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Implications for the thermomechanics of the San Andreas fault zone Wayne Thatcher, Philip C. England
Yihe Huang Ge277 02/10/2011
Ductile shear zone beneath strike-slip faults:
• Outline
What is ductile shear zone (DSZ)?
1-D ductile shear zone
Let’s go to San Andreas Fault Zone.
Conclusion and Discussion
Introduction
Physics
End
Physics
Application
2-D ductile shear zone
•Ductile shear zone is the deep-level equivalent of faults.
•If shear resistance significantly impedes fault motions, there should be substantial generation of heat.
• Ductile Shear Zone
( http://www.see.leeds.ac.uk/structure/shearzones/gallery/picturegallery.htm )
• Ductile Shear Zone
• 1-D Ductile Shear Zone
• η=(T/2B)exp(Q/RT), where T is absolute temperature, Q is the activation energy, R is the gas constant and B is a material constant.
• δT~2(κt)1/2, where κ is thermal diffusivity and t is time since slip began.
• Tmax~log(v0), where Tmax is the steady state temperature at the center of the shear zone, v0 is the slip velocity.
• 1-D Ductile Shear Zone
η=(T/2B)exp(Q/RT)δT~2(κt)1/2
Tmax~log(v0).
• 2-D Ductile Shear ZoneThe differences from 1-D are:
•The shear zone also loses heat toward the land surface.
•The shear stress is no longer constant throughout the deforming medium.
•The temperature before shearing increases with depth (gradient β0).
X
Z
• 2-D Ductile Shear Zone
The shear zone is treated as being buried beneath a conductive lid of thickness H within which no dissipation occurs.
• 2-D Ductile Shear Zone: Model 1
The greatest temperature increase and highest rates of dissipation are concentrated into a small region at the top of the shear zone.
• 2-D Ductile Shear Zone: Model 2
The zone of concentrated shear heating has a blade-like cross-sectional shape and much greater lateral extent than the dissipative zone for model 1.
• 2-D Ductile Shear Zone
The width of shear zone:
δM ~ δTRTmax/Q(1-T0/Tmax)
Where δM is the width within which v<0.8v0 and δT is the width within which (Tmax-T)>0.8(Tmax-T0).
Model 1
Model 2
• Application to San Andreas Fault Zone
• Application to San Andreas Fault Zone
• Conclusion and Discussion
• Heat flow is a useful tool to analyze the deep structure like ductile shear zone.
• However, it is difficult to estimate shear zone property only using heat flow data.
• Is there any other constraint?
• Conclusion and Discussion
http://earthquake.usgs.gov/regional/asl/pubs/Alsina_JGR/fig1.php