The Spectrum of Fault Slip BehaviorsThe Spectrum of Fault Slip Behaviors18 Sep. 2013, C. Marone, Geosc500

• Mechanics of Earthquakes and FaultingMechanics of Earthquakes and Faulting

• Stick-slip dynamics and Instability. Introduction to "normal earthquakes”

• Fault models and the spectral signature of (normal) earthquakes

• Aseismic creep and creep events, slow tectonic slip

• Slow earthquakes, Low frequency earthquakes

• Non-volcanic tremor: tectonic fault tremor

Stick Slip vs. Stable Sliding

Earthquakes and aseismic creep events

THE SPECTRUM OF FAULT SLIP BEHAVIORS

Stick Slip vs. Stable Sliding

Incomplete

Continuous & Slow: cm/yr

Aseismic: fault creep

Discrete & Fast: m/s

Seismic: earthquake

The Anime Sante church after the MW = 6.3 L’Aquila earthquake (2009)The Anime Sante church (1713) after the MW = 6.3 L’Aquila earthquake (2009)

10 seconds

Borehole casing deformation along the San Andreas

3 k

m

15 m

2 years

THE SPECTRUM OF FAULT SLIP BEHAVIORS

After Collettini, 2010

Hollister, CA

http://earthquake.usgs.gov/research/creep/index.php

• Aseismic slip• Creep events• Strain transients• Slow earthquakes• Episodic tremor • Silent earthquakes• Afterslip and transient

postseismic deformation• Slow precursors to “normal”

earthquakes• Earthquakes with a distinct

nucleation phase• Normal (fast) earthquakes• Earthquakes with supersonic

rupture velocity

Seismic slip and aseismic faulting are end members of a continuous spectrum of behaviors

A single fault, and perhaps even a single fault patch, may exhibit both seismic and aseismic slip

Fault Mechanics & Earthquake Physics

• Aseismic slip• Creep events• Strain transients• Slow earthquakes• Episodic tremor • Silent earthquakes• Afterslip and transient

postseismic deformation• Slow precursors to “normal”

earthquakes• Earthquakes with a distinct

nucleation phase• Normal (fast) earthquakes• Earthquakes with supersonic

rupture velocity

•What causes this range of behaviors?

One (earthquake) mechanism, or several?

•How best do we describe the rheology of brittle fault zones?

• Brittle fault zones exhibit complex rheologic behavior• Need to monitor crustal deformation at a wide range of spatio-

temporal scales

Plate Tectonics 1. Plates are rigid2. 3 types of plate boundaries: divergent, convergent, transform3. Plates are created at divergent, destroyed at convergent plate boundaries.4. Transform faults form small circles to poles of rotation.

Isacks, B., J. Oliver, and L. Sykes, Seismology and the New Global Tectonics J. Geophys. Res., 73, 5855-5899, 1968.

What is the strength of a What is the strength of a major, plate boundary major, plate boundary tectonic fault?tectonic fault?

Average frictional strength Average frictional strength at seismogenic depth (10-15 at seismogenic depth (10-15 km)km)Is it 100-200 MPa, µ ≈ 0.6, Is it 100-200 MPa, µ ≈ 0.6, or 10-20 MPa, µ ≤ 0.3 ? or 10-20 MPa, µ ≤ 0.3 ?

SAFOD The San Andreas Fault Observatory at Depth

NSF EarthScope, MREFCSAFOD The San Andreas Fault Observatory at Depth $25M

Earthquakes and Fault Mechanics

February 2010 Mw 8.8 Maule EQ. Lange et al., EPSL 2012

M7.3 1992 Landers Earthquake, Wald, 1996

6 m

Dynamic Rupture Propagation Velocities are several km/s, as expected for elastic wave propagation

Reid’s Hypothesis of Elastic Rebound (1910)

N

K Fs

f

xx´

Brittle Friction Mechanics, Stick-slip

• Stick-slip (unstable) versus stable shear

slip duration = rise time

Stick-slip dynamics

Slip

s

d

sd

Static-Dynamic Friction

Laboratory Studies

Slip

s

d

L

Slip Weakening Friction Law

(v)d≠

N

K Fs

f

xx´

B

C

For

ce

Displacement

Slope = -K

Slip

s

x´x

f

Quasistatic Stability Criterion

K< Kc; Unstable, stick-slip

K > Kc; Stable sliding

Plausible Mechanisms for Instability

Frictional Instability Requires K < Kcn (a b)

Dc

Kc =

(a-b) > 0 Always Stable, No Earthquake Nucleation, Dynamic Rupture Arrested

(a-b) < 0 Conditionally Unstable, Earthquakes May Nucleate if K < Kc, Dynamic Rupture Will Propagate Uninhibited

Friction Laws and Their Application to Seismic Faulting

a b( + )( )

Seismicity

SeismogenicZone

Earthquake Stress Drop( + )( )

Key Observations, Outstanding Questions

• Aseismic slip• Slow earthquakes, Creep events,

Tsunamogenic earthquakes• Slow precursors to “normal” earthquakes• Earthquakes with a distinct nucleation phase• Afterslip and transient postseismic

deformation• Normal (fast) earthquakes

Seismic and Aseismic Faulting: End Members of a Continuous Spectrum of Behaviors

What causes this range of behaviors? One (earthquake) mechanism, or several?

How best do we describe the rheology of brittle fault zones?

Marone, 1998

2. THE SPECTRUM OF FAULT SLIP BEHAVIORS

Stick Slip vs. Stable Sliding

Tremor, Slow Slip, Swarms, Low frequency earthquakes, Creep, Geodetic transients, Dynamic triggering, Postseismic slip

Incomplete

Episodic Tremor and Slip

Rogers and Dragert, 2003

Cascadia

Obara et al., 2004

Southwest Japan

After D. Shelly (NSF EarthScope mtg.2008)

Earthquake warning

A Weeklong Tremor and Slip Episode

• April 15-21, 2006• Moment Magnitude=6.0

(April 17-20)• Average slip = 1.2 cm

Sekine and Obara, 2006

Sekin

e a

nd

Obara

, 20

06

After D. Shelly (NSF EarthScope mtg.2008)

Family of slow, shear-slip events

Ide et al., Nature, 2007

VLFEs

LFEs

SSEs

Megathrust

After D. Shelly (NSF EarthScope mtg.2008)

Tectonic Tremor is modulated by Love wave shear stress (Denali) and Tides

* * **Rubinstein et al., Nature, 2007

Rubinstein et al., Science, 2008

Faults exhibit a wide spectrum of slip behaviors

EarthScope Facility:

• Fault Mechanics

• Frictional Rheology

• Earthquake Physics

• Earthquake Hazzard

• 5 MPa normal stress

• background shearing rate of 5 µm/sec

apparatusaccelerometer wave

source

Effects of acoustic waves on stick–slip frictionJohnson, Savage, Knuth, Gomberg & Marone, Nature, 2008.

Laboratory Evidence for Complex Friction Behavior

Stress drop in slow, quasi-stick-slip events scales with acoustic vibration amplitude

Johnson, P., Carpenter, B. M., Knuth, M., Kaproth, B. M., Le Bas, P.-Y., Daub, E. G.; and C. Marone, JGR, 2012

True Triaxial Stress State, Direct Shear, Pore fluid

Angular quartz particles (100-150 µm), 3 mm thick, 25 MPa normal stress. Marone, 1998

Steady state friction & the rate of healing vary with sliding velocity

Frictional Healing

Fault surface

Load point

Fault surface

Load point

Stress relaxation via creep

Sliding Friction

Coulomb, 1785

c

Rate and State Friction

Dieterich, Ruina, Rice

Dieterich State Evolution

V=2 V=1 m/s

Empirical laws, based on laboratory friction data

Velocity weakening frictional behavior in granular fault gouge

(a-b)

Thermally-activated process

Frictional Instability Requires K < Kcn (a b)

Dc

Kc =

(a-b) > 0 Always Stable, No Earthquake Nucleation, Dynamic Rupture Arrested

Friction Laws and Their Application to Seismic Faulting

a b( + )( )

Seismicity

SeismogenicZone

(a-b) < 0 Conditionally Unstable, Earthquakes May Nucleate if K < Kc, Dynamic Rupture Will Propagate Uninhibited

Earthquake Stress Drop( + )( )

Dep

th