Local Shear Wave Research Articles

Three‐dimensional distribution of seismic anisotropy in the Hikurangi subduction zone beneath the central North Island, New Zealand

We use earthquake arrival time data in the central North Island, New Zealand, in inversion for 3‐D Vp azimuthal anisotropy. It is parameterized with an isotropic component and two azimuthal anisotropy parameters for each node, and local earthquake shear wave splitting observations define the initial anisotropy model. Our results suggest that mantle flow, either within the mantle wedge or below the subducted slab, is not the primary source of anisotropy in the Hikurangi subduction zone. The largest region of anisotropy that we image is within the subducted slab, where anisotropy is consistently trench‐parallel and 5–9% magnitude from 32 to 185 km depth. Bending‐induced yielding in the slab offshore and as it passes through the trench provides an explanation for this slab anisotropy. Beneath the Taupo Volcanic Zone (TVZ), there is 1–4% trench‐normal anisotropy within 30 km of the surface of the slab, within a region entrained with motion of the slab. In contrast, only very weak (0–2%) anisotropy is imaged in the region of high‐temperature partial melt arising from active corner flow in the mantle wedge. In the crust geologic structure is important, with the largest crustal anisotropy (14%) related to schist. We image significant anisotropy aligned with the margins of the TVZ, related to extensive fracturing on the margins as the TVZ actively extends. Within the heavily intruded and underplated TVZ lower crust, the orientation of anisotropy switches to align with the extension direction. This orientation is consistent with other geophysical data suggesting the presence of connected melt in this region.

Near-source ground motion attenuation relationship for PGA and PSA of the vertical and horizontal components

In this paper, empirical ground-motion models for the vertical and average horizontal components of peak ground-motion and acceleration response spectra from shallow crustal earthquakes are derived using near-source database. These attenuation relationships were derived using a worldwide dataset consisted of corrected and processed accelerograms of 678 strong-motion records recorded with 60 km of the rupture plane of earthquakes between Mw 5.2 and 7.9. Ground motion models are functions of earthquake mechanism, distance from source to site, local average shear wave velocity, nonlinear soil response, sediment depth, depth-to-top of the rupture, hanging wall effects and faulting mechanism.

Propagation of shear waves generated by a modulated finite amplitude radiation force in a viscoelastic medium

An effective way to generate localized narrowband low-frequency shear waves within tissue noninvasively, is by the modulated radiation force, resulting from the interference of two confocal quasi-CW ultrasound beams of slightly different frequencies. By using approximate viscoelastic Green's functions, investigations of the properties of the propagated shear-field component at the fundamental modulation frequency were previously reported by our group. However, high-amplitude source excitations may be needed to increase the signal-to-noise-ratio for shear-wave detection in tissue. This paper reports a study of the generation and propagation of dynamic radiation force components at harmonics of the modulation frequency for conditions that generally correspond to diagnostic safety standards. We describe the propagation characteristics of the resulting harmonic shear waves and discuss how they depend on the parameters of nonlinearity, focusing gain, and absorption. For conditions of high viscosity (believed to be characteristic of soft tissue) and higher modulation frequencies, the approximate shear wave Green's function is inappropriate. A more exact viscoelastic Green's function is derived in k-space, and using this, it is shown that the lowpass and dispersive effects, associated with a Voigt model of tissue, are more accurately represented. Finally, it is shown how the viscoelastic properties of the propagating medium can be estimated, based on several spectral components of the shearwave spectrum.

Quantitative Viscoelasticity Mapping of Human Liver Using Supersonic Shear Imaging: Preliminary In Vivo Feasability Study

This paper demonstrates the feasibility of in vivo quantitative mapping of liver viscoelasticity using the concept of supersonic shear wave imaging. This technique is based on the combination of a radiation force induced in tissues by focused ultrasonic beams and a very high frame rate ultrasound imaging sequence capable of catching in real time the transient propagation of resulting shear waves. The local shear wave velocity is recovered using a dedicated time-of-flight estimation technique and enables the 2-D quantitative mapping of shear elasticity. This imaging modality is performed using a conventional ultrasound probe during a standard intercostal ultrasonographic examination. Three supersonic shear imaging (SSI) sequences are applied successively in the left, middle and right parts of the 2-D ultrasonographic image. Resulting shear elasticity images in the three regions are concatenated to provide the final image covering the entire region-of-interest. The ability of the SSI technique to provide a quantitative and local estimation of liver shear modulus with a millimetric resolution is proven in vivo on 15 healthy volunteers. Liver moduli extracted from in vivo data from healthy volunteers are consistent with those reported in the literature (Young's modulus ranging from 4 to 7.5 kPa). Moreover, liver stiffness estimation using the SSI mode is shown to be fast (less than one second), repeatable (5.7% standard deviation) and reproducible (6.7% standard deviation). This technique, used as a complementary tool for B-mode ultrasound, could complement morphologic information both for fibrosis staging and hepatic lesions imaging (E-mail: jl.gennisson@espci.fr).

Broadband simulations for Mw 7.8 southern San Andreas earthquakes: Ground motion sensitivity to rupture speed

Using the high‐performance computing resources of the Southern California Earthquake Center, we simulate broadband (0–10 Hz) ground motions for three Mw 7.8 rupture scenarios of the southern San Andreas fault. The scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0.96, 0.89, and 0.84 times the local shear wave velocity. Consistent with previous simulations, a southern hypocenter efficiently channels energy into the Los Angeles region along the string of basins south of the San Gabriel Mountains. However, we find the basin ground motion levels are quite sensitive to the prescribed rupture speed, with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15%. These results have important implications for estimating seismic hazards in Southern California and emphasize the need for improved understanding of earthquake rupture processes.

Strong variations in seismic anisotropy across the Hikurangi subduction zone, North Island, New Zealand

Shear wave splitting measurements from SKS, SKKS, S and ScS phases reveal the anisotropic structure of North Island, New Zealand. Waveforms were recorded on temporary and permanent broadband seismographs. Strong anisotropy varies rapidly across the Hikurangi subduction zone. These changes constrain the width of the deformation associated with the plate boundary and define three different regions of mantle flow. Stations in the fore-arc region, eastern central North Island record fast polarisations subparallel to the trench and moderate delay times of around 2.5 s, consistent with earlier studies of North Island. This is interpreted as caused by trench-parallel mantle flow beneath the subducted slab with a possible contribution of trench-parallel fossil anisotropy within the subducted slab. Delay times increase towards the extending Central Volcanic Region (CVR) with values up to 4.5 s, one of the largest delay times measured worldwide. Strong S-wave anisotropy (7.5%) through 80 km in the mantle wedge in addition to the sub-slab anisotropy can explain the observed high delay times. One mechanism to create such high anisotropy is melt segregation of partially molten rock. A frequency dependence of this mechanism could also explain persisting discrepancies between local and teleseismic shear wave splitting measurements. To the west, delay times decrease systematically. Measurements in the far back-arc region of western central North Island show no apparent splitting. This suggests that mantle wedge dynamics terminate beneath the western border of the CVR. The apparent isotropy beneath the far back-arc may be related to local small-scale mantle convection or vertical mantle flow, possibly caused by the detachment of lithosphere.

Lithospheric dismemberment and magmatic processes of the Great Basin–Colorado Plateau transition, Utah, implied from magnetotellurics

To illuminate rifting processes across the Transition Zone between the extensional Great Basin and stable Colorado Plateau interior, we collected an east‐west profile of 117 wideband and 30 long‐period magnetotelluric (MT) soundings along latitude 38.5°N from southeastern Nevada across Utah to the Colorado border. Regularized two‐dimensional inversion shows a strong lower crustal conductor below the Great Basin and its Transition Zone in the 15–35 km depth range interpreted as reflecting modern basaltic underplating, hybridization, and hydrothermal fluid release. This structure explains most of the geomagnetic variation anomaly in the region first measured in the late 1960s. Hence, the Transition Zone, while historically included with the Colorado Plateau physiographically, possesses a deep thermal regime and tectonic activity like that of the Great Basin. The deep crustal conductor is consistent with a rheological profile of a brittle upper crust over a weak lower crust, in turn on a stronger upper mantle (jelly sandwich model). Under the incipiently faulted Transition Zone, the conductor implies a vertically nonuniform mode of extension resembling early stages of continental margin formation. Colorado Plateau lithosphere begins sharply below the western boundary of Capitol Reef National Park as a resistive keel in the deep crust and upper mantle, with only a thin and weak Moho‐level crustal conductor near 45 km depth. Several narrow, steep conductors connect conductive lower crust with major surface faulting, some including modern geothermal systems, and in the context of other Great Basin MT surveying suggest connections between deep magma‐sourced fluids and the upper crustal meteoric regime. The MT data also suggest anisotropically interconnected melt over a broad zone in the upper mantle of the eastern Great Basin which has supplied magma to the lower crust, consistent with extensional mantle melting models and local shear wave splitting observations. We support a hypothesis that the Transition Zone location and geometry ultimately reflect the middle Proterozoic suturing between the stronger Yavapai lithosphere to the east and the somewhat weaker Mojave terrane to the west. We conclude that strength heterogeneity is the primary control on locus of deformation across the Transition Zone, with modulating force components.

Transient elastography in heterogeneous tissues

The Fibroscan® (Echosens, Paris, France) is a transient elastography based device used to quantify liver fibrosis by following the propagation of a low frequency shear wave and measuring the mean Young's modulus of the liver. This device has been successfully applied to homogeneous tissues such as liver in patients with chronic hepatitis C. Current developments in transient elastography are now headed toward the characterization of heterogeneous tissues. The estimation of the shear wave velocity can be achieved by solving the elastic wave equation taking into account either the 1D, the 2D, or the 3D components of the displacement spatial derivatives. The objective of this study is to characterize focal nodules in human liver and to quantify heterogeneous fibrosis. We present the methods used to estimate the local shear wave velocity and the results of experiments conducted on heterogeneous phantoms and in the liver in vivo.

Quantitative Assessment of Breast Lesion Viscoelasticity: Initial Clinical Results Using Supersonic Shear Imaging

This paper presents an initial clinical evaluation of in vivo elastography for breast lesion imaging using the concept of supersonic shear imaging. This technique is based on the combination of a radiation force induced in tissue by an ultrasonic beam and an ultrafast imaging sequence capable of catching in real time the propagation of the resulting shear waves. The local shear wave velocity is recovered using a time-offlight technique and enables the 2-D mapping of shear elasticity. This imaging modality is implemented on a conventional linear probe driven by a dedicated ultrafast echographic device. Consequently, it can be performed during a standard echographic examination. The clinical investigation was performed on 15 patients, which corresponded to 15 lesions (4 cases BI-RADS 3, 7 cases BI-RADS 4 and 4 cases BI-RADS 5). The ability of the supersonic shear imaging technique to provide a quantitative and local estimation of the shear modulus of abnormalities with a millimetric resolution is illustrated on several malignant (invasive ductal and lobular carcinoma) and benign cases (fibrocystic changes and viscous cysts). In the investigated cases, malignant lesions were found to be significantly different from benign solid lesions with respect to their elasticity values. Cystic lesions have shown no shear wave propagate at all in the lesion (because shear waves do not propage in liquid). These preliminary clinical results directly demonstrate the clinical feasibility of this new elastography technique in providing quantitative assessment of relative stiffness of breast tissues. This technique of evaluating tissue elasticity gives valuable information that is complementary to the B-mode morphologic information. More extensive studies are necessary to validate the assumption that this new mode potentially helps the physician in both false-positive and false-negative rejection.

The analytic properties and uniqueness of the solutions to problems of scattering by compact obstacles in an infinite plate described by the Uflyand-Mindlin model

The three-dimensional problem of the sound wave scattering by a compact obstacle of a general form in an Uflyand-Mindlin plate is considered. A formula that expresses the scattering field in terms of the analytic continuation of the directivity pattern is derived, and the formulas that describe the coupling of the scattering channels and allow the calculation of the surface wave amplitudes from the residues of the directivity pattern are obtained. For the case of nonradiating obstacles, the uniqueness of the solution to the scattering problem in the absence of absorption is established. An example of a localized shear wave is presented.

Two-Dimensional Sonoelastographic Shear Velocity Imaging

We introduce a novel 2-D sonoelastographic technique for estimating local shear velocities from propagating shear wave interference patterns (termed crawling waves) in this paper. A relationship between the local crawling wave spatial phase derivatives and local shear wave velocity is derived, with phase derivatives estimated using a 2-D autocorrelation technique. Comparisons were made between the 2-D sonoelastographic shear velocity estimation technique and its computationally simpler 1-D precursor. In general, the 2-D sonoelastographic shear velocity estimator outperformed the 1-D–based technique in terms of accuracy and estimator noise minimization. For both approaches, increasing the estimator kernel size reduces noise levels but lowers spatial resolution. Homogeneous elastic phantom results demonstrate the ability of sonoelastographic shear velocity imaging to quantify the true underlying shear velocity distributions as verified using time-of-flight measurements. Results also indicate that increasing the estimator kernel size increases the transition zone length about boundaries in heterogeneous elastic mediums and may complicate accurate quantification of smaller elastically contrasting lesions. Furthermore, analysis of contrast-to-noise ratio (CNR) values for sonoelastograms obtained in heterogeneous elastic phantoms reveal that the 2-D sonoelastographic shear velocity estimation technique outperforms the 1-D version for a given kernel size in terms of image noise minimization and contrast enhancement. Experimental results from an embedded porcine liver specimen with a radiofrequency ablation (RFA) lesion demonstrates that the 2-D sonoelastographic shear velocity estimation technique minimizes image noise artifacts and yields a consistent lesion boundary when compared with gross pathology. Volume measurements of the RFA lesion obtained from shear velocity sonoelastograms was comparable to that obtained by fluid displacement of the dissected lesion as illustrated by 3-D volume reconstructions. Overall, 2-D sonoelastographic shear velocity imaging was shown to be a promising new approach to characterizing the shear velocity distribution of elastic materials. (E-mail: hoyt@ece.rochester.edu)

The correlation of microtremors: empirical limits and relations between results in frequency and time domains

SUMMARY The use of the correlation of microtremor records is on its way to develop into a common tool to estimate local shear wave velocity structure. For this reason, the establishment of the conditions for the correct use of this method and its limitations when applied to real data is becoming increasingly important. In addition to the use of frequency domain spatial correlation technique [the Spatial Autocorrelation (SPAC) method], the use of time domain correlation to obtain the Green's function of the medium is rapidly gaining presence. We explore the use of microtremor correlation techniques in the time domain to determine local velocity structure and compare with previous results obtained with the same data using SPAC. Our data come from three experiments carried out in Parkway and Wainuiomata valleys in New Zealand, using broad-band portable stations. Interstation distances range from 5 m to 2.1 km, and our results are useful in the frequency band from 0.1 to 7 Hz. Frequency domain correlation requires an isotropic microtremor field, a condition that need not be satisfied in the time domain. Two station correlations provide useful results due to the temporal stationarity and isotropy, in average, of the microtremor wavefield. This manifests itself in the symmetry of the temporal correlation functions with respect to zero time. Our results show that the local velocity structure and the interstation distance are the key factors conditioning the frequency range where surface wave dispersion can be correctly measured either in frequency or time domains. We confirm that, when the interstation distance becomes much larger than the dominant wavelengths, only the correlation in time domain is useful. All our results indicate that the signal obtained in the correlation of vertical component microtremors is due to the fundamental mode of Rayleigh waves, which appears as the most stable propagation mode, without any indication of body waves.

Real-Time Shear Velocity Imaging Using Sonoelastographic Techniques

In this paper, a novel sonoelastographic technique for estimating local shear velocities from propagating shear wave interference patterns (termed crawling waves) is introduced. A relationship between the local crawling wave spatial phase derivatives and local shear wave velocity is derived with phase derivatives estimated using an autocorrelation technique. Results from homogeneous phantoms demonstrate the ability of sonoelastographic shear velocity imaging to quantify the true underlying shear velocity distributions as verified using time-of-flight measurements. Heterogeneous phantom results reveal the capacity for lesion detection and shear velocity quantification as validated from mechanical measurements on phantom samples. Experimental results obtained from a prostate specimen illustrated feasibility for shear velocity imaging in tissue. More importantly, high-contrast visualization of focal carcinomas was demonstrated introducing the clinical potential of this novel sonoelastographic imaging technique. (E-mail: hoyt@ece.rochester.edu)

Combining genetic and linearized algorithms for a two-step joint inversion of Rayleigh wave dispersion andH/Vspectral ratio curves

SUMMARY The joint inversion of Rayleigh wave dispersion and H/V curves from environmental noise measurements allows the retrieval of S-wave velocity profiles for the shallow subsoil. For this purpose, genetic and linearized algorithm have been combined in a two-step inversion procedure, that allows the principal drawbacks typical of the application of each algorithm separately to be overcome. In the first step, a genetic algorithm procedure is used to constrain the subvolume of the parameter space where the absolute minimum of the misfit function is located. In the second step, a linearized inversion algorithm, having as an initial guess the minimum misfit model deduced from the first step, is applied to force the inversion towards the optimal solution. To evaluate the feasibility and effectiveness of this approach, seismic noise recordings at a test site in the Po river valley (North Italy) have been analysed. Here, detailed geophysical and geological information is available along with earthquake recordings, which allow a well constrained definition of both the local shear wave profile and transfer function. Comparisons between theoretical and experimental S-wave velocity profiles and, above all, between the theoretical and experimental site response functions shows that this combination of inversion procedures can very efficiently to manage the extreme non-linearity of the problem.

Structure of the Grímsvötn central volcano under the Vatnajökull icecap, Iceland

The subglacial Grímsvötn central volcano, lying within a volcanic zone directly above the core of the Iceland mantle plume, is one of the most active in Iceland. Local, regional and teleseismic earthquake data recorded on a temporary seismometer array across western Vatnajökull icecap during the summer of 1998 have provided a three-dimensional image of the shallow crustal structure of the volcano. Microearthquake activity at depths of 1–4 km along the Grímsvötn caldera rim coincided with inflation of a shallow magma chamber beneath the caldera, which culminated in a 0.1 km3 eruption in December 1998. Tomographic inversion of these earthquakes define the extent of a low-velocity body beneath Grímsvötn with a volume of ∼20 km3 extending to ∼3 km below the surface. This low-velocity body is flanked by high velocities under the caldera rim. Delays in the P-wave arrival times through the Grímsvötn caldera from regional and teleseismic earthquakes and from two detonations ∼150 km east of Grímsvötn are 0.10–0.15 s greater than the delays through the uppermost 3–4 km of crust shown by local earthquake arrivals. This suggests the presence of a further low-velocity body at depths greater than 3–4 km beneath Grímsvötn, presumed to be due to the presence of melt. Using the distribution of local seismicity and shear wave attenuation we estimate the maximum lateral extent of the region containing partial melt to be 7–8 km E–W and 4–5 km N–S. P-wave delays require a thickness of less than 1 km of pure/high percentage partial melt, assuming a sill-like magma chamber.

Sonoelastographic imaging of interference patterns for estimation of shear velocity distribution in biomaterials

The authors have recently demonstrated the shear wave interference patterns created by two coherent vibration sources imaged with the vibration sonoelastography technique. If the two sources vibrate at slightly different frequencies omega and omega+deltaomega, respectively, the interference patterns move at an apparent velocity of (deltaomega/2omega)upsilon(shear), where upsilon(shear) is the shear wave speed. We name the moving interference patterns "crawling waves." In this paper, we extend the techniques to inspect biomaterials with nonuniform stiffness distributions. A relationship between the local crawling wave speed and the local shear wave velocity is derived. In addition, a modified technique is proposed whereby only one shear wave source propagates shear waves into the medium at the frequency omega. The ultrasound probe is externally vibrated at the frequency omega-deltaomega. The resulting field estimated by the ultrasound (US) scanner is proven to be an exact representation of the propagating shear wave field. The authors name the apparent wave motion "holography waves." Real-time video sequences of both types of waves are acquired on various inhomogeneous elastic media. The distribution of the crawling/holographic wave speeds are estimated. The estimated wave speeds correlate with the stiffness distributions.

Mantle upwellings, melt migration and the rifting of Africa: insights from seismic anisotropy

Abstract The rifting of continents and eventual formation of ocean basins is a fundamental component of plate tectonics, yet the mechanism for break-up is poorly understood. The East African Rift System (EARS) is an ideal place to study this process as it captures the initiation of a rift in the south through to incipient oceanic spreading in north-eastern Ethiopia. Measurements of seismic anisotropy can be used to test models of rifting. Here we summarize observations of anisotropy beneath the EARS from local and teleseismic body-waves and azimuthal variations in surface-wave velocities. Special attention is given to the Ethiopian part of the rift where the recent EAGLE project has provided a detailed image of anisotropy in the portion of the Ethiopian Rift that spans the transition from continental rifting to incipient oceanic spreading. Analyses of regional surface-waves show sub-lithospheric fast shear-waves coherently oriented in a north-eastward direction from southern Kenya to the Red Sea. This parallels the trend of the deeper African superplume, which originates at the core-mantle boundary beneath southern Africa and rises towards the base of the lithosphere beneath Afar. The pattern of shear-wave anisotropy is more variable above depths of 150 km. Analyses of splitting in teleseismic phases (SKS) and local shear-waves within the rift valley consistently show rift-parallel orientations. The magnitude of the splitting correlates with the degree of magmatism and the polarizations of the shear-waves align with magmatic segmentation along the rift valley. Analysis of surface-wave propagation across the rift valley confirms that anisotropy in the uppermost 75 km is primarily due to melt alignment. Away from the rift valley, the anisotropy agrees reasonably well within the pre-existing Pan-African lithospheric fabric. An exception is the region beneath the Ethiopian plateau, where the anisotropy is variable and may correspond to pre-existing fabric and ongoing melt-migration processes. These observations support models of magma-assisted rifting, rather than those of simple mechanical stretching. Upwellings, which most probably originate from the larger superplume, thermally erode the lithosphere along sites of pre-existing weaknesses or topographic highs. Decompression leads to magmatism and dyke injection that weakens the lithosphere enough for rifting and the strain appears to be localized to plate boundaries, rather than wider zones of deformation.

Radiation force of ultrasound as shear wave source in microscopic magnetic resonance elastography

Microscopic magnetic resonance elastography (micro-MRE) is a high-resolution imaging technique for measuring the viscoelastic properties of small synthetic and biological samples. Taking MRE to the microscopic scale requires stronger static fields, stronger magnetic field gradients, higher performance RF coils, and more compact, higher frequency shear wave actuators. Prior work by our group has been conducted at 11.74 T. A needle attached to a vibrating cantilever beam was placed in contact with the surface of the sample to generate shear waves up to 800 Hz. At higher frequencies, the excited shear waves attenuate within an extremely short distance such that only a very small region in the vicinity of the actuator can be studied due to inherent dynamic range limitations. In principle, modulated focused radiation force of US should be able to create a localized shear wave source within the test sample at a distance from the US transducer, thereby enabling micro-MRE probing of the sample at very high frequencies (up to 5 kHz). A confocal US transducer was fabricated to create such a source within the working constraints of the micro-MRE system. Initial feasibility studies are reviewed in this presentation. [Research supported by NIH Grant No. EB004885-01.]

Shear wave interferometry, an application of sonoelastography

Sonoelastography is an ultrasound imaging technique where low-amplitude, low-frequency (LF) vibration is detected and displayed via real-time Doppler techniques. When multiple coherent shear wave sources exist, shear wave interference patterns appear. Two shear wave sources at the same frequency create hyperbolic shaped interference patterns in homogeneous, isotropic elastic media. Shear wave speed can be estimated from the fringe separation and the source frequency. If the two sources are driven at slightly different sinusoidal frequencies, the interference patterns no longer remain stationary. It is proven that the apparent velocity of the fringes is approximately proportional to the local shear wave velocity. With this approach, local shear wave speed in elastic media can be estimated. In addition, with a single shear wave source at frequency f and the ultrasound probe externally vibrated at frequency f−Δf, a novel type of moving interference between the shear waves and the frame of reference motion is created. The moving interference fringes represent the shape of shear wave wavefronts while traveling at a much slower speed. This approach provides a real-time visualization of shear wave propagation and local wave speed estimation from which local stiffness is inferred. [Work supported by NIH.]

Detailed mapping of seismic anisotropy with local shear waves in southeastern Kamchatka

SUMMARY The Kamchatka Peninsula lies over a vigorous subduction zone where Pacific and North American plates converge at a rate of almost 80 mm yr −1 . Earthquakes associated with the subduction process provide an excellent source of seismic data for the study of anisotropic properties of the upper mantle and crust overlying the downgoing lithospheric slab. We collected a large set of shear waves from events within the slab recorded by a variety of seismic stations in Kamchatka. Data from permanent and temporary networks cover the entire ∼700 km length of the subduction zone, with 50‐200 km spacing between observing sites, resulting in an unprecedented coverage of the supraslab mantle wedge. We estimated shear wave splitting in selected S waves using two techniques and applied quality tests to ensure measurement stability. Fast directions vary from station to station, and they can vary with backazimuth at individual stations and with direction of propagation for individual sources. In over 350 measurements we recovered meaningful splitting delays, up to 1 s, with most delays in the 0.2‐0.6 s range. Additionally, in nearly 200 measurements splitting could not be resolved, yielding ‘NULL’ observations. Anisotropic properties of the Kamchatka supraslab mantle wedge vary greatly along the volcanic arc and forearc of the subduction zone. Observed anisotropic indicators in the arc and forearc correlate spatially with some tectonic features (e.g. volcanoes). Inland of the volcanic arc most splitting values indicate trench-parallel fast polarization. We do not observe depth dependence in local S-wave splitting delays, consistent with a shallow coherence of anisotropic texture. In the vicinity of Petropavlovsk-Kamchatsky observed anisotropic indicators are coherently trench-normal, and thus consistent with 2-D corner flow. However, splitting above the fragmented slab edge near the Klyuchevskoy volcanic centre is variable and trench-oblique. Birefringence between Petropavlovsk and Klyuchevskoy is weak. Overall, our observations are incompatible with a regional slab-driven corner flow regime.