1. 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) Sleuthing Slow Slip Phenomena

2. Slow Slip ‘slow slip event’ long-term motion motioninter-slipmotion4. Dragert et al. (2004)

3. THE PHENOMENA THE PHENOMENA Tremor TremorEarthquake seconds

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

5. Hallmarks of Tremor (& other Slow Phenomena) Duration ~ Moment 0.85 Amplitude doesn’t grow with moment, & is limited. Earthquakes: Duration ~ Moment 1/3 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. Dilatant Stabilization vs Thermal Pressurization: Control on Slow vs Fast Fault Slip? Segall and Bradley, SCEC Annual Mtg., 2009

11. Transitional? The basic model: Transform Faults

12. Transitional? The basic model: Transform Faults 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. Cascadia Tremor Rate, 2008 ETS Event Earthquake Rate & Uplift

19. Cascadia Tremor Rate, 2008 ETS Event Earthquake Rate & Uplift Swarms & tremor share irregular energy release, limited max. amplitudes, temporal migration, seismic m 0 << geodetic m 0. (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 m 0 << geodetic m 0

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 m 0 vs. duration scaling.

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

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

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

33. Savage et al., JGR, 2007 The geodetic m 0 >> seismic m 0.

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

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?