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Earthquake triggering

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kalei
18 diapositives · 562 Views · Jul 23, 2014

Earthquake triggering. Schuyler Ozbick. The trigger. http://www.eqecat.com/catwatch/virginias-m-5-8-wake-up-call-2011-09-07/. The trigger. Triggered earthquakes can be seen at distances larger than a regional fault network

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  1. Earthquake triggering Schuyler Ozbick

  2. The trigger http://www.eqecat.com/catwatch/virginias-m-5-8-wake-up-call-2011-09-07/

  3. The trigger • Triggered earthquakes can be seen at distances larger than a regional fault network • They can also occur anytime between seconds and decades after the initial earthquake in the sequence

  4. Coulomb Stress Coulomb failure criterion Coulomb stress = shear stress – friction coef. (normal stress-pore fluid P) Fault brought closer to rupturing if shear stress is increased or the effective normal stress is decreased.

  5. Coulomb Stress Changes in Coulomb stress for a vertical strike-slip fault where green represents no change in stress

  6. 1933 Long Beach sequence • 1933 Long Beach. M= 6.4 • 1952 Kern Country California. M= 7.3 • 1971 San Fernando. M= 6.7 • 1994 Northridge. M= 6.7 http://content.cdlib.org/ark:/13030/kt8p3014k2/

  7. 1933 Long Beach sequence • 1933 Long Beach. M= 6.4 • 1952 Kern Country California. M= 7.3 • 1971 San Fernando. M= 6.7 • 1994 Northridge. M= 6.7 http://www.ngdc.noaa.gov/hazardimages/picture/show/109

  8. 1933 Long Beach sequence • 1933 Long Beach. M= 6.4 • 1952 Kern Country California. M= 7.3 • 1971 San Fernando. M= 6.7 • 1994 Northridge. M= 6.7 http://earthquake.usgs.gov/earthquakes/states/events/1971_02_09_photos.php

  9. 1933 Long Beach sequence • 1933 Long Beach. M= 6.4 • 1952 Kern Country California. M= 7.3 • 1971 San Fernando. M= 6.7 • 1994 Northridge. M= 6.7 http://www.flickriver.com/places/United+States/California/Los+Angeles/Northridge/search/

  10. Rainbow Mountain sequence • July 6, 1954 at south end of Rainbow Mountain fault • August 24, 1954 along Rainbow Mountain fault • December 16, 1954 at Fairview peak • December 16, 1954 at Dixie Valley • (4 min 30 sec later) • March 29, 1959 south end of Dixie Valley fault • June 23, 1959 in SW Fairview Peak region

  11. Rainbow Mountain sequence bssa.geoscienceworld.org

  12. Landers-Big Bear sequence • April 1992 Joshua Tree quake of M=6.1 • June 1992 Landers quake of M=7.3 • The Landers quake caused increased seismic activity in ranges from a few meters to beyond 1000 km and triggered many small (M=1-3) events

  13. Landers-Big Bear sequence • Joshua Tree and Landers earthquakes created a new positive Coulomb stress change pattern • The Big Bear earthquake was triggered 3.5 hours after Lander quake. • Big Bear earthquake M=6.3

  14. Landers-Big Bear sequence • After the Big Bear quake, the Coulomb stresses were altered. After Big Bear Before Big Bear

  15. Landers-Big Bear sequence • April 1992 Joshua Tree quake of M=6.1 • June 1992 Landers quake of M=7.3 • June 1992 Big Bear quake of M=6.3 • 3.5 hours after Landers • October 1999 Hector Mine quake of M=7.1

  16. Trigger Happy • Does this earthquake belong to a sequence? • Was it triggered by a previous earthquake? • What does the time delay suggest? • Redistributed stress postseismatically by relaxation, rebound and afterslip? • Does it conform to an increased Coulomb stress? • Disagreements over stress shadows

  17. Trigger Happy Coulomb stress and observed aftershocks of Homestead Valley earthquake of 1979 M=5.5

  18. References • Earthquake triggering by static, dynamic, and postseismic stress transfer, Andrew M. Freed, Annu. Rev. Earth Planet. Sci. 2005 33:335-67 • Earthquake processes in the Rainbow Mountain-Fairview Peak-Dixie Valley, Nevada, region 1954-1959, Diane I. Doser, Journal of Geophysical Research, vol 91 no. B12 pg. 572-586, Nov 1986 • Delayed triggering of 1999 Hector Mine Earthquake by viscoelestic stress transfer, Andrew M. Freed and Jian Lin, Nature vol 411 pg 180-181, May 2001