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EQ Mechanisms Bay Area Faults EQ Magnitude

EQ Mechanisms Bay Area Faults EQ Magnitude. Earthquake Waves. Frequency. 0.1 Hz to 10 Hz (outside human sensory range). Types of Motion. P waves. velocity. S waves. amplitude. surface waves. What is an Earthquake?. A release of energy stored on a fault. What is a fault?.

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EQ Mechanisms Bay Area Faults EQ Magnitude

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  1. EQ MechanismsBay Area FaultsEQ Magnitude

  2. Earthquake Waves Frequency 0.1 Hz to 10 Hz (outside human sensory range) Types of Motion P waves velocity S waves amplitude surface waves

  3. What is an Earthquake? A release of energy stored on a fault What is a fault? A roughly planar surface where rock has broken and separated Why does an earthquake happen? Built-up energy exceeds frictional resistance on the fault

  4. How does “slip” on the fault happen? Elastic rebound Remember the fence • Rocks accumulate stress as two sides of fault move past each other • Elastic strainis built up in rocks as they deform • Stress = force per unit area • Strain = change in shape of rocks due to stresses • Elastic = returns to original shape when released

  5. Fault Geometry (focus) from: http://www.seismo.unr.edu/ep/nvguide/sbg1.html and http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/faults.html

  6. Normal Fault Reverse Fault Strike-slip Fault Thrust Fault Faults Types from: http://www.tinynet.com/faults.html

  7. Find faults? How do geologists....

  8. How do geologists find faults?

  9. Find faults? How do geologists.... The Hayward Fault is open for you to walk down into until October 31, 2006 See: http://1906centennial.org/activities/calendar/?id=135

  10. How do geologists....determine whether a fault is active? State of California (A-P act): An active fault is one that has slipped once in the last 11,000 years (or 2 or more times in the last 700,000 years) Consider this schematic roadcut/seacliff: fault #1 fault #2 fault #3

  11. Spaced-based measurements (VLBI* and GPS) show that PAC-NA motion in CA is ~50 mm/yr. *Very Long Baseline Interferometry

  12. Earthquakes in California & Nevada, 1970-2003

  13. Some of the Bay Area’s active faults

  14. The San Andreas is NOT “the PAC-NA plate boundary.” Red arrow: predicted motion: 50 mm/yr Blue arrows: subsets of the motion that “add up” to the predicted motion. This diagram applies at the latitude of Bakersfield or San Luis Obispo.

  15. 4-8? About 36 mm/yr happens on the San Andreas in central CA, but northwest of Hollister, things are a LOT messier. 9 23 >6 ~Stockton 9 17-23 2-5? Farallon Islands The ~36 mm/yr must be divided up on many faults. Geologists study each to determine individual rates. 6 9 17 7-10? 1-3? Let’s add up the slip on faults along four paths to see whether we’ve found the ~36 mm/yr. 15 17? 23?

  16. from: http://pubs.usgs.gov/fs/2003/fs039-03/fs039-03.pdf

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