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Fault Friction and the Transition From Seismic to Aseismic Faulting Chris Marone 1 and Demian M. Saffer 2 1 Penn. State University 2 University of Wyoming. RESIZE. Riser drilling of the seaward limit of the seismogenic zone. Characterizing the incoming material by non-riser drilling.

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slide1

Fault Friction and the Transition From Seismic to Aseismic FaultingChris Marone1 and Demian M. Saffer21Penn. State University2University of Wyoming

RESIZE

Riser drilling of the seaward limit of the seismogenic zone

Characterizing the incoming material by non-riser drilling

Seismogenic zone

Updip limit

Quantify lateral changes In the physical, chemical, and hydrogeologic properties of the fault

Image the seismogenic zone using earthquakes and artificial sources

The Seismogenic Zone Experiment Revisited

SEIZER

MARGINS Theoretical Institute

The Seismogenic Zone Revisited

slide2

Fault Friction and the Transition From Seismic to Aseismic FaultingChris Marone1 and Demian M. Saffer21Penn. State University2University of Wyoming

  • : 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?

Riser drilling of the seaward limit of the seismogenic zone

Characterizing the incoming material by non-riser drilling

Seismogenic zone

Updip limit

Quantify lateral changes in the physical, chemical, and hydrogeologic properties of the fault

Image the seismogenic zone using earthquakes and artificial sources

The Seismogenic Zone Experiment Revisited

slide3

: 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

  • 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)?
slide4

JOI –USSSP, ODP-Japan

K. M. Frye, S. Mazzoni, K. Mair

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.

slide5

SW Nankai Subduction Zone

Parkfield, CA Seismicity

20%

0

0

5

5

Depth Below Sea Floor (km)

10

10

15

Marone & Scholz, 1988

slide6

Aseismic

Seismogenic

Aseismic

The seismogenic zone is defined by the transitions from stable to unstable frictional deformation

  • Key Questions about Fault Zone Friction
  • Stability: Why is deformation stable in some cases and unstable in others?

SW Nankai Subduction Zone

Parkfield, CA Seismicity

20%

0

0

5

5

10

10

15

slide7

N

x

1-D fault zone analog, Stiffness K

K

F

s

f

Slope = -K

B

m

s

f

Force

x

C

Slip

Displacement

  • Brittle Friction Mechanics
  • Stable versus Unstable Shear

Parkfield, CA Seismicity

Aseismic

Seismogenic

zone

Aseismic

slide8

N

x

1-D fault zone analog, Stiffness K

K

F

s

f

  • Brittle Friction Mechanics
  • Stable versus Unstable Shear

Parkfield, CA Seismicity

Aseismic

Seismogenic

zone

Aseismic

Frictional stability is determined by the combination of1) fault zone frictional properties and 2) elastic properties of the surrounding material

Slope = -K

B

m

s

f

Force

x

C

Slip

Displacement

slide9

N

x

1-D fault zone analog, Stiffness KMassless

K

F

s

f

  • Brittle Friction Mechanics
  • Stable versus Unstable Shear

Parkfield, CA Seismicity

aseismic

seismogenic

zone

aseismic

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

Slope = -K

B

m

s

f

Force

x

C

Slip

Displacement

slide10

m

Slip Weakening Friction Law

s

N

x

m

d

K

F

m

(v)

s

d

f

L

Slip

Slope = -K

Quasistatic Stability Criterion

B

m

nms-md

s

Kc =

L

f

K< Kc; Unstable, stick-slip

K > Kc; Stable sliding

Force

x

C

Slip

Displacement

Laboratory Studies

Plausible Mechanisms for Instability

slide11

Rate and State Dependent Friction Law

Vo

V1 = e Vo

Slip rate

N

m

x

K

F

Velocity Weakening

a

b

s

f

b-a >0

Dc

Slip

Slope = -K

Quasistatic Stability Criterion

B

m

s

n (  )

Kc =

Dc

f

K < Kc; Unstable, stick-slip

K > Kc; Stable sliding

Force

x

C

Slip

Displacement

Laboratory Studies

Plausible Mechanisms for Instability

slide12

Stick-Slip Instability Requires Some Form of Weakening: Velocity Weakening, Slip Weakening, Thermal/hydraulic Weakening

Rate and State Dependent Friction Law

m

Slip Weakening Friction Law

s

Vo

V1 = e Vo

Slip rate

m

m

d

Velocity Weakening

a

b

m

(v)

d

L

b-a >0

Dc

Slip

Slip

Stability Criterion

Stability Criterion

nms-md

Kc =

n (  )

Kc =

L

Dc

K < Kc; Unstable, stick-slip

K > Kc; Stable sliding

K < Kc; Unstable, stick-slip

K > Kc; Stable sliding

slide13

n (a  b)

Kc=

Dc

Earthquake Stress Drop

( - )

( + )

Friction Laws and Their Application to Seismic Faulting

Frictional Instability Requires K < 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

a  b

Seismicity

( - )

( + )

seismogenic

zone

slide14

Seismic Moment Released Continuously as the Event Ruptures to the Surface?

Or

Negative Stress Drop in the Upper Region with Resulting Postseismic Afterslip

slide15

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

6 m

No Evidence of Buried Slip

No Shallow Postseismic Afterslip

Wald, 1996

1 m

Wald, 1996

slide16

1979, M6.6

a  b

Earthquake Stress Drop

Seismicity

( - )

( + )

( - )

( + )

seismogenic

zone

Observations:

Shallow Region is Poorly Consolidated Sediment.

Shallow Region:Coseismic Slip Deficit Negative Stress Drop

1 m

Wald, 1996

slide17

Strength of the Subduction Fault Zone

n (a  b)

Kc=

Dc

Fault Strength and Frictional Stability Are Independent

Unstable Behavior Requires That the Local Stiffness, K, be less than Kc

  • Prism material is weak and therefore aseismic?
  • Prism material is aseismic and therefore weak?
slide18

Laboratory Measurements of Frictional Strength (Granular Gouge)

Strong Material, Stable (aseismic) Deformation

Weak Material, Unstable (seismic) Deformation

slide19

n (a  b)

Kc=

Dc

  • Frictional Strength Does Not Dictate Deformation Stability
slide20

What controls the updip seismic limit and rupture extent for subduction zone earthquakes?

  • Hypotheses for velocity weakening
  • 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
laboratory friction experiments
Laboratory Friction Experiments

Displacement

Clay Gouge Layer

  • 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-shale
    • 2) Pure smectite
    • 3) Smectite-quartz mixtures
    • 4) Natural gouge: Nankai, San Gregorio Fault

Transducer

Aligned smectite grains

R

B

1 mm

materials
Materials

Clay Mineralogy

Illite-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
slide23

Results: Stress-Strain Characteristics Failure Envelope Absolute Frictional Strength

results velocity stepping measuring the velocity dependence of friction1
Results: Velocity stepping Measuring the velocity dependence of friction

Frictional Instability Requires K < Kc

n (a  b)

Kc=

Dc

Illite-shale exhibits steady-state velocity strengthening: (a-b) > 0

results velocity stepping measuring the velocity dependence of friction2
Results: Velocity stepping Measuring the velocity dependence of friction

Constitutive Modelling

Rate and State Friction Law

Elastic Interaction, Testing Apparatus

results velocity stepping measuring the velocity dependence of friction3
Results: Velocity stepping Measuring the velocity dependence of friction

Constitutive Modelling

Rate and State Friction Law

Elastic Interaction, Testing Apparatus

comparison of smectite and illite frictional properties

Illite exhibits only velocity strengthening

Comparison of Smectite and Illite Frictional Properties

Smectite exhibits both velocity weakening and velocity strengthening

normal stress dependence of the friction rate parameter for smectite and illite shale
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

(Saffer, Frye, Marone, and Mair, GRL 2001)

(Saffer and Marone, 2002)

slide30

What controls the updip seismic limit and rupture extent for subduction zone earthquakes?

  • Hypotheses for velocity weakening
  • 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
slide32

a

500

m

m

5

0

0

m

m

slide33

a

500

m

m

Fracture and Consolidation (Rate Strengthening Processes)

Adhesive Friction at Contact Junctions (Potentially Rate Weakening)

5

0

0

m

m

1

mm

slide34

Highly Consolidated Gouge

Water Weakening at Adhesive Contact Junctions

Hydrolytic Weakening causes enhanced rate of strengthening, but base level frictional strength is unchanged

Frye and Marone, JGR 2002

slide35

Highly Consolidated Gouge

Frictional Character Dominated by Adhesion at Contact Junctions

Frye and Marone, JGR 2002

slide36

Effect of Consolidation/Lithification on Frictional Properties

Highly Consolidated Granular Gouge Exhibits Velocity Weakening Frictional Behavior

Marone, Raleigh, and Scholz, JGR, 1990

slide37

Seismicity

  • What Causes the Updip Transition from Stable to Unstable Frictional Regimes?
  • 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
summary of laboratory data related to the updip seismic limit

a  b

( - ) ( + )

Seismicity

Field Observations

These data, collected at room temperature, indicate that Illite-rich shales and mudstones are unlikely to host earthquake nucleation

Summary of laboratory data related to the updip seismic limit

Effect of Clay Mineralogy

Smectite

Illite

slide39

a  b

( - ) ( + )

Seismicity

Field Observations

These data, collected at room temperature, are consistent with an upper stability transition and shallow aseismic fault behavior

Quartz Gouge, Effect of Shear Strain and Consolidation

summary of laboratory data related to the updip seismic limit1

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
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
slide41

What is the nature of the fault zone at depth? Materials, fluid conditions, fault structure?

Future Work

  • 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
summary of laboratory and field observations related to the updip stability transition
Summary of laboratory and field observations related to the updip stability transition

(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

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
Key Observations, Outstanding Questions

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?