Download Spectrum of Fault Slip Behavior

The Spectrum of Fault Slip Behaviors
18 Sep. 2013, C. Marone, Geosc500
• Mechanics 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
Earthquakes and aseismic creep events
Stick Slip
vs.
Stable Sliding
THE SPECTRUM OF FAULT SLIP BEHAVIORS
Stick Slip
vs.
Stable Sliding
Incomplete
THE SPECTRUM OF FAULT SLIP BEHAVIORS
Discrete & Fast: m/s
Continuous & Slow: cm/yr
Seismic: earthquake
Aseismic: fault creep
3 km
10 seconds
Borehole casing deformation
along the San Andreas
The Anime Sante church (1713)
after the MW = 6.3 L’Aquila earthquake (2009)
After Collettini, 2010
2 years
15 m
Hollister, CA
http://earthquake.usgs.gov/research/creep/index.php
Fault Mechanics & Earthquake Physics
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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
• Brittle fault zones exhibit complex rheologic behavior
• Need to monitor crustal deformation at a wide range of spatiotemporal scales
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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?
Plate Tectonics
1.
2.
3.
4.
Plates are rigid
3 types of plate boundaries: divergent, convergent, transform
Plates are created at divergent, destroyed at convergent plate boundaries.
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
major, plate boundary tectonic
fault?
Average frictional strength at
seismogenic depth (10-15 km)
Is it 100-200 MPa, µ ≈ 0.6,
or 10-20 MPa, µ ≤ 0.3 ?
SAFOD The San Andreas Fault Observatory at Depth
NSF EarthScope, MREFC
SAFOD The San Andreas Fault
Observatory at Depth $25M
Earthquakes and Fault Mechanics
Dynamic Rupture
Propagation
Velocities are
several km/s, as
expected for
elastic wave
propagation
February 2010 Mw 8.8 Maule EQ.
Lange et al., EPSL 2012
6m
M7.3 1992 Landers Earthquake, Wald, 1996
Stage 1
Stage 2
Reid’s Hypothesis of
Elastic Rebound (1910)
Stage 1
Stage 2
Stage 1
Stage 2
Brittle Friction Mechanics, Stick-slip
• Stick-slip (unstable) versus stable shear
Stick-slip dynamics
N
x´
x
K
Fs
f
Static-Dynamic Friction
s

d
sd
Slip
slip duration = rise time
Laboratory Studies
Plausible Mechanisms for Instability
Slip Weakening Friction Law
N
x´
s
x
K
Fs

d ≠
f

(v)
d
L
Slip
Slope = -K
Quasistatic Stability Criterion
 s
B
Force
f
K< Kc; Unstable, stick-slip
x
x´
Slip
Displacement
C
K > Kc; Stable sliding
Friction Laws and Their Application to Seismic Faulting
Frictional Instability Requires K < Kc
Kc = n (a
b)
Dc
(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
()
a
b
(+)
Seismicity
Earthquake Stress Drop
()
Seismogenic
Zone
(+)
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
s
s
(-)
us
Velocity
Strengthening
h
Coseismic
Slip Distribution
Lithified
Fault Gouge
Velocity
Weakening
H
(+)
ic
i
(a-b)
(-) (+)
Dynamic
Ds Stress
Drop
Se
ism
Fault Zone Friction
Rate Dependence
ty,
%
Unconsolidated
Fault Gouge
ud
Marone, 1998
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?
2. THE SPECTRUM OF FAULT SLIP BEHAVIORS
Tremor, Slow Slip, Swarms, Low frequency
earthquakes, Creep, Geodetic transients,
Dynamic triggering, Postseismic slip
Stick Slip
vs.
Stable Sliding
Incomplete
Rogers and Dragert, 2003
Cascadia
Episodic
Tremor
and Slip
Southwest Japan
Obara et al., 2004
After D. Shelly (NSF EarthScope mtg.2008)
Earthquake warning
Sekine and Obara, 2006
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
After D. Shelly (NSF EarthScope mtg.2008)
Family of slow, shear-slip events
LFEs
VLFEs
SSEs
Megathrust
Ide et al.,
Nature, 2007
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
Laboratory Evidence for Complex Friction Behavior
Effects of acoustic waves on stick–slip friction
Johnson, Savage, Knuth, Gomberg & Marone, Nature, 2008.
apparatus
• 5 MPa normal
stress
• background
shearing rate of
5 µm/sec
wave
source
accelerometer
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
Frictional Healing
Load
point
Fault
surface
Steady state
friction &
the rate of
healing vary with
sliding velocity
Angular quartz particles (100-150 µm), 3 mm thick,
25 MPa normal stress. Marone, 1998
Load
point
Fault
surface
Stress
relaxation
via creep
Sliding Friction


c
Coulomb, 1785
Empirical laws, based on laboratory friction data
Rate and State Friction
V=2
Dieterich State Evolution
Coefficient of Friction
Dieterich, Ruina, Rice
V=1 m/s
Data
Ruina law
Dieterich law
0.640
(a-b) 
Velocity weakening
frictional behavior in
granular fault gouge
0.635
25.3
25.4
Displacement (mm)
Thermally-activated process
Friction Laws and Their Application to Seismic Faulting
Frictional Instability Requires K < Kc
Kc =
n (a
Db)
c
(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
Depth
()
a
b
(+)
Seismicity
Earthquake Stress Drop
()
Seismogenic
Zone
(+)