HR: 11:10h
AN: T52A-04    [Abstracts]
TI: The Distribution of Interseismic Locking on the Central Cascadia Subduction Zone Inferred From Coastal Uplift Rates in Oregon
AU: * Schmidt, D
EM: das@uoregon.edu
AF: University of Oregon, Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, United States
AU: Burgette, R
EM: rburgett@uoregon.edu
AF: University of Oregon, Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, United States
AU: Weldon, R
EM: ray@uoregon.edu
AF: University of Oregon, Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, United States
AB: We invert for the distribution of locking along the Oregon portion of the Cascadia subduction zone using an updated dataset of the interseismic vertical displacement rates. Uplift rates are inferred from spirit leveling that is tied into an absolute vertical reference frame using tide gauge records. With absolute uncertainties less than 1 mm/yr, the data provide good constraints on the accumulation of interseismic strain along the Oregon coast. The slip rate deficit on the subduction interface is modeled using a backslip calculation in an elastic half-space. Static Green's functions are calculated using a triangular fault model that approximates the 3D geometry of the plate interface. We assume a slip rate deficit that is equivalent to the full convergence rate in an offshore locked zone and tapers to zero at depth across a transition zone. The convergence rate is calculated using the published Euler vector for motion of the Juan de Fuca oceanic plate relative the Oregon continental forearc. To minimize the number of free parameters in the inversion, the down-dip extent of locking is defined by the lower edge of the fully locked zone and the lower edge of the transition zone. These two free parameters are optimized at various latitudes by minimizing the misfit of the east-west leveling lines through a grid search of the parameter space. The north-south leveling route that runs along the coast is then used to further optimize the model by interpolating the slip deficit distribution along-strike. The inversion prefers models where the locked zone is forced up-dip (i.e. farther offshore) at the east-west profile near Newport on the central Oregon coast. This is in contrast to inversion results near Astoria where the locked and transition zones extend farther down-dip relative to a constant depth contour on the plate interface. Our optimal model of the slip-rate deficit distribution is compared to previously published models of strain accumulation constrained by only horizontal displacement rates. We also compare the distribution of locking to the extent of Siletzia in the continental forearc, gravity lows, and forearc basins to better understand the potential location of long-lived asperities on the subduction interface.
DE: 1204 Control surveys
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8104 Continental margins: convergent
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting