The Spectrum of Fault Slip Behaviors 18 Sep. 2013, C. Marone, Geosc500 Mechanics of Earthquakes and...
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Transcript of The Spectrum of Fault Slip Behaviors 18 Sep. 2013, C. Marone, Geosc500 Mechanics of Earthquakes and...
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
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
• 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
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
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)
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
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
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