Showing papers on "Slab published in 2014"
TL;DR: In this article, the authors address the questions of what caused Oligocene rollback initiation, and how its subsequent evolution split up an originally coherent fore arc into circum-southwest Mediterranean segments.
Abstract: The western Mediterranean recorded subduction rollback, slab segmentation and separation. Here we address the questions of what caused Oligocene rollback initiation, and how its subsequent evolution split up an originally coherent fore arc into circum-southwest Mediterranean segments. We kinematically reconstruct western Mediterranean geology from subduction initiation to present, using Atlantic plate reconstructions as boundary condition. We test possible reconstructions against remnants of subducted lithosphere imaged by seismic tomography. Transform motion between Africa and Iberia (including the Baleares) between ~120 and 85 Ma was followed by up to 150 km convergence until 30 Ma. Subduction likely initiated along the transform fault that accommodated pre-85 Ma translation. By the ~30 Ma inception of rollback, up to 150 km of convergence had formed a small slab below the Baleares. Iberia was disconnected from Sardinia/Calabria through the North Balearic Transform Zone (NBTZ). Subduction below Sardinia/Calabria was slightly faster than below the Baleares, the difference being accommodated in the Pyrenees. A moving triple junction at the trench-NBTZ intersection formed a subduction transform edge propagator fault between the Baleares and Calabria slab segments. Calabria rolled back eastward, whereas the Baleares slab underwent radial (SW-S-SE) rollback. After Kabylides-Africa collision, the western slab segment retreated toward Gibraltar, here reconstructed as the maximum rollback end-member model, and a Kabylides slab detached from Africa. Opening of a slab window below the NBTZ allowed asthenospheric rise to the base of the fore arc creating high-temperature metamorphism. Western Mediterranean rollback commenced only after sufficient slab-pull was created from 100 to 150 km of slow, forced subduction before ~30 Ma.
273 citations
TL;DR: In this article, a three-dimensional finite element model was proposed to investigate the interface damage occurred between prefabricated slab and CA (cement asphalt) mortar layer in the China Railway Track System (CRTS-II) slab track system.
Abstract: This paper presents a three-dimensional finite element model to investigate the interface damage occurred between prefabricated slab and CA (cement asphalt) mortar layer in the China Railway Track System (CRTS-II) slab track system. In the finite element model, a cohesive zone model with a non-linear constitutive law is introduced and utilized to model the damage, cracking and delamination at the interface. Combining with the temperature field database obtained from the three-dimensional transient heat transfer analysis, the interface damage evolution as a result of temperature change is analyzed. A three-dimensional coupled dynamic model of a vehicle and the slab track is then established to calculate the varying rail-supporting forces which are utilized as the inputs to the finite element model. The non-linearities of the wheel–rail contact geometry, the wheel–rail normal contact force and the wheel–rail tangential creep force are taken into account in the model. Setting the maximum interface damaged state calculated under temperature change as the initial condition, the interface damage evolution and its influence on the dynamic response of the slab track are investigated under the joint action of the temperature change and vehicle dynamic load. The analysis indicates that the proposed model is capable of predicting the initiation and propagation of cracks at the interface. The prefabricated slab presents lateral warping, resulting in severe interface damage on both the sides of the slab track along the longitudinal direction during temperature drop process, while the interface damage level does not change significantly under vehicle dynamic loads. The interface damage has great effects on the dynamic responses of the slab track.
157 citations
TL;DR: In this paper, the effect of initial subducting-and overriding-plate ages on slab transition-zone interaction was investigated using 2D thermo-mechanical models with a mobile trench, an overriding plate, a temperature and stress-dependent rheology, and a 10, 30 or 100fold increase in lower mantle viscosity.
Abstract: Transition zone slab deformation influences Earth's thermal, chemical and tectonic evolution. However, the mechanisms responsible for the wide-range of imaged slab morphologies remain debated. Here, we use 2-D thermo-mechanical models with a mobile trench, an overriding plate, a temperature- and stress-dependent rheology, and a 10, 30 or 100-fold increase in lower mantle viscosity, to investigate the effect of initial subducting- and overriding-plate ages on slab transition-zone interaction. Four subduction styles emerge: (i) a “vertical folding” mode, with a quasi-stationary trench, near-vertical subduction and buckling/folding at depth (VF); (ii) slabs that induce mild trench retreat, which are flattened/“horizontally deflected” and stagnate at the upper-lower mantle interface (HD); (iii) inclined slabs, which result from rapid sinking and strong trench retreat (ISR); (iv) a two-stage mode, displaying backward-bent and subsequently inclined slabs, with late trench retreat (BIR). Transitions from regime (i) to (iii) occur with increasing subducting-plate age (i.e. buoyancy and strength). Regime (iv) develops for old (strong) subducting and overriding plates. We find that the interplay between trench motion and slab deformation at depth dictate the subduction style, both being controlled by slab strength, which is consistent with predictions from previous compositional subduction models. However, due to feedbacks between deformation, sinking rate, temperature and slab strength, the subducting-plate buoyancy, overriding-plate strength and upper-lower mantle viscosity jump are also important controls in thermo-mechanical subduction. For intermediate upper-lower mantle viscosity jumps (×30), our regimes reproduce the diverse range of seismically imaged slab morphologies.
154 citations
TL;DR: In this article, the authors grouped the geological and geophysical phenomena associated with water in the slab into three different categories: those related to 1) the storage of water at the surface, 2) the subduction of a hydrated slab and 3) its dehydration that ultimately leads to mantle regassing.
146 citations
TL;DR: In this article, the role of compaction pressure gradients in modifying fluid flow was explored through a series of simplified models and it was shown that these gradients are produced by variations in fluid flux interacting with the permeability and viscosity structure of the solid mantle.
134 citations
TL;DR: This work is able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.
Abstract: Convergent margin volcanism originates with partial melting, primarily of the upper mantle, into which the subducting slab descends. Melting of this material can occur in one of two ways. The flow induced in the mantle by the slab can result in upwelling and melting through adiabatic decompression. Alternatively, fluids released from the descending slab through dehydration reactions can migrate into the hot mantle wedge, inducing melting by lowering the solidus temperature. The two mechanisms are not mutually exclusive. In either case, the buoyant melts make their way towards the surface to reside in the crust or to be extruded as lava. Here we use magnetotelluric data collected across the central state of Washington, USA, to image the complete pathway for the fluid-melt phase. By incorporating constraints from a collocated seismic study into the magnetotelluric inversion process, we obtain superior constraints on the fluids and melt in a subduction setting. Specifically, we are able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.
132 citations
TL;DR: In this paper, a 3D thermo-mechanical numerical joint model of continental collision, oceanic subduction and slab tearing is presented, which allows self-consistent reproduction of first-order Tethyan tectonic structures such as back-arc rifting and large-scale strike-slip faults accommodating continental escape.
122 citations
TL;DR: In this paper, a 3D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography was presented, where the authors analyzed the fundamental mode in the 20-167 s period band (6.0-50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays.
Abstract: [1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20–167 s period band (6.0–50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two-plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African-European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from ∼70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near-vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.
118 citations
TL;DR: In this article, a compact metamaterial was proposed for enhanced magnetic coupling in a resonator coupled wireless power transfer system operating at around 6.5 MHz, which is constructed by realizing an array of three-turn spiral resonators on a thin slab.
Abstract: We investigate a compact metamaterial for enhanced magnetic coupling in a resonator coupled wireless power transfer system operating at around 6.5 MHz. The metamaterial is constructed by realizing an array of three-turn spiral resonators on a thin slab. Although the metamaterial has its own loss, the experimental results show that the proposed metamaterial slab enhances the power transmission capability. The number of unit cells in the array is an important parameter, because exceeding a certain number of unit cells does not enhance the efficiency due to the loss of the slab. Furthermore, strong surface mode resonance is observed when two slabs are assembled with proper gap spacing between them. By using the optimization approach, we achieve a significant efficiency improvement at a mid-range distance. The measured efficiencies are 71.1% and 54.3% at a 0.6 and 1.0 m distance, respectively. At a 1.0 m distance, this efficiency performance corresponds to a 270% improvement compared to a case with no metamaterial slab. In addition, we experimentally confirm the threshold distances above which the metamaterial shows enhanced performance.
110 citations
TL;DR: In this article, the authors use geodynamic models with imposed plate velocities to test the forward-modeled history of subduction based on a particular plate motion model against alternative seismic tomography models.
106 citations
TL;DR: In this paper, five magnetotelluric (MT) profiles have been acquired across the Cascadia subduction system and transformed using 2-D and 3-D nonlinear inversion to yield electrical resistivity cross sections to depths of ∼200 km.
Abstract: Five magnetotelluric (MT) profiles have been acquired across the Cascadia subduction system and transformed using 2-D and 3-D nonlinear inversion to yield electrical resistivity cross sections to depths of ∼200 km. Distinct changes in plate coupling, subduction fluid evolution, and modes of arc magmatism along the length of Cascadia are clearly expressed in the resistivity structure. Relatively high resistivities under the coasts of northern and southern Cascadia correlate with elevated degrees of inferred plate locking, and suggest fluid- and sediment-deficient conditions. In contrast, the north-central Oregon coastal structure is quite conductive from the plate interface to shallow depths offshore, correlating with poor plate locking and the possible presence of subducted sediments. Low-resistivity fluidized zones develop at slab depths of 35–40 km starting ∼100 km west of the arc on all profiles, and are interpreted to represent prograde metamorphic fluid release from the subducting slab. The fluids rise to forearc Moho levels, and sometimes shallower, as the arc is approached. The zones begin close to clusters of low-frequency earthquakes, suggesting fluid controls on the transition to steady sliding. Under the northern and southern Cascadia arc segments, low upper mantle resistivities are consistent with flux melting above the slab plus possible deep convective backarc upwelling toward the arc. In central Cascadia, extensional deformation is interpreted to segregate upper mantle melts leading to underplating and low resistivities at Moho to lower crustal levels below the arc and nearby backarc. The low- to high-temperature mantle wedge transition lies slightly trenchward of the arc.
TL;DR: In this article, the authors reconstruct the coupled subduction-continent deformation history using tomographic imaging, kinematics constraints and numerical modeling, showing one major breakoff occurred between India and the Tethys Ocean ~ 45 Ma, which renewed Indian lithosphere underthrusting below Asia.
TL;DR: In this paper, three disparate tectonic evolution scenarios are identified, each portraying slab rollback as the driving mechanism but with rollback starting from strongly different subduction geometries.
Abstract: No consensus exists on the tectonic evolution of the western Mediterranean since ~35 Ma. Three disparate tectonic evolution scenarios are identified, each portraying slab rollback as the driving mechanism but with rollback starting from strongly different subduction geometries. As a critical test for the validity of each tectonic scenario we employ thermomechanical modeling of the 3-D subduction evolution. From each tectonic scenario we configure an initial condition for numerical modeling that mimics the perceived subduction geometry at ~35 Ma. We seek to optimize the fit between observed and predicted slab morphology by varying the nonlinear viscoplastic rheology for mantle, slab, and continental margins. From a wide range of experiments we conclude that a tectonic scenario that starts from NW dipping subduction confined to the Balearic margin at ~35 Ma is successful in predicting present-day slab morphology. The other two scenarios (initial subduction from Gibraltar to the Baleares and initial subduction under the African margin) lead to mantle structure much different from what is tomographically imaged. The preferred model predicts slab rotation by more than 180°, east-west lithosphere tearing along the north African margin and a resulting steep east dipping slab under the Gibraltar Strait. The preferred subduction model also meets the first-order temporal constraints corresponding to Mid-Miocene (~16 Ma) thrusting of the Kabylides onto the African margin and nearly stalled subduction under the Rif-Gibraltar-Betic arc since the Tortonian (~8 Ma). Our modeling also provides constraints on the rheological properties of the mantle and slab, and of continental margins in the region.
TL;DR: In this article, the authors proposed a new lithospheric scenario for the regional evolution in the Aegean-Anatolian-Near East region that combines a recent compilation of surface geology data with the structure of the upper mantle.
TL;DR: In this paper, the impact behavior of composite sandwich slabs was investigated using an instrumented drop weight machine and the impact data such as deflection and impact force-time history and permanent deformation after impact were reported.
TL;DR: In this paper, the Critical Shear Crack Theory is applied to flat slabs subjected to impact loading and the model is particularly useful for progressive collapse analysis and flat slab-column connections subjected to an impulsive axial load in the column.
TL;DR: In this paper, an upper mantle model of the Pacific Northwest was constructed using a full-wave ambient noise tomographic method. But the authors focused on the upper mantle of the Cascade volcanic arc.
TL;DR: In this paper, the nitrogen concentrations [N] and isotopic compositions of ultramafic mantle rocks were investigated to assess the role of such rocks in deep-Earth N cycling.
Abstract: The nitrogen concentrations [N] and isotopic compositions of ultramafic mantle rocks that represent various dehydration stages and metamorphic conditions during the subduction cycle were investigated to assess the role of such rocks in deep-Earth N cycling. The samples analyzed record low-grade serpentinization on the seafloor and/or in the forearc wedge (low-grade serpentinites from Monte Nero/Italy and Erro Tobbio/Italy) and two successive stages of metamorphic dehydration at increasing pressures and temperatures (high-pressure (HP) serpentinites from Erro Tobbio/Italy and chlorite harzburgites from Cerro del Almirez/Spain) to allow for the determination of dehydration effects in ultramafic rocks on the N budget. In low-grade serpentinites, δ15Nair values (−3.8 to +3.5 ‰) and [N] (1.3–4.5 μg/g) are elevated compared to the pristine depleted MORB mantle (δ15Nair ~ −5 ‰, [N] = 0.27 ± 0.16 μg/g), indicating input from sedimentary organic sources, at the outer rise during slab bending and/or in the forearc mantle wedge during hydration by slab-derived fluids. Both HP serpentinites and chlorite harzburgites have δ15Nair values and [N] overlapping with low-grade serpentinites, indicating no significant loss of N during metamorphic dehydration and retention of N to depths of 60–70 km. The best estimate for the δ15Nair of ultramafic rocks recycled into the mantle is +3 ± 2 ‰. The global N subduction input flux in serpentinized oceanic mantle rocks was calculated as 2.3 × 108 mol N2/year, assuming a thickness of serpentinized slab mantle of 500 m. This is at least one order of magnitude smaller than the N fluxes calculated for sediments and altered oceanic crust. Calculated global input fluxes for a range of representative subducting sections of unmetamorphosed and HP-metamorphosed slabs, all incorporating serpentinized slab mantle, range from 1.1 × 1010 to 3.9 × 1010 mol N2/year. The best estimate for the δ15Nair of the subducting slab is +4 ± 1 ‰, supporting models that invoke recycling of subducted N in mantle plumes and consistent with general models for the volatile evolution on Earth. Estimates of the efficiency of arc return of subducted N are complicated further by the possibility that mantle wedge hydrated in forearcs, then dragged to beneath volcanic fronts, is capable of conveying significant amounts of N to subarc depths.
TL;DR: In this article, a finite element modeling technique is developed to simulate punching and post-punching behavior of flat plates, which is verified against an available punching experiment, however, the experiment did not impose lateral restraints on the slab, but, the punching strength of the same experiment accounting for the effects of lateral restraint is numerically investigated.
TL;DR: In this article, the authors investigated the robustness of a seismically designed steel moment frame building using 3-D nonlinear models and found that the prototype building can be more vulnerable to loss of columns in the upper stories than in the lower ones.
Abstract: This study investigates the robustness of a seismically designed steel moment frame building using 3-D nonlinear models. Computational simulations are carried out using validated models to investigate building response to loss of internal and external columns as well as columns in lower, middle and upper floors. Studies are conducted to gain insight into the sources of collapse resistance of the prototype building, focusing in particular on the role of composite action between the slab and underlying steel beams and slab membrane action. The simulation results suggest that the prototype building can be more vulnerable to loss of columns in the upper stories than in the lower ones and is particularly vulnerable to loss of interior gravity columns at all floor levels. The role of the slab is quantified and it is shown that it can contribute significantly to the robustness of the structure, but it is a double edge sword that can also be detrimental, especially in the final stages of collapse.
TL;DR: In this paper, ion probe microanalyses of F, Cl and S in serpentine minerals were performed to represent the P-T evolution of the oceanic lithosphere, from its serpentinization at the ridge, to its dehydration at around 100 km depth during subduction.
Abstract: The abundances of F, Cl and S in arc magmas are systematically higher than in other mantle-derived magmas, suggesting that these elements are added from the slab along with H2O. We present ion probe microanalyses of F, Cl and S in serpentine minerals that represent the P–T evolution of the oceanic lithosphere, from its serpentinization at the ridge, to its dehydration at around 100 km depth during subduction. F, Cl and S are incorporated early into serpentine during its formation at mid-ocean ridges, and serpentinized lithosphere then carries these elements to subduction zones. More than 50% of the F, Cl and S are removed from serpentine during the prograde metamorphic lizardite/antigorite transition. Due to the low solubility of F in water, and to the low amount of water released during this phase transition, the fluids mobilizing these elements must be dominated by SOX rather than H2O.
TL;DR: In this article, the authors investigated the structural behavior of RC flat slabs supported on rectangular interior columns and the influence of the loading conditions (one or two-way bending) on their punching shear strength.
TL;DR: In this paper, a finite element model is proposed and verified by experimental data using interface element to model the bond properties between steel decking and concrete slab and investigate the ultimate strength of composite slabs.
TL;DR: In this paper, the authors used a stereoscopic Particle Image Velocimetry (sPIV) technique to map the 3D mantle flow on 4 vertical cross-sections for one experiment and on 3 horizontal depth-section for another experiment.
TL;DR: In this article, the authors investigate the impact of slab detachment in collision systems that are subjected to along-trench variations using high-resolution thermomechanical numerical models, encompassing experimentally derived flow laws and a pseudo free surface.
Abstract: Understanding the three-dimensional (3-D) dynamics of subduction-collision systems is a longstanding challenge in geodynamics. We investigate the impact of slab detachment in collision systems that are subjected to along-trench variations. High-resolution thermomechanical numerical models, encompassing experimentally derived flow laws and a pseudo free surface, are employed to unravel lithospheric and topographic evolutions. First, we consider coeval subduction of adjacent continental and oceanic lithospheres (SCO). This configuration yields to two-stage slab detachment during collision, topographic buildup and extrusion, variable along-trench convergence rates, and associated trench deformation. The second setting considers a convergent margin, which is laterally limited by a transform boundary (STB). Such collisional system is affected by a single slab detachment, little trench deformation, and moderately confined upper plate topography. The effect of initial thermal slab age on SCO and STB models are explored. Similarities with natural analogs along the Arabia-Eurasia collision are discussed.
TL;DR: In this article, the effects of internal curing on the developments of internal relative humidity and free shrinkage in high strength concrete slab are analyzed by continually measuring the interior humidity of concrete immediately after slab casting until 28 days.
TL;DR: In this paper, the authors compare the seismic properties between the flat and normal subduction regions in central Chile, to better understand the links between the slab geometry, surface deformation and the deeper structures.
Abstract: Our study compares the seismic properties between the flat and normal subduction regions in central Chile, to better understand the links between the slab geometry, surface deformation and the deeper structures. In comparison with previous studies, we show the most complete 3-D regional seismic tomography images for this region, in which we use (1) a larger seismic data set compiled from several short-term seismic catalogues, (2) a denser seismic array allowing a better resolution of the subduction zone from the trench to the backarc and into the upper ∼30 km of the slab and (3) a starting 1-D background velocity model specifically calculated for this region and refined over the years. We assess and discuss our tomography results using regional seismic attenuation models and estimating rock types on the basis of pressure and temperature conditions computed from thermomechanical models. Our results show significant seismic differences between the flat and normal subduction zones. As expected, the faster seismic velocities and increased seismicity within the flat slab and overriding lithosphere are generally consistent with a cooler thermal state. Our results are also consistent with dehydration of the mantle above the subducted Juan Fernandez Ridge at the eastern tip of the flat slab segment, indicating that the latter retains some fluids during subduction. However, fluids in the upper portion of the flat slab segment are not seismically detected, since we report instead fast slab seismic velocities which contradict the argument of its buoyancy being the cause of horizontal subduction. The forearc region, above the flat slab, exhibits high Vs and very low Vp/Vs ratios, uncorrelated with typical rock compositions, increased density or reduced temperature; this feature is possibly linked with the aftershock effects of the Mw7.1 1997 Punitaqui earthquake, the flat slab geometry and/or seismic anisotropy. At the surface, the seismic variations correlate with the geological terranes. The Andean crust is strongly reduced in seismic velocities along the La Ramada–Aconcagua deformation belt, suggesting structural damage. Slow seismic velocities along the Andean Moho match non-eclogitized hydrated rocks, consistent with a previous delamination event or a felsic composition, which in turn supports the extent of the Chilenia terrane at these depths. We confirm previous studies that suggest that the Cuyania terrane in the backarc region is mafic and contains an eclogitized lower crust below 50-km depth. We also hypothesize major Andean basement detachment faults (or shear zones) to extend towards the plate interface and canalize slab-derived fluids into the continental crust.
TL;DR: In this article, a combination of published arc-type volcanic ages and earthquake locations in the subducting Pacific plate was used to investigate the evolution of slab geometry under the North Island of New Zealand.
Abstract: Evolution of slab geometry beneath the North Island, New Zealand, has been investigated using a combination of published arc-type volcanic ages and earthquake locations in the subducting Pacific plate. Arc-front volcanoes migrated SE by 150 km in the last 8 myr subparallel to the present active arc. Migration of the arc is interpreted to mainly reflect slab rollback along the Tonga–Kermadec subduction system changing to fixed hinge slab steepening beneath the central North Island. The strike of the Pacific plate beneath the North Island, imaged by Benioff zone seismicity (50–200 km) and positive mantle velocity anomalies (200–600 km), is parallel to the NE–SW trend of arc-front volcanism. Arc parallelism since 16 Ma indicates that the strike of the subducting plate beneath the North Island was constant over this time interval, in contrast to clockwise vertical-axis rotations of ≥50° of the overriding plate over the same period along the eastern and southern Hikurangi margin. Acceleration of arc-front migration rates (from c . 4 to c . 18 mm a −1 ), eruption of high-Mg# andesites, increasing eruption frequency and size, and uplift of the overriding plate indicate an increase in the hydration, temperature and size of the mantle wedge beneath the central North Island from c . 7 Ma.
TL;DR: In this article, a new composite beam and floor system was developed to achieve a higher strength and ductility, as well as to yield a more economical design purpose, which consists of three elements: reinforced concrete slab on corrugated cold-formed metal deck, back to back coldformed steel joists, and continuous coldformed furring shear connector.
TL;DR: In this article, the authors used teleseismic Rayleigh waves to image large-scale variations in shear wave structure for the subducting Pacific/Yakutat slab.
Abstract: Southcentral Alaska is a complex tectonic region that transitions from subduction of Pacific crust to flat slab subduction—and collision—of overthickened Yakutat crust. Because much of the Yakutat crust has been subducted, seismic imaging is needed in order to understand the crustal and upper mantle structural framework for this active tectonic setting. Here we use teleseismic Rayleigh waves to image large-scale variations in shear wave structure. Our imaging technique employs a two-plane wave representation with finite frequency sensitivity kernels. Our 3-D isotropic model reveals several features: the subducting Pacific/Yakutat slab, slow wave speeds characterizing the onshore Yakutat collision zone, slow wave speeds of the Wrangell subduction zone, and a deep tomographic contrast at the eastern edge of the Pacific/Yakutat slab. We produce anisotropic phase velocity maps that exhibit variations in the fast direction of azimuthal anisotropy. These maps show the dominance of the Yakutat slab on the observed pattern of anisotropy. West of the Yakutat slab the fast directions are approximately aligned with the plate convergence direction. In the region of the Yakutat slab the pattern is more complicated. Along the margins of the slab the fast directions are roughly parallel to the margins. We identify notable differences and similarities with published SKS splitting measurements. Integrative modeling using 3-D anisotropy models and different seismic measurements will be needed in order to establish a detailed 3-D anisotropic velocity model for Alaska. This study provides a large-scale starting point for such an effort.