Ge 277-

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Ge 277- From rock mechanics to seismotectonics

• Objective of seminar
• Review major results form rock mechanics
  laboratory experiments and discuss how these
  results shed light on seismotectonics processes.

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Motivation

• A major goal in seismotectonics is to develop
  some mechanical model of fault behavior that
  would reproduce the various phase over the
  seismic cycle (co-seismic rupture, afterslip
  and postseismic relaxation, interseismic stress
  and strain build up, preseismic deformation and
  nucleation).

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Organization

• During each seminar students will present
  selected papers (20 minutes per presentations).
• Pleas pick your choice within a week from now.
• Interact with me ahead of the presentation.
• The selected papers will be posted on JPA webs
  page.
• Students are required to have read, ahead of
  time, the papers to be presented

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Experimental Rock mechanics
(Dieterich, Tullis, Marone, Blanpied,
Lockner,Kholstedt, Byerlee, )

• Frictional sliding can be stable or unstable,
  depending on the lithology, water content,
  confining pressure and temperature.
• For quartz and granite the transition occurs
  around 300C, probably in relation to thermally
  activated ductility.
• Some clay minerals and serpentinite undergo
  stable sliding at low temperature but (may)
  undergo unstable sliding at higher temperature.
• Olivine? There are no data on frictional
  properties of olivine. Far less ductile than
  quartzofeldspathic rocks (the transition to fully
  plastic flow occurs at a temperature of the order
  of 700C). Presumably the transition from
  unstable to stable sliding occurs at a
  temperature much higher than for Quartz, hence
  above 300C.
• Fluid contents favors ductility through the
  effect of temperature on crystalline plasticity
  and on pressure-solution deformation
  (dissolution-precipitation)

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Rate and state friction laws
Dc
from Marone, 1998.

• t/smma ln(V/V)b ln(q/q)
• dq/dt1-Vq /Dc (Dieterich, Ruina)
• Stationary state qss Dc /V? mss m(a-b)
  ln(V/V)

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mss m(a-b) ln(V/V)

• a-blt0
• slip is potentially unstable
• stick-slip

• a-bgt0
• stable slip
• creeping fault
• post-seismic relaxation

a-b
a
Correspond to T350 C
from Blanpied et al, 1991.
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Depth distribution of EQ, flexural rigidity and
the strength of the Lithopshere
(Watts and Burov, 2003)
Transition to stabe sliding or to ductile
creep? Why do we have EQ in the oceanic Upper
Mantle but few in the Continental Upper
Mantle? Where is the strength of the continental
lithosphere?
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(No Transcript)
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The rheological laws behind the seismic cycle

• Elastic behavior of the medium surrounding the
  fault.
• Rate-weakening or slip-weakening friction
  behavior on a portion of the fault,
• Viscous behavior in parallel to the Seismogenic
  fault zone.

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Co-seismic Static Deformation
Coseismic deformation due to the 1992, Ms 7.3,
Landers Earthquake
This case-example validates that co-seismic
deformation can be modeled assuming that
deformation is localized on a fault plane
embedded in an elastic half space.
(Hernandez et al, 1999)
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What is the rheology behind dynamic fault rupture?
Probably a frictional process, but are
seismological observations consistent with
Laboratory derived friction laws?
(Aochi etal, 2003)
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Slip weakening friction
stress
slip
Aochi et al, (2003)
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• Stress Field
• Rotation of direction
• One parameter for its level
• Fracture Criterion
• Uniform Horizontally

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SSE
Emerson
Kickapoo
Camp Rock
Johnson Valley
Homestead Valley
NW
slip distribution
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Simulation Result
Aochi et al (2003)
Wald and Heaton (1994)
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Mechanics interseismic loading?

• Most faults slip only during episodic slip
  events.
• Geodetic measurements generally indicate that a
  fault portion is locked (LFZ ), to depths of
  40-50km for subduction zones, and 15-20km for
  intra-continental faults.
• At greater depth aseismic deformation occurs all
  along the seismic cycle (creeping zone).

(Simoes et al, JGR,2004)
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(Chlieh et al, 2004)
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(Chlieh et al, 2004)
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What controls Postseismic relaxation and
afterschocks?
? Postesimic record suggests a combination of
frictional afterslip and broader scale and longer
term postseismic viscous relaxation.
Displacement at AREQ relative to stable South
America, before and after the 2001 Mw 8.4 peru
Earthquake.
(Perfettini, Avouac and Ruegg, submitted)
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Current Paradigm for Subduction zone
(Oleskevich et al, 1999)
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A conceptual Fault Model
(Perfettini and Avouac, 2004)
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Stress transfer during the seismic cycle
Fh gtgt DFfr
F Driving Force (assumed constant) DFfr
Co-seismic drop of frictional resistance Fh
Viscous resistance
Fh ? DFfr
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Some questions in seismotectonics

• What controls the transition from fully locked to
  a fully unlocked plate interface? Is it
  lithology, temperature, pressure, fluids?
• Is this transition stable with time?
• How does coseismic slip distribution during the
  very large earthquakes compare with the LFZ?
• What controls the co-seismic rupture? (fault
  geometry? prestress? lithology?)

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• 1- Brittle deformation, friction laws and
  semi-brittle processes
• Lockner, 1998 Marone, 1998 Scholz, 1998
  Blanpied et al, 1991, 1995, Moore et al., 1997.
• 2- Ductile Creep
• Kohlstedt et al, 1995 Karato and Wu, 1993
  Shimizu, 1995 Molnar, 1991 Hirth and Kolhstedt,
  1996.
• 3- Static friction, fluids and crustal stress
• Brudy et al, 1997 Townend and Zoback, 2000
  Hardebeck and Hauksson 1999 Bollinger et al,
  2004.
• 4- Seismicity and the depth dependent rheology of
  the lithosphere.
• Chen and Molnar, 1983 Sibson, 1982 Magistrale,
  2002 Blanpied et al, 1991, 1995.
• 5- Fluids and seismicity.
• Sibson, 1985 Sleep and Blanpied, 1992.

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• 6- Friction laws and seismic rupture
• Bouchon et al, 1998 Aochi et al, 2003 Guatteri
  and Spudich, 2000.
• 7- Postseismic relaxation, afterslip and
  lithosphere rheology.
• Marone et al, 1991  Moresi, 2004  Perffetini
  and Avouac, 2004a  Khazaradze et al, 1998 
  Melbourne et al, 2002.
• 8- Afterschocks and triggered seismicity
• King and Cocco, 2001 Dieterich, 1994 Deng et
  al, 1999 Bosl and Nur, 2002 Perfettini and
  Avouac, 2004a Perfettini et al, 2003.
• 9- Rheological model of fault zones.
• Sibson, 1982 Chester, 1995.
• 10- Observation and Models of the seismic cycle.
• Chlieh et al, 2004 Tse and Rice, 1981 Hyndman
  et al, 1997, Perfettini and Avouac, 2004b