Full‐wave effects on shear wave splitting

Lin, Yu‐Pin; Zhao, Li; Hung, S.

doi:10.1002/2013gl058742

Cited by 23 publications

(23 citation statements)

References 28 publications

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“…Niu & Perez 2004); however, we must first rule out heterogeneous upper-mantle anisotropy or full waveform effects as making major contributions to the observed discrepancies. Previous work taking into account finite frequency wave propagation (for homogeneous upper-mantle anisotropy models) has shown that modest differences in SI (up to ∼ 0.2) for SKS and SKKS phases of the same event-station pair can result from waveform interference effects (Lin et al 2014). Specifically, Lin et al (2014) showed that waveform interference can strongly affect SKS-SKKS SI measurements for shallow sources (<20 km) at epicentral distances less than than ∼100 • .…”

Section: Sks-skks Splitting Intensity Discrepancies and Their Interprmentioning

confidence: 97%

“…Previous work taking into account finite frequency wave propagation (for homogeneous upper-mantle anisotropy models) has shown that modest differences in SI (up to ∼ 0.2) for SKS and SKKS phases of the same event-station pair can result from waveform interference effects (Lin et al 2014). Specifically, Lin et al (2014) showed that waveform interference can strongly affect SKS-SKKS SI measurements for shallow sources (<20 km) at epicentral distances less than than ∼100 • . In the epicentral distance range, we use in this study (108 • -140 • ), we expect waveform interference in the upper mantle to alter the SIs of the same station-event SKS-SKKS pairs by at most 10 per cent, with maximum interference at distances of ∼130 • (Lin et al 2014).…”

Section: Sks-skks Splitting Intensity Discrepancies and Their Interprmentioning

confidence: 97%

“…Specifically, Lin et al (2014) showed that waveform interference can strongly affect SKS-SKKS SI measurements for shallow sources (<20 km) at epicentral distances less than than ∼100 • . In the epicentral distance range, we use in this study (108 • -140 • ), we expect waveform interference in the upper mantle to alter the SIs of the same station-event SKS-SKKS pairs by at most 10 per cent, with maximum interference at distances of ∼130 • (Lin et al 2014). (One important but subtle point is that Lin et al (2014) used a slightly different formulization for SI than that of Chevrot 2000, which is the formulation we use in our work; these formulations are different by a factor of 0.5).…”

Section: Sks-skks Splitting Intensity Discrepancies and Their Interprmentioning

confidence: 99%

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Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: constraints from SKS–SKKS splitting intensity measurements

Deng¹,

Long²,

Creasy³

et al. 2017

Geophysical Journal International

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Seismic anisotropy has been documented in many portions of the lowermost mantle, with particularly strong anisotropy thought to be present along the edges of large low shear velocity provinces (LLSVPs). The region surrounding the Pacific LLSVP, however, has not yet been studied extensively in terms of its anisotropic structure. In this study, we use seismic data from southern Peru, northern Bolivia and Easter Island to probe lowermost mantle anisotropy beneath the eastern Pacific Ocean, mostly relying on data from the Peru Lithosphere and Slab Experiment and Central Andean Uplift and Geodynamics of High Topography experiments. Differential shear wave splitting measurements from phases that have similar ray paths in the upper mantle but different ray paths in the lowermost mantle, such as SKS and SKKS, are used to constrain anisotropy in D. We measured splitting for 215 same station-event SKS-SKKS pairs that sample the eastern Pacific LLSVP at the base of the mantle. We used measurements of splitting intensity(SI), a measure of the amount of energy on the transverse component, to objectively and quantitatively analyse any discrepancies between SKS and SKKS phases. While the overall splitting signal is dominated by the upper-mantle anisotropy, a minority of SKS-SKKS pairs (∼10 per cent) exhibit strongly discrepant splitting between the phases (i.e. the waveforms require a difference in SI of at least 0.4), indicating a likely contribution from lowermost mantle anisotropy. In order to enhance lower mantle signals, we also stacked waveforms within individual subregions and applied a waveform differencing technique to isolate the signal from the lowermost mantle. Our stacking procedure yields evidence for substantial splitting due to lowermost mantle anisotropy only for a specific region that likely straddles the edge of Pacific LLSVP. Our observations are consistent with the localization of deformation and anisotropy near the eastern boundary of the Pacific LLSVP, similar to previous observations for the African LLSVP.

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Section: Sks-skks Splitting Intensity Discrepancies and Their Interprmentioning

confidence: 97%

Section: Sks-skks Splitting Intensity Discrepancies and Their Interprmentioning

confidence: 97%

Section: Sks-skks Splitting Intensity Discrepancies and Their Interprmentioning

confidence: 99%

See 1 more Smart Citation

Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: constraints from SKS–SKKS splitting intensity measurements

Deng¹,

Long²,

Creasy³

et al. 2017

Geophysical Journal International

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“…Before we can interpret our splitting intensity discrepancy data set in detail, however, we first consider to what extent effects other than lower mantle anisotropy may contribute to the observed discrepancies, such as full waveform interference effects or heterogeneous anisotropic structure in the shallow upper mantle or crust (Deng et al, 2017). Lin et al (2014) 10.1029/2018JB017160…”

Section: 1029/2018jb017160mentioning

confidence: 99%

Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting

2019

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We investigate seismic anisotropy in the lowermost mantle in the vicinity of the African large low shear velocity province (LLSVP) using observations of differential SKS‐SKKS shear‐wave splitting. We use data from 375 permanent and temporary stations in Africa which enable us to map the spatial distribution of the anisotropic regions of the lowermost mantle in unprecedented detail. Our results corroborate previous findings that anisotropy is most clearly observed at the margins of the LLSVP, indicating strong deformation at its border, and they are generally consistent with a mostly isotropic LLSVP interior. We find that most discrepant SKS‐SKKS measurements sample the lowermost mantle close to what is inferred to be the root of the Afar plume. We also identify strongly discrepant splitting in the vicinity of a previously mapped ultralow velocity zone (ULVZ) at the base of the LLSVP, beneath Central Africa. This represents an unusual observation of lowermost mantle anisotropy that is spatially coincident with a ULVZ and may reflect a unique anisotropic mechanism such as alignment of partial melt or the presence of strongly anisotropic magnesiowüstite. We interpret discrepant measurements outside of the LLSVP as likely reflecting a change in flow direction from the horizontal plane to a more vertical direction, which may be caused by deflection at the steep LLSVP border. We propose that our observations of D″ anisotropy associated with the African LLSVP can be explained by a mantle flow regime that maintains passive thermochemical piles with slab‐driven flow and allows for the formation of upwellings at their edges.

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“…Monteiller & Chevrot (2011) used data from dense seismic networks in southern California to apply finitefrequency SKS splitting tomography, producing a model of lateral and depth variations of anisotropy parameters. Lin et al (2014a) applied a full-wave approach to the computation of sensitivities and a multiscale parametrization to the inversion of a similar data set from southern California, based on insights from full-wave modelling of SKS phases (Lin et al 2014b).…”

Section: Finite Frequency Sks Splitting Tomography 239mentioning

confidence: 99%

A model space search approach to finite-frequency SKS splitting intensity tomography in a reduced parameter space

Mondal

Long

2019

Geophysical Journal International

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Here we develop a theoretical and practical framework for the tomographic inversion of shear wave splitting intensity measurements for anisotropic structure in the upper mantle using a model space search approach. Treating the anisotropic scatterers as a first order perturbation to the background isotropic state, we implement the Born approximation to compute the integral sensitivity kernels in a finite frequency framework. We implement a parametrization of the anisotropy based on insights from olivine elasticity and fabric development that involves three parameters (corresponding to the azimuth and dip of the anisotropic symmetry axis, plus a strength parameter). Previous work on finite-frequency shear wave splitting tomography has implemented a linearization technique to invert splitting intensity data for the spatial distribution of anisotropic scatterers. The inverse problem, however, is strongly non-linear in terms of several of the involved parameters (those that describe the orientation of the symmetry axis), and their variation is not of first order. Therefore, in the case of a realistic upper mantle where anisotropic structure varies in a complicated manner, a linearization technique may not be adequate. To ameliorate these problems, we implement a model space search approach (specifically, a Markov chain Monte Carlo with Gibbs sampling algorithm) to the tomographic inversion of splitting intensity data. This approach allows for the visualization of posterior probability distributions for anisotropic parameters in the inversion. We perform a suite of synthetic resolution tests to demonstrate the reliability of our method, using a station distribution from an actual deployment of a dense seismic network. These resolution tests show that anisotropic structure may be resolved up to a length scale of roughly 50 km with teleseismic SKS waves for station spacing of 10-15 km.

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Full‐wave effects on shear wave splitting

Cited by 23 publications

References 28 publications

Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: constraints from SKS–SKKS splitting intensity measurements

Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: constraints from SKS–SKKS splitting intensity measurements

Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting

A model space search approach to finite-frequency SKS splitting intensity tomography in a reduced parameter space

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