Crustal and Mantle Anisotropy in the Transitional Region from Oblique Subduction to Oblique Collision along the North American-Caribbean Plate Boundary
Abstract
The North American-Caribbean plate boundary demonstrates a change between oblique subduction in the east and a transform plate boundary in the west, with the island of Hispaniola situated at the critical point in the transition. As a result, Hispaniola has a transpressional stress regime with deformation accommodated by numerous strike-slip, thrust and oblique fault structures that bisect the island. Here we use shear wave splitting measurements from S waves of local (0-50 km) and intermediate depth (50-150 km) earthquakes as well as SKS phases from teleseismic earthquakes to ascertain good spatial and vertical resolution of the azimuthal anisotropic structure. From this we are able to place new constraints on the pattern of deformation in the crust and mantle beneath this transitional region of plate boundary tectonics.
In total, measurements were made on 134 SKS phases, 17 on S phases from intermediate depth earthquakes and 614 on S phases from local earthquakes. SKS results are dominated by plate boundary parallel (E-W) fast directions with ~1.9 s delay times, indicating sub-slab trench parallel mantle flow is continuing westward along the plate boundary. Intermediate depth earthquakes originating within the subducting North American plate show a mean fast polarization direction of 065° and delay time of 0.46 s, sub-parallel to the relative plate motion between the Caribbean and North American plates (070°). We suggest a basal shear zone within the lower ductile crust and upper lithospheric mantle as being a major source of anisotropy above the subducting slab. Upper crustal anisotropy is isolated using shear wave splitting measurements on local seismicity, which show consistent delay times on the order of 0.2 s. The fast polarization directions indicate the anisotropy is controlled by the fault networks in close proximity to the major strike-slip faults, which bisect the north and south of Haiti, and by the regional stress field where faulting is less pervasive.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S41D0544P
- Keywords:
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- 7203 Body waves;
- SEISMOLOGY;
- 7255 Surface waves and free oscillations;
- SEISMOLOGY;
- 7299 General or miscellaneous;
- SEISMOLOGY