Velocity Anisotropy Research Articles

How Do the Velocity Anisotropies of Halo Stars, Dark Matter, and Satellite Galaxies Depend on Host Halo Properties?

We investigate the mass (M 200) and concentration (c 200) dependencies of the velocity anisotropy (β) profiles for different components in the dark matter halo—including halo stars, dark matter, and subhalos—using systems from the IllustrisTNG simulations. Beyond a critical radius, β becomes more radial with the increase of M 200, reflecting more prominent radial accretion around massive halos. The critical radius is r ∼ r s , 0.3 r s , and r s for halo stars, dark matter, and subhalos, with r s being the scale radius of the host halos. This dependence on M 200 is the strongest for subhalos and the weakest for halo stars. In central regions, the β of halo stars and dark matter particles get more isotropic with the increase of M 200 in TNG300 due to baryons. By contrast, the β of dark matter from the dark-matter-only TNG300-Dark run shows much weaker dependence on M 200 within r s . Dark matter in TNG300 is slightly more isotropic than in TNG300-Dark at 0.2 r s < r < 10 r s and log10M200/M⊙<13.8 . Halo stars and dark matter also become more radial with the increase in c 200, at fixed M 200. Halo stars are more radial than the β profile of dark matter by approximately a constant beyond r s . Dark matter particles are more radial than subhalos. The differences can be understood, as subhalos on more radial orbits are more easily stripped, contributing more stars and dark matter to the diffuse components. We provide the fitting formula for the differences between the β of halo stars and dark matter at r s < r < 3 r s as βstar−βDM=(−0.034±0.012)log10M200/M⊙+(0.772±0.163) for log10M200/M⊙≥13 and as β star − β DM = 0.328 for log10M200/M⊙<13 .

Seismic radial anisotropy in southeastern Tibetan Plateau and its implications for regional geodynamic evolution

The southeastern Tibetan Plateau exhibits intricate crustal tectonics, encompassing recent seismic megathrust events. Previous research suggested the presence of north-south-oriented channelized viscous flow within the crust. However, recent investigations have unveiled a notable northeast-southwest-oriented geological structure, potentially rigid, intersecting with the presumed crustal channelized flow. Several questions persist regarding the composition of the northeast-southwest-oriented structure, the continuity of crustal channelized flow, and the interplay between them. In this study, dispersion data from a dense seismic array are employed to significantly refine regional crustal models for shear wave velocity and radial anisotropy through ambient noise tomography. The resulting high-resolution model further reveals the style of the crustal deformation and supports the interpretation that the northeast-southwest structure, which shows higher velocity and significant negative radial anisotropy, results from mafic material at the base of crust, obstructing the crustal channelized flow. However, the northeast-southwest structure is not as rigid as the Sichuan Block and exhibits depth-dependent deformation. The interpretation proves useful in further understanding regional earthquake focal mechanisms and strain distribution. Additionally, this research identified a region of generalized negative radial anisotropy in the crust of the western Chuan-Dian fragment, suggesting a reduced horizontal channel crustal flow in this area. Drawing upon various geophysical and geological evidence, we present a geodynamic evolution model, proposing a sequence of events: Permian plume activity resulting in mafic material at the base of the crust near Anninghe-Zemuhe fault, northward advancement of the east Himalayan syntaxis inducing crustal compressional stress field, reduced lower crustal channel flow in the western Chuan-Dian fragment leading to the regional east-west extension, and initiation of the Xianshuihe fault causing shift of strain concentration and depth-dependent deformation near the Anninghe-Zemuhe fault. The geodynamic model provides valuable insights into the regional distribution of crustal strain and the underlying mechanisms of large seismic events.

Azimuthal seismic anisotropy of the Iran plateau: Insights from ambient noise analysis

The continental lithosphere of the Iran plateau is complicated by many tectonic processes that affected both the Arabian and Eurasian plates before and after their convergence. To investigate the deformation mechanisms of the crust and mantle lithosphere, we directly invert Rayleigh wave phase velocity dispersion data (5–60 s) for a 3-D shear wave velocity and depth-dependent azimuthal anisotropy model using ambient noise tomography from the surface down to 100 km with data recorded in 84 seismic stations. The shear wave velocity maps reveal a reasonable match with geological domains and agree with those previously published. The projections of the fast axes of Rayleigh wave azimuthal anisotropy in the subcrustal lithosphere allowed us to divide the Iran plateau into two main regions: the Zagros Mountains and the rest of the country. Furthermore, the anisotropy pattern illustrates a prominent contrast between the NW and SE Zagros Mountains. In both the crust and subcrustal lithosphere, the NW Zagros shows relatively weak but coherent azimuthal anisotropy in the NE-SW direction (i.e., orogen-perpendicular orientation). We ascribe the orogen-perpendicular fast axis in NW Zagros to stress-induced anisotropy. However, in the SE Zagros, the north-northwest orientations of the fast axes are attributed to the N-S trending basement structures, which are inherited from the Pan-African construction phase. The azimuthal anisotropy pattern displays an overall NW-SE trend dominant over the rest of the country. This NW-SE direction can be explained by an NW-SE extension due to transpressional deformation beneath Central Iran resulting from the oblique indentation of the Arabian plate into Eurasia. Nevertheless, strike-parallel anisotropy directions along the western and central Alborz Mountains throughout the entire lithosphere may be related to pure shear deformation. The persistence of azimuthal anisotropy patterns in the crust and subcrustal lithosphere implies that the whole lithosphere deforms coherently in the NW Zagros, west Iran, the Alborz Mountains, and across the Lut block. However, strong contrasts between the crustal and subcrustal pattern of anisotropy observed in the SE Zagros as well as in north Central Iran suggest that in these regions, the crust and the underlying mantle lithosphere do not deform coherently. A strong correlation between the Rayleigh wave anisotropy directions at subcrustal depths and the anisotropy patterns estimated from the shear-wave core phases suggests that in many places over the plateau, the SKS directions may have been dominated by the deformation of the lithosphere.

Prograde and retrograde stars in nuclear cluster merger. Evolution of the supermassive black hole binary and the host galactic nucleus

Nuclear star cluster (NSC) mergers, involving the fusion of dense stellar clusters near the centres of galaxies, play a pivotal role in shaping galactic structures. The distribution of stellar orbits has significant effects on the formation and characteristics of extreme mass ratio inspirals (EMRIs). In this study, we address the orbital distribution of stars in merging NSCs and the subsequent effects on supermassive black hole binary (SMBHB) evolution. We ran dedicated direct-summation $N$-body simulations with different initial conditions to do a detailed study of the resulting NSC after their progenitors had merged. Our findings reveal that prograde stars form a flattened structure, while retrograde stars have a more spherical distribution. The axial ratios of the prograde component vary based on the presence and mass ratio of the SMBHs. The fraction of prograde and retrograde stars depends on the merger orbital properties and the SMBH mass ratio. The interactions of retrograde stars with the SMBHB affect the eccentricity and separation evolution of the binary. Our analysis reveals a strong correlation between the angular momentum and eccentricity of the SMBH binary. This relationship could serve as a means to infer information about the stellar dynamics surrounding the binary. We find that prograde orbits are particularly close to the binary of SMBHs, a promising fact regarding EMRI production. Moreover, prograde and retrograde stars have different kinematic structures, with the prograde stars typically rotating faster than the retrograde ones. The line-of-sight velocity and velocity dispersion, as well as the velocity anisotropy of each NSC, depend on the initial merger orbital properties and SMBH mass ratios. The prograde and retrograde stars always show different behaviours. The distribution of stellar orbits and the dynamical properties of each kinematic population can potentially be used as a way to tell the properties of the parent nuclei apart, and has an important impact on expected rates of EMRIs, which will be detected by future gravitational wave observatories such as the Laser Interferometer Space Antenna (LISA).

Wave propagation in poroviscoelastic vertical transversely isotropic media: A sum-of-exponentials approximation for the simulation of fractional Biot-squirt equations

The presence of porous, viscoelastic, and anisotropic structures profoundly influences the propagation of seismic waves. Poroelasticity, based on the Biot-squirt (BISQ) theory, can characterize the impact of fluid flow on seismic waves. However, an improved mechanistic understanding and mathematical representation of seismic wave propagation in porous formations require the accounting of velocity and attenuation anisotropy. We derive the wave equations based on an efficient sum-of-exponentials (SOE) approximation by combining the porous BISQ equations with Kjartansson’s constant- Q dissipative model to describe seismic wave propagation in poroviscoelastic vertical transversely isotropic media. The approximation represents the fractional differential equations as an SOE, enabling a reduction in computational costs and storage compared with the traditional L2 scheme. Numerical examples prove that the extended BISQ model can describe the wave propagation characteristics in poroviscoelastic anisotropic media and effectively captures potentially strong, direction-dependent attenuation phenomena.

The influence of lamination and fracture on the velocity anisotropy of tectonic coals

The elastic anisotropy of coal formations is important for the prediction of unconventional coalbed methane reservoir performance and hydraulic fracturing. Although essential for several geophysical applications, the elastic anisotropy of coals is still poorly understood. Therefore, three sets of cylindrical coal samples are drilled parallel and perpendicular to the bedding plane, and the ultrasonic velocities under different confining pressures are measured in the laboratory. We combine experimental observations and modeling analysis to evaluate the elastic anisotropy of the coals. The results suggest that the velocity of coals parallel to the bedding plane is less sensitive to confining pressure than those perpendicular to the bedding plane. The fracture densities of coals parallel to the bedding plane are much lower than those perpendicular to the bedding plane, and most of the fractures are closed when the pressure is higher than 15 MPa. The organic matter (OM), clay content, and their preferred orientation play dominant roles in velocity anisotropy, and the fracture effect can significantly enhance it. The velocity anisotropy parameters of coals are positively correlated with the OM and clay content, and the preferred orientation of OM and clay plays a significant role in coal anisotropy. The results in this study are helpful in the characterization of the fractures of coals and can provide an important rock-physics basis for microseismic fracture monitoring and reservoir prediction.

Effects of multi-scale wave-induced fluid flow on seismic dispersion, attenuation and frequency-dependent anisotropy in periodic-layered porous-cracked media

The wave-induced fluid flow (WIFF) occurring in the ubiquitous layered porous media (e.g., shales) usually causes the appreciable seismic energy dissipation, which further leads to the frequency dependence of wave velocity (i.e., dispersion) and elastic anisotropy parameters. The relevant knowledge is of great importance for geofluid discrimination and hydrocarbon exploration in the porous shale reservoirs. We derive the wave equations for a periodic layered transversely isotropy medium with a vertical axis of symmetry (VTI) concurrently with the annular cracks (to PLPC medium) based on the periodic-layered model and anisotropic Biot’s theory, which simultaneously incorporate the effects of microscopic squirt fluid flow, mesoscopic interlayer fluid flow and macroscopic global fluid flow. Notably, the microscopic squirt shorten fluid flow emerges between the annular-shaped cracks and stiff pores, which generates one attenuation peak. Specifically, we first establish the stress-strain relationship and pore fluid pressure in a PLPC medium, and then use them to derive the wave equations by means of the Newton’s second law. The plane analysis is implemented on the wave equations to yield the analytic solutions for phase velocities and attenuation factors of four waves, namely, fast P-wave, slow P-wave, SV-wave and SH-wave, and the anisotropy parameters can be therefore computed. Simulation results show that P-wave velocity have three attenuation peaks throughout the full frequency band, which respectively correspond to the influences of interlayer flow, the squirt flow and the Biot flow. Through the results of seismic velocity dispersion and attenuation at different incident angles, we find that the WIFF mechanism also has a significant impact on the dispersion characteristics of elastic anisotropy parameters within the low-mid frequency band. Moreover, it is shown that several poroelastic parameters, such as layer thickness ratio, crack aspect ratio and crack density have notable influence on seismic dispersion and attenuation. We compare the proposed modeled velocities with that given by the existing theory to confirm its validity. Our formulas and result can provide a better understanding of wave propagation in PLPC medium by considering the unified impacts of micro-, meso- and macro-scale WIFF mechanisms, which potentially lays a theoretical basis of rock physics for seismic interpretation.

Unveiling the shape: A multi-wavelength analysis of the galaxy clusters Abell 76 and Abell 1307

We analyse the dynamical state of the galaxy clusters Abell 76 and Abell 1307 from the optical point of view, presenting a coherent scenario that responds to the X-ray emissions observed in these structures. Our study is based on 231 and 164 spectroscopic redshifts, for the clusters A76 and A1307, respectively, obtained mostly with the Telescopio Nazionale Galileo, and complemented with others collected from the SDSS DR16 spectroscopic database and the literature. We find that A76 and A1307 are two galaxy clusters at z = 0.0390 and 0.0815, respectively, with a velocity dispersion of 650 ± 56 km s−1 and 863 ± 85 km s−1, and they show velocity distributions following, in practice, Gaussian profiles. From our dynamical analysis, X-ray studies and SZ-Planck emission, we obtain a mean total mass M500 = 1.7 ± 0.6 ⋅ 1014 M⊙ and 3.5 ± 1.3 ⋅ 1014 M⊙ for A76 and A1307, respectively. Using the SDSS DR16 photometric database, we find that the spatial distribution of likely cluster members in the case of A76 is very anisotropic, while A1307 shows a compact distribution of galaxies, but it is double peaked and elongated in the south-north direction. Using XMM-Newton X-ray data, we compared the surface brightness maps with galaxy distributions and noticed that both distributions are correlated. We reconstructed the total mass profile and velocity anisotropy of both clusters by analysing the full projected phase space, through the MG-MAMPOSSt code. Our study reveals a slight indication of radial orbits for A76, while A1307 seems to prefer more isotropic orbits in the whole cluster range. In summary, A76 represents a typical young cluster, in an early stage of formation, with a very low X-ray surface brightness but a high temperature showing a very anisotropic galaxy distribution. A1307 is however more consolidated and massive showing in-homogeneous galaxy distribution and an asymmetric X-ray emission, which suggest a scenario characterised by recent minor mergers.

Effects of background elastic and permeability anisotropy on dynamic seismic signatures of a fluid-saturated porous rock with aligned fractures

Seismic dispersion, attenuation, and frequency-dependent anisotropy due to wave-induced fluid flow in fluid-saturated porous and fractured rocks have been widely studied. However, most of these studies do not consider the effects of background elastic and permeability anisotropy. In this work, we study such effects by considering a fluid-saturated porous rock with penny-shaped fractures embedded in the isotropic plane of a transversely isotropic (TI) background. Starting with P waves propagating perpendicularly to the fracture plane, we obtain the wavefields in the fluid-saturated porous TI background scattered from a single fracture. This allows for the calculation of the effective P wavenumber through the Foldy approximation and the derivation of a frequency-dependent fracture compliance matrix. The angle-dependent seismic dispersion and attenuation, as well as frequency-dependent anisotropy, can thus be calculated. Using this model, we study a fractured tight sandstone with a TI background. The results indicate that the background elastic anisotropy primarily affects the seismic frequency-dependent anisotropy, whereas the background permeability anisotropy not only affects seismic frequency-dependent anisotropy but also influences seismic dispersion and attenuation. In particular, the background permeability anisotropy alters the rate of change in seismic velocities and velocity anisotropy parameters with frequencies and the peaks of seismic attenuation and attenuation anisotropy parameters. By comparing the theoretical predictions of our model with other theories and with two sets of experimental data, our model is validated. Our model can be applied to characterize the fractured layered earth.

Guided wave multi-frequency damage imaging method of aero-engine blades

The intricate structural characteristics and anisotropic material properties of aero-engine blades pose challenges to accurate damage detection of guided waves. This research introduces a multi-frequency damage imaging method for blades. By accounting for the curved propagation path resulting from thickness variations, this method enhances the precision of damage localization. The material anisotropy contributes to frequency-dependent velocity anisotropy. Damage locus identified through echo times at different frequencies converges solely at the damage site, reducing the sensor count required in the detection system. Experimental validation of curved propagation path and frequency-dependent velocity anisotropy in a blade is conducted. Damage localization within the blade is successfully achieved with only two sensors. The imaging results of the multi-frequency imaging method, exhibit the capability to diminish sensor requirements while enhancing imaging accuracy. This method holds promise for real-time monitoring of composite materials with variable thickness.

A triangular acoustic emission source location method considering its anisotropic propagation behavior on the surface of finger-joint-laminated board

ABSTRACT To understand the anisotropic propagation characteristics of acoustic emission (AE) signals in finger-joint-laminated boards, an improved planar localization method for AE sources is proposed. Initially, the AE source was generated by the pencil-lead break (PLB) at a fixed position on the surface of the glued wood specimen, and two AE sensors were arranged in different directions at a fixed distance of 60 mm, and the AE propagation velocity was calculated according to the time difference of arrival (TDOA). For clarity, the grain parallel direction was defined as 0 degrees, with velocities measured every 10 degrees through a counterclockwise rotation. Using these measurements, two angular anisotropic wave velocity models were developed. Subsequently, three AE sensors arranged linearly on the specimen surface pinpointed the AE source’s location. This source location problem was formulated as a multi-parameter optimization model, constrained by the geometric relationships between the AE source and the sensors. A particle swarm optimization (PSO) algorithm was utilized to estimate the AE source’s angles relative to each sensor. The findings indicate that the located AE sources deviated by 6.0–19.0 mm from the predetermined PLB positions, with inaccuracies largely attributed to the anisotropic AE wave velocity models’ precision.

Fully Kinetic Simulations of Proton-beam-driven Instabilities from Parker Solar Probe Observations

The expanding solar wind plasma ubiquitously exhibits anisotropic nonthermal particle velocity distributions. Typically, proton velocity distribution functions (VDFs) show the presence of a core and a field-aligned beam. Novel observations made by the Parker Solar Probe (PSP) in the innermost heliosphere have revealed new complex features in the proton VDFs, namely anisotropic beams that sometimes experience perpendicular diffusion. In this study, we use a 2.5D fully kinetic simulation to investigate the stability of proton VDFs with anisotropic beams observed by PSP. Our setup consists of a core and an anisotropic beam population that drift with respect to each other. This configuration triggers a proton beam instability from which nearly parallel fast magnetosonic modes develop. Our results demonstrate that before this instability reaches saturation, the waves resonantly interact with the beam protons, causing perpendicular heating at the expense of the parallel temperature.

Surviving the waves: evidence for a dark matter cusp in the tidally disrupting Small Magellanic Cloud

ABSTRACT We use spectroscopic data for ${\sim }6000$ red giant branch stars in the Small Magellanic Cloud (SMC), together with proper motion data from Gaia Early Data Release 3, to build a mass model of the SMC. We test our Jeans mass modelling method (binulator + gravsphere) on mock data for an SMC-like dwarf undergoing severe tidal disruption, showing that we are able to successfully remove tidally unbound interlopers, recovering the dark matter density and stellar velocity anisotropy profiles within our 95 per cent confidence intervals. We then apply our method to real SMC data, finding that the stars of the cleaned sample are isotropic at all radii (at 95 per cent confidence) and that the inner dark matter density profile is dense, $\rho _{\rm DM}(150\ {\rm pc}) = 1.58_{-0.58}^{+0.80}\times 10^8 \ {\rm M}_{\odot }\, \rm kpc^{-3}$, consistent with a $\Lambda$ cold dark matter cusp. Our model gives a new estimate of the SMC’s total mass within 3 kpc $(M_{\rm tot} \le 3\ {\rm kpc})$ of $2.29\pm 0.46 \times 10^9 \ {\rm M}_{\odot }$. We also derive an astrophysical ‘J-factor’ of $18.99\pm 0.16$ GeV$^2$ cm$^{-5}$ and a ‘D-factor’ of $18.73\pm 0.04$ GeV$^2$ cm$^{-5}$, making the SMC a promising target for dark matter annihilation and decay searches. Finally, we combine our findings with literature measurements to test models in which dark matter is ‘heated up’ by baryonic effects. We find good qualitative agreement with the Di Cintio et al. model but we deviate from the Lazar et al. model at high $M_*/M_{200} &amp;gt; 10^{-2}$. We provide a new, analytical, density profile that reproduces dark matter heating behaviour over the range $10^{-4} &amp;lt; M_*/M_{200} &amp;lt; 10^{-1}$.

First-principles calculations of the elastic anisotropy, thermal conductivity, and optical properties of MAX-phase M2AlC (M = V, Nb, Ta) series carbides

Materials from the MAX phase, such as the M2AlC (M = V, Nb, Ta) series carbides, exhibit superior mechanical, electronic, and thermodynamic properties, making them highly promising for research. Density functional theory (DFT) has been employed to study the elastic anisotropy, thermal conductivity, electronic, and optical properties of these carbides. The results indicate that the formation enthalpies of the M2AlC (M = V, Nb, Ta) series are negative and the phonon spectra do not exhibit imaginary frequencies, confirming the thermodynamic and dynamic stability of these carbides. Additionally, the calculated Poisson's ratios and B/G ratios suggest that these materials are brittle and contain covalent and ionic bonds—a conclusion further corroborated by analyses of electronic structures. The elastic anisotropy is illustrated through anisotropy indices, three-dimensional (3D) surface configurations, and two-dimensional (2D) projections, with the sequence of anisotropy being: Nb2AlC > Ta2AlC > V2AlC. Further investigations into the sound velocities, Debye temperature, anisotropy of sound velocity, thermal conductivity, and optical properties of the M2AlC (M = V, Nb, Ta) series provide substantial theoretical support for the research on MAX phase M2AlC (M = V, Nb, Ta) series carbides.

Understanding the effects of pore pressure–induced crack deformation on the acoustic anisotropy of rocks with aligned cracks

AbstractCracks are extensively existing in rocks and play a significant role in the acoustic anisotropy of cracked rocks. Rocks in nature are affected by pore pressure, whereas the crack deformation with pore pressure and the impacts of the crack deformation on the anisotropic acoustic properties remain little known. Combining the theoretical model with the laboratory measurements of the anisotropic velocities of artificial sandstone samples with and without aligned penny‐shaped cracks, we invert for the crack parameters that characterize the crack deformation as a function of pore pressure and theoretically simulate the impacts of pore pressure–induced variation in the crack parameters on the anisotropic velocities. The results show that with increasing pore pressure, the inverted crack porosity increases exponentially, whereas the inverted crack aspect ratio decreases exponentially and the two crack parameters are linearly correlated. Moreover, model calculation demonstrates that the anisotropic velocities exhibit distinct reductions with the variation in the crack parameters caused by increasing pore pressure. In particular, the reduction in the velocity of the shear wave travelling parallel to the crack plane with polarization perpendicular to the crack plane is the most pronounced. We also demonstrate that the effects of the pore pressure–induced increasing crack porosity on the anisotropic velocities are more pronounced than the impacts of the decreasing crack aspect ratio. The findings not only reveal the variation of the crack geometry with pore pressure and the effects of the crack deformation on the anisotropic velocities of the cracked rocks but also can provide theoretical support for improving the characterization of the cracks through seismic survey.

Collisional Mechanism of Expanding Wavenumbers Range of Weibel-Type Instability in Magnetoactive Plasma

For plasma with anisotropic velocity distribution of particles in the form of two counter-propagating bi-Maxwellian beams, including bi-Maxwellian plasma, in the presence of external magnetic field parallel to the beams, it is shown that in a wide range of parameters, particle collisions lead to the expansion of the wavenumbers range, generally towards the long-wavelength region, and weaken the conditions for the occurrence of the Weibel-type instability. In the specified expanded range, its growth rate, found by means of solving the dispersion equation for the wave vectors orthogonal to the external magnetic field, turns out to be less than or on the order of the frequency of particle collisions. Thus, in this range of parameters, the instability development and formation of large-scale magnetic turbulence in a plasma with weak particle collisions require the long-term injection of particles with anisotropic velocity distribution.

Wudalianchi volcanism and mantle dynamics in Northeast China: New insight from Pn and Sn tomography

We determine new tomographic models of Pn anisotropic velocity and Sn isotropic velocity in and around the Wudalianchi volcanic area by inverting high-quality Pn and Sn arrival times manually picked from waveforms recorded at the newly deployed high-dense WAVESArray portable seismic stations. Our high-resolution Pn and Sn velocity models reveal strong lateral heterogeneities in the uppermost mantle under the study region. The average Pn and Sn velocities in the uppermost mantle are 8.2 and 4.5 km/s, respectively. Both Pn and Sn velocity models exhibit obvious low-velocity (low-V) anomalies under the Wudalianchi and Keluo volcanoes, whereas under the Songliao basin distinct high-velocity (high-V) zones are revealed. In particular, our Pn model reveals two separate low-V anomalies under the Nuominhe and Halaha volcanic groups, suggesting that they have different deep origins. A large-scale L-shaped low-V zone exists under the Keluo, Wudalianchi, Erkeshan, and Xunke volcanoes, characterized by Pn-wave fast propagation directions (FPDs) parallel with the low-V zone, suggesting that these volcanoes may have the same deep origin. Furthermore, southeast-opened U-shaped Pn FPDs exist around the Wudalianchi volcano, whereas NE-SW FPDs appear under the Great Xing'an range, which are generally consistent with SKS splitting measurements. This feature may reflect lithosphere-asthenosphere coupling beneath the Wudalianchi volcano associated with horizontal flows in the big mantle wedge and compressional tectonics under the Great Xing'an range. These results shed new lights on the Wudalianchi volcanism and mantle dynamics beneath Northeast China.

Insight into wave propagation in polyimide films and resistive grid sandwich structures towards a hybrid monitoring of hypervelocity impact

Micro-Meteoroid and Orbital Debris pose a significant threat to the safe operation of orbiting spacecraft, potentially leading to mission failure in space exploration. Quantitative characterization of hypervelocity impact (HVI) is crucial to ensure the safety and successful completion of on-orbit missions. Firstly, this study designed a three-layer sandwich structure of polyimide film with orthogonally laid resistive wires, combined with piezoelectric and resistive wire sensors, for the simultaneous acquisition of acoustic emission (AE) signals generated by HVI and measurement of perforation dimensions. Secondly, a semi-analytical finite element (SAFE) analysis of wave dispersion properties in the periodic sandwich structure is conducted with Bloch’s theorem, together with a hybrid model based on three-dimensional smoothed particle hydrodynamics and finite element methods (SPH-FEM) to comprehensively understand the AE waves and damage characteristics induced by HVI. The resulting anisotropic wave propagation characteristics with SAFE and SPH-FEM are closely matched. Thirdly, a time delay-multiplication (TDM) imaging algorithm considering wave velocity anisotropy is proposed for accurate real-time “visualization” of HVI locations. Lastly, correlations are established between projectile and perforation dimensions. The proposed algorithm for HVI multi-parameter quantification and damage detection helps evaluate the space HVI environment and HVI-induced damage to spacecraft.

Guided wave multi-frequency damage localization method in variable-thickness structures by one pair of sensors based on frequency-dependent velocity anisotropy

Variable thickness structures are prevalent in aircraft, ships, and other machines, necessitating numerous sensors for health monitoring to reduce safety hazards. This paper presents a guided wave multi-frequency localization method based on frequency-dependent velocity anisotropy. This method achieves damage localization in variable-thickness structures with a pair of sensors and can effectively reduce the number of sensors used for monitoring. Variations in structural thickness cause a gradient in guided wave velocity that bends the propagation path. Different thickness variations with different directions cause wave velocity anisotropy. As a result, variations in thickness cause possible damage loci determined by echo time to deviate from an elliptical shape. Because the velocity anisotropy is frequency-dependent, damage loci at different frequencies are close but do not overlap and intersect only at the damage location. So, the multi-frequency method can increase the damage information acquired by a single pair of sensors, enabling damage localization. Experimental validation was conducted on a steel plate with linearly varying thicknesses. The feasibility of the multi-frequency localization method was verified by successfully locating the damage at three different locations using a pair of receiver-excitation sensors. In addition, the experiments demonstrated the capability of this multi-frequency method in improving the localization accuracy of sensor networks. The method has potential applications in monitoring systems lightweight, phased arrays, and imaging enhancement.

Crustal 3‐D S‐Wave Velocity and Azimuthal Anisotropy in the Sanjiang Lateral Collision Zone in the SE Margin of the Tibetan Plateau

AbstractThe eastward extrusion of the Tibetan Plateau materials has caused intricate tectonic deformations and frequent seismic activities in the Sanjiang lateral collision zone (SLCZ). To reveal crust structures and deformation mechanisms, we investigate high‐resolution structural features of crustal depth (≤40 km). A 3‐D S‐wave velocity and azimuthal anisotropy model is constructed by the direct tomography method with Rayleigh phase velocity at periods of 2–40 s from multiple temporary seismic arrays and regional permanent network. In the middle‐to‐lower crust, an obvious low‐velocity zone is confined by the large‐scale fault systems of Jinhe‐Qinghe fault and Chenhai fault (CHF) to the northeast and east, Lancangjiang fault (LCJF) and Red River fault (RRF) to the west, with strong N‐S‐oriented anisotropy, which evident differs from the ENE‐WSW‐oriented weak anisotropy in the high‐velocity zone on the northeastern side. We consider that the weak material may be obstructed by large faults and the high‐velocity zone, resulting in complex crustal deformation and tectonic boundary. The crustal low‐velocity materials beneath the Tengchong volcano (TCV) are probably separated with those from the Tibetan Plateau. The low‐velocity beneath the Chuxiong basin (CXB) may be combinations of partial melts and fluid derived from shear deformation and deep material upwelling. The segmented anisotropy at the NW end of the RRF suggests complex deformation by crustal flow, emphasizing the important influence of faults on anisotropic pattern. The complex anisotropy in the fault intersection of the Lijiang‐Xiaojinhe fault and RRF also highlights the important role of these faults in shaping crustal deformation.