Surface(mo+ons(and(deforma+on:
D(I(S(C(U(S(S(I(O(N
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Crustal Velocity Changes & Tectonic Boundaries: Pacific-North America Plate Study, Slides of Geology
The findings of two research papers that investigate crustal velocity changes along the pacific-north america plate boundary. The first paper, published in nature in 2006, reports a sharp boundary near the center of the boundary, which may be explained by various factors such as non-tectonic deformation, post-seismic relaxation, or deep crustal sources. The second paper, published in geophysical research letters in 2000, examines the rotation and plate locking at the southern cascadia subduction zone. Both studies contribute valuable insights into the dynamics of tectonic boundaries and the processes shaping the earth's crust.
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Surface mo+ons and deforma+on:
D I S C U S S I O N
1: Subcon+nental-‐scale crustal velocity changes
along the Pacific-‐North America plate boundary
Davis et al. Nature (2006) vol. 441 (7097) pp.1131-‐ DATA: Con+nuous GPS data (1996~2005) RESULT: A sharp boundary near the centre of the BR oriented parallel to N-‐NW rela+ve plate mo+on vector. ( Davis et al., 2006) From Pa(y’s March 3 presenta4on
Base of crust detachment horizon
- Mantle translates or stretches smoothly below horizon: creates a westward component of shear trac+on on base of crust before 1997 to 2000.
- To east of ‘boundary’, plas+c deforma+on internal stretching, crustal movement eastward
- Thus, contrast in lithospheric proper+es on either side of boundary (Vs: par+al melt to west of bdy?)
- Large scale strain transfer, starts in east, propagates west over ~ 1 yr +me scale
2: Rota+on and place locking at the southern
Cascadia subduc+on zone
McCaffrey et al. Geophysical Research Le?ers (2000) vol. 27 (19) pp. 3117-‐ DATA: GPS vectors and surface +lt rates RESULT: Rota+on of western Oregon and plate locking on the southern Cascadia subduc+on thrust fault ( McCaffrey et al., 2000 ) From Pa(y’s March 3 presenta4on
Inland locked zone: ar+fact
- Base of lithosphere: assumed NO SLIP boundary (produces unrealis+cally high resistance to trench-‐ perpendicular contrac+on of lithosphere)
- Steep reduc+on in surface veloci+es above down-‐ dip edge of coupled zone (contradicts w/ F.E. modeling)
- Thus: only oceanic area assumed LOCKED.