Ge 277 Seminar Nature 1998 Nina Lin Jan

Ge 277 Seminar (Nature, 1998) Nina Lin Jan 27 2011

Two Key Questions 1. Where does lithospheric strength mostly lie, in the upper mantle or in the crust?

Two Key Questions 1. Where does lithospheric strength mostly lie, in the upper mantle or in the crust? 2. Below the seismogenic depth, is deformation localized or distributed?

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

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

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

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

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

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