Search Results (132)

This study develops a novel transverse steel damper (TSD) to enhance the seismic performance of tall-pier girder bridges, featuring superior lateral strength and energy dissipation capacity. The TSD’s design and arrangement are presented, with its hysteretic behavior simulated in ABAQUS. Key parameters (yield strength: 3000 kN; initial gap: 100 mm; post-yield stiffness ratio: 15%) are optimized through seismic analysis under near-fault ground motions, incorporating pulse characteristic investigations. The optimized TSD effectively reduces bearing displacements and results in smaller pier top displacements and internal forces compared to the bridge with fixed bearings. Due to the higher-order mode effects, there is no direct correlation between top displacements and bottom internal forces. As pier height decreases, the S-shaped shear force and bending moment envelopes gradually become linear, reflecting the reduced influence of these modes. Medium- to long-period pulse-like motions amplify seismic responses due to resonance (pulse period ≈ fundamental period) or susceptibility to large low-frequency spectral values. Higher-order mode effects on bending moments and shear forces intensify under prominent high-frequency components. However, the main velocity pulse typically masks the influence of high-order modes by the overwhelming seismic responses due to large spectral values at medium to long periods. Full article

Based on drilling, core and seismic data, combined with the regional tectonic sedimentary evolution background, the sedimentary environment of the Triassic carbonate rocks in the Mangeshlak Basin was studied. A sedimentary facies model of this set of carbonate rocks was established. Research has shown that the Mangeshlak Basin underwent a complete large-scale marine transgression–regression sedimentary evolution process during the Triassic. During the early to middle Triassic, seawater gradually invaded the northwest region of the basin from northwest to southeast and gradually regressed in the late Middle Triassic. In the lower part of the Triassic carbonate rocks, the primary components are developed granular limestone or dolomite with oolitic structures, interspersed with a small amount of thin mudstone, which is a good reservoir; the upper part of the Triassic is mainly composed of sedimentary mudstone and mudstone, which can form good sealings. The hill-shaped reflections of the platform edge facies, along with the high-frequency, strong-amplitude, and moderately continuous reflections within the restricted platform interior, are clearly visible on the seismic profile. These features are consistent with the sedimentary environment and lithofacies characteristics revealed by drilling data along the profile. Drilling and seismic data revealed that the sedimentary environment of the early and middle Triassic in the basin is mainly composed of shallow water platform edges and restricted platforms, as well as carbonate rock slopes and open non-marine shelves in deep water areas. A sedimentary facies model of the Triassic carbonate rock segment in the basin was established, comprising restricted platforms, platform edges, carbonate rock slopes, and non-marine shelves. Unlike the modified Wilson marginal carbonate rock platform model, the carbonate rock platform edge in the Mangeshlak Basin does not develop reef facies. Instead, it is mainly composed of oolitic beach (dam) sediments, making it the most favorable sedimentary facies zone for the Triassic reservoir development in the basin. Full article

The Davie Fracture Zone (Davie FZ)—among the longest offshore transform systems in East Africa—mediated Madagascar’s southward displacement following Gondwana’s Early Jurassic breakup. This giant structure has a distinct topography and gravity field signals. However, it is buried by thick sediments in its northern segment offshore Tanzania, hindering understanding of the internal structures and their origin. In this study, we applied 2-D multichannel seismic to analyze the structural characteristics and evolution of the Davie FZ. The Davie FZ is located in the oceanic domain, which is bordered by the landwards-dipping overthrust fault at the continent–ocean boundary. Volcano sediments atop the basement with undulating Moho reflection below depict a typical oceanic domain. Distinct compressive deformation characterized by the crustal undulation of around 40 km wavelength forms folded oceanic crust, and Late Jurassic sediments onlap onto the crest of the folded basement. The Davie FZ is localized in a corridor with the thickened oceanic crust and is presented by positive flower structures with faulted uplifted basement and deepened Moho. The Davie FZ evolved from a proto-transform fault located in Gondwana before the spreading of the West Somali Basin. During the Late Jurassic, a kinematic change shifted the spreading direction from NW–SE to N–S, resulting in a strike-slip of the Davie FZ and contemporaneous transpressional deformation offshore Tanzania. The Davie FZ is an excellent case to understand the tectonic-magmatic process forming this transform margin. Full article

This study aims to overcome the technical bottleneck of non-invasive differentiation between the rammed earth layer and pebble layer in complex shallow subsurface environments, particularly focusing on the challenge of detecting highly heterogeneous pebble layers with complex wavefield characteristics. Using the western city wall of the Baodun site (Xinjin, Sichuan, China) as a case study, we introduce a high-resolution seismic detection technique combined with controllable high-frequency seismic source excitation to investigate the response characteristics of high-frequency components and energy variations of seismic waves in different strata, thereby revealing differences in physical properties between the rammed earth layer and pebble layer. Through high-frequency data acquisition, specialized processing, and interpretative analysis of seismic data, we successfully distinguish the two strata and delineate pebble-related anomalous zones. The results also indicate that, due to complex geological conditions, the reflection and refraction patterns of seismic waves in the pebble layer are exceptionally intricate. Moreover, the interplay of abrupt seismic velocity variations, interference waves, and other contributing factors leads to pronounced heterogeneity and strong scattering characteristics in the seismic data across the time, frequency, and phase domains. This research overcomes the limitations of conventional geophysical methods and confirms the applicability of high-frequency seismic techniques to complex near-surface archaeological contexts. It provides robust scientific support for the archaeological study of the Baodun site and offers a methodological reference for subsurface mapping of pebble layer in prehistoric urban landscapes. Full article

This study focuses on the fundamental mechanical behavior of frame–shear wall split-foundation structures with shear walls at both upper and lower ground ends, investigating their basic mechanical characteristics, internal force redistribution patterns, and the influencing factor of intra-stiffness ratio on seismic performance. From the analysis results, it can be found that the relative drop height of frame–shear wall split-foundation structures significantly affects their internal force patterns. Shear-bending stiffness should be adopted in stiffness calculations to reflect the stiffness reduction effect of drop height on lower embedding shear walls. In frame–shear wall split-foundation structures, the existence of drop height causes upper embedding columns to experience more unfavorable stress conditions compared to lower embedding shear walls, potentially preventing lower embedding shear walls from serving as the primary seismic defense line. Strengthening lower embedding shear walls to reduce the intra-stiffness ratio can mitigate this issue. Performance evaluation under bidirectional rare earthquakes shows greater along-slope directional damage than cross-slope directional damage. Increasing shear wall length to reduce the intra-stiffness ratio improves component rotation-based performance, but shear strain-based evaluation of upper embedding shear walls indicates a limited improvement in shear capacity. Special attention should therefore be paid to along-slope directional shear capacity of upper embedding shear walls during structural design. Full article

The Chaoshan Depression, situated in the northern South China Sea, is a Mesozoic residual depression beneath the Cenozoic Pearl River Mouth Basin. Borehole LF35-1-1 has confirmed the existence of marine Jurassic layers rich in organic carbon within this depression. However, the understanding of petroleum geology in this area is limited due to the complex interplay of Mesozoic and Cenozoic tectonic activities and the poor quality of seismic imaging from previous surveys, which have obstructed insights into the characteristics of Mesozoic reservoirs and the processes of oil and gas accumulation. Recent quasi-3D seismic data have allowed for the identification of Mesozoic bioherms and carbonate platforms in the Middle Low Uplift of the Chaoshan Depression. This research employs integrated geophysical data (MCS, gravity, magnetic) and well data to explore the factors that influenced Middle Jurassic reef development and their implications for reservoir formation. The seismic reflection patterns of reefs and carbonate platforms are primarily characterized by high-amplitude discontinuous to chaotic reflections, with occasional blank reflections or weak, sub-parallel reflections, as well as significant high-velocity, high Bouguer gravity and low reduced-to-pole (RTP) magnetic anomalies. Atolls, stratiform reefs, and patch reefs are located on the local topographic highs of the platform. Three vertical evolutionary stages have been identified based on the size of atolls and fluctuations in relative sea level: initiation, growth, and submergence. The location of bioherms and carbonate platforms was influenced by paleotectonic topography, while their horizontal distribution was affected by variations in relative sea level. Furthermore, the reef limestone reservoirs from the upper member of the Middle Jurassic, combined with the mudstone source rocks from the Lower Jurassic and the lower section of the Middle Jurassic, as well as the bathyal mudstone caprocks from the lower part of the Late Jurassic, create highly favorable conditions for hydrocarbon accumulation. Full article

Recent exploration efforts in the Qiongdongnan Basin have revealed hydrocarbon resources within granitic basement rocks in buried hill traps. However, the formation mechanisms and primary controlling factors of these reservoirs remain poorly understood. In this study, we utilized data from six wells in the Qiongdongnan Basin, including sidewall cores, thin sections, imaging logging, and seismic reflection profiles, to analyze the petrological characteristics, pore systems, and fracture networks of the deep basement reservoir. The aim of our study was to elucidate the reservoir formation mechanisms and identify the key controlling factors. The results indicate that the basement lithology is predominantly granitoid, intruded during the late Permian to Triassic. These rocks are characterized by high felsic mineral content (exceeding 90% on average), with them possessing favorable brittleness and solubility properties. Fractures identified from sidewall cores and interpreted from image logging can be categorized into two main groups: (1) NE-SW trending conjugate shear fractures with sharp dip angles and (2) NW-SE trending conjugate shear fractures with sharp angles. An integrated analysis of regional tectonic stress fields suggests that the NE-trending fractures and associated faults were formed by compressional stresses related to the Indosinian closure of the ancient Tethys Ocean. In contrast, the NW-trending fractures and related faults resulted from southeast-directed compressional stresses during the Yanshanian subduction event. During the subsequent Cenozoic extensional phase, these fractures were reactivated, creating effective storage spaces for hydrocarbons. The presence of calcite and siliceous veins within the reservoir indicates the influence of meteoric water and magmatic–hydrothermal fluid activities. Meteoric water weathering exerted a depth-dependent dissolution effect on feldspathoid minerals, leading to the formation of fracture-related pores near the top of the buried hill trap during the Mesozoic exposure period. Consequently, the combination of high-density fractures and dissolution pores forms a vertically layered reservoir within the buried hill trap. The distribution of potential hydrocarbon targets in the granitic basement is closely linked to the surrounding tectonic framework. Full article

Slope instability often brings serious threats to human production and life, which causes huge economic losses. The slope displacement calculation under seismic action is very important to ensure the safety and stability of a slope. At present, there are few studies on the displacement calculation of multi-stage loess slopes under seismic action. Based on the basic theory of soil dynamics and the introduction of the comprehensive slope ratio, this paper proposes a new displacement calculating method of multi-stage homogeneous loess slopes under seismic action and provides the calculation formula. The rationality of the theoretical calculation is verified using the numerical simulation software Geo Studio (V2022). The study shows that it is feasible to simplify the geometric characteristics of multi-stage loess slopes by adopting the comprehensive slope ratio, which can also reasonably reflect the displacement characteristics of multi-stage loess slopes under seismic action. The example verification shows that the deviation of the peak horizontal displacement between the calculating method of this paper and the numerical simulation result is 5.5%, which shows that the calculation method of this paper is reasonable and has a certain application value. Full article

Earthquakes, as serious natural disasters, have greatly harmed human beings. In recent years, the combination of acoustic emission technology and information entropy has shown good prospects in earthquake prediction. In this paper, we study the application of acoustic emission b-values and information entropy in earthquake prediction in China and analyze their changing characteristics and roles. The acoustic emission b-value is based on the Gutenberg–Richter law, which quantifies the relationship between magnitude and occurrence frequency. Lower b-values are usually associated with higher earthquake risks. Meanwhile, information entropy is used to quantify the uncertainty of the system, which can reflect the distribution characteristics of seismic events and their dynamic changes. In this study, acoustic emission data from several stations around the 2008 Wenchuan 8.0 earthquake are selected for analysis. By calculating the acoustic emission b-value and information entropy, the following is found: (1) Both the b-value and information entropy show obvious changes before the main earthquake: during the seismic phase, the acoustic emission b-value decreases significantly, and the information entropy also shows obvious decreasing entropy changes. The b-values of stations AXI and DFU continue to decrease in the 40 days before the earthquake, while the b-values of stations JYA and JMG begin to decrease significantly in the 17 days or so before the earthquake. The information entropy changes in the JJS and YZP stations are relatively obvious, especially for the YZP station, which shows stronger aggregation characteristics of seismic activity. This phenomenon indicates that the regional underground structure is in an extremely unstable state. (2) The stress evolution process of the rock mass is divided into three stages: in the first stage, the rock mass enters a sub-stabilized state about 40 days before the main earthquake; in the second stage, the rupture of the cracks changes from a disordered state to an ordered state, which occurs about 10 days before the earthquake; and in the third stage, the impending destabilization of the entire subsurface structure is predicted, which occurs in a short period before the earthquake. In summary, the combined analysis of the acoustic emission b-value and information entropy provides a novel dual-parameter synergy framework for earthquake monitoring and early warning, enhancing precursor recognition through the coupling of stress evolution and system disorder dynamics. Full article

This review article provides an in-depth exploration of the recent advancements in the seismic analysis and design of steel–concrete composite structures, as reflected in the literature from the last ten years. It investigates key factors, such as material behavior, connection detailing, analytical modeling techniques, and design methodologies. The article highlights the synergistic benefits derived from the combination of steel and concrete components to improve seismic performance. Various composite systems, including composite beams, beam-columns, frames, shear walls, foundations, and beam–column joints, are analyzed through experimental studies to assess their dynamic response characteristics under extreme earthquake conditions. The article evaluates advanced numerical modeling methods, including finite element analysis and fiber-based models, for their capability to predict the nonlinear behavior of composite buildings and bridges. A comparative analysis of modern seismic isolation and energy dissipation techniques is also included. Furthermore, the optimization of composite structures in seismically active regions is discussed. The article concludes by identifying areas where additional research is necessary to enhance the seismic resilience of steel–concrete composite structures. Full article

The behavior of the soils under dynamic loads is of great importance for the structures to be built in earthquake zones. As a result of the determination of the site-specific dynamic parameters of the soils and the analyzes to be made with these parameters, the ground response that will occur on the surface during the earthquake will be determined. Turkey is located in one of the important earthquake belts of Europe. Studies are carried out on the North Anatolian Fault Zone (NAFZ), which is one of the important and active fault lines here. In this study, as a result of 4 drilling studies on NAFZ, firstly, dynamic triaxial (TRX) and resonant column (RC) test systems were used to obtain site-specific shear modulus and damping curves depending on depth. 11 earthquake acceleration records reflecting the seismic characteristics of the region were selected and scaled in both time-history and frequency-time domains. Two different scaling methods were compared with the nonlinear soil amplification analysis. In addition, surface response spectra were examined according to the Turkish Building Earthquake Code (TEC 2018). Although there is not a big difference in amplification values in two different scaling methods, it has been determined that the design spectrum values are very different. Full article

The two-phase source rocks deposited during the Lower Cretaceous in the Persian Gulf Basin play a pivotal role in the regional hydrocarbon system. However, previous studies have lacked a macroscopic perspective constrained by the Tethyan Ocean context, which has limited a deeper understanding of their developmental patterns and hydrocarbon control mechanisms. To address this issue, this study aims to clarify the spatiotemporal evolution of the two-phase source rocks and their hydrocarbon control effects, with a particular emphasis on the critical impact of terrestrial input on the quality improvement of source rocks. Unlike previous studies that relied on a single research method, this study employed a comprehensive approach, including time series analysis, sequence stratigraphy, lithofacies, well logging, well correlation, seismic data, and geochemical analysis, to systematically compare and analyze the depositional periods, distribution, and characteristics of the two-phase source rocks under different sedimentary facies in the region. The goal was to reveal the intrinsic relationship between the Neo-Tethyan Ocean context and regional sedimentary responses. The results indicate the following: (1) the late Tithonian–Berriasian and Aptian–Albian source rocks in the Northern Persian Gulf were deposited during periods of extensive marine transgression, closely aligning with the global Weissert and OAE1d anoxic events, reflecting the profound impact of global environmental changes on regional sedimentary processes; (2) in the early stages of the Neo-Tethyan Ocean, controlled by residual topography, the Late Tithonian–Berriasian source rocks exhibited a shelf–intrashelf basin facies association, with the intrashelf basin showing higher TOC, lower HI, and higher Ro values compared to the deep shelf facies, indicating more favorable conditions for organic matter enrichment; (3) with the opening and deepening of the Neo-Tethyan Ocean, the Aptian–Albian source rocks at the end of the Lower Cretaceous transitioned to a shelf–basin facies association, with the basin facies showing superior organic matter characteristics compared to the shelf facies; (4) the organic matter content, type, and thermal maturity of the two-phase source rocks are primarily controlled by sedimentary facies and terrestrial input, with the Aptian–Albian source rocks in areas with terrestrial input showing significantly better quality than those without, confirming the decisive role of terrestrial input in improving source rock quality. In summary, this study not only reveals the differences in the depositional environments and hydrocarbon control mechanisms of the two-phase source rocks, but also highlights the core role of terrestrial input in enhancing source rock quality. The findings provide a basis for facies selection in deep natural gas exploration in the Zagros Belt and shale oil exploration in the western Rub’ al-Khali Basin, offering systematic theoretical guidance and practical insights for hydrocarbon exploration in the Persian Gulf and broader tectonic domains. Full article

Seismic data reveal that the shelf edge of the Pearl River Mouth Basin in the northern South China Sea is characterized by slope channels that have consistently migrated in a north-easterly direction over millions of years. Previous research suggests that the channel migration is driven by the interplay between along-slope bottom currents and downslope turbidity currents. Here, we propose an alternative interpretation, suggesting the migrating channels are actually a series of channel–levee systems and the migration is driven by their own evolution of erosion–deposition under the influence of the Coriolis force. A detailed interpretation of high-resolution seismic data reveals seven types of architectural elements, characteristic of channel–levee systems, which are erosional bases, outer levees, inner levees, channel-axis fills, marginal slumps, drapes, and lobes. An analysis of the sequence stratigraphy and stacking pattern of channels suggests that channel migration from the middle Miocene to the present is discontinuous with at least three regional discontinuities within the channel migration sequence marked by regional drapes. Down-dipping reflections along the margin of channels, previously interpreted as bottom-currents deposits, are here reinterpreted as mass-transport processes along steep channel walls. The migration is most prominent in the middle reach, where erosion and deposition coexist and dominate alternately in two different phases. During the long-term canyon-filling turbidity currents prevailing phase, deposition dominates, leading to the development of a prominent asymmetric right-hand (west) inner levee due to the Coriolis force. In contrast, during the canyon-flushing turbidity currents prevailing phase, erosion dominates and the preferred right-hand (west) inner levee enforces the flow to erode eastward, then drives the channel migrating eastward. The alternating effects of erosion and deposition ultimately result in unidirectional channel migration. Full article

Various glutenite reservoirs, developed by fans, can be found in the Junggar Basin. Among these, there are different interpretations of the glutenite reservoirs formed by shallow-water fan deltas in the Triassic system in the northwestern margin of the basin. The characteristics of these deltas and their reservoir architecture have not been understood clearly. It seriously restricts the advancement of the subsequent development of the oilfield. Therefore, it is of great significance to carry out the fine reservoir architecture characterization of the shallow-water fan delta in this area. In this study, the upper member of the Triassic Karamay Formation in the Bai 21 area was selected as the study site. Through core analysis, nine types of sedimentary microfacies, including mudflow deposit, braided river, flood plain, underwater main channel, underwater distributary channel, overbank channel, interchannel deposition, estuary bar, and sheet sand, are found. Through mixed-phase wavelet frequency extension, the main frequency of seismic data is moderately increased and the frequency band is broadened, which makes it possible to identify the thin layer of about 10 m. Through continuous stratal slicing, the thin-layer sedimentary bodies that are difficult to be distinguished in the vertical direction are depicted, and the distribution of sedimentary bodies at different vertical positions is obtained by browsing the slices. Through color fusion based on seismic frequency decomposition, the fusion results contain information reflecting the thickness, and the characterization effect of the fan boundary is significantly improved. In summary, this study depicts the distribution of single-stage fans and recognizes the sand body development characteristics of the two-stage fans. Research suggests that two large shallow-water fan-delta complexes were discovered in the S3 sand group within the study area. Each fan possesses a multilevel branching distributary channel system, resulting in multiple horizontally oriented lobes. Within the fan-delta complex in S3, which is the third sand group in the Upper Triassic Karamay Formation, the fan complex can be divided into two single-stage fans recorded in the sublayer S31 and S32 upward. The two-stage fan deltas show inherited development characteristics in sedimentary characteristics and form in a regression sequence. The sand bodies formed during the low-water-level stage in S31 are thick, with few interlayers developed. Most sand bodies intersect each other vertically. In the shallow fan delta, a widespread estuary bar is deposited, which develops along the underwater distributary channel. This research enhances the understanding of shallow-water fan-delta reservoirs in the study area, and it provides a precise target for oilfield development and solves the key problem of unclear understanding of sand body distribution and combination relationships, which restricts development. Full article

Be stars are rapidly rotating B-type stars surrounded by circumstellar disks formed from self-ejected material. Understanding the mechanisms driving mass ejection and disk formation, known as the Be phenomenon, requires a detailed investigation of their variability and underlying physical processes. In this study, we analyze the photometric, spectroscopic, and seismic characteristics of three Be stars—HD 212044, 28 Cyg, and HD 174237—using high-cadence data from the TESS mission and spectral data from the BeSS database. Photometric variability was analyzed through iterative prewhitening and wavelet techniques, revealing distinct frequency groups associated with non-radial pulsations (NRPs). Spectral data provided equivalent width measurements of the H$\alpha$ line, which correlated with photometric changes, reflecting dynamic interactions between the stars and their disks. Seismic analysis identified core rotation rates and buoyancy travel times for HD 212044 and 28 Cyg, offering insights into internal stellar processes and angular momentum distribution. HD 212044 exhibits a strong negative correlation between photometric brightness and H$\alpha$ equivalent width, whereas this correlation is weaker in the case of 28 Cyg. The findings for these two stars highlight the interplay between NRPs, rapid rotation, and circumstellar disk dynamics. In contrast, the case of HD 174237 presents an example of how a binary system with mass transfer and a B-type component is revealed when observed simultaneously with space-based photometry and ground-based spectroscopy, demonstrating the importance of distinguishing classical Be stars from interacting binaries. Full article