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

Slow SlipSlow Slip

‘‘slow slip event’slow slip event’

long-termlong-term motionmotion

inter-slipinter-slipmotionmotion

4.4.

Dragert et al. (2004)

THE PHENOMENA THE PHENOMENA Tremor Tremor

EarthquakeEarthquake

seconds

24 hours (9/11/2005)

Tremor Envelopes

Hallmarks of Tremor (& other Slow Phenomena)

• Duration ~ Moment0.85

• Amplitude doesn’t grow with moment, & is limited.

Earthquakes:

• Duration ~ Moment1/3

• Amplitude grows with moment.

Slow Slip, Tremor:

Houston, 2008

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

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.

Plate-scale Observations

The basic model:

Subduction Zones

The basic model:

Subduction Zones

Dilatant Stabilization vs Thermal Pressurization: Control on Slow vs Fast Fault Slip? Segall and Bradley, SCEC Annual Mtg., 2009

Transitional?

The basic model:

Transform Faults

Transitional?

The basic model:

Transform Faults

On the Mechanics of Earthquake Afterslip, Marone et al., JGR, 1991A Two-layer Model for Slip on the Superstition Hills Fault, California, Bilham and Behr, BSSA, 1992

The basic model:

Landslides

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

Clues from

a shallow creeping segment of the San Andreas fault,

an earthquake swarm in eastern Washington,

a translational landslide in southwest Colorado.

The ‘Wooded Island’ Swarm (Hanford, WA)

from W. Thelen, Univ. of Washington

InSAR-detected uplift of several cm!

from C. Wicks, USGS

Earthquake Rate & Uplift

Cascadia Tremor Rate, 2008 ETS Event

Earthquake Rate & Uplift

Cascadia Tremor Rate, 2008 ETS Event

Earthquake Rate & Uplift

Swarms & tremor share

irregular energy release,

limited max. amplitudes,

temporal migration,

seismic m0 << geodetic m0.

(Propagation paths differ.)

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

Shallow Slow Slip at San Juan Bautista - No tremor?

NO clear tremor for 4 slow slip events, but increased earthquake rates clearly correlate.

Shallow Slow Slip at San Juan Bautista - No tremor?

Slow slip and seismicity not co-located.

seismic m0 << geodetic m0

The Slumgullion landslide - a Natural Laboratory.

Basal Slip

Transform-fault Slip

Seismic Network Installation

Robotic Displacement Meter

Slumgullion Instrumentation

Ide et al. (2007) propose 2 distinct slip modes, with differing m0 vs. duration scaling.

Swarms scale like slow (or slower) slip events.

Roland & McGuire, GJI, 2009

This study.

Beroza & Jordan, JGR, 1990

Matsuzawa et al., JGR, 2009

Harrington & Brodsky, GRL, 2009

Is there a gap between slow & ‘regular’ seismic slip?

?

Savage et al., JGR, 2007

Aftershocks scale like slow (or slower) slip events.

Savage et al., JGR, 2007

The geodetic m0 >> seismic m0.

Ekstrom et al., Science, 2003

Nettles & Ekstrom, BSSA, 2004

What about landslides & other slip events?

InferenceTremor, 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?

THANK YOU!

Questions?