Seismic anisotropy in Texas and Oklahoma and its relationship to tectonic events that shaped southern Laurentia.

We present new shear wave splitting measurements of approximately 1500 SKS phases recorded at 176 broadband seismic stations deployed in Texas and Oklahoma. SKS splitting on the North American (NA) craton show NE-SW fast axis polarization directions that are generally parallel to the average motion of the NA plate. Around the Southern Oklahoma Aulacogen the fast axis polarization direction changes to NW-SE and parallels the strike of the Aulacogen. Along the transition zone (COTZ), SKS phases show NE-SW polarization direction and parallel to the NA plate. However, larger delay times are observed on the COTZ. Observed patterns of fast axis directions parallel to plate motions, small delay times, and a shallower anisotropic depth are consistent with a lithospheric origin for the observed anisotropy on the craton. Larger delay times and a deeper anisotropic source suggest that asthenospheric flow is responsible for the seismic anisotropy observed along the COTZ.