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.

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).

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

web’s page.• Students are required to have read, ahead of

time, the papers to be presented

Experimental Rock mechanics

• 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 300°C, 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 700°C). Presumably the transition from unstable to stable sliding occurs at a temperature much higher than for Quartz, hence above 300°C.

• Fluid contents favors ductility through the effect of temperature on crystalline plasticity and on pressure-solution deformation (dissolution-precipitation)

(Dieterich, Tullis, Marone, Blanpied, Lockner,Kholstedt, Byerlee, …)

Rate and state friction laws

from Marone, 1998.

=*+a ln(V/V*)+b ln(*)

d/dt=1-V /Dc (Dieterich, Ruina)

Stationary state: ss= Dc /V ss*+(a-b) ln(V/V*)

Dc

ss*+(a-b) ln(V/V*)

a-b>0

stable slip creeping fault

post-seismic relaxation

a-b<0

slip is potentially unstable

stick-slip

from Blanpied et al, 1991.

a-b a

Correspond to T~350 °C

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?

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.

Co-seismic Static Deformation

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)

Coseismic deformation due to the 1992, Ms 7.3, Landers Earthquake

Probably a frictional process, butare seismological observations consistent with Laboratory derived friction laws?

What is the rheology behind dynamic fault

rupture?

(Aochi etal, 2003)

Aochi et al, (2003)

p

r0stress

slip

b

cD

Slip weakening friction

• Stress Field: Rotation of directionOne parameter for its level

• Fracture Criterion: Uniform Horizontally

1

0 0( ) ( ) 1/19p rS

SSE

NW

Johnson Valley

Emerson

Camp Rock

Homestead Valley

Kickapoo

slip distribution

Simulation Result

Wald and Heaton (1994)

Aochi et al (2003)

• 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)

Mechanics interseismic loading?

(Chlieh et al, 2004)

(Chlieh et al, 2004)

Postesimic record suggests a combination of frictional afterslip and broader scale and longer term postseismic viscous relaxation.

(Perfettini, Avouac and Ruegg, submitted)

What controls Postseismic relaxation and afterschocks?

Displacement at AREQ relative to ‘stable South America’, before and after the 2001 Mw 8.4 peru Earthquake.

Current Paradigm for Subduction zone

(Oleskevich et al, 1999)

A conceptual Fault Model

(Perfettini and Avouac, 2004)

Stress transfer during the seismic cycle

F : Driving Force (assumed constant)Ffr : Co-seismic drop of frictional resistanceF: Viscous resistance

F >> Ffr

F Ffr

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?)

• 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.

• 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