Search Results (101)

The Diaoyu Islands Folded-Uplift Belt consists of metamorphic basement, magmatic rocks and Paleogene series in the Eastern Depression Zone of the East China Sea Basin which was deformed and uplifted by magma emplacement. The emplacement of the magma resulted in an unclear understanding of the Paleogene geomorphy in the paleo-uplift, further affecting the analysis of the eastern boundary and the sedimentary environment of Paleogene prototype basin in the Eastern Depression Zone. To explore the Paleogene geomorphy and magma emplacement process of the Diaoyu Islands Folded-Uplift Belt, we conducted a detailed interpretation of 2-D seismic profiles and identified nearshore subaqueous fans and fan deltas within the deformed strata. The development scale of them helps to determine the approximate location of the Paleogene eastern boundary of the Eastern Depression Zone. We integrated the boundary location with gravity, magnetic, and well data to obtain the Paleogene geomorphy of the Diaoyu Islands Folded-Uplift Belt. Our results indicate that the subduction direction of the Pacific Plate was almost perpendicular to the Eurasian Plate during the late Eocene, leading to the development of numerous left-lateral strike-slip faults within the East China Sea Basin, further forming channels within the paleo-uplift, which connected the Eastern Depression Zone and the ocean. In the Early Oligocene, the subduction rate of the Pacific Plate abruptly increased, resulting in large-scale and significant exhumation of the paleo-uplift, and the Eastern Depression Zone had transformed into a lacustrine sedimentary environment. Furthermore, due to the continuous retreat of the Pacific Plate, the extension center of the back-arc basin moved to the eastern margin of the Eastern Depression Zone in the late Oligocene. This work provides a method for recovering the geomorphology of complex tectonic units in back-arc basins based on fine seismic interpretation, solving the key problem that constrained the recovery of boundaries and sedimentary environment of the prototype basin. Full article

The Shahejie Formation in Nanpu Sag is a crucial region for deep-layer hydrocarbon exploration in the Bohai Bay Basin. To address the impact of faults on sublacustrine fan formation and spatial distribution within the study area, this study integrated well logging, laboratory analysis, and 3D seismic data to systematically analyze sedimentary characteristics of sandbodies from the first member of the Shahejie Formation (Es₁) sublacustrine fans, clarifying their planar and cross-sectional distributions. Further research indicates that Gaoliu Fault activity during Es₁ deposition played a significant role in fan development through two mechanisms: (1) vertical displacement between hanging wall and footwall reshaped local paleogeomorphology; (2) tectonic stresses generated by fault movement affected slope stability, triggering gravitational mass transport processes that remobilized fan delta sediments into the central depression zone as sublacustrine fans through slumping and collapse mechanisms. Core observations reveal soft-sediment deformation features, including slump structures, flame structures, and shale rip-up clasts. Seismic profiles show lens-shaped geometries with thick centers thinning laterally, exhibiting lateral pinch-out terminations. Inverse fault-step architectures formed by underlying faults control sandbody distribution patterns, restricting primary deposition locations for sublacustrine fan development. The study demonstrates that sublacustrine fans in the study area are formed by gravity flow processes. A new model was established, illustrating the combined control of the Gaoliu Fault and reverse stepover faults on fan development. These findings provide valuable insights for gravity flow exploration and reservoir prediction in the Nanpu Sag, offering important implications for hydrocarbon exploration in similar lacustrine rift basins. Full article

As a strategic replacement area for hydrocarbon exploration in the Tarim Basin, the Kuqa Depression has been the subject of relatively limited research on the sedimentary characteristics of the Triassic strata within its western Wushi Sag, which constrains exploration deployment in this region. This study focuses on the Wushi Sag, systematically analyzing the sedimentary facies types, the evolution of sedimentary systems, and the distribution patterns of the Triassic Kelamayi and Huangshanjie formations. This analysis integrates field outcrops, drilling cores, wireline logs, and 2D seismic data, employing methodologies grounded in foreland basin theory and clastic sedimentary petrology. The paleo-geomorphology preceding sedimentation was reconstructed through balanced section restoration to investigate the controlling influence of foreland tectonic movements on the distribution of sedimentary systems. By interpreting key seismic profiles and analyzing vertical facies successions, the study classifies and evaluates the petroleum accumulation elements and favorable source–reservoir-seal assemblages, culminating in the prediction of prospective exploration areas. The research shows that: (1) The Triassic in the Wushi Sag mainly develops fan-delta, braided-river-delta, and lacustrine–shallow lacustrine sedimentary systems, with strong planar distribution regularity. The exposed strata in the northern part are predominantly fan-delta and lacustrine systems, while the southern part is dominated by braided-river-delta and lacustrine systems. (2) The spatial distribution of sedimentary systems was demonstrably influenced by tectonic activity. Paleogeomorphological reconstructions indicate that fan-delta and braided-river-delta sedimentary bodies preferentially developed within zones encompassing fault-superposition belts, fault-transfer zones, and paleovalleys. Furthermore, Triassic foreland tectonic movements during its deposition significantly altered basin configuration, thereby driving lacustrine expansion. (3) The Wushi Sag exhibits favorable hydrocarbon accumulation configurations, featuring two principal source–reservoir assemblages: self-sourced structural-lithologic gas reservoirs with vertical migration pathways, and lower-source-upper-reservoir structural-lithologic gas reservoirs with lateral migration. This demonstrates substantial petroleum exploration potential. The results provide insights for identifying favorable exploration targets within the Triassic sequences of the Wushi Sag and western Kuqa Depression. Full article

A multidisciplinary approach was employed to construct a three-dimensional model of the bedrock top surface within the Palermo Plain, Sicily, Italy. This urban area is characterized by a dense and extensive built environment that largely obscures its geological features, thereby emphasizing the value of geophysical methods for enhancing subsurface understanding. In this sector, Numidian Flysch deposits constitute the geological bedrock of the plain. The morphology of the top surface of this unit was reconstructed by integrating borehole stratigraphic data with both passive and active seismic surveys. Ambient noise recordings were analyzed using the Horizontal-to-Vertical Spectral Ratio (HVSR) method to obtain spectral curves. These were then inverted into seismostratigraphic models using shear wave velocity profiles derived by Multichannel Analysis of Surface Waves (MASW) and lithostratigraphic information from borehole logs. Finally, the depth of the top of the Numidian Flysch, determined from both the borehole data and the inverted seismic models, was interpolated to generate a comprehensive 3D model of the bedrock top surface. Full article

Many urbanised areas of the Apennines, in Italy, have complex soil stratifications. A typical example is the outskirts of the city of L’Aquila, which is founded on highly heterogeneous soil layers and was severely affected by a strong earthquake in 2009. In such conditions, shear wave velocity profiles (V_S) obtained from in situ tests such as the Seismic Dilatometer Marchetti Test (SDMT) provide reliable analyses of the local seismic response. This article presents the mono-dimensional (1D) and two-dimensional (2D) seismic response analyses conducted to characterise the soil foundation of the hospital complex and adjacent university buildings in L’Aquila before their seismic retrofitting. This study emphasises the importance of accurate soil characterisation prior to repair interventions, especially in deposits where there are V_S inversions and in the presence of geometrically irregular and large structures. Under these conditions, estimating the motion amplitudes of the deposit’s higher modes beyond the fundamental level is essential in accurately characterising the seismic response, especially for buildings where higher structural modes play a significant role. The results show that approximating the V_S profile with simplified procedures, as proposed by the Italian Building Code of 2018 (equivalent V_S, similar to average), leads to incorrect estimates of seismic action. Full article

The northwestern slope of the Dongdao Platform in the Xisha Sea exhibits a complex geomorphological structure. Utilizing high-resolution multibeam bathymetric data and 2D seismic profiles, this study systematically reconstructs the slope morphology and its evolutionary processes. The study area displays a distinct threefold zonation: the upper slope (160–700 m water depth) has a steep gradient of 15°–25°, characterized by deeply incised V-shaped channels and slump deposits, primarily shaped by gravity-driven erosion; the middle slope (700–1200 m water depth) features a gentler gradient of 10°–15°, where channels stabilize, adopting U-shaped cross-sections with the development of lateral accretion deposits; the lower slope (1200–1500 m water depth) exhibits a milder gradient of 5°–10°, dominated by a mixture of fine-grained carbonate sediments and hemipelagic mud–marine sediments originating partly from the open ocean and partly from the nearby continental margin. The slope extends from 160 m to 1500 m water depth, hosting the C1–C4 channel system. Seismic facies analysis reveals mass-transport deposits, channel-fill facies, and facies modified by bottom currents—currents near the seafloor that redistribute sediments laterally—highlighting the interplay between fluid activity and gravity-driven processes. The slope evolution follows a four-stage model: (1) the pockmark formation stage, where overpressured gas migrates vertically through chimneys, inducing localized sediment instability and forming discrete pockmarks; (2) the initial channel development stage, during which gravity flows exploit the pockmark chains as preferential erosional pathways, establishing nascent incised channels; (3) the channel expansion and maturation stage, marked by intensified erosion from high-density debris flows, resulting in a stepped longitudinal profile, while bottom-current reworking enhances lateral sediment differentiation; (4) the stable transport stage, wherein the channels fully integrate with the Sansha Canyon, forming a well-connected “platform-to-canyon” sediment transport system. Full article

In practice, site-specific one-dimensional (1D) seismic site response analyses are conducted to compute surface acceleration time histories considering shear wave velocity profile, modulus reduction, damping, and site-specific ground motions. The computed surface responses depend not only on the geologic and seismic characteristics but also on the type of 1D analysis (i.e., equivalent linear or nonlinear) and the software. Equivalent linear analysis (EQLA) is preferred by practicing engineers because the analysis procedure is well defined, but the accuracy of the results is questionable for certain geologic and input motion characteristics. On the other hand, nonlinear analysis (NNLA) is accurate for any geologic and input motion characteristics, but it is complicated because certain steps in the analysis procedure are complicated and not well defined. The objective of this study is to compare the responses computed from EQLA and NNLA procedures and make recommendations on when to use EQLA and NNLA, considering Charleston, South Carolina; geology; and seismicity. About 18,000 NNLAs (DMOD2000 and DEEPSOIL) and EQLAs (SHAKE2000) were performed, considering variations in shear wave velocity profiles, shear modulus reduction curves, damping curves, and ground motions. Based on the results from each software, three seismic site factor models were developed and compared with the published models. Results show that the EQLAs produced conservative estimates compared to the NNLAs. It is also observed that the site factor model based on EQLA diverges from the models based on NNLA even at the lowest amplitude shaking considered in the study (0.05 g), particularly for profiles with low shear wave velocity. This indicates that soils behave nonlinearly even at low amplitude shaking. Although a similar shear stress/shear strain model is used in DMOD2000 and DEEPSOIL, the site factor models show significant differences. Finally, an easy-to-use chart was developed to select suitable software and analysis types for accurately computing the surface responses based on the peak ground acceleration (PGA) of the input motion at the reference rock outcrop and average shear wave velocity in the top 30 m. Full article

The high-magnetic anomaly belt in the northern slope of the South China Sea has long been associated with a Mesozoic volcanic arc. However, its crustal architecture remains unclear, limiting the understanding of its geological implications. We assembled high-resolution reduced-to-the-pole aeromagnetic anomaly data around the northern South China Sea and then applied the 3-D magnetic inversion method based on mixed L_p norm regularization, with the constraint of multiple deep seismic reflection profiling data, to obtain high-resolution 3-D crustal susceptibility model. Our model confirms that the high-magnetic anomaly belt is caused by deep-seated magnetic bodies, which, supported by borehole and seismic data, are identified as a Mesozoic volcanic arc. We found that the Mesozoic volcanic arc described by high susceptibility bodies extends northeastward from the Dongsha Rise to Taiwan Island and primarily distributes within the depth range of 20~28 km. Our findings provide important constraints for understanding the pre-Cenozoic tectonic evolution of the northern South China Sea. Full article

The Makran Subduction Zone (MSZ) is a tectonic plate boundary where the Arabian Plate is subducting beneath the Eurasian Plate. This study investigated the dynamic response in the Gwadar region, located in the eastern part of the MSZ. A suite of seismic records compatible with the Building Code of Pakistan (BCP:2021) rock design spectrum was used as the input ground motions at the bedrock. The amplification characteristics were assessed through a series of one-dimensional (1D) site response analyses utilizing a non-linear (NL) approach. The results revealed significant de-amplification in soft soils at short spectral periods. A general depth-wise decrease in the shear stress ratio and peak ground acceleration values was observed, influenced by shear-strain-induced effects and shear wave velocity reversals within the site profiles. The code spectra, compared to the proposed design spectra, underestimated the site amplification for stiff soils (i.e., Site Class D) for periods of less than 0.32 s and overestimated it for soft soils (i.e., Site Class E) across all periods. These findings underscore the necessity for site-specific ground response analyses, particularly within the framework of the China–Pakistan Economic Corridor (CPEC). Full article

Passive seismic surveys have attracted interest for use in many geological and geotechnical applications in the past few decades, mainly in reconstructing models of near-surface properties. They are also of interest in the mineral exploration of shallow deposits where targets lay on or within the bedrock and are covered by loose sediments above. The goal of this article was to test the effectiveness of cheap methods to understand the cover thickness and its lateral variations, which is essential to map the top of the bedrock. We investigated the use of passive seismic surveys to retrieve Rayleigh surface waves and invert them by analyzing their dispersion to reconstruct near-surface shear-wave velocity profiles. Using readily available passive seismic sources is advantageous compared to using costly active sources. Passive seismic data acquired by geophones and DAS showed the potential and challenges of using different sensing technologies. We demonstrated an approach combining passive seismic interferometry and multichannel analysis of surface waves (MASW). Computed dispersion images from both geophone and DAS data provided an improved understanding of their usability for subsurface model building and factors affecting their quality. Some of these factors are related to the surrounding environment, present noise sources, acquisition setup, and the methods used in reconstructing the dispersion images and inverting them. Successful demonstration of MASW was achieved with a relatively short period of continuous recording using a 2D array of geophones at a mineral exploration site in the Pilbara region of Western Australia. Full article

Applying deep neural networks (DNNs) to broadband seismic wave impedance inversion is challenging, especially in generalizing from synthetic to field data, which limits the exploitation of their nonlinear mapping capabilities. While many research studies are about advanced and enhanced architectures of DNNs, this article explores how variations in input data affect DNNs and consequently enhance their generalizability and inversion performance. This study introduces a novel data pre-processing strategy based on histogram equalization and an iterative testing strategy. By employing a U-Net architecture within a fully convolutional neural network (FCN) exclusively trained on synthetic and monochrome data, including post-stack profile, and 1D linear background impedance profiles, we successfully achieve broadband impedance inversion for both new synthetic data and marine seismic data by integrating imaging profiles with background impedance profiles. Notably, the proposed method is applied to reverse time migration (RTM) data from the Ceduna sub-basin, located in offshore southern Australia, significantly expanding the wavenumber bandwidth of the available data. This demonstrates its generalizability and improved inversion performance. Our findings offer new insights into the challenges of seismic data fusion and promote the utilization of deep neural networks for practical seismic inversion and outcomes improvement. Full article

Airwave interference presents a major source of noise in seismic exploration, posing significant challenges to the quality control of raw seismic data. With the increasing data volume in 3D seismic exploration, manual identification methods fall short of meeting the demands of high-density 3D seismic surveys. This study employs the YOLOv5 model, a widely used tool in object detection, to achieve rapid identification of airwave noise in seismic profiles. Initially, the model was pre-trained on the COCO dataset—a large-scale dataset designed for object detection—and subsequently fine-tuned using a training set specifically labeled for airwave noise data. The fine-tuned model achieved an accuracy and recall rate of approximately 85% on the test dataset, successfully identifying not only the presence of noise but also its location, confidence levels, and range. To evaluate the model’s effectiveness, we applied the YOLOv5 model trained on 2D data to seismic records from two regions: 2D seismic data from Ningqiang, Shanxi, and 3D seismic data from Xiushui, Sichuan. The overall prediction accuracy in both regions exceeded 90%, with the accuracy and recall rates for airwave noise surpassing 83% and 90%, respectively. The evaluation time for single-shot 3D seismic data (over 8000 traces) was less than 2 s, highlighting the model’s exceptional transferability, generalization ability, and efficiency. These results demonstrate that the YOLOv5 model is highly effective for detecting airwave noise in raw seismic data across different regions, marking the first successful attempt at computer recognition of airwaves in seismic exploration. Full article

In recent years, numerous studies highlighted the crucial role of the soil–structure interaction (SSI) in the seismic performance of basement structures. However, there remains a limited understanding of how this interaction affects buildings with basement structures under varying site conditions. Based on the three-dimensional (3D) numerical analysis method, the influence of the SSI on the seismic response of high-rise steel frame–core wall (SFCW) structures situated on shallow-box foundations were investigated in this study. To further investigate the effects of the SSI and site conditions, three types of soil profiles—soft, medium, and hard—were considered, along with a fixed-foundation model. The results were compared in terms of the maximum lateral displacement, inter-story drift ratio (IDR), acceleration amplification coefficient, and tensile damage for the SFCW structure under different site conditions, with both fixed-base and shallow-box foundation configurations. The findings highlight that the site conditions significantly affected the seismic performance of the SFCW structure, particularly in the soft soil, which increased the lateral deflection and inter-story drift. Moreover, compared with non-pulse-like ground motion, pulse-like ground motion resulted in a higher acceleration amplification coefficient and greater structural response in the SFCW structure. The RC core wall–basement slab junction was a critical region of stress concentration that exhibited a high sensitivity to the site conditions. Additionally, the maximum IDRs showed a more significant variation at incidence angles between 20 and 30 degrees, with a more pronounced effect at a seismic input intensity of 0.3 g than at 0.2 g. Full article

Investigating the primary influencing factors that regulate the enrichment of shallow gas not only deepens our understanding of the rules governing shallow gas enrichment in deep-ocean environments but also has the potential to enhance the success rate of locating shallow gas reservoirs. Recent drilling activities in the LS36 gas field located in the central Qiongdongnan Basin have revealed a substantial shallow gas reserve within the sediments of the Quaternary Ledong Formation, marking it as the first shallow gas reservoir discovered in the offshore region of China with confirmed natural gas geological reserves surpassing 100 billion cubic meters. However, the formation mechanism and influencing factors of shallow gas enrichment remain elusive due to the limited availability of 3D seismic and well data. This study employs seismic interpretation and digital simulation to decipher the dynamics of shallow gas accumulation and utilizes the carbon isotope composition of methane to ascertain the origin of the shallow gas. Our results show that the shallow gas is primarily concentrated within a large-scale submarine fan, covering a distribution region of up to 2800 km², situated in the deep-sea plain. The δ¹³ C₁ methane carbon isotope data ranges from −69.7‰ to −45.2‰ and all δ¹³ C₂ values are above −28‰, suggesting that the shallow gas within the Ledong Formation is derived from a mix of biogenic gas produced in shallow strata and thermogenic gas generated in deeper source rocks. The results of gas sources, seismic profiles, and digital simulations suggest that thermogenic gas originating from the Lingshui and Beijiao sags was transported to the Quaternary submarine fan via a complex system that includes faults, gas chimneys, and channel sands. The mass-transported deposits (MTDs) in the upper reaches of the submarine fan have effectively acted as a seal, preventing the escape of shallow gas from the fan. Therefore, the factors contributing to the enrichment of shallow gas in the Qiongdongnan Basin include the presence of favorable submarine fan reservoirs, the availability of two distinct gas sources, the effective sealing of MTDs, and the presence of two efficient transport pathways. A conceptual model for the accumulation of shallow gas is developed, illuminating the complex formation–migration–accumulation process. This study underscores the importance of aligning multiple influencing factors in the process of shallow gas accumulation, and the suggested accumulation model may be pertinent to shallow gas exploration in other marginal sea basins. Full article

Constructing an accurate three-dimensional (3D) geological model is crucial for advancing our understanding of subsurface structures and their evolution, particularly in complex regions such as the South China Sea (SCS). This study introduces a novel approach that integrates multimodal deep learning with multipoint statistics (MPS) to develop a high-resolution 3D crustal P-wave velocity structure model of the SCS. Our method addresses the limitations of traditional algorithms in capturing non-stationary geological features and effectively incorporates heterogeneous data from multiple geophysical sources, including 44 wide-angle seismic crustal structure profiles obtained by ocean bottom seismometers (OBSs), gravity anomalies, magnetic anomalies, and topographic data. The proposed model is rigorously validated against existing methods such as Kriging interpolation and MPS alone, demonstrating superior performance in reconstructing both global and local spatial features of the crustal structure. The integration of diverse datasets significantly enhances the model’s accuracy, reducing errors and improving the alignment with known geological information. The resulting 3D model provides a detailed and reliable representation of the SCS crust, offering critical insights for studies on tectonic evolution, resource exploration, and geodynamic processes. This work highlights the potential of combining deep learning with geostatistical methods for geological modeling, providing a robust framework for future applications in geosciences. The flexibility of our approach also suggests its applicability to other regions and geological attributes, paving the way for more comprehensive and data-driven investigations of Earth’s subsurface. Full article