1 minute 700-3000 killed 8.3M estimated $400 million in damages (Image © Archive Photos) Earthquake Hazard SUBSIDENCE & UPLIFT Alaska Earthquake 1964 Prince William Sound Fault Scarp of 16 feet USGS Earthquake Hazard LANDSLIDES & AVALANCHES Unstable material shaken loose Rock, sediment or ice Steep slopes 2002 Alaska Earthquake Yungay, Peru 8M earthquake 20,000 killed in Yungay 50,000 more killed elsewhere Overlandy.com about 2003 Earthquake Hazard TSUNAMIS Seismic Sea Wave Causes: Submarine landslide Fault displacement Volcanic eruption TASA Tsunami Tsunamis in the Pacific Hilo, Hawaii April 1, 1946 – 159 Deaths NOAA Indian Ocean Tsunami NOAA Natl. Inst. of Advanced Industrial Science & Technology Indian Ocean Tsunami Dec. 26, 2004 Patong Beach, Phuket Banda Aceh, Sumatra Reuters Banda Aceh, 2004 Tsunami Japan, 2011 Tsunami video2 video1 video2 HAZARD ASSESSMENT Develop understanding of the earthquake source Determine earthquake potential Predict effects of earthquakes Apply research results Coalinga, CA 1983 Earthquake USGS Shaking Hazard Map World Seismic Hazard Press & Siever San Andreas Fault south of San Francisco R.E. Wallace, USGS EARTHQUAKE PREDICTION (when) verses EARTHQUAKE FORCASTING (where) Earthquake Studies Tilt of rocks Swarms of micro earthquakes Groundwater changes Radio Waves Creep verses locked faults Foreshocks/Aftershocks Animal behavior and more . . . Parkfield, CA - SAFOD San Andreas Fault Observatory at Depth USGS Parkfield, CA Earthquake Capitol of the World 6M earthquakes - 21 year average 1881 1901 1922 1934 1966 1992 (4.5 M) 1994 (5 M) 2004! Earthquake Probability San Andreas Fault Chinese Predict Haicheng Earthquake February 1975 Prediction based on: Foreshocks Many large foreshocks before main event Animal Behavior Snakes came out of hibernation Rats scurried around Large farm animals behaved differently near epicenter Collapsed Factory China Virtual Earthquake Museum Chinese fail to predict Tangshan Earthquake July 28, 1976 2nd most devastating earthquake in history (worst was also in China 1556, 830,000 died) 8.2 M 750,000 died No foreshock events ChinaStock