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MU GLY 110 - Earthquake facts

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Slide 1Slide 2Slide 3Slide 4http://www.youtube.com/watch?v=w3AdFjklR50&feature=related http://www.youtube.com/watch?v=-DSSssHxm4Y&feature=related http://www.youtube.com/watch?v=s8L2kikyVzkSlide 6Slide 7Slide 8Slide 9Slide 10Measurement of EarthquakesSlide 12Slide 13Slide 14Slide 15Destructive Effects of EarthquakesSlide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Elastic Rebound – causes earthquakesElastic ReboundStick-slip FaultsSlide 29Slide 30Seismic WavesSlide 32Slide 33Surface WavesSlide 35Determining Distance to Point of Energy ReleaseSlide 37Slide 38Slide 39Slide 40Slide 41MEASUREMENT OF EARTHQUAKESSlide 43Measurement (cont.)Slide 45Slide 46Slide 47Slide 48Earthquake PredictionSlide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Seismic Character of Earth’s Internal DivisionsSlide 58Seismic waves, like light waves, will bend, or refract, when they encounter different materialP-wave Shadow ZoneS Wave Shadow ZoneSlide 62Earthquake factsEarthquake facts• Earthquakes are caused by a build-up of stress Earthquakes are caused by a build-up of stress within the crust, causing rocks to fail suddenly.within the crust, causing rocks to fail suddenly.•Some 80 percent of all the planet's earthquakes Some 80 percent of all the planet's earthquakes occur along the Pacific rim.occur along the Pacific rim.• On average, a magnitude 8 (M8) quake strikes On average, a magnitude 8 (M8) quake strikes somewhere every year.somewhere every year.• Most deaths during an earthquake are due to Most deaths during an earthquake are due to collapsing buildings.collapsing buildings.•Why earthquakes? Where earthquakes?Distribution of earthquakes with R.S. mag > 5 from 1980-1990.•Why earthquakes? Where earthquakes?•Why earthquakes? Where earthquakes?http://www.youtube.com/watch?v=w3AdFjklR50&feature=related http://www.youtube.com/watch?v=-DSSssHxm4Y&feature=related http://www.youtube.com/watch?v=s8L2kikyVzkHonshu tsunami videosLocating EQsM=9.011 March 20115:46:23 UTCfocusepicenterLocating EQsFaults are where rocks break and move suddenly30-40 m movement along subduction zone fault in HonshuNorth American PlatePacific PlateTsunami (seismic sea wave) caused by seafloor displacement . Tsunamis slow and steepen (up to 30 m) as they enter shallow water.Tsunami wave predictionsMeasurement of Earthquakes•Magnitude -an index of the amount of energy released, proportional to amount of ground motion; -Richter Scale - a logarithmic scale: each number represents >30X more energy and 10X more ground motion than preceding number; examples….Richter magnitude depends on: 1)Separation time (distance)2)Amplitude (ground shaking)Measurement of Earthquakes•Intensity -based on damage, effects-will vary from place to placeDestructive Effects of Earthquakes•Structural damage from seismic waves-•fire•mass wasting - landslides, liquefaction•tsunami (seismic sea waves)Kobe, Japan,1995http://environment.nationalgeographic.com/environment/natural-disasters/earthquake-profile.html?fs=video.nationalgeographic.com (National Geographic)http://www.youtube.com/watch?v=SgRry6GZxUo&feature=related(hole in highway)http://www.youtube.com/watch?v=6iNUvlU0SJY (global EQs for 2-month period)http://www.youtube.com/watch?v=reDKxgb_IBQ&feature=related (7.2 quake hits Japan, 2008)http://www.youtube.com/watch?v=7TQDQAesJvM&feature=related(NYC EQ)Types of Stress Plate Tectonics Setting• Confining None• Compressive Convergent• Extensional Divergent• Shear TransformStress is force concentrated over an area F =100 lbs 10 lbs/ft2A =10 ft2Strain is the response of a material to stress• Elastic *Rubber ball *Earthquake • Plastic*Modeling clay*Folded rocks • Brittle*Pencil*FaultsType of Strain depends on:• Temperature• Pressure• Material• Timehttp://www.pirate4x4.com/tech/billavista/PR-BV60/Materials/stress_strain%201.jpgPlastic flowFolding: plasticresponse to stress• strain energy used up in folding • no earthquakesFaulting: brittle response to stress•slow or sudden release of small or large amounts of energy•may cause earthquakesElastic Rebound – causes earthquakesElastic ReboundStick-slip Faults•Fault zone may have segments characterized by creep •These may altternate with segments which are stuck (snagged) •As elastic strain accumulates, energy is stored;Subsequently released as large earthquake•Creeping segments store little energy (less dangerous)Stick-slip FaultsSeismic Waves•body waves- move only through earth’s interior; -p wave: primary (compressional) wave, fastest, first to arrive at seismic station; 2.4 – 3.2 miles / second ~10,000 mph compare to F-15 ~0.5 miles / second -s wave: secondary (shear) wave -1.8 – 2.4 miles / second - cannot be transmitted through liquid (ex molten rock)P WAVE (compressional wave)S WAVE (SHEAR WAVE)Surface Waves•move only along the surface; •- slowest wave type• Rayleigh, Love wavesSurface WavesDetermining Distance to Point of Energy Release •Example : thunder and lightning, same source 1) light travels 186,000 miles per sec, instantaneous over 1-25 miles 2) sound travels ~ 1,100 ft per sec Ex. Light-sound time interval of 20 sec indicates lightning was ~ 4 miles awayBasic principles of a seismograph…Record (seismogram) of an earthquake; time separation of arrivals based on wave type. S-P interval shown is ~ 5 minutes.S-P intervalDetermining EQ EpicenterTravel-time graph, used to determine distance from seismic stationto epicenter.The location of an epicenter on the midoceanic ridge in the South Atlantic Ocean. S-P time intervals are used from 3 seismic stations.MEASUREMENT OF EARTHQUAKES•Magnitude -an index of the amount of energy released, proportional to amount of ground motion; -Richter Scale - a logarithmic scale: each number represents >30X more energy and 10X more ground motion than preceding number; examples….Richter magnitude depends on: 1)Separation time (distance)2)Amplitude (ground shaking)Measurement (cont.)•Intensity - an index of structural damage -based on modified Mercalli Scale I-XII (see Table ); - structural damage depends on:-magnitude and duration of EQ -distance to epicenter -structural design -character of surface materials upon which buildings rest.USGS, 2005San Francisco


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