Linear Seismic Array Research Articles

Extracting fault-zone structures using the virtual seismometer method: from theoretical to synthetic test

Summary Rocks near a fault plane are commonly damaged by multiple earthquake ruptures, forming damage zones. The damage zone is important structures controlling various properties of a fault, yet its fine scale (tens to hundreds of meters) structure is difficult to resolve with surface seismic observations. We propose to use earthquakes that occur at depth within a fault zone as virtual seismometers (VSs) and use surface observations to extract Green's function (GFs) between VS pairs (VSGFs) . This method resembles that of ambient noise tomography and the retrieved VSGFs are related to the structures between event pairs. In this study, we develop the theory about how to extract VSGFs using surface stations deployed across a fault zone. Firstly, we use a half-space model and Fresnel zone analysis to determine the upper and lower limits of the GF frequency band, which is controlled by the station spacing and aperture of a given seismic array. Then, for VS in a fault zone, we demonstrate that the VSGF can be retrieved by linear seismic arrays deployed across the fault, and that the VSGF is equivalent to waves emitted simultaneously from an array of mirror sources of one event and received by the other. Secondly, the half-space result is directly adopted to determine the corresponding frequency band in the damage zone situation. Thirdly, we analyze different combinations of VS pair geometry and conclude that a relatively larger VS distance (much larger than the damage zone width) is more effective to recover damage zone structures for the available frequency bands. In this situation, VSGFs are trapped waves, that is represented by the interference of mirror sources. In such a case, the trapped waves are equivalent to surface waves, which have dispersion features to extract damage zone structures. Finally, we adopt the VSGF method to the Ridgecrest earthquake aftershock monitoring array and use a profile of aftershocks to extract 6 pairs of VSGFs. The spatial variation of VSGFs may reflect the depth-dependent variation of damaged zone. Our analysis shows a promising direction to use VSGFs to extract spatial variations of fault damaged zones.

Fine Crust‐Mantle Structure of the Major Tectonic Boundaries Between the North China Craton and Central Asian Orogenic Belt Revealed From Rayleigh Wave Phase Velocities and Receiver Functions

AbstractThe Tanlu Fault Zone (TLFZ) and Chifeng‐Kaiyuan Fault (CKF) serve as tectonic boundaries between the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB). Clarifying the refined structure of these tectonic boundaries is crucial for understanding the relationships between the tectonic units and the heterogeneity in the destruction of the NCC. In this study, two linear seismic arrays were deployed across these tectonic boundaries. Based on the phase velocity dispersion and receiver functions extracted from the seismic arrays, the Hamiltonian Monte Carlo algorithm was employed for the joint inversion of the S‐wave velocity (Vs) in the crust and uppermost mantle. The Vs model was then used to correct the time differences in common conversion point (CCP) stacking. The CCP stacking results indicate that the boundary faults TLFZ and CKF are both whole‐crustal faults that separate the NCC and CAOB. The Vs structure showed a significant low‐velocity anomaly in the mantle beneath the NCC, with intense seismic activity within the crust. This suggests that the NCC was affected by the subduction of the Western Pacific, leading to crustal and mantle destruction. In contrast, the CAOB exhibited a clear high‐velocity anomaly with relatively stable crustal structures. We believe that the NCC and CAOB have undergone structural modification and destruction due to the closure of the Paleo‐Asian Ocean and the activities of the TLFZ since the Late Mesozoic. During the Cenozoic, the region east of the TLFZ experienced more significant destruction in the NCC than the other adjacent tectonic units.

Shear wave splitting and mantle dynamics of the southern Great Xing'an orogenic belt

We deployed a linear seismic array consisting of 50 broadband stations in the southern part of the Great Xing'an orogenic belt to investigate seismic anisotropy in the Songliao Basin, the orogenic belt and the Erlian Basin by making SKS wave splitting measurements. Different features of anisotropy are revealed on the two sides of the north-south gravity lineament. The anisotropy on the east side of the gravity lineament primarily results from mantle flows in the big mantle wedge above the flat Pacific slab in the mantle transition zone, and the SKS fast polarization direction is generally NW-SE, being consistent with the subduction direction of the western Pacific plate. On the west side of the gravity lineament, the SKS splitting is attributed to freezing anisotropy in the stable lithosphere under the Erlian Basin. The SKS splitting delay times show some changes with azimuths of the teleseismic events, but the fast polarization directions are generally the same, indicating that the anisotropies below these seismic stations have the same origin in the continental lithosphere and active flows in the big mantle wedge.

Ambient noise tomography of a linear seismic array based on an improved Voronoi tessellation

Ambient noise tomography, when applied to a dense linear seismic array, has the capability to provide detailed insights into the fine velocity structures across diverse tectonic settings. The linear station arrangement naturally generates parallel and concentrated ray paths along the array trend. This unique geometry requires specific optimization of the inversion methodology and model parameterization. The Bayesian-based transdimensional inversion method, characterized by its fully non-linear nature and high degree of freedom in parameter settings, offers a powerful tool for ambient noise inversion. To effectively adapt this method to a linear array layout, we propose a modification to the Voronoi cell tessellation built in the transdimensional method. By introducing spatial priority to the Voronoi kernels, we strategically increased the density of Voronoi cells along the direction of the array. We then applied the modified approach to a linear seismic array in the North China Craton and validated its robustness through phase velocity images and resolution tests. Our improved non-uniform sampling technique in the 2-D model space accelerates convergence while simultaneously enhancing model accuracy. Compared with the conventional damped least-squares method, the proposed algorithm revealed a shear-wave velocity map with notable low-velocity anomalies situated in the middle and lower crust beneath the borders of the Ordos block and its surrounding orogenic belt. Aligned with the crustal structures revealed by receiver function and electrical imaging, our findings indicated that the western and eastern margins of the Ordos block had experienced intensive crustal wedge deformation and re-melting, respectively.

High Frequency Passive Surface Wave Dispersion Extraction by Linear Seismic Array Aligned with Noise Source Azimuth

Due to the uneven spatial and temporal distribution of noise sources, the dispersion data extracted from high-frequency (>1Hz) ambient noise data would be contaminated and biased. Based on the azimuth analysis of the noise sources, we propose a linear array data acquisition strategy that considers the noise source direction to get high quality dispersion data.

The Crustal Magmatic Structure Beneath the Denali Volcanic Gap Imaged by a Dense Linear Seismic Array

AbstractThe crustal structure in south‐central Alaska has been influenced by terrane accretion, flat slab subduction, and a modern strike‐slip fault system. Within the active subduction system, the presence of the Denali Volcanic Gap (DVG), a ∼400 km region separating the active volcanism of the Aleutian Arc to the west and the Wrangell volcanoes to the east, remains enigmatic. To better understand the regional tectonics and the nature of the volcanic gap, we deployed a month‐long north‐south linear geophone array of 306 stations with an interstation distance of 1 km across the Alaska Range. By calculating multi‐component noise cross‐correlation and jointly inverting Rayleigh wave phase velocity and ellipticity across the array, we construct a 2‐D shear wave velocity model along the transect down to ∼16 km depth. In the shallow crust, we observe low‐velocity structures associated with sedimentary basins and image the Denali fault as a narrow localized low‐velocity anomaly extending to at least 12 km depth. About 12 km, below the fold and thrust fault system in the northern flank of the Alaska Range, we observe a prominent low‐velocity zone with more than 15% velocity reduction. Our velocity model is consistent with known geological features and reveals a previously unknown low‐velocity zone that we interpret as a magmatic feature. Based on this feature's spatial relationship to the Buzzard Creek and Jumbo Dome volcanoes and the location above the subducting Pacific Plate, we interpret the low‐velocity zone as a previously unknown subduction‐related crustal magma reservoir located beneath the DVG.

Ambient noise differential adjoint tomography reveals fluid-bearing rocks near active faults in Los Angeles

Water scarcity is a pressing issue in California. We develop ambient noise differential adjoint tomography that improves the sensitivity to fluid-bearing rocks by canceling bias caused by noise sources. Here we image the shallow S-wave velocity structure using this method beneath a linear seismic array (LASSIE) in Los Angeles Basin, which shows significant velocity reduction marking a major regional water producer, the Silverado aquifer, along with other fluid-bearing structures. Based on the S-wave tomography and previous P-wave studies, we derive the porosity in Long Beach and discover that the rock from 1-2 km depth surrounding the Newport-Inglewood Fault contains abundant fluids with pore-fluid fraction ~0.33. The high-porosity rock around the fault coincides with previously observed week-long shallow seismicity south of LASSIE array in Long Beach. The imaged S-wave velocity in the top layer shows a similar trend in the geotechnical layer Vs 30, suggesting additional applications to ground motion prediction.

Shear-wave velocity imaging of weathered granite in La Campana (Chile) from Bayesian inversion of micro-tremor H/V spectral ratios

Subsurface imaging of the regolith layer is an important tool for weathering zone characterization. For example, the extent of bedrock modification by weathering processes can be modelled by means of differing seismic velocities. We acquired a 360 m-long seismic profile in central Chile to characterise weathering at a semi-arid site. We used 87 3-component geophones, which continuously recorded ambient seismic noise for three days. The seismic line was centered at an 88 m deep borehole, providing core and downhole logging data for calibration. We extract Horizontal-to-Vertical Spectral Ratio (HVSR) curves along the seismic line to image the subsurface. Temporal analysis of the HVSR curves shows that the ambient noise vibrations recorded during the nighttime provide more stable HVSR curves. The trans-dimensional Bayesian Markov chain Monte Carlo (McMC) approach was used to invert the micro-tremor HVSR curves at each station to reconstruct 1D shear-wave velocity (Vs) models. The resulting individual 1D Vs models were merged to create a 2D Vs model along the linear seismic array in La Campana. The resulting Vs model shows an increase from 0.85 km/s at the surface to ca. 2.5 km/s at 100 m depth. We use the interface probability as a by-product of the Bayesian inversion to apply a more data-driven approach in identifying the different weathering layers. This method identified the boundary between saprolite and fractured bedrock at 42 m depth at the borehole, as evidenced by the interpretation of downhole logging data such as magnetic susceptibility. The resulting 2D Vs model of this site in Mediterranean climate shows a strong correlation between the interpreted weathering front at around 90-m depth and a higher precipitation rate in the study site compared to arid sites. The horizontal alignment of the weathering front indicates a correlation between the weathering front depth with topography and fractures in the bedrock.

Multi-source wavefield reconstruction combining interferometry and compressive sensing: application to a linear receiver array

SUMMARY Seismic interferometry (SI) is a technique that allows one to estimate the wavefields accounting for the wave propagation between seismometers, any of which can act as a virtual source (VS). Interferometry, particularly noise interferometry, has been applied to several geophysical disciplines such as passive monitoring and distributed acoustic sensing. In practice, one requires long recordings of seismic noise for noise interferometry. Additionally, one can have missing seismic interferometric traces because some receivers in seismic arrays may be absent or inoperative due to issues of receiver installation and malfunction. Thus, filling the gap of seismic interferometric profile requires wavefield reconstruction and regularization techniques. Compressive sensing (CS) is one such method that can reconstruct seismic interferometric wavefields and help mitigate the limitations by exploiting the sparsity of seismic waves. In our work, we use CS to reconstruct missing seismic interferometric wavefields. One can interpolate interferometric wavefields using correlograms provided by one VS. We call this method of reconstructing an individual VS gather single-source wavefield reconstruction. We propose an alternative technique called multi-source wavefield reconstruction, which applies CS to reconstruct multiple interferometric wavefields using a volume of VS gathers provided from all available VSs. Using numerical examples, we show that one can apply CS to recover interferometric wavefields resulting from interferometry of a linear seismic array. To exploit the sparsity of interferometric wavefields, we apply the Fourier and Curvelet transforms to the two reconstruction schemes. Using the signal-to-noise ratio (SNR) to compare reconstruction of interferometric wavefields, the Fourier multi-source method improves the recovery of interferometric wavefields by approximately 50 dB compared to the Fourier and Curvelet single-source wavefield reconstructions.

Hot mantle upwelling and Mesozoic mineralization in Southeast China

Our study region is located in the Cathaysia block (CB), Southeast China. The most significant feature of the CB is the widespread Mesozoic magmatism and poly-metallic mineralization. However, there is still no consensus on their genesis and related tectonic processes. In this study, we determine high-resolution (0.3° in the horizontal direction) tomographic images of Vp and Vs and Vp/Vs ratio in the crust and upper mantle using 6773 P-wave and 4526 S-wave travel-time data of teleseismic events recorded by a broadband linear seismic array. The array was deployed by our team in the middle part of the CB, consisting of 81 portable stations with an interval of 5–8 km. Our tomographic results reveal two obvious low-velocity (low-V) zones with high Vp/Vs ratio (high-σ) beneath the Nanling ore belt and the Wuyishan terrane, which may reflect magmatic channels formed by partial melting that may provide heat for metal mineralization. Two high-V anomalies with low-σ are located beneath the western Wuyishan terrane and the eastern CB, which may represent refractory lithosphere or remnants of delaminated lithospheric material caused by underplating of the magma due to the subduction of the paleo-Pacific plate and its following rollback. There exists an anomaly with low-Vp, high-Vs and low-σ at depths of 150–300 km beneath the western Wuyishan terrane, which may be related to the reserved trace of magmatic conduits. On the basis of the tomographic results, we propose a geodynamic model to explain the deep mechanism of mineralization beneath the CB.

Subduction‐Induced Asthenospheric Flow Around the Songliao Basin in NE China Revealed by Shear Wave Splitting Measurements of Dense Seismic Arrays

AbstractThe traditional mantle plume model fails to explain late Cenozoic intraplate volcanism in Northeast China (NEC). We constrained the pattern of upper mantle deformation to study the origin of intraplate volcanism by quantifying the shear wave splitting parameters captured by three NW‐SE linear seismic arrays in NEC. The dense station spacing (10 km) allowed us to image the small‐scale variations in anisotropic structures in unprecedented detail. The WNW‐ESE oriented subduction‐parallel anisotropy is likely induced by the asthenospheric return flow in the big mantle wedge convection associated with Pacific subduction. Therein the most notable feature is a toroidal pattern of anisotropy beneath the Songliao Basin, which is distinguished by a larger splitting time (approximately 1.0 s) relative to weak anisotropy in the center. The toroidal anisotropy pattern coincides with a high‐velocity anomaly extending from uppermost mantle down to ∼300 km depth, presumably indicating early stage foundering lithosphere. The asthenospheric return flow then moved around the foundering lithosphere and induced the corresponding toroidal anisotropy. The decompression partial melting of upwelling asthenospheric materials erupted along weak zones generating late Cenozoic intraplate basalts on both flanks of the Songliao Basin. The high‐density seismic array reveals that the Pacific subduction and early stage lithospheric foundering processes controlled the genesis of late Cenozoic volcanism in NEC.

Using Passing Trains as Seismic Sources for Refraction Microtremor Site Characterisation Surveys: Rugeley, Staffordshire, UK

Microtremor seismic surveys are routinely used to provide shear wave velocities that are converted to soil stiffness site profiles. In this paper, we look to assess the feasibility of using trains as seismic sources to characterize near-surface geology, define the optimum survey parameters to collect train-induced vibrations (i.e., array location and orientation to the railway) and find how the geology affects train-induced vibration characteristics. Three-component train-induced shear wave vibrations were recorded on short (44 m) and long (115 m) linear seismic arrays, both parallel and orthogonal to the nearby railway embankment, using standard seismic refraction recording equipment. The collected data were divided into short/long array size/orientation and seismic components for each survey configuration. 1D shear wave velocity-depth profiles were also generated for all data sets. Results showed thst long linear arrays with vertical components, parallel to the railway embankment, was optimal with the greater depth ranges. The vertical component amplitude of train-induced vibrations was found to be affected by the site geology, increasing with the thickening of Quaternary deposits and having different magnitudes for trains traveling in different directions. Results showed that different apparent shear-wave velocities were obtained from different train groups and different seismic components. The passenger trains (i.e. Virgin Trains Pendolino and British Midland 319 series) generate Rayleigh waves at higher frequencies than the freight trains.

Internal Structure of the Central Garlock Fault Zone From Ridgecrest Aftershocks Recorded by Dense Linear Seismic Arrays

AbstractWe provide high‐resolution seismic imaging of the central Garlock fault using data recorded by two dense seismic arrays that cross the Ridgecrest rupture zone (B4) and the Garlock fault (A5). Analyses of fault zone head waves and P‐wave delay times at array A5 show that the Garlock fault is a sharp bimaterial interface with P waves traveling ∼5% faster in the northern crustal block. The across‐fault velocity contrast agrees with regional tomography models and generates clear P‐wave reflections in waveforms recorded by array B4. Kirchhoff migration of the reflected waves indicates a near‐vertical fault between 2 and 6 km depth. The P‐wave delay times imply a ∼300‐m‐wide transition zone near the Garlock fault surface trace beneath array A5, offset to the side with faster velocities. The results provide important constraints for derivations of earthquake properties, simulations of ruptures and ground motion, and future imaging studies associated with the Garlock fault.

Seispy: Python Module for Batch Calculation and Postprocessing of Receiver Functions

Abstract Seispy is a graphical interface Python module for receiver function (RF) calculation and postprocessing in seismological research. Automated workflows of RF calculations facilitate processing large volume of different types of seismic data. The graphical user interface enables an intuitive and straightforward evaluation of RF quality. All parameters about the preprocessing for RF estimation can be adjusted based on user preference. Water-level frequency-domain deconvolution and iterative time-domain deconvolution for RF estimation are available in Seispy. The current version of Seispy contains five main modules for the postprocessing of RF, such as H-κ stacking, crustal anisotropic estimation, harmonic decomposition, and 2D and 3D common conversion point (CCP) stacking. The CCP stacking in the different application scenarios can be handled by a rich collection of modules, such as time-to-depth conversion, 2D or 3D CCP stacking, and adaptive station or bin selection for CCP stacking profiles in a dense seismic array or a linear seismic array. As a Python module, functions in the Seispy can be called easily in Python scripts for other purposes. The modular design allows new functionality to be added in a collaborative development environment. Licensed under GPLv3, Seispy allow users and developers to freely use, change, share, and distribute copies of the package.

Remnants of the amalgamation of the east and west Cathaysia blocks revealed by a short-period dense nodal array

The Cathaysia block located at the southeast South China block (SCB) is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao–Huilai and Zhenghe–Dapu deep faults (here referred as GHF and ZDF, respectively). Although the extension of the ZDF to the northeast, which represents the amalgamation of the two sub-blocks has been confirmed, the development of the GHF to the southwest remains to be verified. To better constrain the detailed deep structure beneath the southwest Cathaysia, which hold great significance for revealing the evolution of the SCB, a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin (SSB). Combining with the regional 10 permanent stations (PA), we obtained two profiles with teleseismic P-wave receiver function stacking. The most obvious feature in our results is the ascending Moho towards the coastal area, which is consistent with the passive margin continental and extensional tectonic setting. The stacking profile from the dense nodal array (DNA) shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB. We deduce that this offset may be casued by the deep extension of the GHF, which represents the remnants of the amalgamation of the Cathaysia block. From the other evidences, we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface. The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB. The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF, which serves as a channel for upwelling hot materials.

Intracontinental deformation of the Tianshan Orogen in response to India-Asia collision

How the continental lithosphere deforms far away from plate boundaries has been long debated. The Tianshan is a type-example of ongoing lithospheric deformation in an intracontinental setting. It formed during the Paleozoic accretion of the Altaids and was rejuvenated in the Cenozoic, which might be a far-field response to the India-Asia collision. Here we present seismic images of the lithosphere across the central Tianshan, which were constructed from receiver functions and Rayleigh wave dispersions along a N–S-trending linear seismic array. We observe an extensively deformed lithosphere in the Tianshan with inherited, structurally controlled brittle deformation in the shallow crust and plastic deformation near the Moho. We find that earlier multiple accretionary structures were preserved in the crust, which was deformed by pure-shear shortening in the south and thick-skinned tectonics in the north but was limitedly underthrusted by surrounding blocks. A balanced cross-section of Moho discontinuities supports the concept that intracontinental deformation in the Tianshan intensified synchronously with the direct contact between the underthrusting Indian slab and the Tarim Craton in the Late Miocene (~10 Ma). These findings provide a robust and unified seismic model for the Tianshan Orogen, and confirm that effective delivery of the India-Asia collision stress induced the rejuvenation of this intracontinental orogen.

Flash Mob Science: from Landmarks to Love Hz

Abstract There is a little seismologist in everyone. One secret to unlocking a student’s science potential at the undergraduate level is to offer laboratory exercises that leverage the inspiration, team spirit, and creativity already present in the current generation of incoming college students. In this lab exercise we do that by using smartphones to cause a bit of scientific mischief. In the Flash Mob Science seismology experiments described here, several groups of 5–15 students download a mobile app that can record time-series data from their phones using the phone’s vibrational sensors. This allows each device to record acceleration in the X, Y, and Z directions. We conduct quantitative experiments using student-created linear seismic arrays and deploy these arrays at prominent San Diego, California, landmarks that are known to vibrate in response to relatively small forces. These include the Spruce Street suspension footbridge in Hillcrest and the top floor of a parking garage at Southwestern College’s Higher Education Center. Our research team of students tested how these landmarks responded to different energy sources (people jumping, rocks dropping, and rubber mallet impacts). To model strike-slip fault motion, we also used a washing machine drip pan loaded with 150 pounds of sand that we attached to a car bumper using 4 × 48 inch bungee cords. For the experiment, the instructor drove forward at speeds of ∼5 mph, and the students recorded the “strike-slip” motions. Students studied individual event recordings and the collective suite of data presented as record sections. Concepts such as wavespeeds, wave types, noise, moveout, and reverberations were all discussed. These data exhibit several distinct sets of waves with different frequency characteristics that the students analyze. We found that when students record the data they study, they become more engaged in analyzing the results and postulating what the data impart.

Crustal deformation in eastern margin of Tibetan Plateau from a dense linear seismic array

Crustal anisotropy beneath a dense broadband seismic array across the Longmenshan fault belt is measured based on P-to-S converted phases from the Moho and an intra-crustal interface. The crustal thickness and the average Vp/Vs values are also estimated by a new H-κ-c method. The crustal anisotropy in Aba sub-block mainly comes from the middle-lower crust and the NW-SE fast polarization directions (FPDs) may reflect the direction of the crustal flow. A sharp variation of FPDs is observed in the vicinity of the Longriba faults, combined with the Vp/Vs values and other geological and geophysical observations, we suggest the Longriba faults may block the eastward flow of crustal materials. East of the Longriba faults, the consistence between the FPDs and the direction of the maximum horizontal compression, and low Vp/Vs values indicated that the crustal thickening may be the dominant deformation mechanism in the Longmenshan sub-block. The crustal anisotropy in the Longmenshan fault belt is mainly manifested as fault-parallel FPDs, probably related to fluid-filled fractures in this area. The Sichuan basin is weakly anisotropic and the NE-SW FPDs may reflect the tectonic strike. Combined with previous observations, our results suggest that the crustal flow and crustal thickening are co-exist in the crustal deformation in eastern Tibet.

Imaging the Ice Sheet and Uppermost Crustal Structures with a Dense Linear Seismic Array in the Larsemann Hills, Prydz Bay, East Antarctica

Abstract Comprehensive geophysical surveys including magnetotelluric, seismic, and aerial gravity–magnetic surveys are essential for understanding the history of Antarctic tectonics. The ice sheet and uppermost structure derived from those geophysical methods are relatively low resolution. Although ice-penetrating radar can provide high-resolution reflectivity images of the ice sheet, it cannot provide constraints on subice physical properties, which are important for geological understanding of the Antarctic continent. To obtain high-resolution images of the ice sheet and uppermost crustal structure beneath the Larsemann Hills, Prydz Bay, East Antarctica, we conduct an ambient noise seismic experiment with 100 short-period seismometers spaced at 0.2 km intervals. Continuous seismic waveforms are recorded for one month at a 2 ms sampling rate. Empirical Green’s functions are extracted by cross correlating the seismic waveform of one station with that of another station, and dispersion curves are extracted using a new phase-shift method. A high-resolution shear-velocity model is derived by inverting the dispersion curves. Furthermore, body waves are enhanced using a set of processing techniques commonly used in seismic exploration. The stacked body-wave image clearly shows a geological structure similar to that revealed by the shear-wave velocity model. This study, which is the first of its kind in Antarctica, possibly reveals a near-vertical intrusive rock covered by an ice sheet with a horizontal extent of 4 km. Our results help to improve the understanding of the subice environment and geological evolution in the Larsemann Hills, Prydz Bay, East Antarctica.

Lateral Seismic Anisotropy Variations Record Interaction Between Tibetan Mantle Flow and Plume‐Strengthened Yangtze Craton

AbstractThe southeastern Tibetan Plateau experienced intense Cenozoic shortening and extrusion along the western Yangtze Craton, SW China, where the Permian Emeishan flood basalts were emplaced. Seismic anisotropy along a dense E–W‐trending linear seismic array across the west Yunnan is determined by shear‐wave splitting analysis to characterize the deformation associated with these processes. Interestingly, a strong N–S‐oriented anisotropic zone collocated with the Eocene–Oligocene potassic magmatism is observed between two weak anisotropic zones in the Three‐River Orogenic Zone and the western Yangtze Craton, respectively. The lateral anisotropy variation and distinct upper mantle structures collectively suggest that the western most Yangtze Craton, strengthened by the Permian mantle plume, acted as a rigid barrier to divert the Cenozoic Tibetan mantle flow into the Three‐River Orogenic Zone. Consequently, the western edge of the Yangtze Craton has been partially eroded and its anisotropic orientation was realigned to the direction of the mantle flow. This observation indicates that both the remodeled anisotropy in the lithosphere and the dynamic flow in the asthenosphere contribute to the mantle anisotropy at the lateral lithosphere‐asthenosphere transition, which is usually hard to seismologically resolve from the vertical lithosphere‐asthenosphere boundary.