AxiSEM3D - an introduction to using the code and its applications

Fernando, Benjamin; Wolf, Jonathan; Leng, Kuangdai; Nissen-Meyer, Tarje; Eaton, Will; Styczinski, Marshall; Walker, Andrew; Craig, Timothy; Muir, Jack; Nunn, Ceri; Long, Maureen

doi:10.31223/x5th7p

Cited by 4 publications

(1 citation statement)

References 16 publications

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“…While ray-theoretical modeling is still popular due to its computational efficiency, we can now model wave propagation through arbitrary seismic anisotropy using global 3D wave propagation solvers (e.g., Cottaar & Romanowicz, 2013;Nowacki & Wookey, 2016;Tesoniero et al, 2020). AxiSEM3D (Fernando et al, 2024;Leng et al, 2016Leng et al, , 2019 is very efficient in this context and, therefore, frequently used (e.g., Tesoniero et al, 2020;Wolf & Long, 2022;Wolf et al, 2022aWolf et al, , 2022bWolf, Long, Frost, & Nissen-Meyer, 2024).…”

Section: Reviews Of Geophysicsmentioning

confidence: 99%

Advances in Mapping Lowermost Mantle Convective Flow With Seismic Anisotropy Observations

Wolf,

Li,

Long

et al. 2024

Reviews of Geophysics

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Convective flow in the deep mantle controls Earth's dynamic evolution, influences plate tectonics, and has shaped Earth's current surface features. Present and past convection‐induced deformation manifests itself in seismic anisotropy, which is particularly strong in the mantle's uppermost and lowermost portions. While the general patterns of seismic anisotropy have been mapped for the upper mantle, anisotropy in the lowermost mantle (called D′′) is at an earlier stage of exploration. Here we review recent progress in methods to measure and interpret D′′ anisotropy. Our understanding of the limitations of existing methods and the development of new measurement strategies have been aided enormously by the availability of high‐performance computing resources. We give an overview of how measurements of seismic anisotropy can help constrain the mineralogy and fabric of the deep mantle. Specifically, new and creative strategies that combine multiple types of observations provide much tighter constraints on the geometry of anisotropy than have previously been possible. We also discuss how deep mantle seismic anisotropy provides insights into lowermost mantle dynamics. We summarize what we have learned so far from measurements of D′′ anisotropy, how inferences of lowermost mantle flow from measurements of seismic anisotropy relate to geodynamic models of mantle flow, and what challenges we face going forward. Finally, we discuss some of the important unsolved problems related to the dynamics of the lowermost mantle that can be elucidated in the future by combining observations of seismic anisotropy with geodynamic predictions of lowermost mantle flow.

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Section: Reviews Of Geophysicsmentioning

confidence: 99%

Advances in Mapping Lowermost Mantle Convective Flow With Seismic Anisotropy Observations

Wolf,

Li,

Long

et al. 2024

Reviews of Geophysics

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The expression of mantle seismic anisotropy in the global seismic wavefield

Wolf,

Long,

Frost

et al. 2024

Geophysical Journal International

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Summary The dependence of seismic wavespeeds on propagation or polarization direction, called seismic anisotropy, is a relatively direct indicator of mantle deformation and flow. Mantle seismic anisotropy is often inferred from measurements of shear-wave splitting. A number of standard techniques to measure shear-wave splitting have been applied globally; for example, KS splitting is often used to measure upper mantle anisotropy. In order to obtain robust constraints on anisotropic geometry, it is necessary to sample seismic anisotropy from different directions, ideally using different seismic phases with different incidence angles. However, many standard analysis techniques can only be applied for certain epicentral distances and source-receiver geometries. To search for new ways to detect mantle anisotropy, instead of focusing on the sensitivity of individual phases, we investigate the wavefield as a whole: we apply a “wavefield differencing” approach to (systematically) understand what parts of the seismic wavefield are most affected by splitting due to seismic anisotropy in the mantle. We analyze differences between synthetic global wavefields calculated for isotropic and anisotropic input models, incorporating seismic anisotropy at different depths. Our results confirm that the seismic phases that are commonly used in splitting techniques are indeed strongly influenced by mantle anisotropy. However, we also identify less commonly used phases whose waveforms reflect the effects of anisotropy. For example, PS is strongly affected by splitting due to seismic anisotropy in the upper mantle. We show that PS can be used to fill in gaps in global coverage in shear-wave splitting datasets (for example, beneath ocean basins). We find that PcS is also a promising phase, and present a proof-of-concept example of PcS splitting analysis across the contiguous United States using an array processing approach. Because PcS is recorded at much shorter distances than KS phases, PcS splitting can therefore fill in gaps in backazimuthal coverage. Our wavefield differencing results further hint at additional potential novel methods to detect and characterize splitting due to mantle seismic anisotropy.

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ScS shear-wave splitting in the lowermost mantle: Practical challenges and new global measurements

Wolf,

Long

2024

Seismica

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Many regions of the Earth's mantle are seismically anisotropic, including portions of the lowermost mantle, which may indicate deformation due to convective flow. The splitting of ScS phases, which reflect once off the core-mantle boundary (CMB), is commonly measured to identify lowermost mantle anisotropy, although some challenges exist. Here, we use global wavefield simulations to evaluate commonly used approaches to inferring a lowermost mantle contribution to ScS splitting. We show that due to effects of the CMB reflection, only the epicentral distance range between 60° and 70° is appropriate for ScS splitting measurements. For this distance range, splitting is diagnostic of deep mantle anisotropy if no upper mantle anisotropy is present; however, if ScS is also split due to upper mantle anisotropy, the reliable diagnosis of deep mantle anisotropy is challenging. Moreover, even in the case of a homogeneously anisotropic deep mantle region sampled from a single azimuth by multiple ScS waves with different source polarizations (in absence of upper mantle anisotropy), different apparent fast directions are produced. We suggest that ScS splitting should only be measured at "null" stations and conduct such an analysis worldwide. Our results indicate that seismic anisotropy is globally widespread in the deep mantle.

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AxiSEM3D - an introduction to using the code and its applications

Cited by 4 publications

References 16 publications

Advances in Mapping Lowermost Mantle Convective Flow With Seismic Anisotropy Observations

Advances in Mapping Lowermost Mantle Convective Flow With Seismic Anisotropy Observations

The expression of mantle seismic anisotropy in the global seismic wavefield

ScS shear-wave splitting in the lowermost mantle: Practical challenges and new global measurements

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