[1] We investigate S velocity variation in the upper mantle beneath North American to better understand the effects of data heterogeneity, model parameterization, and regularization. To this end, we analyzed and fit regional S and Rayleigh wave trains generated by earthquakes around North America that occurred between the years 2000 through 2006, including waveforms from the Transportable Array stations of EarthScope's USArray. These new data were combined with constraints used for the 3-D S velocity model NA04 in order to create a new model, NA07. Another model, NA07, was created from a suite of good-fit models to provide a useful guide for model velocities and uncertainties by estimating ranges of probable velocity variations throughout the upper mantle. We find that the southern and eastern edges of the North American craton appear to be defined by Paleozoic orogens rather than Proterozoic ones. On average, the Archean portion of the craton is $200 km thick, while the Paleozoic part averages $175 km thick with an $80 m/s lower S velocity. The horizontal gradients in velocity are over $1.0%/100 km at the western margin of the craton, $0.5%/100 km in the south, and $1%/100 km at the eastern margin.

1] We construct a new three-dimensional S velocity model and Moho map by jointly inverting regional S and Rayleigh waveform fits, teleseismic S and SKS arrival times, fundamental mode Rayleigh wave group velocities, and independent Moho depth estimates for the region that extends from the mid-Atlantic ridge through northern Africa, southern Europe, and western Asia. The joint inversion benefits from both better resolution and wider data coverage than when using only individual data sets. Resolution tests confirm that the joint inversion yields good resolution ranging from the Moho to a depth of 1400 km. The complementary and overlapping nature of the different data sets' resolving power has reduced disparities in resolving power that exist for individual data sets, for example between resolving power for crustal and lower-mantle structure. This increases the utility of the new tomographic model for explaining and predicting a variety of observations and dynamics. The new model derived from the joint inversion assembles a large number of mantle structures known from a wide variety of previous studies into one model and in some cases reconciles different local studies that previously seemed contradictory. Finally, the model shows that shallow low-velocity anomalies beneath the Pannonian basin and the Iranian plateau are connected to similar anomalies in the transition zone, the latter possibly related to a deep dehydration process in the subducted lithosphere of the Neo-Tethys Ocean. The model shows the Hellenic slab penetrating the lower mantle, the Calabrian slab extending flatly in the transition zone, and discontinuous slabs beneath the Apennines and the Zagros belt. (2010), Joint inversion for three-dimensional S velocity mantle structure along the Tethyan margin,

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S U M M A R YWe estimate radial anisotropy along the Tethyan margin by jointly fitting regional S and Love waveform trains and fundamental-mode Love-wave group velocities. About 3600 wave trains with S and Love waves and 5700 Love-wave group velocity dispersion curves are jointly inverted for SH-velocity perturbations from a pre-existing, 3-D SV -velocity model. These perturbations are predominantly positive (SH faster than SV ) and consistent with PREM, but our model also shows significant lateral variation in radial anisotropy that appears to be correlated with tectonic environment. SH waves travel faster than SV wave beneath backarc basins, oceans and orogenic belts such as the Tyrrhenian and Pannonian basins, the Ionian Sea, the Alps, the Apennines, the Dinarides and the Caucasus. The Algero-Provençal basin, however, is underlain by faster SV velocity. Faster SV velocity of radial anisotropy is also detected within cratons such as the East European platform and the Arabian shield. Beneath hotspots we detect a change in radial anisotropic polarity with depth, which may be caused by transition between the lattice-preferred orientation from horizontal deformation in the asthenosphere and the shape-preferred orientation from vertically oriented melt channels in the lithosphere. We also find significant portion of radial anisotropy within subducting slabs depends on the slab's dip angle.

Introduction Tectonic SettingThe United States portion of the long-lived part of the North American continent consists of Precambrian cratons, including Archean cratons such as the Wyoming craton, and the Proterozoic Interior Platform (Bleeker, 2003;Hoffman, 1988). Since cratonic accretion, the Cenozoic-Mesozoic Rocky Mountain Cordillera and Paleozoic Appalachian Mountains formed on the west and east sides of the craton (Figure 1), respectively. Extending further out from the relatively stable core of the continent and to the east of the Appalachian range, the Atlantic Coastal Plain province in the east is a Paleozoic passive plate margin (Bally et al., 1989). The western edge of North America has a more complex tectonic history. Its seismically and tectonically active continental margin, Mesozoic-Cenozoic orogenies, and arc volcanism are controlled by the interaction between oceanic Pacific, Kula and Farallon plates and the North American plate (Atwater, 1989). Currently, the Juan de Fuca plate, a remnant of the Farallon plate, is subducting beneath North America at the Cascadia subduction zone (Atwater, 1970), causing arc volcanism, earthquakes, and episodic tremor and slip (Rogers & Dragert, 2003). The further inland location of the Laramide orogeny and eastward migration of magmatism during the Mesozoic can be explained by the contemporaneous flattening of the Farallon slab, which was likely caused by the increase in subduction rate and slab buoyancy (Engebretson et al., 1984(Engebretson et al., , 1985Molnar & Atwater, 1978). The Tertiary extensional system of the Basin and Range is likely due to the steepening of the Farallon Plate (Coney & Reynolds, 1977;Davis, 1980). Compared to tectonically active western North America, there is minimal tectonic activity and topographic variation in the central and eastern United States. However, variations in crustal and mantle structure do exist and have been the

Gas hydrates in the oceanic subsurface are often difficult to image with reflection seismic data, particularly when the strata run parallel to the seafloor and in regions that lack the presence of a bottom-simulating reflector (BSR). To address and understand these imaging complications, rock-physics modeling and seismic attribute analysis are performed on modern 2D lines in the Pegasus Basin in New Zealand, where the BSR is not continuously imaged. Based on rock-physics and seismic analyses, several seismic attribute methods identify weak BSR reflections, with the far-angle stack data being particularly effective. Rock modeling results demonstrate that far-offset seismic data are critical in improving the imaging and interpretation of the base of the gas hydrate stability zone. The rock-physics modeling results are applied to the Pegasus 2009 2D data set that reveals a very weak seismic reflection at the base of the hydrates in the far-angle stack. This often-discontinuous reflection is significantly weaker in amplitude than typical BSRs associated with hydrates. These weak far-angle stack BSRs often do not appear clearly in full stack data, the most commonly interpreted seismic data type. Additional amplitude variation with angle (AVA) attribute analyses provide insight into identifying the presence of gas hydrates in regions lacking a strong BSR. Although dozens of seismic attributes were investigated for their ability to reveal weak reflections at the base of the gas hydrate stability zone, those that enhance class 2 AVA anomalies were most effective, particularly the seismic fluid factor attribute.

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Initially studied from the surface of the Earth, cratons are large regions of stable continental crust that have undergone minimal deformation since Precambrian time. Whereas cratons were originally believed to be enduring features of the lithosphere, recent studies have revealed that some Archean cratons are susceptible to the tectonic forces that shape the planet and have been modified by subsequent events (e.g.,