A Uniform Database of Teleseismic Shear‐Wave Splitting Measurements for the Western and Central United States: December 2014 Update

Abstract

We present a shear wave splitting (SWS) database for the western and central United States as part of a lasting effort to build a uniform SWS database for the entire North America. The SWS measurements were obtained by minimizing the energy on the transverse component of the PKS, SKKS, and SKS phases. Each of the individual measurements was visually checked to ensure quality. This version of the database contains 16,105 pairs of splitting parameters. The data used to generate the parameters were recorded by 1774 digital broadband seismic stations over the period of 1989-2012, and represented all the available data from both permanent and portable seismic networks archived at the Incorporated Research Institutions for Seismology Data Management Center in the area of 26.00 N to 50.00 N and 125.00 W to 90.00 W. About 10,000 pairs of the measurements were from the 1092 USArray Transportable Array stations. The results show that approximately 2/3 of the fast orientations are within 30 from the absolute plate motion (APM) direction of the North American plate, and most of the largest departures with the APM are located along the eastern boundary of the western US orogenic zone and in the central Great Basins. The splitting times observed in the western US are larger than, and those in the central US are comparable with the global average of 1.0 s. The uniform database has an unprecedented spatial coverage and can be used for various investigations of the structure and dynamics of the Earth.

Seismic azimuthal anisotropy beneath the eastern United States and its geodynamic implications

“…Only a small fraction of the stations have previously reported SWS measurements, and Long et al [] observed a set of null‐dominated stations in Regions A2 and A3 (Figure ). The mean splitting times for the three regions are 0.91–0.95 s, which are smaller than the global average of 1.0 s and are consistent with those observed on the western part of the stable North American continent using the same procedure [ Yang et al , ]. While the majority of the fast orientations are within 20° from the APM, larger deviations are found in the Great Lakes area.…”

“…As a nearly ubiquitous characteristic of the Earth's upper mantle, the azimuthal dependence of seismic velocities, i.e., azimuthal anisotropy, has been investigated for decades by numerous studies, mostly using shear wave splitting (SWS) analyses [e.g., Francis , ; Leven et al , ; Mainprice and Nicolas , ; Silver and Chan , ; Gao et al , ; Savage , ; Yang et al , , ]. In particular, splitting of P ‐to‐ S converted phases ( S K S , S K K S , and P K S , hereafter collectively called X K S ) from the core‐mantle boundary is among the most frequently employed structural seismological techniques to determine mantle anisotropy beneath the stations.…”

Lithospheric Deformation and Asthenospheric Flow Associated With the Isabella Anomaly in Southern California

“…(a) Comparison of fast velocity directions (white bars) of P wave azimuthal anisotropy at 75‐km depth determined by this study with the distribution of delay times (colors) of shear wave splitting (SWS) measurements (Barak & Klemperer, ; Ramsay et al, ; Yang et al, ). (b) Comparison of the lithospheric thickness (Lekic et al, ) with P wave azimuthal anisotropy (white bars) at 200‐km depth determined by this study.…”

Azimuthal Anisotropy of the North American Upper Mantle Based on Full Waveform Inversion

“…We calculate predicted SKS splitting delay time and fast direction using the above equations, and elastic parameters from model . These predictions are compared with station‐averaged SKS splitting measurements from Yang et al (, ) (Figure ). The overall magnitudes of the predicted delay times are smaller than actual measurements, with mean value and standard deviation equaling to 0.64 s and 0.35 s, respectively.…”

“…To date, the azimuthal anisotropy structures of the North American crust and upper mantle have been explored using a variety of seismic techniques, including shear wave (SKS) splitting (Barruol et al, ; Fouch et al, ; Long et al, ; Savage & Sheehan, ; Wagner et al, ; Yang et al, , ), joint inversion of surface wave waveforms and SKS results (Marone & Romanowicz, ; Yuan & Romanowicz, ; Yuan et al, ), Pn tomography (Buehler & Shearer, ; Smith & Ekström, ), receiver functions (Ford et al, ; Wirth & Long, ), ambient noise tomography (Lin et al, ; Lin & Schmandt, ), and P wave tomography (Huang & Zhao, ).…”