Abstract The Altyn Tagh Fault, as the northern edge of the Tibetan Plateau, is crucial for understanding the plateau evolution and continental convergence processes. Using teleseismic waveforms recorded by a 300‐km‐long broadband seismic array deployed by our team in northern Tibet, we investigate the detailed crustal and upper mantle structure beneath the middle section of the Altyn Tagh Fault system and the eastern Kunlun Fault. Our receiver function results reveal complex intra‐crustal discontinuities and a laterally variable Moho beneath the study region. These features suggest a vertically partitioned shortening mode in northern Tibet. The upper crust accommodates horizontal shortening through brittle faulting and folding, whereas the mid‐lower crust responds through ductile deformation, distributed shear, and basal thickening. Along with lateral extrusion, far‐field compressional stresses from the India‐Asia collision and the blocking effect from the rigid Tarim Basin craton have contributed to the crustal shortening in the brittle middle section between the Altyn Tagh Fault and the eastern Kunlun Fault.

The Changbai volcano is the most active intraplate volcano in East Asia. However, the spatial distribution and melt fraction of its magma chambers in the crust remain poorly understood. In this study, we investigate the detailed 3-D S-wave velocity (Vs) structure beneath the volcano using high-quality data recorded by a dense seismic array. Distinct low-Vs anomalies are revealed in the shallow and middle crust. The shallow crustal (similar to 3-5 km depths) and middle crustal (similar to 8-15 km depths) anomalies directly beneath the Tianchi caldera are interpreted as magma chambers, whereas the low-Vs anomaly at the shallower depths (< 3 km) may be a zone rich in volcanic fluids. From the Vs reductions, the basalt melt fraction of the shallow magma chamber is estimated to be similar to 11-19 %. Integrating the distribution pattern of surface basaltic scoria cones and previous results, we deem that a complex multi-stage magma system exists beneath the Changbai volcano.

Abstract In this study, we develop a 3D S‐wave velocity model extending to 120 km depth beneath Northeast China, featuring high resolution for the crust and uppermost mantle, based on physics‐informed neural network framework for eikonal tomography. Notably, this model provides a characterization of the transitional lithosphere‐asthenosphere boundary (LAB) beneath the volcanic regions, while also illuminating its connections to the formation of Quaternary intraplate volcanoes in the region. Key observations include a prominent large‐scale high‐velocity anomaly beneath the Songliao Basin (SLB), which suggests a thicker lithosphere in that area. In addition, we identify undulations in the LAB, as well as diverse low‐velocity features underlying the volcanoes. Drawing from a schematic representation of lithospheric and upper mantle convection, we interpret these patterns as stemming from regional variations in the water‐carbon cycle and lithospheric thickening within the SLB. For instance, inputs from the deep Big Mantle Wedge not only promote lithospheric thickening beneath the SLB, but also enhance asthenospheric mobility, facilitating sodic volcanism in the southeastern and western sectors. In contrast, the Wudalianchi (WDLC) and Nuominhe (NMH) volcanoes, which lack intense deep convection, produce potassic lavas instead. Overall, these insights improve our understanding of intraplate volcanic mechanisms in this region.

Accurate early smoke detection is crucial for timely wildfire monitoring. However, the spectral heterogeneity of complex land surfaces often causes background misclassification, leading to significant errors in smoke identification and concentration retrieval. To address this issue, we propose an improved Mahalanobis distance (MD)-based smoke detection framework that integrates fine-grained background identification with a scattering-absorption physical model. A theoretical relationship between MD and smoke column concentration is derived, elucidating the separability of background clusters under smoke interference. Furthermore, a normalized spectral variation index (NSVI) is introduced to quantify band-level resistance to smoke effects, identifying the near-infrared bands as optimal for background recognition. Building upon these findings, a comprehensive workflow-comprising background identification, smoke detection, concentration retrieval, and fire localization-is established. The framework combines MD, the maximum likelihood method (MLM), and the spectral angle mapper (SAM) for background classification, employs a dual-threshold MD for smoke pixel discrimination, and applies the Laplacian operator to extract smoke concentration peaks as potential fire sources. Cross-platform validation using UAV, Landsat 8/OLI, and MODIS data demonstrates that the proposed method achieves smoke detection accuracies of 94.99%, 84.51%, and 89.24%, respectively, reduces concentration retrieval errors (RMSE by 3.34% and MAE by 23.42%), and localizes fire points within 8 pixels. These results highlight the framework's capability to significantly enhance smoke detection accuracy and provide a physically interpretable foundation for high-precision background identification and early stage wildfire monitoring.

The 1975 Ms 7.3 Haicheng earthquake occurred in northwestern Liaodong Peninsula, which was successfully forecasted and marked a landmark achievement in seismology. However, the seismogenic mechanism of this earthquake remains poorly known. In this study, we obtain high-precision earthquake catalog and 3-D models of crustal P- and S-wave velocities (Vp, Vs) and their ratio (Vp/Vs) in the Haicheng seismic zone (HSZ) from an unprecedentedly dense seismic array that we recently deployed. Our results show the seismicity pattern in the HSZ is predominantly controlled by an interconnected conjugate fault system, comprising the WNW-striking Haichenghe fault and its NE-striking concealed secondary fault. Furthermore, a prominent fluid-rich zone characterized by low Vp, low Vs and high Vp/Vs ratio is clearly revealed in the middle crust at similar to 15 km depth, directly beneath the hypocentral region of the 1975 Haicheng earthquake. A distinct seismic cluster is also observed adjacent to the main shock hypocenter, exhibiting spatial correlation with the underlying crustal fluid reservoir. This geometric correspondence indicates a fluid-driven triggering mechanism that contributes to the localized seismicity. We deem that the reactivation of preexisting seismogenic faults induced by crustal fluid migration could be a possible mechanism for the nucleation of such a large intraplate earthquake.

We determine the first P-wave azimuthal and radial anisotropy tomography beneath the Caribbean and its adjacent regions. The Cocos and Atlantic Plates are imaged as high-velocity (high-V) zones down to similar to 1,600 km depth and they have subducted independently beneath the Caribbean Plate. A high-V zone adjacent to the Nazca slab, characterized by continuous seismicity and downward extension to 200 km depth, is considered to be the subducted Caribbean slab. The Cocos plate is imaged as a high-V zone that is torn into two parts below 300 km depth along the Motagua Polochic fault zone. Trench-parallel and toroidal FVDs (fast velocity directions) exist in low-velocity (low-V) anomalies above and below the southern Cocos slab and around the Panama, respectively, which may reflect large-scale toroidal mantle flow around the southern Cocos slab, bypassing the Panama, from the asthenosphere to the mantle wedge. Azimuthal anisotropy in the Lesser Antilles shows a trench-normal FVDs in the subducted Atlantic slab, perpendicular to seafloor isochrons of plate reconstruction. Above the Atlantic slab, a low-V zone with negative radial anisotropy reflects widespread vertical mantle flow, which appears not only in the upper mantle but also in the mantle transition zone and lower mantle. Beneath the Colombia-Ecuador volcanic arc, low-V anomalies passing through and surrounding a slab gap exhibit positive radial anisotropy. This feature indicates that horizontal mantle flow occurs in the mantle wedge and also originates from asthenosphere entering into the mantle wedge through a slab tear.

The driving mechanism behind the anomalously thick crust and surface uplift of the Tibetan Plateau remains controversial. Here we present seismic images of the lithosphere in southern Tibet, derived from P and S receiver functions along a newly deployed 200 km‐long broadband seismic array that strikes north at 91.15°E longitude. An offset of the Moho discontinuity is revealed at ∼70 km depth beneath the Yarlung‐Zangbo suture zone (YZS). The subducted Indian lithospheric mantle is thrusting beneath southern Tibet with a flat‐ramp‐flat geometry and is undergoing crust‐mantle detachment beneath the YZS. As an intermediate stage in the underplating and delamination of the Indian plate, the crust‐mantle detachment plays an important role in the process of surface uplift and crustal thickening in southern Tibet. It is the main cause of the Moho offset, facilitating upwelling of asthenospheric materials from the upper mantle to the crust. These materials underplate in the lower crust, promote the formation of juvenile lower crust in southern Tibet, and lead to widespread low‐velocity zones within the crust.

The Changbaishan volcano (CBV) is the largest Cenozoic intraplate stratovolcano in Northeast China. Although many seismic imaging studies have been conducted in the CBV area during the past two decades, the detailed crustal structure beneath the Tianchi caldera is still poorly understood due to the sparse seismic observations limited by the harsh natural conditions. In this study, we deployed dense linear seismic arrays along three slopes of the Changbaishan‐Tianchi volcanic area for the first time to obtain unprecedented high‐resolution images of the crustal structure by using the teleseismic receiver‐function imaging technique. Our results reveal detailed variations of crustal interface characteristics beneath the Tianchi caldera and adjacent areas. Several intracrustal interfaces are clearly revealed that correspond well to geological bodies, which might indicate boundaries of consolidated igneous bodies related to the primitive magmatic activities. A continuous Moho discontinuity at ∼37 km depth is revealed, whereas a weak Moho zone with a vertical offset of ∼4 km appears directly beneath the Tianchi caldera, which shows a clear positive correlation with the average crustal Vp/Vs ratio. We deem that the prominent crustal thickening and the higher Vp/Vs ratio beneath the Tianchi caldera might be closely associated with the complicated mantle‐derived mafic materials underplating at the crust‐mantle boundary. The joint effect of the multilevel magmatic plumbing system and a narrow magma conduit beneath the Tianchi caldera could account for the distinctive bimodal volcanic eruption history of the CBV.

A northwest-southeast trending high-density seismic array was deployed in the southern Xing'an-Mongolian Orogenic Belt, spanning the Songliao basin, the North-South gravity gradient lineament, the Great Xing'an Mountains, and the Erlian basin. The high-density seismic array included 1000 stations with an interval of -0.5 km. We image the lithospheric structure using the teleseismic receiver function method. Our results show that the Moho depth gradually increases from -35 km beneath the Songliao basin to -40 km beneath the Great Xing'an Mountains. In the vicinity of the North-South gravity lineament, the Moho is slightly inclined with a continuous depth of -5 km, which forms a transition zone from the basin to the orogenic belt. A middle crustal discontinuity, or the Conrad discontinuity, is imaged beneath the Songliao-Xilinhot block and the northern margin of the North China Craton. The Conrad and Moho discontinuities beneath the suture zones show traces of bidirectional subduction of the Paleo-Asian Ocean plate. Meanwhile, we find subtle changes in the receiver functions due to variations in the sedimentary layer thickness. The sedimentary layer beneath the southern Songliao basin is estimated to be -1.2 km thick and it thins toward its edge. Moreover, we find a middle lithospheric discontinuity below the Moho under the Songliao-Xilinhot block. Combining with previous findings, we deem that the middle lithospheric discontinuity reflects a high-temperature layer in the upper lithosphere mantle associated with hot and wet upwelling flows in the big mantle wedge under NE China.

Debris flows originating in glacier and snow-covered catchments in cold high mountains exhibit distinctive initiation mechanisms and runout dynamics. However, due to limited records and data, their mechanisms and dynamics have been poorly studied, hindering effective monitoring and mitigation efforts. The Tianmo Gully (TMG) in the southeastern Tibetan Plateau has experienced repeated debris flows in recent years, presenting us with a unique opportunity to study their initiation mechanisms and dynamics. This study investigates the characteristics of five glacial debris flow events in TMG by employing a combination of field investigations and remote sensing interpretation and analyzes the spatial–temporal distribution of debris source materials and frozen water that control the initiation of debris flows. The results of this study reveal two distinct mechanisms responsible for the initiation of glacial debris flow in TMG, each exhibiting significant variations in triggering conditions. Specifically, the catastrophic event in 2007 was triggered by a rock collapse, subsequently leading to an ice avalanche. In contrast, the remaining four events were triggered by the deposition of snow avalanches. Notably, the velocity and discharge of glacial debris flow surpass those rainfall type debris flow events, with a 50

The tectonic evolution of the Tibetan Plateau has been influenced by continental collision and postcollisional convergence of Indian and Eurasian plates, both of which have undoubtedly imposed their imprints on the lithosphere and upper-mantle structures beneath the collision zone. However, the mode by which the Indian Plate has subducted beneath Tibet, and its driving forces, have been highly uncertain. Here, we present seismic evidence from a full-waveform tomographic model that reveals flat subduction of the Indian Plate beneath nearly the entire plateau at ∼ 300 km depth, implying that the slab may have transitioned to positive/neutral buoyancy and is no longer capable of supporting steep-angle deep subduction. The horizontal distance over which the flat slab slides northward increases from west (where it collides with the Tarim lithospheric keel) to east (where it has resided approximately north of the Songpan-Ganzi Fold Belt beyond the Qiangtang Block). The Asian lithosphere is subducting beneath northeastern Tibet without colliding with the Indian slab. The low-velocity zone, with a thickness of 50 to 110 km, sandwiched between the Tibetan crust and Indian slab, is positively correlated with the high-elevation, low-relief topography of Tibet, suggesting partial melting of the uppermost mantle that has facilitated the growth and flatness of the plateau by adding buoyant material to its base. We propose that deep mantle convective currents, traced to the Réunion plume and imaged as large-scale low-velocity anomalies from the upper mantle under the Indian Plate downward toward the uppermost lower mantle under the Baikal-Mongolia Plateau, are the primary force driving the ongoing India–Asia postcollisional convergence.

The Wudalianchi volcanic field (WVF) has the latest unambiguous major eruption in China. However, its magmatic system is still not well-understood. In this study, we deployed a dense seismic array of 193 short-period seismographs in the WVF to study its local seismicity and fine 3-D crustal velocity structure. Our results show that a high-Vp/Vs anomaly exists at 7-13 km depths below Weishan accompanied by relatively intense seismicity, which might indicate a magma chamber in the upper-middle crust. The magma chamber is likely responsible for the most recent eruption of the WVF similar to 300 years ago. In addition, a high-Vp/Vs anomaly is visible at 3-8 km depths below Yaoquanshan and Wohushan. Taking into account the development of carbonate mineral water near Yaoquanshan, we suggest that this high-Vp/Vs anomaly reflects a hydrothermal-rich zone. The magma chamber below Weishan and the hydrothermal-rich zone below Yaoquanshan and Wohushan might share the same magma source in the upper mantle.

Time-frequency analysis serves as a useful approach to solve different complex problems in seismic data processing. From a practical standpoint, the majority of time-frequency transform techniques frequently grapple with the trade-off between time and frequency localization adaptability, flexibility in sampling time and frequency, and the pursuit of computational efficiency. To address this, we tailor the streaming computation to implement a fast time-frequency transform, namely the streaming local time-frequency transform (SLTFT), which can significantly decrease the computational cost of adaptive time-frequency analysis. We add a localization scalar to the proceeding streaming algorithm to circumvent the need for taper functions, which provides rapid forward and inverse transforms and applicability in various scenarios.We demonstrate the adaptive time-frequency characteristics of the proposed method, which offers a nonstationary time-frequency representation with variable time-frequency localization. Numerical tests indicate that the proposed SLTFT is a more balanced method compared to previous time-frequency adaptive transforms. It proves suitable for a range of practical applications in nonstationary seismic data processing, including ground-roll attenuation, inverse-Q filtering, and multicomponent data registration.

The Arxan Volcanic Field (AVF) is an active volcanic region in Northeast Asia, and its last eruption occurred approximately 2000 years ago. Its eruption mechanism remains unknown. To investigate the shallow magma system beneath the volcanic cones in the AVF, we deployed a dense seismic array consisting of 227 portable seismographs and conducted high-resolution ambient noise tomography (ANT). The results of checkerboard test (CRT) and restoring resolution test (RRT) demonstrate that our imaging results are reliable. These results reveale significant slow-velocity anomalies at depths of 5~9 km below the Tianchi caldera and GD1213 volcano in Arxan, with the highest anomaly reaching up to approximately 15%. These anomalies suggest partial melting in a shallow magma chamber, indicating ongoing volcanic activity in the AVF. The velocity of the magma chamber corresponding to a melt fraction of approximately 7.4~12.9%. Therefore, the presence of the magma chamber poses potential hazards to the Arxan region, including volcanic eruptions and their associated risks.

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 at two sides of the north-south gravity lineament. The anisotropy in the east 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. In the west of the gravity lineament, the SKS splitting is attributed to freezing anisotropy in the stable lithosphere under the Erlian Basin. The SKS splitting delay time shows some changes with the teleseismic events in different azimuths, 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.

Seismic traveltime is critical information conveyed by seismic waves, widely utilized in various geophysical applications. Conventionally, the simulation of seismic traveltime involves solving the eikonal equation. However, the efficiency of traditional numerical solvers is hindered, as they are typically capable of simulating seismic traveltime for only a single source at a time. Recently, deep learning tools, particularly physics-informed neural networks (PINNs), have proven effective in simulating seismic traveltimes for multiple sources. Nonetheless, PINNs face challenges such as limited generalization capabilities across different models and difficulties in training convergence. To address these issues, we have developed a method for simulating multi-source seismic traveltimes in variable velocity models using a deep-learning technique, known as the physics-informed Fourier neural operator (PIFNO). The PIFNO-based method for seismic traveltime generation takes both velocity and background traveltime as inputs, generating the perturbation traveltime as the output. This method incorporates a factorized eikonal equation as the loss function and relies solely on physical laws, eliminating the need for labeled training data. We demonstrate that our proposed method is not only effective in calculating seismic traveltimes for velocity models used during training but also shows promising prediction capabilities for test velocity models. We validate these features using velocity models from the OpenFWI dataset.

Ambient noise surface wave exploration is one of the fields of interest in geophysical research. Extracting dispersion curves and inverting the S-wave velocity structure from the dispersion characteristics is also of primary importance. The accuracy of dispersion curves has great significance for the subsequent inversion result and its interpretation. The phase-shift method is widely used in dispersion imaging of surface waves. This method possesses advantages on stability but also suffers a lot from low resolution and low noise resistance. Therefore, we propose an improved phase-shift method based on semblance coefficients. This method replaces linear stacking in the traditional phase-shift method by calculating semblance coefficients and, therefore, can effectively improve the resolution and noise resistance of surface wave dispersion spectrum imaging. Tests are implemented on both synthetic ambient noise data and field data recorded by a short-period dense seismic array located in the ChangbaiShan region to evaluate the proposed method. The dispersion spectrum imaging results of the model and field data show that the semblance phase-shift (SPS) method has better noise resistance and computational accuracy than the traditional phase-shift method. The inversion results indicate that it is possible to obtain a reasonable S-wave velocity structure by inverting the dispersion curves resulting from the semblance phase-shift method. By constructing a 3 km deep and 4.8 km long S-wave velocity image, the velocity structure and abnormal conditions beneath the array in the ChangbaiShan region are presented. The results indicate a significant low-velocity anomaly at a depth of 1 km. It is inferred that it may be a fluid-rich structure.

The Changbai volcano, a globally recognized hotspot of volcanic activity, has garnered significant attention due to its persistent seismicity and ongoing magma activity. The volcano’s discontinuities and magma dynamics have raised concerns about the likelihood of future eruptions, which would likely result in substantial ecological, climatic, and economic impacts. Consequently, a comprehensive understanding of the Changbai volcanic system is essential for mitigating the risks associated with volcanic activity. In recent years, the P-wave coda autocorrelation method has gained popularity in lithosphere exploration as a reliable technique for detecting reflection coefficients. Additionally, the Common Reflection Point stacking approach has been employed to superimpose reflection signals in a spatial grid, enabling continuous observation of reflection coefficients in the study area. However, the accuracy of this approach is heavily reliant on better spatial data coverage. To better understand the internal dynamics of the Changbai volcano, we applied this approach to a densely packed short-period seismic array with an average station spacing of less than 1 km. Our results were constrained using waveform data of reflection coefficients and Moho dip angles. Our findings revealed a discontinuity in the Moho, which may indicate a conduit for mantle magma entering the crust. Furthermore, we identified two low-velocity anomalies within the crust, likely representing a magma chamber comprising molten and crystallized magma. Notably, our results also provided a clear definition of the lithosphere–asthenosphere boundary.

Studies on granites in the North Lancang River suture were mainly focused on the Indosinian period, but little on the Cretaceous. Based on the field geological survey, the petrogeochemistry, zircon U-Pb dating and Hf isotope of the newly discovered granites in Leiwuqi area, East Tibet are carried out. The results show that the diagenetic ages of the two granites are 75.06±0.82 Ma（MSWD=1.90） and 74.89±0.65 Ma（MSWD=1.05）, respectively, which are the products of Late Cretaceous magmatic activity. The granites contain muscovite（～5%） and are characterized by high SiO 2 （69.07%-69.39%）, rich K 2 O（5.31%-5.77%） and low Mg # （0.30-0.33）, with A/CNK ratio of 1.11-1.15, and are enriched in large ion lithophile elements（LILE, e.g., Rb, Th, U and Pb） and LREE, depleted in high field strength elements（HFSE, e.g., Ba, Nb, Sr, P and Ti） and HREE, with strong fractionation of light and heavy rare earth elements and significant negative Eu anomaly. These features suggest that the granites belong to the peraluminaceous S-type granite, and the source rocks are metamorphic argillaceous rocks and greywacke. The zircon ε Hf （t） value of the granite（-4.6 to 1.1） varies widely and are of ancient two-stage Hf isotopic model ages(T DM2 , 1.07-1.43 Ga). Comprehensive analysis shows that the Late Cretaceous granites in the North Lancang River suture were generated by a degree of separation crystallization of parent magma, derived from mantle derived mafic magma formed by the upwelling and decompression melting of asthenosphere materials caused by the delamination of the thickened lithosphere,underplating into the ancient crust, inducing the melting of the ancient crust and mixing with it, which indicates that the orogenic evolution of the Leiwuqi area in East Tibet was in the late orogenic destruction stage during Late Cretaceous.

Abstract Knowledge of lithospheric structure is essential for understanding the impact of continental collision and oceanic subduction on surface tectonic configurations. Full‐waveform tomographic images reveal lateral heterogeneities and anisotropy of the lithosphere and asthenosphere in Asia. Estimating lithospheric thickness from seismic velocity reductions at depth exhibits large variations underneath different tectonic units. The thickest cratonic roots are present beneath the Sichuan, Ordos, and Tarim basins and central India. Radial anisotropy signatures of 11 representative tectonic provinces uncover the different nature and geodynamic processes of their respective past and present deformation. The large‐scale continental lithospheric deformation is characterized by low‐velocity anomalies from the Himalayan Orogen to the Baikal rift zone in central Asia, coupled with the post‐collision thickening of the crust. The horizontal low‐velocity layer of ∼100–300 km depth extent below the lithosphere points toward the existence of the asthenosphere beneath East and Southeast Asia, with heterogeneous anisotropy indicative of channel flows.