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Earthquakes: Shakin' & Risks in Oklahoma

Learn about the definitions, types, measurements, and risks of earthquakes, with a focus on seismic activity in Oklahoma. Discover the historical earthquakes in the area, potential impact scenarios, and how to respond in case of a tremor.

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Earthquakes: Shakin' & Risks in Oklahoma

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  1. Earthquakes:There’s a whole lotta shakin’ goin’ on Dr. William D. (Bill) Underwood Chesapeake Energy Chair of Geosciences Ok. School of Science & Math.

  2. Definition An earthquake is a sudden movement of the earth resulting from abrupt release of accumulated strain. Earthquakes are classified according to their depth. Shallow < 60 km Intermediate < 300 km Deep > 300 km (sometimes > 450 km)

  3. Wave Types • Surface waves • Travel at interface • Love waves • Rayleigh waves • Eg ocean waves • Body waves • P-waves • S-waves

  4. Seismograms 3 seismometers used to measure 3 components (x, y, z)

  5. Seismograms

  6. Seismograms

  7. Fault Types • Strike-slip Fault • Lateral motion • Normal Fault • Extension • Reverse Fault • Compression • Thrust Fault • Low-angle reverse fault

  8. Strike-slip Fault Left-lateral Right-lateral

  9. San Andreas Fault (r-l) Miller

  10. Normal Fault

  11. Normal Fault Miller

  12. Reverse Fault

  13. Thrust Fault Maher

  14. Earth Structure Shows P-waves No S-waves through core

  15. The Mid-Continent

  16. Plate Tectonics

  17. Plate Tectonics

  18. World’s Largest Earthquakes

  19. Why do we care?Earthquake Risk

  20. Oklahoma Let’s look closer to home USGS

  21. Oklahoma1977-2001

  22. Magnitude 3.5 or Greater

  23. Oklahoma Jones January 15, 2010

  24. Oklahoma Where the people are

  25. Oklahoma Prague Nov. 5, 2011 M 5.6

  26. Oklahoma Who felt it?

  27. OklahomaNovember 5, 2011 • M 5.6 main shock at 10:52 PM • M 4.7 foreshock at 2:12 AM • Hundreds (thousands?) of aftershocks • Felt over a wide area • No loss of life; few (no?) injuries • Little damage to property • Tremendous excitement (and anxiety)

  28. OklahomaNovember 5, 2011 • Along a known fault (Wilzetta Fault) of a known tectonic feature (Seminole Uplift) • In basement rock, well below oil activity • Injection is at very low pressures • Major faults have been know in recent geologic past (e.g. Meers) • Mid-continent quakes studied < 200 yrs

  29. New Madrid Earthquakes

  30. New Madrid Earthquakes1811-1812

  31. NewMadridFaultZone

  32. Earthquake Motion

  33. What worries us!

  34. Alaska, 1964 Molnia

  35. San Francisco1906 USGS

  36. Sumatra2004-12-24 Landslide Dam USGS

  37. San Francisco1906Even geologists are not immune! Stanford

  38. The Mid-Continent

  39. New Madrid Fault Zone

  40. New Madrid cf. San Francisco Steven Dutch, UWGB Steven Dutch, UWGB

  41. Mercalli Scale • Giuseppe Mercalli, 1884 • Subjective • Measures damage • Modified to modern usage http://en.wikipedia.org/wiki/Mercalli_intensity_scale

  42. Richter Scale • Replaced Mercalli scale • Charles Richter, 1935 • Logarithmic measure of amplitude • Each number 10x previous • Each number 30x previous energy • Measured from instruments • Mostly objective http://en.wikipedia.org/wiki/Richter_magnitude_scale

  43. Mercalli vs Richter(rough comparison)

  44. Probability In the next 50 years (USGS): • 1811 – 1812 magnitude (7.5 – 8.0) • 7 – 10 % • 6.0 or greater • 25 – 40%

  45. In Oklahoma • Expected (mb 6.0): • Mercalli IV to V • Likely (mb 6.6): • Mercalli V to VI • Possible (mb 7.0): • Mercalli VI to VII • Worst-case (mb 7.4): • Mercalli VII to VIII

  46. Expected (6.0) • Intensity IV to V • Felt by all, few or no injuries • Rumbling, thunderous sounds • Described as "strong" • Hung objects swung, small objects shift • Trees, buildings sway • Vibrations like light truck • Plaster cracked

  47. Likely (6.6) • Worse in eastern Oklahoma • Some structural damage • Many run outside; few minor injuries • Trees, bushes, buildings shaken strongly • Objects off shelf; large furniture disturbed • Plaster falls, chimneys cracked • Small church bells ring

  48. Possible (7.0) • Similar to 5.6 in Prague, Nov. 2011 • Reaction important (drop, cover, hold on) • General alarm and fright; injuries probable • Free-standing masonry walls crack • Well-built structures damaged • Tall chimneys broken • Landslides; springs and wells change

  49. Worst case (7.4) • Panic widespread, injuries common • Reaction critical (drop, cover, hold on) • Free-standing walls & external masonry fall • Ordinary, substantial buildings damaged • Waves seen on ground surface • Telephones out of service • Chimneys, factory stacks, monuments fall

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