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 (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 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)

Rate and state friction laws Dc from Marone, 1998. t/s=m=m*+a ln(V/V*)+b ln(q/q*) dq/dt=1-Vq /Dc (Dieterich, Ruina) Stationary state: qss= Dc /V mss= m*+(a-b) ln(V/V*)

mss= m*+(a-b) ln(V/V*) slip is potentially unstable stick-slip a-b>0 stable slip creeping fault post-seismic relaxation a-b a Correspond to T~350 °C from Blanpied et al, 1991.

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 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)

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)

Slip weakening friction stress slip Aochi et al, (2003)

Stress Field: Rotation of direction One parameter for its level Fracture Criterion: Uniform Horizontally

SSE Emerson Kickapoo Camp Rock Johnson Homestead Valley Valley NW We show our result. This is a snapshot of rupture propagation for fault slip distribution. Rupture didn’t propagate on this branch, but progress on parallel running fault. It transferred further on the last segment, and was arrested spontaneously. NW slip distribution

Simulation Result Aochi et al (2003) Wald and Heaton (1994) However, when we compare our simulation quantitatively with the inversion result, there are still some discrepancies. For example, this slide shows the final slip distribution of ours and the inversion by Wald and Heaton. The large slip area appears horizontally 4 times briefly speaking, but they always appeared around the depth of 10 km, and didn’t show such kind of variety as shown in the observation. And then, this portion on the last segment was not expressed very well. Main discrepancy was insufficient slip near surface. Wald and Heaton (1994)

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)

(Chlieh et al, 2004)

(Chlieh et al, 2004)

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)

Current Paradigm for Subduction zone (Oleskevich et al, 1999)

A conceptual Fault Model (Perfettini and Avouac, 2004)

Stress transfer during the seismic cycle Fh >> DFfr F : Driving Force (assumed constant) DFfr : Co-seismic drop of frictional resistance Fh: Viscous resistance Fh  DFfr

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