The West Qinling Orogen (WQO) is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen, Songpan-Garze Orogen and Yangtze Block, and also the key position of Triassic collision orogenic event. The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys. We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance, depositional age, and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO. The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon. The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic, with the youngest detrital zircon age of 253 ± 3 Ma. The ages can be divided into five age groups: 3 346–1 636 Ma, with two peak ages of ca. 2 495 and ca. 1 885 Ma; 1 585–1 010 Ma, with a peak age at ca. 1 084 Ma; 992–554 Ma, with a peak age at ca. 939 Ma; 521–421 Ma, with a peak age at ca. 445 Ma; 418–253 Ma, with a peak age at ca. 280 Ma. Apparently, the sources of the Longwuhe Formation include the northern margin of the WQO, the Qilian Orogen (QLO) and the basement of the southern margin of the North China Block (NCB), of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation. Combined with previous studies, we propose that the Longwuhe Formation was formed in a fore-arc basin, which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block (YZB). This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.
Obtaining geological and landform dislocation features, as well as the measured stratigraphic activity age, provides direct evidence to evaluate fault activity, which is more difficult to do in areas with low tectonic activity, such as eastern and central China. A detailed investigation of the fault activity, trenching, drilling joint geological profile, geological survey, and chronological analysis were used to obtain the spatial geometry, fault kinematics, and activity chronology of the Jiulong fault. The conclusions are as follows: (1) The Jiulong fault was a fracture zone composed of four branch faults, with a width of around 30–40 m and good extendibility, while the maximum surface rupture length was 373 m. (2) The Jiulong fault has many strata dislocations, and the dislocation distance decreased from bottom to top, demonstrating synsedimentary structure characteristics, with a maximum stratigraphic dislocation distance of 18.2 m. (3) Preliminary analysis suggested the Jiulong fault as a secondary fracture of the Xiangfan-Guangji fault zone and provided evidence of the southeastward extension of the Xiangfan-Guangji fault. A preliminary hypothesis purported the Xiangfan-Guangji fault as the seismogenic fault of the Ms 5.0 magnitude earthquake in 1911. (4) According to OSL and ESR dating analyses, the upper breakpoint of the Jiulong fault cuts into the Late Pleistocene Xingang Formation (Qp3 x) strata, and the latest active age of the Jiulong fault was 57.6 ka. The chronology analysis confirmed an active fault from the Late Pleistocene and identified a weak tectonic in Jiujiang Province, which represents the largest active fault outcrop uncovered in the area so far. This study provides evidence and research materials for the evaluation of fault activity and seismic stability in this region.
Detrital U-bearing minerals (e.g., zircon, apatite) U-Pb ages with specific trace-element geochemistry, are frequently used in provenance analyses. In this study, we focus on the Yarlung River drainage in South Tibet, characterized by two distinct lithologic units: The Gangdese batholith to the north (mainly granitoids) and the Tethyan Himalaya (mainly sedimentary rocks) to the south, which plays a crucial role in the erosion of the Tibetan Plateau. To constrain the provenance of the Yarlung River Basin, we performed trace-element and U-Pb age analyses of detrital apatite from the river sands of the Yarlung River and its tributaries. Our findings indicate that the detrital apatite U-Pb age patterns of the north tributaries exhibit main peaks at approximately 40 and 60 Ma, consistent with the corresponding U-Pb age patterns of detrital zircon published. Further, their trace element casts fall mainly in the Type I granite region, also indicating the Gangdese arc-dominated source. However, those of the south tributaries (∼60–20 Ma) exhibit a different age distribution from the detrital zircon U-Pb groups (∼110–150, ∼500, and 1 100 Ma), suggesting that the detailed apatite U-Pb signals can provide excellent constraints on the provenance of igneous and metamorphic rock sources but less so for sedimentary rock sources. Combined with previous detrital zircon data in the study area, our detrital apatite information can highlight young metamorphic events from a complex background (i.e., Niyang and Nianchu rivers), which offers additional constraints on the provenance of the Yarlung River Basin. Generally, a combination of geochemistry and geochronology of multi-detrital heavy minerals, such as zircon and apatite, can provide powerful tools for provenance analysis.
Abundant mafic-felsic intrusions distributed in the Altyn Orogen record orogenic histories related to Proto-Tethys and Paleo-Tethys evolution. Zircon U-Pb dating of the intrusive rocks in the eastern Altyn Orogen identifies at least three major tectono-magmatic episodes, yielding ages of ∼426, ∼376–373 and ∼269–254 Ma. The first two emplacement episodes correspond to the post-collisional magmatism in the Altyn Orogen. The ∼426 Ma granitoids possess adakitic characteristics coupled with enriched isotopes, suggesting that they originated from partial melting of thickened lower continental crust induced by upwelling asthenospheric mantle after slab break-off of the South Altyn Ocean Plate. Next, the ∼376–373 Ma mafic-intermediate rocks and coeval granitoids represent a large thermal event that involved mantle melting with induced new juvenile lower continental crust melting in a post-collisional extensional setting. Finally, the ∼254 Ma diabase dykes intruded into the ∼269 Ma granitoids, which were related to the widespread Late Paleozoic magmatism resulting from Paleo-Tethys Ocean subduction. Post-collisional magmatism in the Altyn Orogen significantly enhances understanding of the tectono-magmatic evolution in the northern Tibetan Plateau. The penetrative influence of Paleo-Tethys Ocean subduction was more extensive than previously thought.
Seismic anisotropy originating within the continental crust is commonly used to determine the deformation and kinematic flow within active orogens and is attributed to regionally oriented mica or hornblende grains. However, naturally deformed rocks usually contain compositional layers (e. g., parallel compositional banding). It is necessary to understand how both varying mineral contents and differing intensities of compositional layering influence the seismic properties of the deep crust. In this study, we analyzed the seismic response of migmatitic amphibolite with compositional banding structures. We present the microstructures, fabrics, calculated seismic velocities, and seismic anisotropies of mylonitic amphibolite from a horizontal shear layer preserved within the Ailao Shan-Red River shear zone, southwestern Yunnan, China. The investigated sample is characterized by pronounced centimeter-scale compositional banding. The microstructures and fabrics suggest that migmatitic amphibolite rocks within deep crust may delineate regions of deformation-assisted, channelized, reactive, porous melt flow. The origin of compositional banding in the studied migmatitic amphibolite is attributed primarily to partial melting together with some horizontal shearing deformation. The microfabrics and structures investigated in this study are considered to be typical for the base of active horizontal shear layers in the deep crust of southeastern Tibet. Seismic responses are modeled by using crystal preferred orientations for minerals of the migmatitic amphibolite by applying the Voigt-Reuss-Hill homogenization method. Calculated P-wave and S-wave velocities are largely consistent in the various layers of the migmatite. However, seismic anisotropies of P-wave (AV p) and S-wave (AV s) are higher in the melanosomes (AV p = 5.6%, AV s = 6.83%) than those in the leucosomes and the whole rock (AV p = 4.2%–4.6%, AV s = 3.1%–3.2%). In addition, there is pronounced, S-wave splitting oblique to the foliation plane in the migmatitic amphibolite. The multiple parallel compositional layers generate marked variation in the geometry of the seismic anisotropy (V s1 polarization) in the whole rock. Combined with the macroscale geographical orientation of fabrics in the Ailao Shan-Red River shear zone, these compositional banding effects are inferred to generate significant variations in the magnitude and orientation of seismic anisotropy, especially for shear-wave anisotropy (AV s) in the deep crust. Hence, our data suggest that layering of various origins (e.g., shear layers, partial-melting layers, and compositional layers) represents a new potential source of anisotropy within the deep crust.
The Wutonggou iron deposit is located in the well-known iron metallogenic belt in the eastern Tianshan, NW China, and has been regarded as a sedimentary iron deposit. Although hydrothermal overprinting could play indispensable roles in the formation of high-grade iron ores in sedimentary iron deposits, previous studies mainly focused on sedimentary-related iron mineralization, while the nature and contribution of hydrothermal fluids are poorly constrained. Accordingly, an integrated study of ore geology, H-O-C isotopes and 40Ar-39Ar dating, is conducted on the Wutonggou deposit, in order to reveal the features, source, and timing of hydrothermal mineralization. The studied deposit includes two mining sections namely the Jianshan and Wutonggou. The δ18O values of early magnetite from the Jianshan section range from +3.0‰ to +5.8‰ that nearly consistent with classic magmatic magnetite, while increase to 6.3‰–8.0‰ in the late stage. Quartz from the two sections shows comparable H-O isotopic compositions and identical fractionation trends, and is plotted in or periphery to the primary magmatic water area. Calcites from the two sections are broadly similar in carbon and oxygen isotopic compositions, and siderite from the Wutonggou section is plotted in the same region. Thus, comparable stable isotopic compositions and evolution trends indicate similar magmatic fluids contributed hydrothermal iron mineralization in the two mining sections. Moreover, water-rock interactions of varying degrees generated distinct mineralization styles in the Jianshan and Wutonggou sections, and caused the isotopic fractionation in late stages. Biotite extracted from a hydrothermal siderite ore yielded a 40Ar-39Ar plateau age of 299.5 ± 2.0 Ma, indicates the timing of hydrothermal iron mineralization is corresponding to the emplacement of vicinity granitoids. Taken together, the hydrothermal mineralization in the Wutonggou iron deposit was the product of remobilization and upgrading of early sedimentary iron ores, and ore-forming fluids were most probably originated from regional granitic magmatism.
Radon (Rn) and helium (He) gases from uranium decay form distinct anomalies related to buried uranium deposits. In order to trace the geochemical anomalous sources from the volcanic-related uranium deposits in deeply buried areas, systematical Rn contents and He isotope ratios were analyzed from the Daguanchang uranium deposit. The soil gas Rn concentrations above the deep uranium are ten times higher than those in barren areas, indicating that instantaneous Rn content measurements can be used to detect deeply buried uranium. The helium isotope ratios (3He/4He) of the unmineralized samples from the mineralized drill hole (ZK1) are relatively lower and uniform compared to those of the samples from no-mineral drill hole (ZK2). However, the Th and U contents of the drill core samples from ZK1 are slightly lower than those of the samples from ZK2, indicating that the lower 3He/4He ratios in ZK1 are most likely due to the addition of 4He from underlying uranium intervals. The differences in the instantaneous Rn contents are consistent with the variations in the He isotope ratios of the drill core samples. These results demonstrate that soil gas Rn and 3He/4He ratios are useful tracers and can indicate the existence of deeply buried volcanic-related hydrothermal uranium ores.
The podiform chromitites in the Luobusha ophiolite have been thought to experience a very deep formation, but the maximum depth is still an open issue. Here, we have investigated the structural stability of natural magnesiochromite using the synchrotron-based powder X-ray diffraction and diamond anvil cells up to 48.6 GPa and 2 450 K. The results have shown that spinel-type magnesiochromite first decomposes into corundum-type ‘Cr2O3’ + B1-type ‘MgO’ at 11–14 GPa and 1 250–1 450 K, then modified ludwigite (mLd)-type ‘Mg2Cr2O5’ + corundum-type ‘Cr2O3’ at 14.3–20.5 GPa and 1 300–2 000 K, and finally CaTi2O4-type phase at 24.5 GPa. During the quenching procession from high-temperature-pressure conditions, the mLd-type phase appeared again and was kept at ambient conditions. We also obtained the isothermal equation states of spinel-type and CaTi2O4-type phases, revealing the composition effect on their elasticities. Based on the updated results, we propose chromitites could not experience pressure exceeding ∼14.3 GPa (approximate maximum depth ∼400 km) in the subduction-recycling genesis model.
The three-dimensional (3D) morphology, anatomy, and in-situ chemical composition analysis of fossils are crucial for systematic paleontology and determining their phylogenetic positions. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), offers valuable structural and chemical information for the analysis of fossils. However, its primary limitation is the restriction to two-dimensional surface data, which limits the exploration of fossils’ 3D complexities. Conversely, 3D X-ray microscopy (3D-XRM), also known as a novel form of micro-computed tomography (micro-CT) facilitates the non-destructive 3D reconstruction of fossil specimens. Nevertheless, it lacks the capability to provide in-situ compositional data. Acknowledging the constraints inherent in these individual techniques, and in response to the evolving requirements of paleontological research, this study introduces an integrated approach that combines 3D-XRM with EDS-coupled focused ion beam scanning electron microscopy (FIB-SEM). This innovative strategy is designed to synergize the advantages of both techniques, thereby addressing challenges that conventional methods cannot. It enables the rapid identification of regions of interest (ROI) within fossil specimens at micrometer resolution. Subsequently, this method collects detailed data on both 3D structures and chemical compositions at the nanometer scale for the identified ROI. This integrated approach represents a significant advancement in paleontological and geological research methodologies, promising to meet the increasing demands of these fields.
Burgess Shale-type deposits provide a wealth of information on the early evolution of animals. Questions that are central to understanding the exceptional preservation of these biotas and the paleoenvironments they inhabited may be obscured by the post-depositional alteration due to metamorphism at depth and weathering near the Earth’s surface. Among over 50 Cambrian BST biotas, the Chengjiang and Qingjiang deposits are well known for their richness of soft-bodied taxa, fidelity of preservation, and Early Cambrian Age. While alteration via weathering has been well-investigated, the thermal maturity of the units bearing the two biotas has not yet been elucidated. Here we investigate peak metamorphic temperatures of the two deposits using two independent methods. Paleogeotemperature gradient analyses demonstrate that the most fossiliferous sections of the Chengjiang were buried at a maximum depth of ∼8 500 m in the Early Triassic, corresponding to ∼300 °C, while the type area of the Qingjiang biota was buried at a maximum depth of ∼8 700 m in the Early Jurassic, corresponding to ∼240 °C. Raman geothermometer analyses of fossil carbonaceous material demonstrate that peak temperatures varied across localities with different burial depth. The two productive sections of the Chengjiang biota were thermally altered at a peak temperature of approximately 300 °C, and the main locality of the Qingjiang biota experienced a peak temperature of 238 ± 22 °C. These results from two independent methods are concordant. Among BST deposits for which thermal maturity has been documented, the Qingjiang biota is the least thermally mature, and therefore holds promise for enriching our understanding of BST deposits.
It is the first time that the fossil footprints of a group of Middle Eocene elephant ancestors have been discovered in the Gonjo Basin, East Tibet Plateau. The Gonjo Formation is attributed to the Middle Eocene Epoch (U-Pb age = 44.7 ± 1.2 Ma) and consists mainly of purplish-red, medium- to coarse-grained sandstones, siltstones interbedded with mudstones, and conglomerates with sedimentary structures like ripple marks, rip-up clasts, and trough-cross bedding, suggesting fluvial-lacustrine systems. The group of fossil footprints has a characteristic oval-concave shape, and the toe impressions are absent. Some fossil footprints are overstepped with a pockmarked texture resembling Proboscipeda enigmatica. More than 165 fossil footprints of the group are relatively well-preserved with different diameters, which is evidence of highly social behavior and trackmakers of different ages, including calves, juveniles, adolescents, and adults. The size frequency of the fossil footprints enabled us to deduce the body mass, shoulder height, and hip-height distribution of the trackmakers that crossed the East Tibet Plateau 44.7 Ma ago. The trackmakers comprised an estimated average hip-height of 111.8 cm, an average shoulder height of 172.8 cm for males/155.9 cm for females, and an average body mass of approximately 1 218.1 kg for males/907.8 kg for females. The abundance of fossil footprints reveals that in the Middle Eocene Epoch, the environment was extraordinarily conducive for the elephant ancestors to live in the East Tibet region.
Conodonts, as a biotic group, next to ammonoids, pollen and spores, crustaceans and vertebrates, provide proxy clues for environment and age assessments of the rocks in which they occur. Conodonts are widely used for Triassic marine biostratigraphy. However, there are various discussions about their multielement taxonomy and evolutionary lineages (e.g., generation, speciation). Although first studies reported that most Triassic conodont species were unimembrate, studies carried out in the following years maintained that all Triassic conodonts were multimembrate. Although statistical reconstructions of a number of Triassic apparatuses were attempted, the discovery of fused clusters and natural assemblages has subsequently demonstrated that Triassic conodonts are indeed multimembrate, and all of the elements exist together in the same apparatus. The present paper aims to clarify the evolutionary relationship and array of some Lower Triassic conodonts. Columbitella dagisi n. sp. is described.
Flexural toppling occurs when a series of layered rock masses bend towards their free face. It is important to evaluate the maximum bending degree and the requirement of supports of flexural toppling rock mass to prevent rock mass cracking and even failure leading to a landslide. Based on the rock tensile strain-softening model, this study proposes a method for calculating the maximum curvature (C ppmax) of flexural toppling rock masses. By applying this method to calculate C ppmax of 9 types of rock masses with different hardness and rock layer thickness, some conclusions are drawn: (1) the internal key factors affecting C ppmax are E ⋆ (E ⋆= E ss/E 0, where E 0 and E ss are the mean deformation moduli of the rock before and after reaching its peak tensile strength, respectively), the strain ε t corresponding to the tensile strength of rock, and the thickness (h) of rock layers; (2) hard rock layers are more likely to develop into block toppling than soft rock layers; and (3) thin rock layers are more likely to remain in flexural toppling state than thick rock layers. In addition, it is found that C ppmax for flexural toppling rock masses composed of bedded rocks such as gneiss is related to the tensile direction.
This paper coupled a water-air two-phase hydrodynamic (WATPH) model with the Iverson’s method to analyze the influence of the Lisse effect on the fast groundwater pressure (P w) response and the slope stability. Furthermore, the sensitivities of the driving force and loess soil parameters were investigated. Results showed that the WATPH model simulated the height and rise of the depth to the water table reasonably well. The depth to water table before rainfall (H 0) had a significant impact on the Lisse effect and the slope stability. When the H 0 was less than approximately 1 m, the rainfall triggered a significant Lisse effect and decreased the slope factor of safety (F s). When the rainfall intensity (R i) was higher than the saturated hydraulic conductivity (K s), the Lisse effect and the Fs slightly changed with the increase of the R i, and the slope tended to be unstable with continuous rainfall. With increasing K s, the Lisse effect noticeably increased, and the minimum F s quickly decreases. The analysis of the normalized sensitivity coefficient revealed that H 0 had a dramatic impact on the Lisse effect and loess slope stability. The different R i and K s values had prominent influences on the Lisse effect and slight impacts on F s.
The curve of landslide thrust plays a key role in landslide design. The commonly used transfer coefficient method (TCM) and Morgenstern-Price method (MPM) are analyzed. TCM does not take into account the moment balance between slices. Although MPM considers the moment balance, the calculation is complex, and it does not consider that the force between slices may be less than zero at the back edge of the landslide. The rationality and feasibility of the improved MPM are verified by calculating the landslide stability coefficient and landslide thrust at different reservoir water levels. This paper studies the law of landslide thrust when the reservoir water level changes, and discusses the determination of design thrust, to provide a certain theoretical basis for the design of reservoir landslides.
The short-term effect of heavy rainfall on gPhone gravimeter observation at Zhengzhou Seismic Station is investigated. According to the observation data during Jul. 17–20, 2021, the corrected gravity residual reflects the gravimetric response caused by heavy rainfall. The observed gravity change is dominated by the local effect considering topographic effect on gravity. The deduced water depth near the observation station is about 300 mm.
Anchor reinforced vegetation system (ARVS) comprises high performance turf reinforcement mats (HPTRM), vegetation and anchors. It is a new attempt to apply the system in expansive soil slope protection. The goal of this paper was to evaluate the effectiveness of ARVS in protecting newly excavated expansive soil slopes. The field tests on the bare slope, grassed slope and ARVS protective slope were carried out, including natural and artificial rainfall. During the test, the soil water content, soil deformation, and anchor axial force were monitored, and then the slope protection mechanism of ARVS was analyzed. It was found that ARVS can effectively protect expansive soil slopes compared with bare slopes and grassed slopes. The vegetation and HPTRM form a reinforced turf, and the anchors fix it to the slope surface, thus restraining the expansion deformation. The axial force on the anchor of ARVS includes frictional resistance and tensile force transmitted by HPTRM, which is maximum at the early stage of support. The neutral point of the anchor of ARVS moves deeper under atmospheric action, but the vegetation and HPTRM on the slope surface can limit this movement.
If progress is to be made toward improving geohazard management and emergency decision-making, then lessons need to be learned from past geohazard information. A geologic hazard report provides a useful and reliable source of information about the occurrence of an event, along with detailed information about the condition or factors of the geohazard. Analyzing such reports, however, can be a challenging process because these texts are often presented in unstructured long text formats, and contain rich specialized and detailed information. Automatically text classification is commonly used to mine disaster text data in open domains (e.g., news and microblogs). But it has limitations to performing contextual long-distance dependencies and is insensitive to discourse order. These deficiencies are most obviously exposed in long text fields. Therefore, this paper uses the bidirectional encoder representations from Transformers (BERT), to model long text. Then, utilizing a softmax layer to automatically extract text features and classify geohazards without manual features. The latent Dirichlet allocation (LDA) model is used to examine the interdependencies that exist between causal variables to visualize geohazards. The proposed method is useful in enabling the machine-assisted interpretation of text-based geohazards. Moreover, it can help users visualize causes, processes, and other geohazards and assist decision-makers in emergency responses.
It is well known that the deformation and damage of reservoir colluvium landslides are often determined by the combined dynamics of reservoir water level change and rainfall. Based on the systematic analysis of the change law of reservoir water level, rainfall and displacements of reservoir colluvium landslide, this paper proposes the compound hydrodynamic action of rainfall and reservoir water as the unload-load parameter, and the landslide displacement as the unload-load response parameter. Based on this, a physical prediction model of the compound hydrodynamic unload-load response ratio of reservoir colluvium landslide was established, and the quantitative relationship between the compound hydrodynamic unload-load response ratio and its stability evolution was in-depth analyzed and determined. On the basis of the above research, taking Shuping landslide, a typical hydrodynamic pressure landslide as an example, the unload-load response ratio model is used to systematically evaluate and predict the stability evolution law and the change trend of the landslide under compound hydrodynamic action. The prediction result shows that the variation law of the compound hydrodynamic unload-load response ratio is consistent with the dynamic evolution law of its stability. Therefore, the above studies show that the compound hydrodynamic unload-load response ratio parameter is an effective displacement dynamic evaluation parameter for reservoir colluvium landslides, so it can be used in the prediction of the reservoir colluvium landslides.
Weathered rock (especially granite) slopes are prone to failure under the action of rainfall, making it necessary to study the response of weathered rock slope to rainfall infiltration for landslide prevention. In this study, a series of model tests of weathered rock slope under different conditions were conducted. The matric suction, volumetric water content, earth pressure and deformation of slope were monitored in real time during rainfall. The response of the slope to rainfall infiltration, failure process and failure mode of slope under different conditions were analyzed, and the early warning criterion for the failure of weathered rock slope caused by rainfall was studied. The results show that the slope deformation evolution process under rainfall condition was closely related to the dissipation of matric suction. When the distribution of the matrix suction (or water content) of slope met the condition that the resistance to sliding of the slip-mass was overcome, the displacement increased sharply and landslide occurred. Three factors including rainfall process, lithologic condition and excavation condition significantly affect the response of weathered rock slope to rainfall. It can be found from the test results under different conditions that compared with intermittent rainfall condition, the rainfall intensity and infiltration depth were smaller when the slope entering accelerated deformation stage under the condition of incremental rainfall. The accumulated rainfall when weathered clastic landslide occurring was greater than that of weathered granite, which results in greater disaster risk. The excavation angle and moisture distribution of a slope were the main factors affecting the stability of a slope. In addition, the evolution processes and critical displacement velocities of slopes were studied by combining the deformation curves and matrix suction curves, which can be used as reference for early warning of rainfall-induced weathered rock landslide.
Landslides are widespread geomorphological phenomena with complex mechanisms that have caused extensive causalities and property damage worldwide. The scale and frequency of landslides are presently increasing owing to the warming effects of climate change, which further increases the associated safety risks. In this study, the relationship between historical landslides and environmental variables in the Hanjiang River Basin was determined and an optimized model was used to constrain the relative contribution of variables and best spatial response curve. The optimal MaxEnt model was used to predict the current distribution of landslides and influence of future rainfall changes on the landslide susceptibility. The results indicate that environmental variables in the study area statistically correlate with landslide events over the past 20 years. The MaxEnt model evaluation was applied to landslide hazards in the Hanjiang River Basin based on current climate change scenarios. The results indicate that 25.9% of the study area is classified as a high-risk area. The main environmental variables that affect the distribution of landslides include altitude, slope, normalized difference vegetation index, annual precipitation, distance from rivers, and distance from roads, with a cumulative contribution rate of approximately 90%. The annual rainfall in the Hanjiang River Basin will continue to increase under future climate warming scenarios. Increased rainfall will further increase the extent of high- and medium-risk areas in the basin, especially when following the RCP8.5 climate prediction, which is expected to increase the high-risk area by 10.7% by 2070. Furthermore, high landslide risk areas in the basin will migrate to high-altitude areas in the future, which poses new challenges for the prevention and control of landslide risks. This study demonstrates the usefulness of the MaxEnt model as a tool for landslide susceptibility prediction in the Hanjiang River Basin caused by global warming and yields robust prediction results. This approach therefore provides an important reference for river basin management and disaster reduction and prevention. The study on landslide risks also supports the hypothesis that global climate change will further enhance the frequency and intensity of landslide activity throughout the course of the 21st Century.
Topography can strongly affect ground motion, and studies of the quantification of hill surfaces’ topographic effect are relatively rare. In this paper, a new quantitative seismic topographic effect prediction method based upon the BP neural network algorithm and three-dimensional finite element method (FEM) was developed. The FEM simulation results were compared with seismic records and the results show that the PGA and response spectra have a tendency to increase with increasing elevation, but the correlation between PGA amplification factors and slope is not obvious for low hills. New BP neural network models were established for the prediction of amplification factors of PGA and response spectra. Two kinds of input variables’ combinations which are convenient to achieve are proposed in this paper for the prediction of amplification factors of PGA and response spectra, respectively. The absolute values of prediction errors can be mostly within 0.1 for PGA amplification factors, and they can be mostly within 0.2 for response spectra’s amplification factors. One input variables’ combination can achieve better prediction performance while the other one has better expandability of the predictive region. Particularly, the BP models only employ one hidden layer with about a hundred nodes, which makes it efficient for training.
The exploration and development of tight sandstone gas reservoirs are controlled by high-quality river channel sand bodies on a large scale in Sichuan Basin. In order to improve the accuracy of sand body prediction and characterization, Multi-component exploration technology research has been carried out in Northwest Sichuan Basin. First, based on the array acoustic logging data, a forward modeling has been established to analyze the seismic response characteristics of the PS-wave data and P-wave data. The result shows that the response characteristics of the P-wave and PS-wave to the sand bodies with different impedance are different. And then through the analysis of logging data, the effectiveness of the forward modeling has been proved. When the sandstone velocity is close to the surrounding rocks, the P-wave performs as a weak reflection, which may lead to reduce the identification range of the sand bodies. However, the PS-wave exhibits strong reflection, which can identify this type of sand bodies. Finally, by comparing and explaining the PS-wave data and P-wave data, and integrating their attributes, the prediction accuracy of sand bodies is improved. Compared with the interpretation of a single P-wave, the results can significantly expand the distribution range of sand bodies, laying a foundation for improving the production capacity of single wells and reserve submission.