Phase Velocities Of Love Waves Research Articles

Phase velocity of love waves as function of heterogeneity and void parameter

The present study looks at the Love wave propagating through an elastic layer containing empty pores situated above a heterogeneous elastic semi-infinite space. We have constructed separate formulations of equations of motion for both media under congruous boundary conditions. The separation of variables approach is used to build the phase velocity frequency relation in compact form using the Whittaker function. The resulting closed-form dispersion equation matches the conventional Love wave equation when heterogeneity has been removed. The propagation of Love waves is strongly influenced by a porous layer of limited thickness across an elastic semi-infinite space. Three wave fronts are demonstrated to have the potential to propagate. The equilibrated inertia and the variation in the void volume fraction are related to two wave fronts that are connected to the characteristics of the void pores. Numerical treatments are applied and graphically illustrated to implement these effects associated to Love waves’ phase velocity.

Cenozoic Volcanic Provinces and Shallow Asthenospheric Volumes in the Circum‐Mediterranean: Evidence From Magmatic Geochemistry, Seismic Tomography, and Integrated Geophysical‐Petrological Thermochemical Inversion

AbstractWe compile an extensive catalog comprising geochemistry and ages of Cenozoic volcanic provinces in the Mediterranean region, distinguishing between three groups according to the geochemistry of magmatic rocks: intraplate (IVP), subduction‐related (SRVP), and mixed‐origin volcanic provinces (MVP; intraplate with subduction imprint). In order to relate their spatial distribution to properties of the lithosphere‐asthenosphere system, we determine temperature‐depth profiles by integrated geophysical‐petrological inversion at representative locations, using Rayleigh and Love wave phase velocities, heat flow, rock densities, and accounting for thermochemical conditions. The results confirm the occurrence of thin lithosphere (<100 km) above warm asthenosphere (>1,300°C) in areas of low shear‐wave velocities in the shallow upper mantle. Nine shallow asthenospheric volumes (SAVs) between 70 and 300 km depths are identified, forming a partly interconnected belt across the Circum‐Mediterranean. A remarkable colocation exists between the SAVs and the intraplate and mixed‐origin volcanic provinces (IMVPs). Whereas dense networks of IMVPs have formed above the SAVs, IMVPs are absent in areas of thick mantle lithosphere. Magmatic activity in IMVPs at 60–70 Ma indicates that several SAVs existed already in the Paleogene (Central European, Adriatic, Western Mediterranean, and Moesian SAVs). The formation of SAVs is related either to asthenospheric upwelling caused by slab rollback and back‐arc extension (Aegean‐Anatolian, Moesian, Pannonian, Western Mediterranean SAVs), or to thermal upwelling (Adriatic, Central European, Middle East [MEA], North African, Rhine‐Rhone SAVs), with some of the latter coupled partly with continental rifting (Central European, MEA, North African, Rhine Rhone SAVs).

Effects of compressive stress on wave Love waves propagation in a piezoelectric semiconductor ZnO/Diamond: A screening effect

The issue of applied stress in hetero-structures is a persistent problem in materials science and technology. Significant efforts have been made from both numerical and experimental points of view to gain a better understanding of how to address this issue in various engineering industrial applications. In this paper, we numerically calculate the effects of compressive stress on Love waves propagation in a pre-stressed piezoelectric semiconductor ZnO/Diamond. The p-type semiconductor is explicitly taken into account, where the concentrations of holes and electrons are p0 = 1 × 1024m−3and n0 = 1 × 1023m−3, respectively. Numerical results show that the phase velocities of Love waves decrease with uniaxial stress equal to -100 MPa. In addition, this uniaxial compressive stress contributes to a decrease in the magnitude of the electric potential and the concentrations of holes and electrons. In the meantime, the “Screening effect” remains similar for both the unstressed and the pre-stressed structures.

Broadband Love Wave Phase Velocity Maps Based on Modified Double‐Beamforming of Ambient Noise Cross‐Correlations

AbstractAmbient noise tomography has become a popular method in the past two decades to image the crust and uppermost mantle structure. To date, broadband Rayleigh wave signals can be obtained from ambient noise, which can be utilized to study the earth's interior structure from the surface down to ∼200–300 km depths. However, it is hard to extract intermediate‐ and long‐period (>50 s) Love wave signals from ambient noise using conventional data processing techniques for ambient noise. Array‐based data processing techniques can enhance weak signals. In this study, we adopt a modified algorithm of the double‐beamforming method to extract broadband Love wave signals from ambient noise. We validate the accuracy of the dispersion curves measured from our method by comparing them to those measured from the conventional method. Then, we use a finite frequency ambient noise tomography method to construct broadband Love wave phase velocity maps across the contiguous USA. These phase velocity maps are consistent with those obtained from conventional methods at short periods (<40 s). Finally, we analyze the resolution of our double‐beamforming method based on checkerboard tests and find that the resolution of phase velocity maps based on our method is close to the aperture of the subarrays used in our double‐beamforming method.

Love wave on a flexoelectric piezoelectric-viscoelastic stratified structure with dielectrically conducting imperfect interface.

The present work investigates the propagation of Love wave in a flexoelectric piezoelectric-viscoelastic stratum imperfectly bonded to a piezoelectric-viscoelastic substrate. To study the impact of imperfect interfaces, the non-traditional boundary conditions for two different types of imperfect interfaces have been taken into account. The frequency relation has been obtained in complex form employing a suitable variable separable technique. The dispersion and damping equations of Love wave have been analytically determined in the closed form by separating the real and imaginary part of the frequency relation for two distinct interfaces, i.e., mechanically compliant and dielectrically weakly/highly conducting interfaces in both electrically open and electrically short cases. Numerical calculations are carried out to reveal the impact of the width of stratum, imperfectness parameter, flexoelectric parameters, and flexoelectric loss moduli on the phase velocity and attenuation coefficient of Love wave and are also depicted through graphs for both the interfaces. For validation purposes, the expressions derived as a result of the present study are matched with the standard Love wave equation.

Crustal and uppermost mantle structure near the Gloria Fault, North Atlantic, from ocean bottom seismometer surface wave observations

SUMMARY In this work, we present both 1-D and 3-D shear wave velocity (Vs) models of the oceanic crust and uppermost mantle below the Deep OCean Test ARray area, located ∼ 70 km north of the central section of the Gloria Fault, in the eastern North-Atlantic Ocean. The velocity models are inferred from the dispersion of surface waves recorded on ocean bottom seismometers. Dispersion measurements are obtained from the analysis of ambient seismic noise at short periods (< 14 s) and teleseismic surface waves at long periods (> 14 s) using the two-station method. The 1-D Vs model is inferred from the joint inversion of Rayleigh wave phase velocities and Love wave group and phase velocities. The 3-D tomographic model is obtained by inversion of 2-D Love wave group velocity maps as a function of depth, further constrained by the average of Love wave phase velocities obtained from ambient noise (4–9 s) and the average Rayleigh and Love wave phase velocities calculated from teleseismic data (14–44 s). The 1-D Vs model shows a sediment layer with a low velocity of 1.05 km s−1, similar to previous studies in the region. Below the sediments, we find an oceanic crust with velocities ranging from 3.3 to 4.5 km s−1. The model reaches an unusually high velocity of 4.9 km s−1 in a 20 km thick layer at depths between 16 and 36 km. We interpret this fast velocity layer as indicative of the presence of harzburgite, a residue of enhanced melting that might have been formed by the proximity between the Mid-Atlantic Ridge and the Azores mantle plume. At greater depths the velocity decreases, forming a low-velocity zone that reaches a minimum at ∼ 70 km depth, which we interpret as the maximum depth for the lithosphere–asthenosphere boundary. The 3-D model shows a structure that is mostly horizontally layered, with Vs isocontours at 3.5–4.5 km s−1 highlighting oscillations of the crustal structure with wavelengths of ∼25–30 km. These oscillations may be due to changes in the rate of mantle upwelling and magma supply rate.

Wavefield Modeling and Analysis of Lightning Quakes Measured by a Distributed Acoustic Sensing Array

ABSTRACT Lightning-induced seismic waves, termed “lightning quakes,” are frequent natural sources in many storm-prone regions. Lightning quakes have been clearly observed in numerous environments by both seismic and acoustic instruments, for example, by distributed acoustic sensing (DAS) array. Despite these numerous observations, the physical nature of lightning quake wavefields detected by ground-based arrays remains poorly understood. The possibility of electroseismic (ES) conversion due to lightning’s powerful electromagnetic fields was, until now, unstudied. This investigation uses 3D numerical simulations of acoustic-to-seismic and ES wavefields alongside a novel data-driven azimuthal strain-rate variation analysis technique to robustly reveal the complex nature of lightning quakes. We show that lightning quakes begin as airborne acoustic waves before coupling with the solid earth as air-coupled Rayleigh waves and Love waves that are generated by local sources near the receiver, such as topography or urban infrastructure. These conclusions suggest thunder observations from a DAS array can be used to infer the structure of the near surface around the receiver, but care needs to be taken in understanding the role of local sources. An estimate of the Rayleigh- and Love-wave phase velocities is produced using a novel data analysis method unique to DAS. Furthermore, we demonstrate that electroseismic coupling does not play a significant role in the lightning quake wavefields. Although these simulations do not fully capture the realistic frequency of the electroseismic coupled wavefield, theory suggests that the wavefield is high frequency and thus quickly attenuated in the saturated near-surface soils. Electroseismic coupled wavefields from lightning may be detectable very close to the bolt.

Propagation of Love Waves Through an Irregular Surface of a Layered Poroelastic Rock Structure

The present study adduces the dynamic properties of the propagating Love waves passing through the irregular upper surface of transversely isotropic poroelastic structure. The dispersion relation for scattered Love waves in a closed form and induced reflected displacement caused by scattering of waves have been derived. The impact of the porosity of the upper layer and half-space on the phase velocity and also on the reflected displacement have also been studied. The porosity of both upper layer and half-space have significant effect on the phase velocity of Love waves. Moreover, the nature of induced reflected displacement with the change in vertical irregularity parameter is also analyzed. The vertical irregularity parameter (associated with the vertical depth of irregularity) has escalating impact on the induced reflected displacement. The comparative analysis of reflected displacement in three distinct scenarios of vertical irregularity has also been done.

Observations of Love Wave Dispersion Properties Using Seismometers and Component Strainmeters

With amplitude ratio of two different types of ground motion, the information of phase velocity could be reflected in the frequency-dependent in the assumption of plane-wave propagation. In this paper, we test the possibility of determining local Love waves dispersion properties using transverse velocity and strain measurement. With the strain seismic wave recording of the four-component borehole strainmeters built at the Balun seismic station in Xinjiang, China., we estimated the Love wave phase velocities using amplitude ratios between transverse velocity and shear strain components. The results show the possibility that we could recover general Love wave dispersion characteristics that conformed to the realistic local structure at periods ranging from 20-120 s.

Propagation of love waves under the effect of parabolic irregularity in isotropic fluid-saturated porous medium

This study represents the Love wave propagation in a fluid-saturated transversely isotropic porous layer resting over a non-homogeneous elastic half-space. The irregularity considered is in the form of parabola at the interface of isotropic fluid saturated medium and non-homogeneous elastic half-space. The dispersion equation has been derived for the concerned problem by using Fourier Transform and inverse Fourier Transform method. The effect of different ratios of the depth of medium and the irregularity on the phase velocity of Love wave in the concerned problem are demonstrated graphically with the help of MATLAB, and it has been observed that the phase velocity is affected wave number, depth and shape of irregularity, and on medium width.

Gradation and porosity’s effect on Love waves in a composite structure of piezoelectric layers and functionally graded porous piezoelectric material

Love waves propagation in a composite structure lying over an elastic half-space are studied. The composite structure contains n piezoelectric layers and a functionally graded porous piezoelectric material(FGPPM) layer. The linear and exponential gradation of mechanical and electrical properties of the FGPPM layer are considered. The WKB technique is applied for obtaining the solution of the equations in the FGPPM layer. The transfer matrix is obtained for multilayers of piezoelectric materials. The frequency equations for both electrically open and short boundaries have been obtained. Numerical computations have been done to solve the frequency equations and to obtain electromechanical coupling, stress and displacements. The effect of porosity, wavenumber and gradation on the phase velocity and group velocity of Love waves have been studied and observed that group velocity is more affected by porosity than the phase velocity. Better resolution without compromising the magnitude of surface wave velocity seems to be achievable for piezoceramic having 20% to 30% porosity. Apart from these, the variations of attenuation and electromechanical coupling factor with grading parameters and porosity have also been examined and noticed that the grading type has a considerable effect on the coupling factor and attenuation quality factor. A relative study is conducted to demonstrate the impact of the number of piezoelectric layers above the FGPPM layer on dispersion curves and it is found that more energy is trapped with layering in a stack and an initial increase in the number of layers in the stack of composites is more effective. The effects of porosity and wavenumber on mechanical displacement, electrical displacement and stress have been studied numerically. Also, lateral and vertical variations of the mechanical displacement, electrical displacement and stress have been studied. The findings of the study are expected of use in improving the efficiency of SAW devices.

Array‐Based Teleseismic Love Wave Tomography

AbstractFundamental mode Love waves from earthquakes can be contaminated by higher modes, which can affect the accuracy of phase velocity measurements. If such contaminations are not well dealt with, models of Earth's interior structures based on Love waves could be significantly biased. In this study, we develop an array‐based teleseismic Love wave tomography method that can mitigate higher‐mode interference effects and therefore obtain more accurate phase‐velocity maps compared to previous studies. By applying our tomography method to synthetic data, we first illustrate the effectiveness of our method in construction phase velocity maps of fundamental Love waves when 30% of Love waves are contaminated by higher modes. In addition, as a case study, we apply our method to field data from the Western United States to construct phase velocity maps at 20–100 s period. By comparing phase velocity maps obtained by our method with those obtained by ambient noise data which do not suffer the interferences of higher modes, we demonstrate our method can obtain Love wave phase velocity maps as accurately as those based on ambient noise data with deviations smaller than 0.5% of the average value of these phase velocity maps, further illustrating the validity of our method in constructing Love wave phase velocity maps.

Love Wave Tomography of the United States

AbstractLove wave phase velocity maps provide essential constraints on radial anisotropy and deformation in the crust and upper mantle. However, the phenomenon of overtone interference causes scatter and systematic bias in the velocity measurements and impedes efforts to image small‐scale anisotropic variations. We develop an approach for identifying Love wave measurements that are biased by overtone interference, demonstrate its efficacy with EarthScope USArray data, and determine the first earthquake‐derived Love wave phase velocity maps for the entire conterminous U.S. in the period range 35–75 s. We show that radial anisotropy in parts of the crust and most of the lithospheric mantle is necessary to reconcile these maps with Rayleigh wave phase velocities. Our results convey the impact and geographic variability of overtone interference, offer an easy‐to‐implement method to ameliorate this impact, and present high‐resolution constraints on radial anisotropy beneath North America.

Application of six-component ambient seismic noise data for high-resolution imaging of lateral heterogeneities

SUMMARY We develop a novel approach for imaging subsurface lateral heterogeneities using six-component (6C) ambient seismic noise data, consisting of three translational components and three rotational components. We first derive the 6C cross-correlation functions (CCFs) from ambient seismic noise data for surface waves and then apply the modified frequency Bessel (MF-J) transform to the 6C CCFs for surface wave dispersion curves. The phase velocities of Rayleigh and Love waves can be directly calculated from the 6C CCFs of a single pair of stations. Traditional array-based surface wave methods derive the surface wave phase velocity based on the presumption of a horizontally layered model. When this assumption breaks down due to the presence of, for example, dipping layer or heterogeneities, the resulting phase velocity can be severely smeared. By contrast, the proposed approach is not limited by the layered model assumption because it relies on single-point measurements to calculate the localized dispersion relations of the formation right beneath a receiver. Our numerical modelling results demonstrate that this approach is applicable to heterogeneous models and can image small-scale subsurface anomalies with very high lateral resolution.

The Radial Anisotropy of the Continental Lithosphere From Analysis of Love and Rayleigh Wave Phase Velocities in Fennoscandia

AbstractRadial anisotropy (RA) in the upper mantle of the Fennoscandian Shield is analyzed by joint inversion of Love and Rayleigh wave phase velocities measured from recordings of teleseismic events at the ScanArray network. The phase velocities are measured by beamforming using three geographical subsets of the network as well as the full network. We analyze how different procedures for determining the phase velocities influence the final result and uncertainty. Joint inversion of the phase velocities in the period range 22–100 s reveals the presence of similar RA in the three subregions, with an average ξ value of about 1.05 in the subcrustal lithosphere down to at least 200 km depth. This corresponds to SH waves faster than SV by 2%–3%, a value very similar to those found in other continental regions. Considering this anisotropy together with other observables pertaining to seismic anisotropy in the area, we cannot propose a unique model satisfying all data. We can show, however, in which conditions different types of olivine crystallographic preferred orientations (CPOs) commonly observed in natural samples are compatible with the observations. CPO types associated with the preferred orientation of the a‐axis, in particular the common A‐type CPO, require a‐axes dipping not more than 25° from the horizontal plane to explain our observations. AG‐type CPO, characterized by preferred orientation of the b‐axis and occurring in particular in compressional settings, can be considered as an interesting alternative interpretation of continental lithospheric anisotropy, provided the olivine b‐axis is dipping by at least 60°.

Crustal structure beneath the northeastern margin of the Tibetan plateau and its surrounding regions revealed by direct surface wave radial anisotropy tomography

We assemble the continuous waveform data recorded by 571 broadband temporary seismic stations from 2014 to 2015 in the northeastern (NE) margin of the Tibetan plateau and its surrounding regions. Rayleigh and Love wave phase velocity dispersion curves (T = 5–50 s) are obtained by the image transformation technique. Then the phase velocity dispersion data are used to jointly invert the 3-D shear wave velocity (Vs) and radial anisotropy (ξ) models in the study region with the direct surface wave radial anisotropy tomography (DRadiSurfTomo) method. The ξ is negative and positive in the upper crust and mid-to-lower crust, respectively, indicating that the crustal deformation pattern is depth-dependent. The middle crust beneath the NE margin of the Tibetan plateau generally exhibits positive ξ. Two low-velocity zones (LVZs) are detected beneath the Songpan-Garzê block and the western Qinling orogen as well as the northern Qilian orogen. High-velocity zone (HVZ) and positive ξ are characterized in the mid-to-lower crust beneath both the Alxa block and the Ordos basin. Combining with the previous results, we propose these two blocks, as a whole belonging to a part of the North China Craton (NCC), effectively restrict the northeastward growth of the Tibetan plateau. The uneven crustal deformation along the boundary between the NE margin of the Tibetan plateau and its surrounding regions is likely to be affected by the far-field stress originating from the collision between the Indian and Eurasian plates.

Measuring the phase of ambient noise cross correlations: anisotropic Rayleigh and Love wave tomography across the Oman Mountains

SUMMARY Ambient seismic noise tomography has, over the last two decades, developed into a well-established tool for imaging seismic properties of the Earth’s crust. Fundamental mode Rayleigh and Love wave phase velocity dispersion curves can be measured from ambient noise cross-correlation functions (CCF) either using a high-frequency approximation theory, or by fitting the spectrum of the CCF to a Bessel function. Here, we advance the latter approach and present an automated algorithm that fits the phase of the Hankel function to the phase of the causal symmetric part of the CCF in order to determine phase velocity curves as continuous functions of frequency. Synthetic tests verify the reliability of the proposed method in the presence of low signal-to-noise ratio (SNR). Moreover, usage of the phase allows for robust phase velocity measurements at longer periods than when using the zero crossings of the Bessel function only and is, therefore, particularly useful at short inter-station distances. In the frequency domain, acceptable bandwidths of smooth phase velocity curves are obtained in an automated procedure using a set of fine-tuned quality criteria. We apply the method to 2.5 yr of continuous waveform data recorded by 58 temporary and permanent broad-band seismic stations in northern Oman. We obtain 1072 and 670 phase velocity curves for Rayleigh and Love waves, respectively, in the period range of 2–40 s. The data are inverted for isotropic and azimuthally anisotropic period-dependent phase velocity maps. Synthetic reconstruction tests show that the phase velocity maps have a lateral resolution of ∼30 km. The results suggest distinctly different middle to lower crustal architecture between the northern and eastern Oman Mountains. Azimuthal anisotropy shows contrasting fast propagation orientations in the shallow and deep crust, which we attribute to stress-induced and structural anisotropy in the upper crust and to lattice-preferred orientation in the lower crust.

Crustal Structure across the West Antarctic Rift System from Multicomponent Ambient Noise Surface Wave Tomography

Abstract Approximately 2 yr (2010–2011) of continuous seismic records from a subset of the Antarctic component of the Polar Earth Observing Network (POLENET-ANET) seismic network deployed in West Antarctica are used to compute the nine components of the correlation tensor between each pair of stations in the network. Rayleigh wave velocity information from the vertical and radial components was extracted in the form of group and phase velocity dispersion curves, whereas the transverse component provided complimentary Love wave velocity information. The multicomponent Rayleigh wave measurements (ZZ, RR, ZR, and RZ) were averaged and used to infer the measurement uncertainties. The Rayleigh and Love wave group and phase velocities were then regionalized in space using a 2D deterministic tomography. A transect that spans the West Antarctic rift system was extracted from the tomography at individual periods between 7 and 60 s for the four types of surface wave velocities (i.e., Rayleigh and Love phase and group velocities). A transdimensional Bayesian joint inversion algorithm was used to invert these four datasets for a 1D model of isotropic shear-wave velocity versus depth at each point along the transect. In this way, surface wave dispersion curves from multicomponent noise correlations were used to build a 2D isotropic shear-wave velocity model down to ∼55 km depth. In this model, the top of the large low-velocity zone beneath Marie Byrd Land was imaged (up to a 5% decrease in velocity at ∼50 km depth), which provides further evidence for a mantle hot spot beneath the crust that supports the high topography in this region. We also observed a large velocity contrast in the lower crust beneath Marie Byrd Land at a depth where previous long-period seismicity has been observed. This strong contrast occurs more shallow than in previous crustal models, which compared to our model identify a deeper Moho (∼5–10 km deeper) beneath Marie Byrd Land. This new model has implications for interpreting earthquake locations in this region and perhaps necessitates that we revisit past hypocenter estimation studies using updated velocity models for the region.

A Short-Period Surface-Wave Dispersion Dataset for Model Assessment of Africa’s Crust: ADAMA

Abstract We present the first in a series of dataset and model assessment products for investigating Africa’s lithosphere (ADAMA). This is a comprehensive catalog of short-period interstation surface-wave dispersion measurements and uncertainties. It is derived from processing continuous recordings of all publicly available three-component seismograms, spanning four decades, from ∼1372 stations, across 62 seismic networks deployed in and around the African continent. It includes Love- and Rayleigh-wave dispersion derived from frequency-domain ambient noise cross-correlation functions (NCFs). Phase and group dispersion, as well as their uncertainties, are then obtained with an iterative nonlinear waveform fitting of the NCFs, using a spectral element representation of a path-average a priori Earth model. Our catalog represents the following advances: (1) a large distribution of short period dispersion measurements: ∼114,000 interstation pairs at periods between 5 s and 40 s, (2) inclusion of uncertainties useful for regularization in continent-wide model building, (3) preliminary model assessments for different tectonic domains on the continent, and (4) an exemplary Love-wave phase velocity map obtained by Bayesian inversion revealing detailed features not previously detected. ADAMA will be used to prepare short-period, high-resolution dispersion maps, and for assessment and updates of widely used seismic velocity models of the crust across a diversity of terranes on the continent.

Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

AbstractMany recent Antarctic seismic structure studies use Rayleigh wave data and thus determine only the SV structure. Love waves provide greater resolution for shallow structure, and coupled with Rayleigh waves, can constrain radial anisotropy by comparing vertically (VSV) and horizontally (VSH) polarized shear velocities. In this study, we jointly analyze Rayleigh and Love wave phase and group velocities from ambient noise to develop a new radially anisotropic velocity model for West and Central Antarctica with an improved shallow crustal resolution using all broadband data collected in Antarctica over the past 20 years. Group and phase velocity maps for Rayleigh and Love waves are estimated and inverted for shear wave velocity structure using a Monte Carlo method. We determine a new sediment distribution map that reveals a thick sedimentary basin (∼4 km) beneath the Southeastern Ross Embayment. Sediment thicknesses at interior basins such as the Polar Subglacial Basin and Bentley Subglacial Trench are modest (<1.5 km), suggesting that these basins are sediment‐starved. The shallow crust as well as the mid‐to‐lower crust in several places shows strong positive anisotropy (VSH > VSV), likely due to lattice preferred orientation of mica‐bearing rocks. However, large regions of the mid‐to‐lower crust show negative anisotropy, likely due to lattice preferred orientation of plagioclase. The uppermost mantle is characterized by strong positive radial anisotropy (4%–8%) in West Antarctica, with the largest anisotropy beneath the Transantarctic and Whitmore Mountains, likely resulting from horizontal olivine preferred orientation due to tectonic activity.