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Remote Earthquake Triggering: (Fault) Failure is Not Always an Option

Remote Earthquake Triggering: (Fault) Failure is Not Always an Option. Heather Savage and Emily Brodsky UC Santa Cruz. Remote Triggering From Denali Earthquake. Gomberg et al., 2004. Triggered Seismicity from the Denali Earthquake. 2002 Denali, Alaska Mw 7.9 Earthquake.

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Remote Earthquake Triggering: (Fault) Failure is Not Always an Option

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  1. Remote Earthquake Triggering: (Fault) Failure is Not Always an Option Heather Savage and Emily Brodsky UC Santa Cruz

  2. Remote Triggering From Denali Earthquake Gomberg et al., 2004

  3. Triggered Seismicity from the Denali Earthquake 2002 Denali, Alaska Mw 7.9 Earthquake Husker and Brodsky, 2004

  4. Laboratory Setup • 5 MPa normal stress • Tectonics stress: • background shear loading • rate of 5 µm/s • Oscillating stress: • Vlp = V0 + Asin(t) • Fault zone materials: granite • blocks, glass beads Stick-slip Failure Courtesy of Anthony 2004 Shear Stress 0.5 MPa Time

  5. Trigger Shear Stress (MPa) t1 t2 Transient Load Point Velocity (µm/s) Savage and Marone, 2008

  6. Shear Stress (MPa) Time (s) No gouge Amplitude Dependence Inter-event Time (s) Increasing gouge thickness Amplitude (µm/s) Savage and Marone, 2008

  7. Triggering Intensity = Normalized Seismicity Rate Change t1 t2 Seismicity Rate: =1/t Normalized Seismicity Rate Change: n (2- 1)/ 1 Felzer and Brodsky, 2005

  8. Changes in Lab Seismicity Rate TriggeringThreshold

  9. Changes in Lab Seismicity Rate

  10. Remote Triggering on the Nicoya Peninsula, Costa Rica Remote Earthquakes Solomon Islands - 04/01/07 Peru - 08/15/07 So. Sumatra - 09/12/07 Indonesia - 09/12/07 Fiji - 12/09/07 Sichuan - 05/12/08 New Zealand - 07/15/09 Seismic data courtesy of S. Schwartz

  11. New Zealand 2009, recorded in Costa Rica Seismic data courtesy of S. Schwartz

  12. Costa Rica Solomon Islands 04/01/07 So. Sumatra 09/12/07 Fiji 12/09/07 Sichuan 04/12/08 Peru 08/15/2007 New Zealand 0715/09 Indonesia 09/12/2007

  13. Remote Triggering in the Western US, Transportable Array Remote Earthquakes New Zealand - 07/15/09 Samoa - 09/29/09 Sumatra - 09/30/09

  14. Samoa 2009, recorded in Eastern Wyoming

  15. Sumatra 09/30/09 New Zealand 07/15/09 Costa Rica and E. Wyoming

  16. Conclusions • Triggered seismicity is a function of strain amplitude (bigger earthquakes trigger more earthquakes) but is also dependent on interseismic history • Large earthquakes that closely follow previous large events are very inefficient at triggering additional seismicity • Experiments suggest that fault zone properties determine the relationship between triggering intensity and strain amplitude • Preliminary seismic observations suggest subduction zones spend more time close to critical failure than old crustal faults

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