The X-discontinuity in the upper mantle of the Earth's interior,typically located at depths of approxi-mately 250-350 km,is critical for unraveling mantle composition and dynamics.However,its global distribution and underlying formation mechanisms remain poorly constrained.Conventional methods for identifying this dis-continuity using teleseismic P-wave receiver functions rely heavily on post-stacking empirical interpretation,which is inefficient and unsuitable for processing large volumes of seismic data.To address the challenges posed by massive datasets and the scarcity of manually labeled samples,this study proposes a transfer learning strategy termed"pretraining on synthetic data followed by fine-tuning with real data".We construct a convolutional neural network-based binary classification model to determine the presence or absence of the X-discontinuity.The proce-dure is as follows:First,synthetic receiver function datasets—with and without the X-discontinuity—are generated through forward modeling based on three classical velocity models(AK135,IASP91,and PREM).Noise augmen-tation and temporal trimming are applied to improve model generalization.Second,high-quality observed data are selected from global seismic networks and manually annotated to create a real dataset.Finally,a two-phase training approach is adopted,where the model is sequentially trained on the synthetic and real datasets to achieve auto-mated detection of the X-discontinuity.Experimental results show that the trained model achieves an accuracy of approximately 90%in classifying receiver function images.In determining the presence of the X-discontinuity be-neath seismic stations,the model exhibits about 80%agreement with results derived from conventional methods,indicating its effectiveness in automated detection.Based on this approach,subsequent research will systematically investigate the global distribution of the X-discontinuity.
On August 8th 2017,a MW6.5 earthquake struck Sichuan Province,China,resulting in significant loss of life and extensive property damage.The absence of significant surface rupture from field investigations made it challenging to identify the fault geometry and estimate the rupture evolution of this event.We applied a newly potency density tensor inversion which introduced the standard deviation of the smoothness constraints for five basis double-couple components by the weight of its each amplitude respectively to estimate the rupture pro-cess of this event.The slip distribution shows that large slip regions coincide with distribution of aftershocks,espe-cially for the depth change in the southeast and northwest epicentre.Both aftershock and slip distribution show deeper depth in northwestern segment than that southeastern segment.The spatial distribution of potency density tensors showed different total focal mechanisms for the northwest and southeast area of the epicentre,indicating that the complex seismogenic fault of the main shock may be divided into two main segments and a secondary seg-ment.The rupture process shows that the initial rupture occurred around the hypocentre in the first 2 s.Main rup-ture propagates to the up-dip part of the hypocentre while partial rupture propagates to down-dip part of the hypo-centre within the southeastern segment of the seismogenic fault during 2-6 s.Then rupture jumps to the northwest-ern area of the hypocentre and propagates with in northwest segment during 6-10 s.In addition,moderate slip ap-pears in the southeast edge of the fault plane from 5 s.High and low-velocity anomalies were identified around the hypocentre and in the northwestern and deeper parts of the hypocentre,respectively.We interpret that the brittle failure of rocks,caused by stress accumulation from middle-to-lower crustal flow and upwelling asthenosphere,may have contributed to the initiation of the 2017 Jiuzhaigou earthquake.Additionally,the deceleration and cessa-tion of the event are inferred to be related to the fault geometry along the strike direction and the seismogenic envir-onment at depth.
On January 7,2025,an MW7.1 earthquake struck Dingri County,Xigaze City,on the southern mar-gin of the Qinghai-Xizang Plateau,China.The epicenter was located at the intersection between the southern seg-ment of the Shenzha-Dingjie Rift and the South Xizang Detachment System,a tectonically complex region charac-terized by active extensional deformation.The earthquake induced large-amplitude coseismic surface deformation with a highly heterogeneous spatial distribution.To clarify the seismogenic structural characteristics and fault slip distribution of this event,we conducted a systematic investigation by integrating Interferometric Synthetic Aper-ture Radar(InSAR)observations with seismic source mechanism and fault slip inversion methods.(1)The InSAR-derived deformation fields reveal that the coseismic deformation was dominated by a nearly north-south-trending subsidence zone,with a maximum line-of-sight(LOS)subsidence of approximately 1.4 m and a maximum uplift of about 0.9 m.The two-dimensional deformation field further indicates pronounced subsidence accompanied by westward horizontal motion on the western side of the fault,while the eastern side exhibits relative uplift and east-ward motion.These deformation characteristics suggest that the earthquake rupture was primarily governed by nor-mal faulting,with a minor strike-slip component.(2)Based on the assumption of a homogeneous elastic half-space,a single-fault model was first employed to invert the observed coseismic deformation,yielding the optimal geomet-ric parameters for the Dengmocuo Fault,with a strike of 184.6° and a dip angle of 54°.Although this single-fault model satisfactorily explains the major deformation features in the vicinity of the main fault,significant residual de-formation remains on the western side of the fault.This result indicates the inherent limitations of a single planar fault model in fully reproducing the complete spatial pattern of the observed deformation field.(3)To reasonably account for the residual deformation,a conjugate double-fault model was introduced for joint inversion.The results demonstrate that the earthquake rupture was dominated by a west-dipping main fault,accompanied by the syn-chronous rupture of an east-dipping,high-angle subsidiary fault.Both faults exhibit typical normal-faulting charac-teristics.Compared with the single-fault model,the conjugate double-fault model significantly improves the de-formation fitting accuracy,particularly within incoherent zones near the subsidiary fault,and provides a more com-prehensive explanation for the overall observed deformation pattern.Assuming a shear modulus of 30 GPa,the joint inversion based on the double-fault model yields a total seismic moment of approximately 3.69×1019 N·m,corresponding to a moment magnitude of MW7.03.The results indicate that the 2025 Dingri earthquake represents a typical conjugate normal-faulting rupture event within the southern Xizang Rift System.This study highlights the important role of conjugate fault systems in strain partitioning and energy release in extensional tectonic settings and provides valuable insights into the regional deformation mechanisms and seismic hazard assessment of the southern Qinghai-Xizang Plateau.
On January 7,2025,anMW 7.1 earthquake struck Dingri,Xizang,causing severe engineering damage in the epicentral area.To scientifically reconstruct the ground motion impact field of this event,a strong ground motion simulation model was established based on the stochastic finite-fault method,incorporating the inverted source rupture process.A systematic study on key sensitive parameters was conducted:by comparing the mean values of 30 stochastic realizations with the pseudo-acceleration spectra(PSA)recorded at early warning stations,the op-timal stress drop was determined to be 10.0 MPa;meanwhile,the high-frequency attenuation parameter(κ)was es-timated as 0.032 6 based on the negative correlation between its median value and site source,path,and site parameters,a reliability test was performed using observational data from the National Seis-mic Intensity Management and Early Warning Project.Consequently,the gridded distributions of peak ground ac-celeration(PGA)and instrumental seismic intensity were generated,and the spatial distribution characteristics and formation mechanisms of the strong ground motion field were quantitatively discussed.The results indicate that:(1)Under a 5%damping ratio,the simulated PSA values match the observations well in both amplitude and spectral shape within the period range of 0.04-4.00 s.The residuals mainly fall within the range of±1.0 without significant period dependence,verifying the reliability of the model in the complex crustal environment of the southern Qing-hai-Xizang Plateau.(2)The simulated ground motion intensity isovalues exhibit a nearly north-south elliptical dis-tribution.The peak PGA near the epicenter reaches 1 184.3 cm/s2,with a calculated instrumental seismic intensity of 9.6.While covering the actual seismic damage risk,the simulation results show good consistency with both macro-seismic investigations and instrumental observations.(3)The ground motion intensity field clearly demon-strates significant rupture directivity and hanging-wall effects.Specifically,the PGA in the forward rupture direc-tion(northward)is approximately 1.82 times that in the backward direction,and the PGA on the hanging wall is amplified by approximately 1.85 times compared to the footwall.These refined spatial distribution characteristics provide a dynamic basis for explaining macro-seismic damage variations and offer important scientific references for the seismic design of rural buildings and emergency response in southern Xizang.
High-precision theoretical modelling of gravity field variations induced by multiple known mechanisms is a prerequisite for studying dynamic processes of the Earth's surface and interior through gravimetry. Temperature fields on the Earth and other celestial bodies, driven by factors such as solar radiation and magmatic eruptions, often exhibit periodic or step-like fluctuations. These thermal perturbations not only generate deformation fields but also disturb the gravity field. In this study, we employ a thermoelastic half-space model and solve the governing partial differential equations analytically to derive explicit expressions for the deformation and gravity changes induced by surface point and disk-shaped heat sources under periodic and step-like temperature fluctuations. The results demonstrate that gravity variations at the surface caused by thermoelastic effects are manifested solely as the free-air gradient effect due to the movement of gravimetric instruments with surface deformation, while the contributions from internal strain and Bouguer-layer surface displacement cancel each other at the first order. Finally, two representative examples are presented to illustrate the magnitude of thermoelastic deformation and its gravitational effects: (1) for periodic temperature fluctuations on the lunar surface, the resulting surface uplift is estimated to be at the sub-millimeter level, with gravity changes smaller than the microgal level; (2) for a sudden temperature disturbance in the permanent Lava Lake of Mount Nyiragongo, assuming a magma lake with a radius of 400 m and a temperature increase of 40 K, the predicted stable thermoelastic vertical displacement at the center is about 10 cm and the associated gravity change is about 30 μGal.
Snow cover dynamics in Greenland are a key driver of regional climate and global sea-level projec-tions,yet continuous snow depth data are scarce due to the harsh observational environment,thereby constraining an accurate understanding of cryosphere changes and surface energy balance in polar regions.We use the Global Navigation Satellite System Interferometric Reflectometry(GNSS-IR)technique to retrieve continuous snow depth series across Greenland.The open-source software package(gnssrefl)is employed to process GNSS signal-to-noise ratio(SNR)observations for this purpose.By optimally configuring key parameters(e.g.,elevation and azimuth angles),we retrieve the vertical distance from the antenna phase center to the reflecting surface.This distance is then used to derive the time series of snow depth.Ultimately,out of GNSS stations located in the marginal regions of Greenland,we successfully retrieve snow depth at 4 stations,as well as at 4 stations in the central regions,ensur-ing a diverse spatial representation.The experimental results indicate that:(1)The GNSS-IR technique performs well in different regions of Greenland.It provides absolute snow depth at marginal sites and primarily reflects snow and ice surface height variations at central sites.The GNSS-IR data show high consistency with nearby in-situ snow depth measurements in numerical values.(2)Snow depth variation shows a striking contrast between Greenland's east and west margins,reaching～1.5 m at eastern sites(MSVG,LYNS)versus only～0.2 m at western sites(SCBY,KAGA).The eastern stations are characterized by a pronounced seasonal accumulation-melt regime(near-complete summer ablation)as well as significant inter-annual variability in snow depth.(3)The MERRA-2(Mod-ern-Era Retrospective Analysis for Research and Applications,Version 2)and GLDAS-2(Global Land Data As-similation System,Version 2)reanalysis datasets generally capture the temporal trends of snow depth well at most sites,with correlation coefficients commonly exceeding 0.5.Nevertheless,both models systematically overesti-mate the specific values of snow depth,underscoring the critical need for other observational data to calibrate and constrain regional climate models.(4)Snow depth across Greenland demonstrates substantial spatial variability at both interannual and intra-annual scales.The marginal zones primarily exhibit intense intra-annual fluctuations driven by significant winter accumulation and summer ablation.In contrast,the snowpack in the central plateau re-mains relatively stable,characterized predominantly by interannual variations with negligible seasonal fluctuations.These result validate the effectiveness and reliability of GNSS-IR technology for snow depth monitoring in Green-land,providing crucial data support and a methodological complement for research on polar ice and snow mass bal-ance,as well as contributing to more accurate future climate projections.
As a tectonic transfer and transition unit between the Yangtze Block and the eastern (southern) margin of the Qinghai-Xizang Plateau, Daliangshan tectonic belt plays a pivotal role in accommodating the differential movements between the Chuandian Block and the South China block. Its deep structure serves as the core for deciphering the deformation mechanisms underlying the southward expansion of crustal material in the Qinghai-Xizang Plateau following the obstruction of its eastward escape. This paper systematically synthesizes existing research findings from multiple perspectives, including tectonic evolution history, block kinematic characteristics, seismicity, and geophysical deep structural exploration. In terms of tectonic evolution, the belt underwent a four-stage, multi-mechanism superimposed process from the Late Mesozoic to Cenozoic, controlled by multiple far-field dynamic sources such as the subduction of the Pacific Plate and the collision between the Indian and Eurasian Plates. Relative to the South China block, Daliangshan tectonic belt is generally dominated by counterclockwise rotation, with a multi-level strain transfer and adjustment system developed within it. Seismic activities are concentrated along the boundary fault zones, while seismicity within itself is weak. However, prominent seismic gaps and strongly locked segments are identified in fault zones such as the Anninghe-Zemuhe fault zone and the Daliangshan fault zone, implying their potential to generate strong earthquakes. Geophysical exploration of deep structures reveals distinct high-velocity and low-velocity anomalous zones in the crust, with significant differences in north-south trending tectonic deformation and stress field characteristics. The crustal material migration hindered by rigid blocks is likely to exhibit complex flowing paths. The research results provide additional scientific insights for investigating the dynamic uplift mechanism of the eastern (southern) margin of the Qinghai-Xizang Plateau and assessing the potential risk of strong earthquakes in the region.
The lithosphere-asthenosphere boundary(LAB),defined seismologically as the interface separating the high-velocity lithosphere from the low-velocity asthenosphere,records key information about the distinct physi-cal and chemical properties of these two layers and their dynamic interactions.Plate tectonic theory holds that rigid lithospheric plates move horizontally over the weaker,ductile asthenosphere,with observed global plate velocities ranging from 1 to 10 cm per year.This substantial variability is widely considered a direct manifestation of litho-sphere-asthenosphere interactions.However,whether systematic relationships exist between LAB structural charac-teristics and plate motion rates remains an open question that is fundamental to understanding plate-driving forces.To address this question,this study focuses on oceanic regions and oceanic-continental transition zones,where lithospheric structure is relatively simple compared to continental interiors.Using teleseismic S-wave receiver functions from 107 globally distributed broadband seismic stations,we applied a consistent grid-search inversion methodology to systematically extract LAB structural parameters—including depth,shear-wave velocity drop mag-nitude,and transition zone thickness—beneath each station.This uniform processing approach minimizes biases in-herent in compiling disparate results from previous studies.The obtained LAB parameters were then analyzed for correlation with absolute plate motion rates from the NUVEL-1A model.Our results reveal three principal findings.First,LAB depth in mature oceanic regions closely follows the 1 100℃isotherm predicted by the plate cooling model,suggesting that the seismically defined LAB may correspond to a rheological boundary where thermally ac-tivated creep becomes dominant.Second,and most significantly,both the magnitude and the gradient of the shear-wave velocity drop across the LAB exhibit strong positive correlations with plate velocity,with Pearson correla-tion coefficients of r=0.686 and r=0.650,respectively.We interpret this as evidence for widespread low-viscosity melt or volatiles within the asthenosphere.Greater velocity drops imply higher melt fractions,which substantially reduce asthenospheric viscosity and promote mechanical decoupling between the lithosphere and underlying mantle.This decoupling effectively lowers the basal shear resistance acting on the plate,enabling higher plate velo-cities.Third,the thickness of the LAB transition zone,consistently measured at less than 30 km across all stations,shows no statistically significant correlation with plate velocity(r=-0.141),indicating that interface sharpness is not a primary control on plate kinematics.This study provides new seismological constraints on lithosphere-as-thenosphere interactions and offers observational support for models in which plate motion is modulated by mantle viscosity and coupling conditions at the LAB.However,several limitations must be acknowledged.The current dataset has uneven global coverage,and the vertical resolution of S-wave receiver functions(typically 5-10 km)imposes limits on parameter precision.Furthermore,our grid-search approach,while systematic,may not fully capture the full complexity of LAB structure.Therefore,the observed relationships,particularly the null cor-relation with thickness,warrant validation through future studies incorporating denser station coverage,multi-fre-quency receiver function analysis,and joint inversion with complementary datasets such as surface wave disper-sion or body wave tomography.Despite these limitations,our findings provide a step toward quantitatively linking plate-scale dynamics with the seismic structure of the upper mantle.
The Longriba fault zone represents a major active structure within the Songpan-Ganzi block,de-marcating pronounced contrasts in surface topography,crustal deformation,and deep crustal properties between the eastern and western parts of the block.Controversy persists regarding its deep geometry:magnetotelluric profiles typically image the fault terminating at the top of a mid-lower crustal conductive layer,whereas active-source seis-mic reflection profiles reveal it as a crustal-penetrating structure extending to the Moho.Teleseismic P-wave travel-time tomography suggests a southeast-dipping fault that extends at least into the mid-lower crust.Low-temperature thermochronology indicates that fault activity likely initiated around 38 Ma,driven by far-field stress propagation following the India-Eurasia collision.Tectonic analyzes further link the fault to regional evolution,noting that the eastern margin of Qinghai-Xizang Plateau experienced significant denudation during the Late Cretaceous and Late Cenozoic,with the latter accounting for～80%of total erosion,focused predominantly between the Longriba and Longmenshan fault zones.This spatial pattern suggests that the Longriba fault zone plausibly acts as a back-thrust to the Longmenshan fault zone,with both structures jointly accommodating crustal uplift and growth deformation in this region.Although current seismicity along the Longriba fault zone is low,its long evolutionary history,sub-stantial surface trace,deep penetration,Late Pleistocene slip higher,and evidence of paleoseismic events from trench studies collectively imply its considerable seismic potential risk.Given the ongoing India-Eurasia conver-gence,this fault zone warrants careful attention in regional seismic hazard assessment.
The Tarim Basin and the Tianshan region are the key interaction zones between the Central Asian orogenic belt and stable blocks, and are natural laboratories for studying the tectonic deformation of the continent, the coupling effect of basin-mountain and the seismic breeding mechanism of the continent. As an "indicator" of lithospheric deformation, seismic anisotropy can effectively reflect the regional tectonic stress field and deep material migration characteristics, which is of great scientific significance for revealing the coupling dynamics mechanism of basin-mountain in this region. In recent years, domestic and international scholars have systematically studied the seismic anisotropy characteristics from the crust to the upper mantle using seismological methods such as receiver functions, shear wave splitting, and surface wave tomography. Research shows that there are significant spatial differences in crustal seismic anisotropy. Generally, the fast wave polarization directions in the Tarim Basin and the Tianshan region are consistent with the regional tectonic stress field and the strike of the Tianshan orogenic belt, which is mainly affected by the long-range effect of the Indian plate collision, the uplift of the Qinghai-Xizang Plateau, and the NS pushing action with the Tianshan Mountains. However, the fast wave polarization directions are dispersed in local areas, and the anisotropic characteristics in regions such as Atushi, Wushi and Keping exhibit a certain degree of complexity, which may be related to stress disturbances caused by local faults. The anisotropic features of the upper mantle are not entirely consistent with those of the crust, and the vertical coherence of lithospheric deformation requires further investigation. Although scholars at home and abroad have made the above progress in the field of seismic anisotropy, the spatial distribution characteristics and dynamic mechanism of seismic anisotropy have not yet reached a unified discussion, and a large number of geophysical observations are still needed to deepen the relationship between seismic anisotropy and tectonic deformation and seismic activity, so as to provide more reliable deep dynamic constraints for regional seismic risk assessment.
High-precision and high-stability measurement is an essential approach for situational awareness of space targets,such as high-precision orbit determination,attitude determination,etc.Satellite Laser Ranging(SLR)technology has been developed for more than 60 years,and its accuracy and stability have been continuously im-proving,the laser pulse width and the jitter of single-photon detectors in the SLR systems are important factors limiting the improvement of ranging accuracy.In this study,a high-stability industrial-grade 532 nm picosecond laser and a high-quantum efficiency MPD single-photon detector(SPAD)are used in the SLR system of the Shang-hai Astronomical Observatory.The pulse width of the laser is～15 ps;the jitter of SPAD is less than 35 ps and the quantum efficiency is about 50%,a matched aspheric len is applied for the SPAD.The measurement accuracy of ground targets is improved from 6-8 mm to 2-3 mm,and the satellite measurement accuracy is enhanced from the optimal 6-10 mm to 2-4 mm,meeting the 24-hour measurement requirements of low-orbit,high-orbit,and geosyn-chronous orbit satellites.Specifically,the measurement accuracy of the beidou compassg8 satellite in the geosyn-chronous orbit(36 000 km)reaches 1.9 mm,which shows significant improvements in system ranging accuracy and long-term operational stability.Continuous day-and-night routine SLR observations are carried out at a repetition rate of 5 kHz,and the data are sent to the International Laser Ranging Service(ILRS).Based on the one-year mea-surement data from July 2024 to June 2025,the annual average ranging accuracy of ground targets reaches 2.4 mm;the normal point accuracy of the lageos satellite reaches 0.9 mm;the short-term stability of orbit evaluation data for the lageos satellite is 5.8 mm;and the long-term stability is 2.1 mm.These results indicate that the quality of SLR ranging data has been improved,ranking among the top in international SLR stations and achieving the best level among domestic SLR systems.Thus it provides an effective approach for high-precision measurement of space tar-gets.
The Chang'e-4 lunar penetrating radar(LPR)has achieved the first in-situ high-resolution detection of the shallow subsurface structure on the far side of the Moon,filling a critical gap in our understanding of the lu-nar far side's subsurface architecture.This paper systematically reviews and synthesizes previous studies on the stratigraphic structure,dielectric property distribution,and genetic evolution mechanisms within the Von Kármán crater located in the South Pole-Aitken Basin.The analysis is based on dual-channel high-frequency(500 MHz)and low-frequency(60 MHz)radar data acquired by the Yutu-2 rover,integrated with multi-source remote sensing information. Regarding the shallow structure(0-40 m),this study consolidates high-frequency radar results and summarizes a five-layer stratigraphy:the top layer(0-12 m)consists of fine-grained regolith(εr=2.35±0.20,density=1.31±0.20 g/cm3),underlain by three layers of coarse-grained ejecta from the Finsen impact(εr=3.2-4.8),with fragmented basaltic rock at the base.It is particularly noted that buried craters 150-270 m in diameter and five thin lava flow sequences,each 2-3 m thick,were identified at depths of 10-25 m,confirming the superposition of mul-tiple impact and eruption events.For the deeper structure(>50 m),findings reveal four basalt flow units(individual thickness:12-100 m)interlaid with two paleo-regolith layers(20 m/5 m).Volcaniclastic rocks detected beyond 280 m depth provide evidence of late-stage volcanic activity on the lunar far side. Dielectric property inversion demonstrates significant vertical heterogeneity:the relative permittivity in-creases from 2.4-3.2 at the surface to 5.0 at depth,with a loss tangent ranging between 0.004 1-0.010 4,and FeO+TiO2 content reaching up to 17.5 wt%.A generalized"permittivity-depth"function model has been estab-lished,improving inversion accuracy by 35%compared to conventional models.Genetic analysis identifies three dominant mechanisms:early(～3.5 Ga)basaltic eruptions forming the material foundation;mid-stage(～3.2-3.1 Ga)impact events(e.g.,Finsen)depositing ejecta;and later space weathering leading to surface fining. Existing research has established a relatively complete radar profile model for the Chang'e-4 landing site and put forward a three-stage evolution theory of"impact ejecta-volcanic deposition-weathering modification",thereby providing a critical scientific basis for lunar geochronology and landing site selection for deep space exploration.The relevant achievements underscore the unique value of dual-frequency radar in planetary subsurface sounding,which holds significant implications for guiding the development of next-generation planetary detection technolo-gies.
The duration of observation of China digital water-tube tiltmeter network has spanned several dec-ades,raising the scientific question regarding the level of high-frequency background noise and the source of the noise.To address this question,this study is the first to examine 11 water-tube tiltmeter observatories in Yunnan Province(SW China)using the power spectral density and probability density function method to establish the high-frequency background noise levels for the water-tube tiltmeters in this region.The findings reveal that:(1)Within the frequency band of 10-4-8.3×10-3 Hz,the background noise level of each observatory exhibits a nonlinear atten-uation pattern as frequency increases;among them,the noise sources in the frequency band of 10-4-5×10-4 Hz are mainly from the fluctuation of barometric pressure,while those in the frequency band of 5×10-4-8.3×10-3 Hz are complicated and diverse.(2)The Mengla,Yunxian,Yunlong,Lijiang,Zhaotong,Yongsheng,Midu,and Baoshan stations had the lowest high-frequency background noise levels,followed by the Chuxiong and Kunming observa-tories,whereas the Eryuan observatory had the highest.(3)Most individual observatories had similar background noise levels between the NS and EW components.These results demonstrate that the above methods and results can provide a reference for the calculation of high-frequency background noise levels of China water-tube tiltmeter net-work and provide empirical evidence for establishing its noise model.
The formation of the Chinese mainland has been a result of the amalgamation of multiple blocks over an extended geological history. The lithospheric structures of these different blocks exhibit significant variations, and their interactions have been intense, leading to the fundamental characteristics of active geological tectonics and severe geological hazards in present-day China. Since the beginning of 21st century, seismology has developed rapidly, revealing high-precision crustal and upper mantle structures. This paper summarizes the latest progress in seismological studies regarding the depths of the Moho and the lithosphere-asthenosphere boundary (LAB) in the Chinese mainland, constructing a fundamental framework for the lithosphere at a first-order scale. Overall, the crust of the Qinghai-Xizang Plateau is the thickest, reaching up to more than 70 km, while the crust in eastern China is the thinnest, averaging around 30 km. However, improvement is necessary particularly in understanding small-scale structures. On one hand, the crustal thickness derived from natural earthquakes is generally smaller than that obtained from artificial seismic sources, which may reflect the complex nature of the Moho. On the other hand, the lateral variations in crustal structure near major tectonic boundaries or fault zones are significant, arguing for dense seismic array observations and research in key areas to better study block interactions. Research on lithospheric thickness remains relatively limited, with reliable results obtained only along certain profiles, and there are notable discrepancies between seismic wave velocity structures and thermal lithospheric structures. Future efforts are required in both data acquisition and methodological advancements. Building on one-dimensional lithospheric layer structures, future research should focus on revealing high-precision three-dimensional lithospheric structures to better constrain the rheological properties and deformation characteristics of the Chinese mainland lithosphere. This will facilitate the exploration of important scientific issues related to the geodynamic evolution of the Chinese mainland.
XKS shear-wave splitting has been widely applied to investigations of anisotropy in both the upper mantle and the lowermost mantle D" layer, and represents a key tool for probing mantle deformation and dynamics. The first part of this paper reviews the basic principles and major approaches of XKS splitting analysis, and summarizes its applications to upper-mantle anisotropy beneath the Chinese mainland, where strong regional variations in deformation are observed, primarily controlled by the subduction of the Indian plate and the western Pacific plate. We further discuss methods, applications, and challenges in using XKS phases to probe D" anisotropy, highlighting that complex and strong anisotropic structures are commonly observed beneath remnant slab regions and large low-shear-velocity provinces, while effective separation of upper-mantle contributions and mitigation of wavefield scattering and interference remain major difficulties. Over the past decade, with the rapid growth of seismic datasets and advances in inversion techniques, XKS-based three-dimensional anisotropic imaging of the upper mantle has become increasingly mature, significantly improving depth resolution of anisotropic structures. The second part of this paper introduces the theoretical framework and development of this imaging approach and summarizes recent results. This method is capable of delineating three-dimensional upper-mantle anisotropy and effectively identifying deep structures such as slab geometries, mantle upwellings, and layered anisotropy, although the imaging quality strongly depends on data coverage and observation density. Finally, we discuss future perspectives of XKS studies in mantle anisotropy research. The field is evolving from traditional parameter-based analyses toward full three-dimensional imaging. However, three-dimensional anisotropic imaging of both the upper mantle and the D" layer beneath the Chinese mainland remains limited. Future efforts should integrate multiple anisotropic constraints, promote multi-layer mantle coupling studies, and incorporate artificial intelligence techniques to improve the accuracy of shear-wave splitting analysis, thereby providing a foundation for constructing high-resolution, high-precision three-dimensional anisotropic models of the mantle beneath China.
To reveal the subduction process of the western Pacific Plate and its impact on the overlying plate,this study utilizes data from the NECsaids-III broadband seismic array deployed in Northeastern China(the Eren-hot-Shuangliao profile)and extracts reflected body wave signals from the mantle transition zone(MTZ)using the ambient noise cross-correlation method.A common reflection point stacked profile is constructed,and by identify-ing and tracking the reflected P-wave phases from the upper and lower boundaries of the MTZ(P410P and P660P),the lateral variations of the MTZ across the north-south gravity lineament(NSGL)are obtained.The results indi-cate that the P410P and P660P phases along the profile exhibit clear segmentation.Near the NSGL,the phases are relatively chaotic and difficult to track,while on both sides,the continuity is better,with multiple strong reflection segments.Specifically,beneath the Erenhot Basin and the Greater Khingan Range region,the phases are clear and stable,with slight fluctuations in their arrival times.The deviations from the reference two-way travel time are,on average,no more than±1 s,corresponding to depth variations of less than 5 km.Beneath the southern Songliao Basin,the phases are advanced and delayed by approximately 4 s,respectively,relative to the reference two-way travel time,indicating a significant thickening of the MTZ by over 30 km.Combined with existing seismic images,it is inferred that the significant thickening of the MTZ and the presence of high-velocity body within it beneath the southern Songliao Basin are related to the stagnation of the subducted western Pacific Plate in the MTZ of this re-gion.In contrast,the high-velocity bodies within or just above the MTZ beneath the Greater Khingan Range and the Erenhot Basin have negligible impact on the MTZ discontinuities,suggesting that these high-velocity bodies differ significantly in nature from the stagnant oceanic plate and are likely derived from the delamination of the overlying continental lithosphere.
The migration mechanisms of helium (He) in anhydrous and hydrous stishovite under Earth's mantle conditions are studied using density functional theory (DFT) and climbing image nudged elastic band (CI-NEB) transition state calculations. In anhydrous stishovite, He diffusion is constrained to the structurally unobstructed [001] channels, with diffusion activation energies along other directions significantly higher than [001], confirming that He migrates almost exclusively through these anisotropic pathways. Hydrous stishovite, however, hosts "one-dimensional superionic conduits", where the activation energy for He diffusion is less than 50% of that in anhydrous stishovite, leading to markedly enhanced He diffusion rate. Pressure exerts a similar effect on both stishovite types—increasing pressure elevates diffusion energy barriers and reduces He diffusion rates. However, hydrous stishovite exhibits weaker pressure sensitivity: a 50 GPa pressure increase causes a far smaller reduction in He diffusion rates compared to anhydrous stishovite. Temperature-dependent retention analysis further reveals that anhydrous stishovite exhibits delayed thermal responsiveness relative to hydrous stishovite, mirroring the trend observed between quartz and coesite—under equivalent He retention levels, quartz sustains higher temperatures than coesite. These findings underscore the decisive role of crystal structural features, specifically, the [001] channels in anhydrous stishovite and superionic conduits in hydrous stishovite are governing noble gas migration dynamics. By quantifying the modulation of He diffusion by pressure, temperature, and grain size, this work advances mechanistic models for subsurface noble gas cycling and deep Earth degassing processes.
Earthquakes represent dynamic processes in rocky planets where accumulated stress leads to sudden rupture, block movement, and energy release. Investigating their origin mechanisms not only advances our understanding of planetary stress accumulation and release, but also reveals deep dynamic processes, including tectonic activity and magmatism. Current research confirms ongoing seismic activity on Mars, providing a critical window into the planet's interior dynamics. The focal mechanism (strike, dip, and slip angles) directly reflects deep tectonic activity and serves as key evidence for understanding Marsquake triggering processes. While Earth focal mechanism inversion typically requires multi-station networks with good azimuthal coverage, Mars is currently limited to single-station data from InSight, posing significant technical challenges. The systematic evaluation of existing methods is crucial for developing novel inversion strategies for single-station observations. This study first reviews Earth-based focal mechanism methods, including those based on first-motion polarity, amplitude, and waveform fitting. Methods relying on first-motion polarity and amplitude require well-distributed station networks for complete focal mechanism sampling. For Mars' single-station inversion, P/S polarities and amplitude ratios alone cannot adequately constrain focal mechanisms. Waveform information must be fully utilized, with polarity/amplitude data typically incorporated into waveform-based inversions. The relative focal mechanism approach is suitable for analyzing clustered events-particularly relevant for Mars' regionally concentrated Marsquakes. In waveform-based Marsquake studies, velocity model uncertainties introduce challenges for full-waveform fitting. Seismic phase windowing with permitted time shifts during waveform modeling helps mitigate velocity model errors, making this approach (e.g. CAP) more viable for single-station inversions on Mars. Next, we summarize single-station inversion techniques (based on body waves, surface waves, full waveforms) developed for limited data on Earth. Finally, we synthesize Marsquake focal mechanism research, covering: 1) InSight mission background (instrumentation, data, Earth-Mars observational differences); 2) Tectonic setting (landing site, crust-mantle structure, stress field, thermal evolution); and 3) Research progress (methods, findings, unresolved challenges). In Mars focal mechanism studies, single-station waveform-fitting methods have been widely developed and applied, effectively addressing the insufficient sampling issue in single-station data. However, current results still exhibit significant uncertainties and inconsistencies across different studies, necessitating further optimization of inversion strategies. The clustered distribution of Marsquakes enables the application of relative focal mechanism methods. Initial solutions obtained through waveform analysis can be further constrained using relative mechanism approaches. Earlier studies were limited by insufficient velocity structure and uncertain event locations, highlighting the need to update existing solutions using improved structural models and more accurate event locations. Through the comprehensive synthesis, we aim to provide methodological and theoretical support for single-station-based Marsquake focal mechanism research.
The long-term atmospheric evolution and ion escape of unmagnetized terrestrial planets under con-tinuous solar wind erosion are fundamental to understanding their habitability,water loss mechanisms,and evolu-tionary pathways.Although Venus and Mars both lack a global intrinsic magnetic field,their ionospheric structures,surface magnetic field distributions,and atmospheric compositions differ significantly,leading to distinct types of induced magnetospheres and ion acceleration environments.Despite extensive observational and modeling efforts,the physical mechanisms governing the differences in their electromagnetic structures,ion dynamics,and escape fluxes remain insufficiently constrained.To address this issue,we develop and employ a unified three-dimensional multi-fluid magnetohydrodynamic(MHD)model to systematically compare the global plasma structures,electric field systems,heavy ion distributions,and escape characteristics of Venus and Mars under solar wind interaction,and further evaluate the performance of Mars four-species single-fluid,four-species multi-fluid,and ten-species multi-fluid models. Our results show that the ion escape processes of both planets are jointly regulated by the solar wind dynamic pressure,Hall electric field,and ionosphere-magnetosphere coupling.Owing to its dense ionosphere and strong photochemical processes,Venus exhibits a pronounced magnetic pileup region,elevated heavy-ion densities,and a nearly symmetric electromagnetic structure.In contrast,Mars is strongly influenced by spatially variable crustal magnetic fields and more prominent Hall effects,which produce complex ion-scale structures and acceleration pathways at the magnetic pileup boundary,dayside plume region,and magnetotail.The Hall electric field contributes a substantially larger fraction of the total electric field at Mars than at Venus,even dominating the local electric field direction in plume source regions and plasma sheet locations,indicating a stronger electromagnetic accelera-tion capability under comparable upstream conditions. Comparisons between simulations and observations show that the ten-species multi-fluid model most accurately reproduces the bow shock and magnetic pileup positions,ionospheric density profiles,local electric field strengths,and overall ion escape rate(～1.4×1025 s-1).The model also reveals a pronounced mass dependence in Martian ion escape:light ions(e.g.,O+)are preferentially accelerated into the magnetotail and dominate tailward escape,where-as heavy ions(e.g.,O+2,CO+2)primarily escape through dayside plume structures.These patterns reflect the com-bined effects of multi-species coupling,Hall physics,and crustal magnetic field geometry. In summary,Hall electric fields,multi-ion coupling,and localized magnetic field structures are identified as key controlling factors that shape the electromagnetic configuration,ion transport pathways,and long-term atmo-spheric loss of unmagnetized terrestrial planets.The findings deepen our understanding of the physical divergence between Venus and Mars and provide new theoretical constraints for modeling atmospheric evolution and assess-ing planetary habitability.
The exploration of the Moon is an extremely important part of aerospace missions. However, the Moon lacks the shielding of a global magnetic field and atmosphere, leaving it directly exposed to high energy space radiation, which poses non-negligible potential risks to lunar exploration missions. High energy particles from deep space may directly impact personnel or instruments on the lunar surface. Moreover, they react with the lunar regolith to generate a large number of secondary particles—including a significant amount of neutrons that are difficult to shield against—thereby introducing additional radiation risks. The lunar radiation environment is relatively complex, constrained by multiple factors (such as radiation sources at different times, varying compositions and densities of lunar soil, etc.). Therefore, in addition to analyzing data from detectors mounted on spacecraft or lunar landers, particle transport simulations tailored to different scenarios are also an important tool. Studying the lunar radiation environment is not only a requirement for the smooth execution of lunar exploration missions but also contributes to addressing scientific issues such as analyzing the mechanisms of cosmic rays and the isotopic composition of lunar samples. As a review article, this paper respectively introduces the main sources of high energy particle radiation on the Moon, the mechanisms of interaction between high energy space radiation particles and lunar regolith, the measurement status of high energy particles and radiation doses on the lunar surface in recent years, the simulation of the lunar surface radiation environment, and the outlook for future research prospects.
