Lecture-5-F10

Lecture-5-F10 - EAS 111 General Announcements 9/8/10 Next...

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Unformatted text preview: EAS 111 General Announcements 9/8/10 Next Week (9/13 and 15) • Monday – Rock deformation I: Faults and Folds • Wednesday – Rock def. II: Mountain building • ALSO Wednesday or shortly thereafter: – Exam 1 Study guide posted to Blackboard • Lab Exam 1 Study guide posted today • Monday, Sept.20 – Exam 1 & Lab Exam 1 review – in class • Tuesday, Sept. 21 – Lab Exam 1 starts • Wednesday, Sept. 22 – Exam 1 in lecture EAS 111: Earth Science News CPS Test Run • We will test the CPS units now – shake the system down. • First a two-part question, and then three questions in the lecture material • Not worth credit today, but will be next time Which College will you Graduate From? Part I A. Agriculture B. CFS C. Education D. Engineering E. Health and Human Sciences F. Liberal Arts G. Krannert H. Not on this list (hang on for Part II) Which College will you Graduate From? Part II A. Pharmacy B. Science C. Technology D. Veterinary Medicine E. Undergraduate Studies F. Already answered in Part I /Other/Unknown Earth and Atmospheric Sciences 111 Fall 2010 Earthquakes, Part 2 -Earthquake Damage, Hazards, and Prediction -Earthquakes and Imaging Earth’s interior structure, composition and physical state -Lecture 5 CPS: A thought question for you and a partner P waves travel faster than S waves. How might this be a useful tool for locating earthquakes? A.If you detect a P wave, then an damaging earthquakes is coming to your location B.The P wave will get larger with distance A.The time difference between a P wave arrival and an S wave arrival should increase with distance How do we determine the location of an earthquake? Earthquake recorded by Earthquake seismic network seismic Select earthquake records 12.05.a Estimate distance Triangulate the epicenter CPS: A thought question for you and a partner Earthquake magnitude is defined by the total energy released in the earthquake itself. The calculated magnitude should then be: A. B. C. D. the same everywhere different everywhere randomly variable we can’t calculate this Measuring the Size of an Earthquake For local magnitude For (Richter): Measure S-wave amplitude S-wave Connect amplitude and distance on plot and There are other ways we measure There the size of an earthquake 12.05.b Magnitude Vs. Intensity Does the same magnitude earthquake produce the same intensity of shaking everywhere? NO! A big earthquake a long ways away yields little shaking (large magnitude, small intensity) The same earthquake (same magnitude) can yield very different shaking intensities on different ground surface types (soft, hard, well packed, not well consolidated, etc. = variable intensities) Major World Major Earthquakes Earthquakes Nicaragua, 1972 Japan, 1999 Armenia, 1988 12.08.a Chile, 1960 Turkey, 1999 Taiwan, 2004 Predict what destruction arises from Loma Prieta Predict Aftershocks Aftershocks ground motion during an cause further earthquake earthquake damage damage Rupture Landslide Structural Structural damage damage Tsunami Bridge failure Bridge on weak materials materials Liquefaction Liquefaction of fill of Worse if poor Worse construction construction Loma Prieta 12.06.a Indonesian Earthquake and Tsunami Before tsunami After tsunami Destruction of Destruction Banda Aceh Banda 12.00.a How Does a Tsunami How Form? Form? Waves radiate Waves away from fault away Higher waves Higher near shore near Most from faults on Most seafloor seafloor Waves Waves inundate land inundate 12.09a Fault movement Fault on ocean floor on Underwater landslides Underwater Volcanic eruptions What areas are most likely to experience earthquakes? Near plate boundaries Messy collision zones Subduction zones Continental rifts 12.11.a What areas in the U.S. are most What likely to experience earthquakes? likely Alaska subduction zone Cascade subduction zone San San Andreas and related faults faults Intermountain Intermountain seismic belt seismic New Madrid area Hawaii Hawaii Big Island Island 12.11.a Earthquake Risk 1. Proximity to active faults – the more active, the worse your risk gets 2. Proximity to active “consequences” of earthquakes (e.g. tsunami, landslides, etc. 3. Building practices 4. Building/ground substrate But how to predict this risk? Long-Range Earthquake Forecasting Top graph indicates earthquakes prior to October, 1989; Top gaps identified based on less earthquake activity gaps 1989 earthquake filled 1989 in Loma Prieta gap in 2004 Parkfield earthquake 2004 filled in other gap filled 12.11.b When will San Francisco gap be filled? Short-Term Earthquake Prediction Lasers monitor Lasers movement along fault movement Numerous seismic Numerous instruments instruments EQ EQ did not occur exactly when predicted predicted 12.11.c Predictions based on past Predictions history of Parkfield segment history Using Earthquakes to understand deep Earth structure Continental Crust Oceanic Crust Mantle Lithosphere - 0–100 km depth (mechanically strong and rigid) Asthenosphere 100-200 km depth (mechanically weak-partially molten (~2%) Below 200 km – regular solid Mantle again 01.03.b1 Exploring the Subsurface: Geophysical Surveys 12.13.a Electrical surveys Magnetic data Seismic-reflection data Gravity Gravity model model Gravity Gravity data data Investigating Deep Investigating Processes Processes Study rocks with deep origins Use computers Use to model processes processes 12.15.a Replicate deep Replicate conditions in a laboratory conditions How Seismic Waves Travel Through Material How 12.14.a Seismic wave radiates in Seismic all directions all At a boundary, wave At will reflect or refract will From faster to From slower material slower From slower to From faster material faster Rising wave from Rising faster to slower faster A seismic seismic wave bends as it travel through crust and mantle and 12.14.b Curved paths permit us to find depth to crust-mantle Curved boundary (Moho) boundary Close to EQ, paths Close through crust arrive first through Farther, paths through Farther, faster mantle arrive first faster Seismic Tomography: Exploring Earth’s Interior Seismic Seismic observations from different direction direction Granite Sedimentary Sedimentary rocks rocks Interpretation Interpretation by comparing observed with what was expected if all same material same Average Average material material Slow material Fast Fast material material 12.15.b Different Kinds of Seismic Waves Surface waves Vertical surface wave compresses materials Horizontal Horizontal surface wave shears material shears Primary body Primary wave (P-wave) compresses material; fastest material; Body waves Secondary body Secondary wave (S-wave) shears material shears 12.04.a CPS: A thought question for you and a partner P waves are compressional waves and S waves are shear waves. If a material has no shear strength, like liquids or gases, then: A.S waves should pass through easily B.S waves should not pass through C.S waves should change course in these materials D.S waves should reflect off these materials completely Examine the ray Examine paths of seismic waves through Earth waves Size of core Size indicated by location of Plocation wave shadow wave zone zone S-waves do S-waves not pass through outer core (so liquid) core 12.14.c 01.03.a1 Seismic Velocities of the Lowermost Mantle Seismic Vary from Place to Place Vary Velocities Velocities (red = slow) (red Model to explain Model velocities velocities 12.15.c EAS 111: Assignments for 9/13/09 • Exploring Geology • 8.1, 8.2, 8.3, 8.4, 8.5, 8.11, 8.13 – Deformation, Faults and Folds – putting it all together to make sense of the sequences of events ...
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