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Yihe Huang Ge277 02/10/2011

Ductile shear zone beneath strike-slip faults:. Implications for the thermomechanics of the San Andreas fault zone Wayne Thatcher, Philip C. England. Yihe Huang Ge277 02/10/2011. Outline. Introduction. Physics. What is ductile shear zone (DSZ)?.

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Yihe Huang Ge277 02/10/2011

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  1. Ductile shear zone beneath strike-slip faults: Implications for the thermomechanics of the San Andreas fault zoneWayne Thatcher, Philip C. England Yihe Huang Ge277 02/10/2011

  2. Outline Introduction Physics What is ductile shear zone (DSZ)? 1-D ductile shear zone Let’s go to San Andreas Fault Zone. Conclusion and Discussion 2-D ductile shear zone Physics Application End

  3. 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. ( http://www.see.leeds.ac.uk/structure/shearzones/gallery/picturegallery.htm )

  4. Ductile Shear Zone

  5. 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.

  6. 1-D Ductile Shear Zone η=(T/2B)exp(Q/RT) δT~2(κt)1/2 Tmax~log(v0).

  7. 2-D Ductile Shear Zone X The 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). Z

  8. 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.

  9. 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.

  10. 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.

  11. 2-D Ductile Shear Zone Model 1 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 2

  12. Application to San Andreas Fault Zone 1 2 1 2

  13. Application to San Andreas Fault Zone 2

  14. 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?

  15. Conclusion and Discussion http://earthquake.usgs.gov/regional/asl/pubs/Alsina_JGR/fig1.php

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