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. Courtesy of Anthony 2004 5 MPa normal stress Tectonics stress: background shear loading rate of 5 µm/s Oscillating stress: V lp = V 0 + Asin(  t) Fault zone materials: granite blocks, glass beads Laboratory Setup 0.5 MPa Time Shear Stress Stick-slip Failure

5. Transient Trigger t2t2 t1t1 Savage and Marone, 2008 Shear Stress (MPa) Load Point Velocity (µm/s)

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

7. Triggering Intensity = Normalized Seismicity Rate Change t2t2 t1t1 Seismicity Rate: =1/t Normalized Seismicity Rate Change: n  ( 2 - 1 )/ 1 Felzer and Brodsky, 2005

8. Changes in Lab Seismicity Rate Triggering Threshold

9. Changes in Lab Seismicity Rate

10. Remote Triggering on the Nicoya Peninsula, Costa Rica Seismic data courtesy of S. Schwartz 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 Remote Earthquakes

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

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

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

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