GEOG 100--Lecture 13--Earthquakes
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The document discusses various concepts related to folding, faulting, and earthquakes. It defines diastrophism as large-scale deformation of the earth's crust. It also describes different types of stresses that cause folding and faulting, including compression, tension, and shearing stresses. Additionally, it outlines different types of crustal fold structures like monoclines, synclines, and anticlines. The document then discusses fault types and features associated with transform faults. Finally, it examines seismic waves and how earthquakes are measured, and relates earthquake activity to plate tectonics.
GEOG 100--Lecture 13--Earthquakes
- 1. 11 Folding, Faulting,Folding, Faulting, and Earthquakesand Earthquakes Chapter 9Chapter 9
- 2. 22 DiastrophismDiastrophism • Folding and faulting causing deformation of Earth’s crust on a large scale is called diastrophism
- 3. 33 Compression, Tension, andCompression, Tension, and Shearing stressesShearing stresses • Compression is force exerted inward • Tension is a pulling apart • Shearing occurs when force is exerted in opposite directions, but parallel to one another
- 4. 44 Crustal Fold StructuresCrustal Fold Structures • monocline—a one-sided slope • syncline—a downfold that creates a U-shape • anticline—an upfold that creates an n-shape • overturned fold—similar to an anticline, but tipped to one side • overthrust fold—an overturned fold pushed completely over on its side, so that the entire fold lays on top of the section in front of it
- 5. 55 FaultsFaults Eventually, even the plastic crust will break…
- 6. 66 Fault Block MountainsFault Block Mountains The Sierra NevadasThe Sierra Nevadas
- 7. 77 Strike-slip/Transform/Transcurrent FaultStrike-slip/Transform/Transcurrent Fault (shear stress)(shear stress)
- 8. 88 The San Andreas runs rightThe San Andreas runs right through the town of Hollister, CA…through the town of Hollister, CA…
- 9. 99 Common Structures AssociatedCommon Structures Associated with Transform Faultswith Transform Faults
- 11. Earthquake Measurement Seismic waves—Energy waves propagated during an earthquake Seismograph—Recording device for measuring the amount of shaking which occurs during an earthquake Seismogram—The printed record made by the seismograph
- 12. 1212 Quantitative vs. QualitativeQuantitative vs. Qualitative Seismic MeasurementsSeismic Measurements • Quantitative—Objective, fact-based measurement; mathematical • Qualitative—Subjective; each person’s interpretation of the same event may be different
- 13. 1313 Measuring Seismic WavesMeasuring Seismic Waves • Richter Scale—A numerical expression of the amount of energy released during an earthquake event (Quantitative) – Based on the physical force exerted by the surface movement of earthquake waves – Logarithmic scale…the difference between one order of magnitude and the next represents 10 times the amount of force – Only useful for expressing surface motion • Moment Magnitude Scale—More accurate at higher magnitudes (Quantitative) – Equations used to compare larger quakes (>4.0)-- best for 7.0+
- 14. 1414 Measuring Seismic WavesMeasuring Seismic Waves • Mercalli Scale – Measures an earthquake’s intensity (Qualitative) – Based on what people feel – Uses questionnaires and personal accounts • Good for: – Earthquakes of the past for which no other records exist – Areas where existing development makes geologic studies more difficult – Can help urban agencies plan for future earthquakes in areas needing upgrades or retrofitting
- 15. 1515 Loma Prieta Quake, 1989Loma Prieta Quake, 1989
- 16. 1616 Loma Prieta QuakeLoma Prieta Quake • On October 17, 1989, at 5:04:15 p.m. (PDT) • Magnitude 6.9 (moment magnitude) • Severely shook the San Francisco and Monterey Bay regions • Epicenter located near Loma Prieta peak in the Santa Cruz Mountains, approximately 14 km (9 mi) NE of Santa Cruz and 96 km (60 mi) S-SE of San Francisco • The Pacific and North American Plates abruptly slipped as much as 2 meters (7 ft) along the San Andreas fault • The rupture began at a depth of 18 km (11 mi) and extended 35 km (22 mi) along the fault, but it did not break the surface of the Earth
- 17. 1717 Loma Prieta Quake, 1989Loma Prieta Quake, 1989
- 18. 1818 Seismic WavesSeismic Waves • Body waves – Travel deep beneath the surface • P-waves • S-waves • Surface waves – Travel at or near the surface • L-waves • R-waves
- 19. Seismic Waves P-waves: Pressure or Primary waves Travel fastest First to arrive Travel through all mediums (solid, liquid, gas) If big enough, they can be felt on the other side of the planet
- 20. Seismic Waves S-waves: Secondary or Shear waves Slower than P-waves Second to arrive Travel only through solids
- 21. 2121 Seismic WavesSeismic Waves • Love waves – Push rocks from side to side as the motion of the wave follows a horizontal ellipse which travels forward
- 22. 2222 Seismic WavesSeismic Waves • Rayleigh waves produce an up and down motion created by a forward roll, much like that of an oscillating water wave on the open ocean – Slower than Love waves • 10 times the speed of sound
- 23. 2323 Both L-waves and R-waves:Both L-waves and R-waves: • Can travel only through solids • May not be felt at every earthquake event • Motion decreases exponentially the further the focus is from the surface • Motions do not dissipate quickly • May continue for an extended period at the tail end of a quake • Can travel much longer distances than body waves • Tend cause the most damage to structures and to landforms prone to mass movement
- 24. 2424 Earthquakes and theEarthquakes and the Relationship to Plate TectonicsRelationship to Plate Tectonics
- 25. 2525 Pinpointing an EarthquakePinpointing an Earthquake
- 26. 2626 Pinpointing an EarthquakePinpointing an Earthquake
- 27. 2727 Earthquake Hazard MapEarthquake Hazard Map
- 28. 2828 Earthquake HazardsEarthquake Hazards • Falling debris and rock material • Crumbling buildings • Ground cracks • Broken bridges • Landslides • Liquefaction • Tsunamis
- 29. 2929 LiquefactionLiquefaction • Liquefaction – (from Latin liquefacere meaning “to liquefy”) – Settling of solid material and rising of water normally stored between the pore spaces, turning surface material into quicksand – Danger where the water table is near the surface and surface material consists of loose, unconsolidated, water-saturated sediments • Land may subside • Structures (and people!) sink – Only occurs during shaking • After shaking, settled material becomes solid again and any water on the surface either percolates back down or runs off into streams.
- 31. 3131 Liquefaction under Kawagishi-choLiquefaction under Kawagishi-cho apartment buildings, Niigata quake, 1964apartment buildings, Niigata quake, 1964
- 32. 3232 San Francisco: Original ShorelineSan Francisco: Original Shoreline Liquefaction Potential?Liquefaction Potential?
- 33. 3333 The Pacific Ring of FireThe Pacific Ring of Fire
- 34. 3434 The Pacific Ring of FireThe Pacific Ring of Fire
- 35. 3535
- 36. 3636 What Does a Tidal WaveWhat Does a Tidal Wave Look Like?Look Like? Truro, Nova Scotia, Canada
- 37. 3737 You meant aYou meant a TsunamiTsunami,, right?right?
- 38. 3838 Produces: – Big earthquakes and volcanic islands, called “island arcs” – A deep ocean trench –High potential for tsunamis Oceanic-Oceanic SubductionOceanic-Oceanic Subduction
- 39. 3939 TsunamisTsunamis • Waves caused by undersea volcanic or tectonic events (earthquakes) • Unnoticed by observers on the open ocean • Can reach up to 100 feet in height when they enter a coastal zone • Can be anticipated wherever deep-focus undersea earthquakes occur • Can be detected with special sensors, allowing time for evacuation
- 40. 4040 Sumatra Quake, Dec. 26, 2004Sumatra Quake, Dec. 26, 2004 http://www.nytimes.com/packages/khtml/2004/12/26/in ternational/20041227_QUAKE_FEATURE.html