HR: 1330h
AN: T52A-0245    [PDF]
TI: A Physical Model for the Motion of the Sierra Nevada-Great Valley Block
AU: * Whitehouse, P L
EM: pippaw@earth.ox.ac.uk
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR United Kingdom
AU: England, P C
EM: Philip.England@earth.ox.ac.uk
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR United Kingdom
AU: Houseman, G A
AF: School of Earth Sciences, The University of Leeds, Leeds, LS2 9JT United Kingdom
AB: We investigate the motion of the Sierra Nevada--Great Valley block, treating it as a rigid inclusion within a viscous lithosphere, whose motion is governed by external in-plane forces applied to the boundary of the North American plate. This aseismic block of continental lithosphere lies within the wide zone of deformation arising from motion along the Pacific--North America plate boundary adjacent to California. Geodetic studies have shown that the motion of the block can be approximated by rigid body motion, and low surface heat flow measurements strengthen the argument that this may be treated as a region of higher viscosity than the surrounding continental lithosphere. We use a numerical method, employing the thin viscous sheet approach, to solve for the motion of a rigid block of a given aspect ratio lying within a non--newtonian fluid undergoing simple shear. We also use a force balance approach to place theoretical bounds upon the motion of such a block in a viscous fluid. We obtain similar results from the two methods for a range of physical parameters. We wish to constrain the value of the stress--strain exponent, \emph{n}, in the constitutive equation which governs the flow of the lithosphere, as represented by a non--linear viscous fluid. We compare GPS estimates for the velocity of the Sierra Nevada--Great Valley block, relative to a North-America-fixed reference frame, to our estimates for the velocity of a rigid block, with the same aspect ratio as the Sierra Nevada--Great Valley block, embedded within viscous fluids of varying power--law rheologies. The best fit to observed velocities, for both numerical and theoretical approaches, is obtained when \emph{n}=3. This result is corroborated by the close agreement between GPS velocity profiles, taken across the Great Valley and perpendicular to the strike of plate boundary motion, and profiles from our numerical method when \emph{n}=3.
DE: 1208 Crustal movements--intraplate (8110)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
DE: 8159 Rheology--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting