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Lithospheric Strength: Upper Mantle or Crust?

This seminar explores the two key questions about lithospheric strength: whether it lies mostly in the upper mantle or in the crust, and if deformation is localized or distributed below the seismogenic depth. The results and implications suggest that basal traction plays a crucial role in the organization of continental blocks, and that short-term motion at the surface directly represents long-term slip rate on faults.

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Lithospheric Strength: Upper Mantle or Crust?

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  1. Ge277 Seminar Nina Lin Jan 27 2011 (Nature, 1998)

  2. Two Key Questions • Where does lithospheric strength mostly lie, in the upper mantle or in the crust?

  3. Two Key Questions • Where does lithospheric strength mostly lie, in the upper mantle or in the crust? • Below the seismogenic depth, is deformation localized or distributed?

  4. The Argument • The longterm velocity of a continental (crustal) block (geologic rate) represents the flow velocity in the mantle lithosphere underneath, and vice versa

  5. Underlying Assumptions • lithosphere strength lies in upper mantle • deformation is distributed at depth

  6. To Test • Newtonian rheology at upper mantle (linear viscous) • Strong coupling between crust and mantle through basal traction

  7. A B C This balanced point in the transition zone represents the flow velocity in upper mantle

  8. Results and Implications • Basal traction is a key mechanism that leads to organized continental blocks • The crustal stress field is controlled by the stress condition in the mantle lithosphere • Short-term motion at the surface directly represents long-term slip rate on faults

  9. Competing Ideas • Stress in the crustal medium and on the fault is a key mechanism that leads to organized continental blocks • The crustal stress field is controlled by the stress condition in the crustal medium or on the fault • Short-term motion at the surface is linked to long-term slip rate on faults through kinematic models

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