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Slab
About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.
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TL;DR: In this article, the authors made 4366 shear wave splitting measurements using high-quality seismograms of many earthquakes occurring in the crust and the subducting Pacific slab and provided important new information on the S wave anisotropy in the upper crust, lower crust, mantle wedge, and subducted Pacific slab.
Abstract: To study the anisotropic structure beneath northeast (NE) Japan, we made 4366 shear wave splitting measurements using high-quality seismograms of many earthquakes occurring in the crust and the subducting Pacific slab. Our results provide important new information on the S wave anisotropy in the upper crust, lower crust, mantle wedge, and subducting Pacific slab. In the upper crust, the anisotropy is mainly caused by the stress-aligned fluid-saturated microcracks. The measured delay times (DTs) increase to 0.10 s at 10–11 km depth; the fast velocity directions (FVDs) are parallel to either the tectonic stress or the strike of active faults. The maximum DTs for the low-frequency earthquakes near the Moho are 0.15–0.17 s, suggesting strong anisotropy at the base of the crust or in the uppermost mantle. The measurements for the intermediate-depth earthquakes in the Pacific slab show dominant E-W (trench-normal) FVDs in the back-arc area and N-S (trench-parallel) FVDs in the fore-arc area. The trench-normal FVDs in the back-arc area are caused by the corner flow in the mantle wedge as a result of the subduction of the Pacific plate. The maximum DTs for the slab earthquakes reach 0.30–0.32 s at 100 km depth, but only half of the total DTs are produced in the mantle wedge. The small DTs in the mantle wedge may result from an isotropic or weak anisotropic zone in the middle of the mantle wedge. In the fore arc, the dominant trench-parallel FVDs for the slab earthquakes are consistent with those for the upper crust earthquakes, and ∼80% of the total DTs can be accounted for by the anisotropy in the crust. In the subducting Pacific slab, the trench-parallel FVDs may reflect either the original fossil anisotropy in the Pacific plate when the plate was produced in the mid-ocean ridge or the preferred orientations of the crystals and cracks in the upper part of the subducting slab.
83 citations
TL;DR: In this article, the authors proposed that the double seismic zones are due to sagging of the slab under its own weight, where the asthenosphere (between about 100 and 200 km) provides little support or resistance to the slab.
Abstract: The seismic zone beneath several island arcs between about 100 and 200 km depth consists of an upper zone having down-dip compression and a lower zone having down-dip tension. Several numerical models of the Aleutian arc were computed to test the hypothesis that these double seismic zones are due to sagging of the slab under its own weight. This sagging occurs because the asthenosphere (between about 100 and 200 km) provides little support or resistance to the slab, which is supported from below by the more viscous mesosphere and from above by the lithosphere. The viscosity of the mesosphere was constrained to the interval between 0.25 x 10 to the 22nd and 0.5 x 10 to the 22nd P by noting that the slab would have mainly down-dip compression at higher viscosities and mainly down-dip tension at lower viscosities. The deviatoric stress in the slab and the fault plane between the slab and the island arc is about 200-300 bars (expressed as shear stress). The models were calibrated to the observed depth and gravity anomalies in the trench.
83 citations
TL;DR: It is shown that oxidised iron and sulfur are found in sub-arc mantle spinel and glass inclusions with elevated U/Th, Pb/Ce, Sr/Nd and δ34S, trace dehydration products of slab serpentinites, which provide a link between liberated slab components and oxidised arc magmas.
Abstract: Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO4) and dissolved SO42− in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe3+/∑Fe in spinel record a S6+–Fe2+ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and δ34S (+ 7 to + 11‰), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas.
83 citations
TL;DR: In this article, a mechanical modeling approach for the simulation of partially restrained (PR, or semirigid) steel and composite connections subjected to any loading regime is described, and verification studies utilizing this approach are presented.
Abstract: A mechanical modeling approach for the simulation of partially restrained (PR, or semirigid) steel and composite connections subjected to any loading regime is described, and verification studies utilizing this approach are presented. This paper first presents a description of the advantages and drawbacks of a previously published component model, which served as the basis for developments discussed here. An original mechanical model is then introduced and described in detail. This model is capable of taking into account the influence of all the main deformation components, including slip in the bolts, partial interaction between the concrete slab and steel girder, shear deformation of the panel zone, and cracking and crushing of the slab. The model also evaluates the energy dissipated by each component, leading to a clear understanding of the connection behavior. Preliminary validation analyses are then presented and discussed. Results indicate that this approach can predict the complex behavior of PR composite connections well, and that the computation effort is minimal when compared to more sophisticated approaches.
83 citations
01 Dec 2011
TL;DR: Ricard et al. as mentioned in this paper modeled the Farallon-Juan de Fucas subduction during the past 40 Ma by assimilating plate motion history, paleo-age of sea floor, and paleogeography of plate boundaries in a 3D numerical model.
Abstract: Article history:Accepted 19 September 2011Available online 5 October 2011Editor: Y. RicardKeywords:Farallon subductionslab segmentationseismic tomographyviscosityB&R extensiontoroidal mantle flow Recent tomography images reveal a complex 3D mantle structure beneath western United States, with fea-ture morphology varying rapidly with depth. By assimilating plate motion history, paleo-age of sea floor,and paleo-geography of plate boundaries in a 3-D numerical model, we simulate the Farallon–Juan de Fucasubduction during the past 40 Ma. We find that the highly segmented upper mantle structure of westernU.S. is a direct result of the Farallon subduction. We show that the tilted ‘horseshoe’-shaped fast seismicanomaly beneath Nevada and Utah at 300–600 km depth range is in fact a segment of curled slab subductedsince 15 Ma, and the shallower linear slab beneath the Cascades is younger than 5 Ma. The distinct morphol-ogy between these two parts of the subduction system indicates the strong influence of the fast trench roll-back since 20 Ma, the northward migrating JF–PA–NA triple-junction, and the toroidal flow around slabedges. The observed mantle structures are used to constrain the rheology of the upper mantle throughmatching the shape, depth, and location of modeled subducted slab segments. The inferred viscosity forthe asthenosphere is 5×10
83 citations