Sleuthing Slow Slip Phenomena

1. Sleuthing Slow Slip Phenomena Joan Gomberg, Bill Schulz, Paul Bodin, Aaron Wech, Roland Burgmann, Jason Kean, Patricia MacQueen, Katie Foster, Bob Nadeau, Chuck Wicks, Wes Thelen (from USGS, University of Washington, University of California Berkeley)

2. ‘slow slip event’ long-term motion 4. Slow Slip inter-slip motion Dragert et al. (2004)

3. THE PHENOMENA Tremor Earthquake seconds

4. Tremor Envelopes 24 hours (9/11/2005)

5. Hallmarks of Tremor (& other Slow Phenomena) Earthquakes: • Duration ~ Moment0.85 • Amplitude doesn’t grow with moment, & is limited. • Duration ~ Moment1/3 • Amplitude grows with moment. Slow Slip, Tremor: Houston, 2008

6. Slow seismic signals depleted in high-frequencies (relative to earthquakes)

7. Premise: To identify key controls & narrow the range of viable models requires a broad search for clues. Conclusion: Slow slip is nothing new, and tremor isn’t so special either.

8. Plate-scale Observations

9. The basic model: Subduction Zones

10. The basic model: Subduction Zones Dilatant Stabilization vs Thermal Pressurization: Control on Slow vs Fast Fault Slip?Segall and Bradley, SCEC Annual Mtg., 2009

11. The basic model: Transform Faults Transitional?

12. The basic model: Transform Faults Transitional? On the Mechanics of Earthquake Afterslip, Marone et al., JGR, 1991 A Two-layer Model for Slip on the Superstition Hills Fault, California, Bilham and Behr, BSSA, 1992

13. The basic model: Landslides Evidence of Dilatant Strengthening as a Mechanism Controlling Landslide Velocity, Schulz et al., AGU Annual Mtg., 2008 The Transition from Stable Creep to Stick-slip Instability in Gravity-driven Landslide Motion, Iverson and Schaeffer, AGU Annual Mtg, 2009

14. Clues from a shallow creeping segment of the San Andreas fault, an earthquake swarm in eastern Washington, a translational landslide in southwest Colorado.

15. The ‘Wooded Island’ Swarm (Hanford, WA) from W. Thelen, Univ. of Washington

16. InSAR-detected uplift of several cm! from C. Wicks, USGS

17. Earthquake Rate & Uplift

18. Earthquake Rate & Uplift Cascadia Tremor Rate, 2008 ETS Event

19. Earthquake Rate & Uplift Cascadia Tremor Rate, 2008 ETS Event Swarms & tremor share irregular energy release, limited max. amplitudes, temporal migration, seismic m0 << geodetic m0. (Propagation paths differ.)

20. Shallow Slow Slip at San Juan Bautista - Is there tremor? “shallow creep is controlled by sediment depth, perhaps due to high pore pressures…”, Wei et al., JGR 2009

21. Shallow Slow Slip at San Juan Bautista - No tremor? NO clear tremor for 4 slow slip events, but increased earthquake rates clearly correlate.

22. Shallow Slow Slip at San Juan Bautista - No tremor? Slow slip and seismicity not co-located. seismic m0 << geodetic m0

23. The Slumgullion landslide - a Natural Laboratory. Basal Slip Transform-fault Slip

24. Seismic Network Installation Robotic Displacement Meter

25. Slumgullion Instrumentation

29. Ide et al. (2007) propose 2 distinct slip modes, with differing m0vs. duration scaling.

30. Swarms scale like slow (or slower) slip events. Roland & McGuire, GJI, 2009 This study.

31. Is there a gap between slow & ‘regular’ seismic slip? ? Beroza & Jordan, JGR, 1990 Matsuzawa et al., JGR, 2009 Harrington & Brodsky, GRL, 2009

32. Aftershocks scale like slow (or slower) slip events. Savage et al., JGR, 2007

33. The geodetic m0 >> seismic m0. Savage et al., JGR, 2007

34. What about landslides & other slip events? Ekstrom et al., Science, 2003 Nettles & Ekstrom, BSSA, 2004

35. Inference • Tremor, swarms, & aftershocks all represent relaxation of residual slip & are driven by slow slip. • These responses differ in the degree to which ruptures are quenched (size limited) & their spectral contents. • Variations in quenching may be due to • the slow slip, • pore pressure changes, • &/or environment*. • Could spectral differences be due to propagation?

36. THANK YOU! Questions?