Lecture-6-F10 - EAS 111 General Announcements 9/13/09 •...

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Unformatted text preview: EAS 111 General Announcements 9/13/09 • Schedule Reminder • Today – Stress, Strain, Geologic Structures • Weds – Folds, Faults, Mountain Building Plan Ahead! • Lecture Exam I review – 9/21/09 – Monday • Exam 1 Study guide posted to Blackboard after class today • EXTRA OFFICE HOURS 9/21/09 – TUES, 2-4 PM • REGULAR OFFICE HOUR 9/22/09 – WED, 1-2 PM • Lecture Exam I – 9/22/09 - Wednesday • Lab Exam II – Starting 9/21/09 (same week as Lecture exam) Earth and Atmospheric Sciences 111 Fall 2010 Rock Deformation I -Earth’s Interior, Part II -Stress and Strain -Brittle and Ductile deformation Faults and Fault Types -Folds and Fold Types -Lecture 6 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 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 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 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 Before, During, and After an Earthquake Slip and Slip earthquake earthquake Stress Stress increase and elastic strain increase Post-slip recovery Post-slip of elastic strain; cycle starts again cycle 12.02.a Observe the Observe topography of part of the Ridge the and Valley Province 08.00.a Words of the Day • Stress • Strain • Brittle • Ductile • Fault • Fold Force and Stress Force is push or pull, expressed Force as amount of acceleration experienced by a mass experienced What happens if same amount of What force is applied to two wooden pillars? force Stress = force per area per 08.01.a How Rocks Respond to Force and Stress Small amount of stress: block only experiences block temporary (elastic) changes temporary Change in Change shape shape 08.01.b Displacement Rotation Consider the structural behavior of rocks at shallow Consider versus deep conditions versus 08.01.c At shallow At depths, most rocks break rocks Temperature and Temperature pressure increase with depth with Rocks flow Rocks in deep conditions conditions Strength of Rock Small Small stress stress Increase Increase stress stress Too much Too stress = failure failure Strength of continental Strength crust crust 08.02.b Observe three kinds of stress and resulting structures Compression Tension Shear Shallow levels: rocks fracture Deeper levels: rocks flow 08.02.c Types of Fractures Joint: Joint: crack where rock pulled apart apart Fault: rocks Fault: have slipped past one another another 08.03.a Describing Faults Strike Dip 08.04.a Strike-slip Strike-slip fault fault Dip-slip fault Oblique-slip fault Sense of Movement Hanging wall Footwall 08.04.b Normal fault Reverse fault or Reverse thrust fault thrust This fault is a: a. reverse fault b. normal fault c. can’t tell from this information Hebgen Lake fault scarp SW Montana, M 7.5, 1959 08.15.b1 Strike-Slip Faults Rocks move Rocks horizontally 08.04.c Left lateral Right lateral EAS 111: Assignments for 9/15/09 • Exploring Geology • 11.1, 11.2, 11.3, 11.4, 11.12, 11.13 • Mountain belts around the world, their formation, and the brief history of American mountains ...
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