HR: 1400h
AN: G33A-02    [Abstracts]
TI: Forearc Sliver Translation, a Lack of Arc-Normal Strain Accumulation, and Interplate Thrust Earthquakes: GPS Geodesy in Western Nicaragua
AU: * Turner, H L
EM: hturner@uark.edu
AF: Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701, United States
AU: * Turner, H L
EM: hturner@uark.edu
AF: Department of Geosciences, 113 Ozark Hall University of Arkansas, Fayetteville, AR 72701, United States
AU: Mattioli, G S
EM: mattioli@uark.edu
AF: Department of Geosciences, 113 Ozark Hall University of Arkansas, Fayetteville, AR 72701, United States
AU: Jansma, P E
EM: pjansma@uark.edu
AF: Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701, United States
AU: Jansma, P E
EM: pjansma@uark.edu
AF: Department of Geosciences, 113 Ozark Hall University of Arkansas, Fayetteville, AR 72701, United States
AU: Styron, R H
EM: rstyron@uark.edu
AF: Department of Geosciences, 113 Ozark Hall University of Arkansas, Fayetteville, AR 72701, United States
AB: We have been investigating the kinematics of the Nicaraguan forearc using campaign GPS measurements of our geodetic network made over the last seven years (Turner et al., 2007). We currently have interseismic velocities for 18 campaign sites and have installed 10 additional sites in the backarc to investigate the nature of the transition from forearc sliver motion to stable Caribbean Plate motion. Our work focusing on the later issue is presented elsewhere at this meeting (Styron et al., 2007). Corrections for modeled coseismic offsets from the Jan. 13, 2001 M_w7.7 earthquake off the coast of El Salvador have been applied to our campaign site velocities. Some of our time-series are also strongly affected by coseismic and postseismic effects of the Oct. 9, 2004 M_w6.9 earthquake off of the coast of Nicaragua. The geodetic effects of this event are being removed from the affected time-series for interseismic velocity analysis. We have also derived interseismic velocities for five continuous GPS sites in the region. Our GPS results confirm previous predictions of northwest transport of a forearc sliver with an average Northwest velocity of ~15 mm yr^-1, but show little evidence for an arc- normal component of strain accumulation associated with locking on the subduction interface. However, the amount of seismicity along this section of the Middle America Trench, including several recent large events such as the 1992 M_w7.6 and 2004 M_w6.9 earthquakes, indicates some amount of locking is present. Several possibilities may account for the apparent contradiction between the GPS results and observed seismicity. The locked zone may be too shallow and too far offshore for the arc-normal component to show up in our network, or the arc-normal signal may be masked by post-seismic effects from the 1992 offshore earthquake. If coupling between the downgoing slab and the overriding plate is weak or limited to a small seismogenic zone, then arc-parallel motion of the forearc sliver may be driven by a more strongly coupled region to the south in Costa Rica. We are developing regional FEM and half-space dislocation models constrained by the GPS-derived kinematics to distinguish between these possibilities and explore the possible driving mechanisms for sliver motion.
DE: 1209 Tectonic deformation (6924)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8185 Volcanic arcs
SC: Geodesy [G]
MN: 2007 Joint Assembly