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The Seismogenic Zone Experiment Revisited
MARGINS Theoretical InstituteThe Seismogenic Zone Revisited
Fault Friction and the Transition From Seismic to Aseismic Faulting
Chris Marone1 and Demian M. Saffer2
1Penn. State University 2University of Wyoming
Seismogenic zone
Updip limit
Characterizing the incoming material by non-riser drilling
Riser drilling of the seaward limit of the seismogenic zone
Quantify lateral changes In the physical, chemical, and hydrogeologic properties of the fault
Image the seismogenic zone using earthquakes and artificial sources
SEIZER RESIZE
The Seismogenic Zone Experiment Revisited : Scientific Objectives(Hyndman, DPG Report, Aug. 1999)
• What controls the earthquake cycle of elastic strain build-up and release?
• What controls the updip and downdip limits of the seismogenic zone in subduction thrusts?
• What controls the updip and downdip limits of great subduction earthquakes?
• Why does fault strength appear to be low?
• What causes tsunami earthquakes?
Fault Friction and the Transition From Seismic to Aseismic Faulting
Chris Marone1 and Demian M. Saffer2
1Penn. State University 2University of Wyoming
Seismogenic zone
Updip limit
Characterizing the incoming material by non-riser drilling
Riser drilling of the seaward limit of the seismogenic zone
Quantify lateral changes in the physical, chemical, and hydrogeologic properties of the fault
Image the seismogenic zone using earthquakes and artificial sources
• Stability: Why is deformation stable in some cases and unstable in others?
• Strength: What controls fault strength?
• Rheology of the fault zone and surrounding materials: Slow earthquakes, postseismic slip, interseismic creep, fault healing, rupture dynamics. What processes, mechanisms, and constitutive law(s)?
: Scientific Objectives(Hyndman, DPG Report, Aug. 1999)
• What controls the earthquake cycle of elastic strain build-up and release?
• What controls the updip and downdip limits of the seismogenic zone in subduction thrusts?
• What controls the updip and downdip limits of great subduction earthquakes?
• Why does fault strength appear to be low?
• What causes tsunami earthquakes?
Key Issues in Fault Mechanics
Saffer, D. M., and C. Marone, Comparison of Smectite and Illite Frictional Properties: Application to the Updip Limit of the Seismogenic Zone Along Subduction Megathrusts, Submitted to EPSL, July 2002.
Saffer, D. M., Frye, K. M., Marone, C, and Mair, K. Laboratory Results Indicating Complex and Potentially Unstable Frictional Behavior of Smectite Clay, GRL, 28, 2297-2300, 2001.
Marone, C., Saffer, D., Frye K. M., and S.Mazzoni, Laboratory results indicating intrinsically stable frictional behavior of illite clay, AGU ABST, F 2001.
Marone, C., Saffer, D., and K. M. Frye, Weak and Potentially Unstable Frictional Behavior of Smectite Clay, AGU ABST, F689, 1999.
K. M. Frye, S. Mazzoni, K. Mair
JOI –USSSP, ODP-Japan
Parkfield, CA Seismicity
SW Nankai Subduction Zone
5
10
15
020%
Dep
th B
elow
Sea
Flo
or (
km)
5
10
0
Marone & Scholz, 1988
SW Nankai Subduction Zone
5
10
5
10
15
00
Parkfield, CA Seismicity
20%
Key Questions about Fault Zone Friction
• Stability: Why is deformation stable in some cases and unstable in others?
The seismogenic zone is defined by the transitions from stable to unstable frictional deformation
Aseismic
Aseismic
Seismogenic
Parkfield, CA Seismicity
Seismogeniczone
Brittle Friction Mechanics
• Stable versus Unstable Shear
Aseismic
Aseismic
N
K Fs
f
xx´1-D fault zone analog, Stiffness K
B
C
For
ce
Displacement
Slope = -K
Slip
s
x´x
f
Parkfield, CA Seismicity
Seismogeniczone
Brittle Friction Mechanics
• Stable versus Unstable Shear
Aseismic
Aseismic
N
K Fs
f
xx´1-D fault zone analog, Stiffness K
Frictional stability is determined by the combination of1) fault zone frictional properties and 2) elastic properties of the surrounding material
B
C
For
ce
Displacement
Slope = -K
Slip
s
x´x
f
Parkfield, CA Seismicity
seismogeniczone
Brittle Friction Mechanics
• Stable versus Unstable Shear
aseismic
aseismic
N
K Fs
f
xx´1-D fault zone analog, Stiffness KMassless
B
C
For
ce
Displacement
Slope = -K
Slip
s
x´x
f
Stability transitions represent changes in frictional properties with depth
Frictional stability is determined by the combination of1) fault zone frictional properties and 2) elastic properties of the surrounding material
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
ns-dL
Kc =
Plausible Mechanisms for Instability
V1 = e Vo
a b
Dc
Slip rate
Rate and State Dependent Friction Law
Velocity Weakening
b-a >0
Slip
Vo
Quasistatic Stability Criterion
K < Kc; Unstable, stick-slip
K > Kc; Stable sliding
n ( )Dc
Kc =
B
C
For
ce
Displacement
Slope = -K
Slip
s
x´x
f
N
K Fs
f
xx´
Plausible Mechanisms for InstabilityLaboratory Studies
Stick-Slip Instability Requires Some Form of Weakening:
Velocity Weakening, Slip Weakening, Thermal/hydraulic Weakening
Slip
s
d
L
Slip Weakening Friction Law
(v)d≠
V1 = e Vo
a b
Dc
Slip rate
Rate and State Dependent Friction Law
Velocity Weakening
b-a >0
Slip
Vo
Stability Criterion
K < Kc; Unstable, stick-slip
K > Kc; Stable sliding
ns-dL
Kc =
Stability Criterion
K < Kc; Unstable, stick-slip
K > Kc; Stable sliding
n ( )Dc
Kc =
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( + )( )
Seismic Moment Released Continuously as the Event Ruptures to the Surface?
Or
Negative Stress Drop in the Upper Region with Resulting Postseismic Afterslip
Observations:
Shallow Region is Poorly Consolidated Sediment.
Shallow Region:Coseismic Slip Deficit Negative Dynamic Stress Drop
Strong Correlation Between Region of Negative Stress Drop and Postseismic Afterslip
1979, M6.7
1 m
Wald, 1996
Wald, 1996
6 m
No Evidence of Buried Slip
No Shallow Postseismic Afterslip
Observations:
Shallow Region is Poorly Consolidated Sediment.
Shallow Region:Coseismic Slip Deficit Negative Stress Drop
1979, M6.6
1 m
Wald, 1996
a b( + )( )
Seismicity
seismogeniczone
Earthquake Stress Drop( + )( )
•Prism material is weak and therefore aseismic?
•Prism material is aseismic and therefore weak?
Strength of the Subduction Fault
Zone
n (a b)
Dc
Kc =
Fault Strength and Frictional Stability Are Independent
Unstable Behavior Requires That the Local Stiffness, K, be less than Kc
Strong Material, Stable (aseismic) Deformation
Weak Material, Unstable (seismic) Deformation
Laboratory Measurements of Frictional Strength (Granular Gouge)
•Frictional Strength Does Not Dictate Deformation Stability
n (a b)
Dc
Kc =
What controls the updip seismic limit and rupture extent for subduction zone earthquakes?
Hypotheses for velocity weakening
1)Clay mineral transformation from smectite to illite structure
•Illite is strong and may exhibit velocity weakening at elevated temperature
•Smectite is weak and exhibits velocity strengthening under some conditions
2) Consolidation/lithification state of fault gouge and accretionary prism materials
•Poorly consolidated granular gouge exhibits velocity strengthening
•Lithified materials and highly localized shear exhibit velocity weakening
Saffer, D. M., and C. Marone, Comparison of Smectite and Illite Frictional Properties: Application to the Updip Limit of the Seismogenic Zone Along Subduction Megathrusts, Submitted to EPSL, July 2002
Marone, C., Saffer, D., Frye K. M., and S.Mazzoni, Laboratory results indicating intrinsically stable frictional behavior of illite clay, AGU ABST, F 2001.
Direct comparison of frictional properties: 1) Illite-shale2) Pure smectite3) Smectite-quartz mixtures4) Natural gouge: Nankai, San Gregorio Fault
Clay Gouge LayerDisplacementTransducer
Aligned smectite grains
1 mm
B R
Laboratory Friction Experiments
Materials
Clay MineralogyIllite-shale: (Rochester shale)
Total clay 68%, quartz 28%, plag 4%
Clay: 87% illite, 13% kaolinite/dickite
Smectite clay: (GSA Resources, Mg-smectite)
100% clay (pure montmorillonite with trace amounts of zeolite and volcanic glass)
(XRD analyses from M. Underwood)
Quartz powder: (US Silica, F-110)
99% SiO2
• Shale crushed, ground, sieved < 500 microns
• Uniform layers produced in a leveling jig
• Initial layer thickness measured on the bench and under applied normal load
QuickTime™ and aPhoto - JPEG decompressor
are needed to see this picture.
Results: Stress-Strain CharacteristicsFailure EnvelopeAbsolute Frictional Strength
Results: Velocity stepping. Measuring the velocity dependence of friction
Results: Velocity stepping Measuring the velocity dependence of friction
Illite-shale exhibits steady-state velocity
strengthening: (a-b) > 0
Frictional Instability
Requires K < Kc
n (a b)
Dc
Kc =
μ θ,v⎛ ⎝
⎞ ⎠ = μ0+aln v
vo
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ +bln voθ
Dc
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
dθdt = 1−vθ
Dc
θss = Dcv
Δμss= a−b( )ln vvo
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
dμdt
= ′ k vlp−v⎛ ⎝
⎞ ⎠
Constitutive ModellingRate and State Friction Law
Elastic Interaction, Testing Apparatus
Results: Velocity stepping Measuring the velocity dependence of friction
100 µmLoad Point Displacement
a=0.0039b=0.0018D
c=56.7 µm
a=0.0057b=0.0026D
c=8.7 µm
a=0.0007b=0.0013D
c=36.4 µm
Illite2-20 µm/s
Smectite10-100 µm/s
Smectite1-10 µm/s
μ θ,v⎛ ⎝
⎞ ⎠ = μ0+aln v
vo
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ +bln voθ
Dc
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
dθdt = 1−vθ
Dc
θss = Dcv
Δμss= a−b( )ln vvo
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
dμdt
= ′ k vlp−v⎛ ⎝
⎞ ⎠
Constitutive ModellingRate and State Friction Law
Elastic Interaction, Testing Apparatus
Results: Velocity stepping Measuring the velocity dependence of friction
Comparison of Smectite and Illite Frictional Properties
Smectite exhibits both velocity weakening and velocity
strengthening
Illite exhibits only velocity strengthening
m506, m514
50 MPa
n=10MPa
100MPa
20 2002 /m s20 20 2
0.25 Shear Strain
Illite Shale
Shear Strain0.5
m414, m422, p036
1 /m s
10
2 /m s 20200
100
1
n=10MPa
n=50MPa
n=100MPa
1 /m s
10
10100
Smectite
Normal stress dependence of the friction rate parameter for smectite and illite-shale
Smectite exhibits velocity weakening at low normal stress and velocity strengthening at higher normal stress (for v < 20 micron/s)
Illite exhibits velocity strengthening for all normal stresses and velocities studied
-0.004
-0.003
-0.002
-0.001
0
0.001
0.002
0.003
0.004
0 20 40 60 80 100 120 140 160
Normal Stress (MPa)
Illite Shale
-0.004
-0.003
-0.002
-0.001
0
0.001
0.002
0.003
0.004
0 20 40 60 80 100 120 140 160
Normal Stress (MPa)
smectite
(Saffer, Frye, Marone, and Mair, GRL 2001)
(Saffer and Marone, 2002)
What controls the updip seismic limit and rupture extent for subduction zone earthquakes?
Hypotheses for velocity weakening
1) Clay mineral transformation from smectite to illite structure
•Illite is strong and may exhibit velocity weakening at elevated temperature
•Smectite is weak and exhibits velocity strengthening under some conditions
2) Consolidation/lithification state of fault gouge and accretionary prism materials
•Poorly consolidated granular gouge exhibits velocity strengthening
•Lithified materials and highly localized shear exhibit velocity weakening
a
500 m
Consolidation, Comminution, and Fabric Development in Granular Gouge
500 m
a
500 m
500 m
1 mm
a
500 m
Fracture and Consolidation (Rate Strengthening Processes)
Adhesive Friction at Contact Junctions (Potentially Rate Weakening)
Frye and Marone, JGR 2002
Water Weakening at Adhesive Contact Junctions
Highly Consolidated Gouge
Hydrolytic Weakening causes enhanced rate of strengthening, but base level frictional strength is unchanged
Frictional Character Dominated by Adhesion at Contact Junctions
Highly Consolidated Gouge
Frye and Marone, JGR 2002
Marone, Raleigh, and Scholz, JGR, 1990
Effect of Consolidation/Lithification on Frictional Properties
Highly Consolidated Granular Gouge Exhibits Velocity Weakening Frictional Behavior
0
0.001
0.002
0.003
0.004
0.005
0.006
50 100 150 200
( )Normal Stress MPa
,4- Quartz gouge mm thick, Rough grooved steel surfaces
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
Grooved120 Grit320 Grit
0 1 2 3 4Gouge Layer Thickness (mm)
Quartz gouge, '=100MPa Westerly granite surfaces
What Causes the Updip Transition from Stable to Unstable Frictional Regimes?
1) Clay mineral transformation from smectite to illite structure
•Illite is strong and may exhibit velocity weakening at elevated temperature
•Smectite is weak and exhibits velocity strengthening under some conditions
2) Consolidation/lithification state of fault gouge and accretionary prism materials
•Poorly consolidated granular gouge exhibits velocity strengthening
•Lithified materials and highly localized shear exhibit velocity weakening
Seismicity
a b( ) ( + ) Seismicity
Field ObservationsEffect of Clay Mineralogy
Smectite
Illite
Summary of laboratory data related to the updip seismic limit
These data, collected at room temperature, indicate that Illite-rich shales and mudstones are
unlikely to host earthquake nucleation
Quartz Gouge, Effect of Shear Strain and Consolidation
0
5
10
15
(a-b)
Qtz gouge
n=25 70to MPa
-0.015 0.015-0.005 0.005
,1999Mair and Marone
a b( ) ( + ) Seismicity
Field Observations
These data, collected at room temperature, are consistent with an upper stability transition and shallow aseismic fault behavior
Summary of laboratory data related to the updip seismic limit
•Fluids: We performed experiments dry and found dilatant porosity changes. Pore pressure and the presence of fluids in our experiments would tend to increase (a-b) and further stabilize frictional shear.
•Fault Stability: At present our data imply that Illite-rich shales and mudstones are unlikely to host earthquake nucleation
We have compared the frictional behavior of smectite-clay and illite-shale under identical conditions.Illite
Intrinsically-stable velocity strengthening frictional behavior for all normal stresses and velocities studied
Smectite:for v < 20 mm/s: Velocity weakening at low normal stress and velocity strengthening for normal stresses above 50 MPa
for v > 20 mm/s: Velocity velocity strengthening
• Extend experiments to higher temperature
• Include controlled pore-pressure
• Investigate the effects of gouge consolidation
• Study natural samples
• Study the smectite-illite transformation in-situ
What is the nature of the fault zone at depth? Materials, fluid conditions, fault structure?
Future Work
Seism
icity,
%
H
( - )a b
Velocity
Strengthening
Velocity
Weakening
UnconsolidatedFault Gouge
Fault Zone FrictionRate Dependence
h
LithifiedFault Gouge
us
ud
CoseismicSlip Distribution
Dynamic StressDropΔ
(-) (+)(-) (+)
(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
Summary of laboratory and field observations related to the updip stability transition
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
Seism
icity,
%
H
( - )a b
Velocity
Strengthening
Velocity
Weakening
UnconsolidatedFault Gouge
Fault Zone FrictionRate Dependence
h
LithifiedFault Gouge
us
ud
CoseismicSlip Distribution
Dynamic StressDropΔ
(-) (+)(-) (+)
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?