Investigating Seismic Anisotropy Beneath the Sabine Uplift of Louisiana-Texas with Shear Wave Splitting Analysis

Abstract:

A collaborative research team installed the 10-station ISLA broadband array across northwestern Louisiana in June 2019 to evaluate potential hazards of extractive industry-induced seismicity in the area. The array also affords the opportunity to analyze shear wave splitting for investigation of seismic anisotropy beneath the Sabine uplift situated between the East Texas and North Louisiana salt basins. The Sabine uplift is a structural high elevated by Cretaceous magmatism in the northern Gulf of Mexico basin and is presently underlain by a deep Moho, shallow basement, and thick crust thinning southward. Our latest objective is to infer mantle dynamics from evaluation of spatial variations in the direction and magnitude of seismic anisotropy influenced by mantle flow patterns along lithosphere-asthenosphere topography and pre-existing mantle lithosphere strain fabrics. Complementary datasets provide a strong contextual framework. We use the SplitRacer algorithm to analyze XKS waveforms of teleseismic earthquakes recorded by the ISLA array in addition to longer time period data from permanent TexNet stations ET01, CRHG, SNAG, HNVL, 237B, and TREL and USNSN stations NATX, VBMS, OXF, and MIAR across Texas, Mississippi, and Arkansas. Our preliminary results show 1-1.4 s split times along a 62-71^o direction of splitting parallel to major faults along the passive margin created by Mesozoic rifting, consistent with earlier studies in the broader region. The amount of splitting exceeds that associated with magmatic rift zones along the East Coast and may be related to the passage of the North American plate over the Bermuda hotspot during the Cretaceous.