HR: 13:55h
AN: T23E-02    [Abstracts]
TI: Shear Wave Splitting Observations on the Caribbean-South American Plate Boundary: Evidence for Vertically Coherent Deformation Induced by Trench Rollback
AU: * Growdon, M A
EM: magrowdo@indiana.edu
AF: Indiana University, 1001 East 10th Street, Bloomington, IN 47401, United States
AU: Pavlis, G L
EM: pavlis@indiana.edu
AF: Indiana University, 1001 East 10th Street, Bloomington, IN 47401, United States
AU: Niu, F
EM: niu@rice.edu
AF: Rice University, 6100 Main Street, Houston, TX 77005, United States
AB: We utilized data from the BOLIVAR project and the permanent national seismic network of Venezuela to investigate the boundary between Venezuela and southeastern Caribbean. We made shear wave splitting measurements on SKS and SKKS phases using techniques developed by Silver and Chan (1991). We examined 3000+ station event pairs and found approximately 300 with visible SKS and/or SKKS phases. From these data we obtained robust measurements for 43 of the 82 stations. Two areas show unusual split times larger then 2.0 seconds: (1) two observations on the northeastern edge of the Maracaibo block and (2) a 200 km2 area between Trinidad and Margarita Island. We interpret the large split times over the Atlantic subduction as further evidence of a shear tear subduction geometry. We hypothesize that the slab edge at depth is forcing the creation of a vertical shear zone. Split times larger then 2.0 seconds are difficult to explain using typical horizontal shear deformation with normal lithosphere thicknesses. We use mineral physics models to predict maximum split times for different geometries and anisotropic layer thicknesses to support the vertical shear zone hypothesis. In addition, we hypothesize that a similar geometry could be created by the northern edge of a paleo- Caribbean subduction and may explain the northeastern Maracaibo split time anomaly.
DE: 7218 Lithosphere (1236)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting