Understanding Earthquakes: Causes, Types, and Effects - Prof. William L. Niemann, Study notes of Geology

Download Understanding Earthquakes: Causes, Types, and Effects - Prof. William L. Niemann and more Study notes Geology in PDF only on Docsity! http://environment.nationalgeographic.com/e nvironment/natural-disasters/earthquake- profile.html?fs=video.nationalgeographic.com (National Geographic) http://www.youtube.com/watch?v=SgRry6GZ xUo&feature=related(hole in highway) http://www.youtube.com/watch?v=6iNUvlU0S JY (global EQs for 2-month period) http://www.youtube.com/watch?v=reDKxgb_I BQ&feature=related (7.2 quake hits Japan, 2008) http://www.youtube.com/watch?v=7TQDQAe sJvM&feature=related (NYC EQ) Earthquake facts • Earthquakes are caused by a build-up of stress within the crust, causing rocks to fail suddenly. •Some 80 percent of all the planet's earthquakes occur along the Pacific rim. • On average, a magnitude 8 quake strikes somewhere every year. • Most deaths during an earthquake are due to collapsing buildings. «Why earthquakes? Where earthquakes? 45° 90° ee Mediterranean-Himalayan Belt = can SS North Ameri plate plate i: Plate boundary Eurasian plate -Philippine Sea plate African plate South \American| Antarotic plate pe te 90° 135° uncenainy Ep ) US > Juan De Fuca lala? \ North American plate e San socal fault cate ~ /atricary? A i = ae La %, sy % t ~ 4 / | f Nazca plate | \ South Peru-Chile Trench American Cocos platey Pacific plate sbpiy ohuenW Antarctic plate L 180 135° pe Divergent boundary J voveren boundary J ranstorm boundary •Why earthquakes? Where earthquakes? Strain is the response of a material to stress • Elastic *Rubber ball *Earthquake • Plastic *Modeling clay *Folded rocks • Brittle *Pencil *Faults Type of Strain depends on: • Temperature • Pressure • Material • Time Strain--response to stress--varies dependi on earth material effected. Gulf of Mexico Figure 16.11 ) hon . @ & = ° £ oO oO — £ & £ a) mo & Increas ssaijs Bu ISBSlDU] c S = ® & hn o & oO oD z £ ra Increasing st Faulting: brittle response to stress •slow or sudden release of small or large amounts of energy •may cause earthquakes Sudden brittle response to stress with elastic rebound Energy released as: • movement of rocks along fault • snapping back of unbroken rocks to original shape • both cause seismic waves • Why earthquakes? • Locations • Driving forces • Response of rocks •elastic, plastic, brittle •all represent release of energy •Sudden release of stored elastic energy (“elastic rebound”) causes earthquakes Fault scarp c We Fault trace Seismic WAVES | atwhere rocks first break along a fault; seismic waves radiate is. The ris the point on the Earth’s surface dire 3  Sap Uni COCO H Particle motion FOOONONCOONO OCTANE NOONE ONY =H OTRO OM an Expand Compress AICO ONNTONOOONOOINE SOOO _—> Wave propagation ~ LCRODNOCCCEICOCENNOCOCTEC | A Primary wave Particle motion Wave propayalion aaa Lie © Love wave Side-to-side motion Directicn of Love wave propagation | Direction of Rayleigh w . propagation B Secondary wave Figure 16.5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Spring Weight stays _ at same level while the ground moves A At rest B_Ground moves up C Ground moves down  Difference in P- and S-wave arrival times gives distance of 1,000 miles to epicenter. But which direction? S1 Circle with radius of 1,000 miles | Staton near focus Surface waves P, S waves B Stabon fae trom tee gure 16.8 ES en P waves, 8 waves, and surface waves innraase will Seismograms e St. John rate 2 De | ee ey po00 400¢ no: BODO 10.000 Distance from epicenter (kilometers) jure 16.9 mo la | ill | ete i Soverriogrann tory slatow A ee halt NA A Wrenn iy | I y/\yp N a | i L | diislanee inunn the i Measuring size / strength of quakes Calculating Richter Magnitude M = log A + 3 log (8 Δt) – 2.92 M = Richter magnitude A = amplitude (in millimeters) from seismogram Δt = separation time (in seconds) from seismogram Liquefaction of soft soils. Buildings are intact but lack support. (Japan, 1964) Copy The McGraw-Hill Companies, Inc. Permission req isplay NORTHEAST TRENCH 7 SOUTHEAST WALL SOUTHWEST METERS v.92, no. F, p. 2851, cou 1857 Ft. Tejon M 7.8 1906 San Francisco M 8.25 1989 Loma Prieta M 7.2 1994 Northridge M 6.7 RI = 105 years based on 14 EQs in 1,500 years 1857 + 105 = 1962 RI = 68 years based on 2 EQs in 68 years 1906 + 68 = 1974 60% chance of M 7.5 – 8.3 on S.A. Fault in 30 years 85% chance of M >= 7 on faults parallel to S.A. Fault <21% chance of M >=8 on S.A. fault in 30 years 62% chance of M >= 6.7 in 30 years on Hayward Fault