Shear wave splitting in the Appalachians and the Urals: A case for multilayered anisotropy

Levin, Vadim; Menke, William; Park, Jeffrey

doi:10.1029/1999jb900168

Cited by 150 publications

(162 citation statements)

References 51 publications

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“…We suggest two possible reasons for the increased scatter. First, a Fresnel zone argument (Alsina and Snieder, 1995) would imply that the low-frequency measurements are sensitive to a larger anisotropic volume than the high-frequency mea- Table 1 Results of all splitting measurements reported in this study, for high-frequency and low-frequency bandpass filters formal errors on the fast direction ϕ and split time δt are reported; errors were calculated using the formulation of Levin et al (1999). Each measurement is classified as null (N), trench-parallel ( ), trench-perpendicular (⊥), or oblique (O).…”

Section: Resultsmentioning

confidence: 99%

“…We visually checked the corrected particle motion diagrams to ensure near-linearity, and the contour plots of the cross-correlation coefficient for each potential pair of splitting parameters were inspected to ensure the best-fitting (ϕ, δt) values were well-constrained. We calculated formal errors based on the formulation of Levin et al (1999). An example of a splitting analysis for a recording at station IGK is shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…This method grid-searches for the fast direction ϕ and split time δt that corrects the horizontal seismogram components to the two most nearly identical pulse shapes. We use an implementation of the cross-correlation algorithm described by Levin et al (1999). Long and van der Hilst (2005b) evaluated the performance of several shear wave splitting methods at Japanese stations and found that this method was generally stable and robust even for complex tectonic regions.…”

Section: Methodsmentioning

confidence: 99%

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Shear wave splitting from local events beneath the Ryukyu arc: Trench-parallel anisotropy in the mantle wedge

Long

Hilst

2006

Physics of the Earth and Planetary Interiors

141

148

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We present shear wave splitting measurements from local slab earthquakes at eight seismic stations of the Japanese F-net array located in the Ryukyu arc. We obtained high-quality splitting measurements for 70 event-station pairs and found that the majority of the measured fast directions were parallel to the strike of the trench and perpendicular to the convergence direction. Splitting times for individual measurements ranged from 0.25 to 2 s; most values were between 0.75 and 1.25 s. Both the fast directions and the split times were similar to results for teleseismic S(K)KS and S wave splitting at the same stations, which suggests that the anisotropy is located in the mantle wedge above the slab. We considered several mantle deformation scenarios that would result in predominantly trench-parallel fast directions, and concluded that for the Ryukyu subduction system the most likely explanation for the observations is corner flow in the mantle wedge combined with B-type olivine fabric. In this model, the flow direction in the wedge is perpendicular to the trench, but the fast axes of olivine crystals tend to align perpendicular to the flow direction, resulting in trench-parallel shear wave splitting.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Shear wave splitting from local events beneath the Ryukyu arc: Trench-parallel anisotropy in the mantle wedge

Long

Hilst

2006

Physics of the Earth and Planetary Interiors

141

148

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“…For a detailed explanation of the splitting methods used we refer to Long and van der Hilst (in press), but for the sake of completeness we summarize them here. The cross-correlation method (Fukao, 1984, and others; we use the implementation due to Levin et al, 1999) yields an estimate of ϕ and ␦t from the horizontal components of a single seismogram by grid-searching for the inverse splitting operator that maximizes the similarity in the pulse shapes of the corrected horizontal seismogram components (which therefore maximizes their cross-correlation). The second method, due to Chevrot (2000), uses the variation of the amplitudes of the transverse components with incoming polarization angle (which for core-refracted phases such as SKS is equivalent to the backazimuth).…”

Section: Methodsmentioning

confidence: 99%

“…Subduction-associated processes, therefore, are likely to lead to anisotropic structures that are more complicated than the simple single-layer anisotropic models that are often assumed when interpreting splitting measurements. Various studies have explored the effects of more complicated anisotropic models on splitting measurements, such as multilayered anisotropy Frazer, 1984, 1987;Silver and Savage, 1994;Özaleybey and Savage, 1994;Levin et al, 1999Levin et al, , 2000, dipping symmetry axes (Hartog and Schwartz, 2000;Chevrot, 2000;Chevrot and van der Hilst, 2003), and smooth variations in fast axis orientation with depth (Saltzer et al, 2000). However, the interpretation of shear wave splitting measurements in the presence of complicated three-dimensional anisotropic structure remains extremely difficult and non-unique.…”

Section: Introductionmentioning

confidence: 99%

Upper mantle anisotropy beneath Japan from shear wave splitting

Long

Hilst

2005

Physics of the Earth and Planetary Interiors

135

151

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In this study, we utilize data from 64 broadband seismic stations of the Japanese F-net network to investigate the threedimensional pattern of anisotropy in the subduction system beneath Japan. We have compiled a database of approximately 1900 high-quality splitting measurements, selected by visual inspection of over 25,000 records of S, SKS, and SKKS phases at F-net stations, covering a wide range of incidence angles, incoming polarization angles, and backazimuths. Analysis of the variations of measured splitting parameters with these parameters allows us to consider complexities in structure such as multiple anisotropic layers, dipping symmetry axes, and small-scale lateral variations in anisotropic properties. Here we focus on the presentation of the splitting measurements themselves; a detailed interpretation in terms of tectonics and mantle flow is beyond the scope of this paper.In the southern part of the F-net array, along the Ryukyu arc, we find that fast directions are consistently trench-parallel, with splitting times of 1 s or more. Moving northward along the array, the measured splitting patterns become more complicated, with significant variations in apparent splitting parameters that indicate complex anisotropic structure. Additionally, measured fast directions vary significantly over short length scales, and stations separated by less than 100 km often exhibit very different splitting behavior. This increase in complexity of anisotropic structure coincides geographically with the complicated slab morphology of the subducting Pacific plate. At stations on Hokkaido, to the north, and Kyushu, to the south, we see some evidence that the fast direction of anisotropy may rotate from trench-parallel close to the trench to subduction-parallel further away from the trench, which may correspond either to a change in stress conditions and/or volatile content, or to a change in flow regime.

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Ambient seismic noise tomography of Canada and adjacent regions: Part I. Crustal structures

et al. 2013

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This paper presents the first continental‐scale study of the crust and upper mantle shear velocity (Vs) structure of Canada and adjacent regions using ambient noise tomography. Continuous waveform data recorded between 2003 and 2009 with 788 broadband seismograph stations in Canada and adjacent regions were used in the analysis. The higher primary frequency band of the ambient noise provides better resolution of crustal structures than previous tomographic models based on earthquake waveforms. Prominent low velocity anomalies are observed at shallow depths (<20 km) beneath the Gulf of St. Lawrence in east Canada, the sedimentary basins of west Canada, and the Cordillera. In contrast, the Canadian Shield exhibits high crustal velocities. We characterize the crust‐mantle transition in terms of not only its depth and velocity but also its sharpness, defined by its thickness and the amount of velocity increase. Considerable variations in the physical properties of the crust‐mantle transition are observed across Canada. Positive correlations between the crustal thickness, Moho velocity, and the thickness of the transition are evident throughout most of the craton except near Hudson Bay where the uppermost mantle Vs is relatively low. Prominent vertical Vs gradients are observed in the midcrust beneath the Cordillera and beneath most of the Canadian Shield. The midcrust velocity contrast beneath the Cordillera may correspond to a detachment zone associated with high temperatures immediately beneath, whereas the large midcrust velocity gradient beneath the Canadian Shield probably represents an ancient rheological boundary between the upper and lower crust.

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Shear wave splitting in the Appalachians and the Urals: A case for multilayered anisotropy

Cited by 150 publications

References 51 publications

Shear wave splitting from local events beneath the Ryukyu arc: Trench-parallel anisotropy in the mantle wedge

Shear wave splitting from local events beneath the Ryukyu arc: Trench-parallel anisotropy in the mantle wedge

Upper mantle anisotropy beneath Japan from shear wave splitting

Ambient seismic noise tomography of Canada and adjacent regions: Part I. Crustal structures

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