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?