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Walker, KT, Shelby R, Hedlin MAH, de Groot-Hedlin C, Vernon F.  2011.  Western US Infrasonic Catalog: Illuminating infrasonic hot spots with the USArray. Journal of Geophysical Research-Solid Earth. 116   10.1029/2011jb008579   AbstractWebsite

In this study reverse time migration is applied to signals recorded by the 2007-08 USArray, presumably due to acoustic-to-seismic coupling, to detect and locate in two-dimensional space and time 901 sources of atmospheric infrasound, defining the Western United States Infrasonic Catalog (WUSIC). The detections are visually inspected and ranked. Uncertainties are estimated using a bootstrap technique. The method correctly locates most rocket motor detonations in Utah and a bolide explosion in Oregon with an average spatial accuracy of 50 km and 25 km, respectively. The origin time statistics for 2007 and 2008 events are nearly identical and suggest a predominant human origin. The event locations illuminate repeating sources of infrasound, or "infrasonic hot spots," in Nevada, Utah, and Idaho that are spatially associated with active military areas. The infrasonic arrivals comprise several branches that are observed to a range between 200 and 1500 km to the east and west of the epicenter in the winter and summer, respectively. The optimum group velocities are Gaussian distributed and centered at 295 m/s. A seasonal variation in optimum group velocities exhibits good correlation with atmospheric temperature. The results show that relatively dense seismic networks fill in the gaps between sparsely located infrasound arrays and provide valuable information for regional infrasonic source location and propagation studies. Specifically, the catalogs presented here can be used to statistically validate and improve propagation models, especially above the middle stratosphere where winds are not directly measured by ground-based weather stations or meteorological satellites.

Wolfe, CJ, Vernon FL.  1998.  Shear-wave splitting at central Tien Shan: Evidence for rapid variation of anisotropic patterns. Geophysical Research Letters. 25:1217-1220.   10.1029/98gl00838   AbstractWebsite

At active collisional belts, the fast polarization axis of shear-wave splitting is generally aligned parallel to the strike of the belt, which has been proposed to indicate mantle strain that is coherent with crustal deformation. A notable exception is central Tien Shan, where anomalous patterns of splitting have previously been observed. We here analyze shear-wave splitting of SKS phases across north central Tien Shan using digital data from the Kyrgyzstan Broadband Seismic Network (KNET). We find a pattern of short-wavelength anisotropic heterogeneity that supports complex mantle flow due to small-scale convection. The along-strike variations in mantle structure contrast with the coherent pattern of crustal shortening, and indicate that mantle flow is not directly coupled to crustal deformation in this region.

Wolfe, CJ, Vernon FL, Al-Amri A.  1999.  Shear-wave splitting across western Saudi Arabia: The pattern of upper mantle anisotropy at a Proterozoic shield. Geophysical Research Letters. 26:779-782.   10.1029/1999gl900056   AbstractWebsite

We constrain upper mantle anisotropy across the Arabian Shield from shear-wave splitting analyses of SKS phases at eight temporary broadband stations that operated in Saudi Arabia. The direction of fast polarization is consistently aligned north-south and the delay time between fast and slow shear waves is generally 1.0 to 1.5 s, indicating that the mantle anisotropy is relatively homogeneous and coherent. We cannot distinguish between two possible models for the origin of this signal. The observed splitting may reflect fossil upper mantle anisotropy associated with the dominantly east-west accretion of oceanic terranes and formation of the Proterozoic Arabian lithosphere. Our results may also be compatible with present-day asthenospheric anisotropy caused by the northward absolute plate motion of the Arabian plate or northward asthenospheric flow from an Ethiopian mantle plume.