The Seismogenic Zone Experiment Revisited MARGINS Theoretical Institute The Seismogenic Zone Revisited 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 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
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. - PowerPoint PPT Presentation
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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:
•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
•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?