Search Results (106)

CO₂ hydrate sequestration in marine sediments has attracted increasing attention as a potential offshore carbon-storage strategy. However, the acoustic response associated with CO₂ injection, fluid migration, hydrate formation, and subsequent storage stabilization remains insufficiently understood, which limits the development of reliable in situ monitoring methods. In this study, we develop a staged acoustic modeling framework based on multiphase poroelastic formulations. According to the evolution of pore components, the sequestration process is divided into three representative stages: a CO₂–water–sediment skeleton system during CO₂ injection, a CO₂–water–CO₂ hydrate–sediment skeleton system during hydrate formation, and a CO₂ hydrate–CO₂–sediment skeleton system during stable sequestration. The acoustic responses at these stages are analyzed in terms of wave velocity, attenuation, and velocity ratio under different CO₂ and hydrate saturation conditions. The results show that the injection stage is mainly controlled by pore-fluid substitution and changes in fluid compressibility. In this stage, P-wave velocity, P-wave attenuation, and VP/VS are sensitive to CO₂ saturation, whereas S-wave velocity varies only weakly. During hydrate formation, the acoustic response is jointly affected by fluid substitution, hydrate-induced solid stiffening, interphase coupling, and viscous dissipation. As hydrate saturation increases, both P1- and S1-wave velocities increase, while the velocity ratio decreases, indicating that hydrate formation significantly enhances sediment shear stiffness. In the stable sequestration stage, hydrate saturation becomes the dominant control on the elastic and dissipative properties of the medium. A comparison with published laboratory P-wave velocity data further supports the ability of the formation-stage model to reproduce the velocity increase associated with CO₂ hydrate generation. Therefore, the combined use of P-wave velocity, S-wave velocity, attenuation, and VP/VS provides a theoretical basis for identifying CO₂ migration, hydrate formation, and stable storage states in marine sediments. Full article

Background/Objectives: Type 2 diabetes mellitus (T2DM) is associated with progressive hepatic alterations, including steatosis and fibrosis, which may affect liver mechanical properties. Shear wave elastography (SWE) is a non-invasive imaging technique that enables quantitative assessment of tissue stiffness; however, its application in diabetic animal models remains limited. This study aimed to evaluate liver elasticity using SWE in a high-fat diet (HFD) and streptozotocin (STZ)-induced rat model of T2DM, using histopathological examination as the reference standard. Methods: Twenty-four rats were randomly allocated to either a control group (n = 12) or a diabetic group (n = 12). Diabetes was induced using HFD feeding followed by low-dose STZ administration. Liver elasticity was assessed in vivo using SWE at two examination sessions. Shear wave velocity measurements were obtained from eight liver regions of interest and expressed in meters per second (m/s). Following euthanasia, liver tissues were subjected to histopathological evaluation using hematoxylin and eosin, Masson’s trichrome, and periodic acid–Schiff staining. Results: Diabetic rats demonstrated marked histopathological alterations, including macrovesicular and microvesicular steatosis, hepatocellular vacuolization, increased collagen deposition, and glycogen depletion. Collagen deposition was significantly greater in diabetic animals, while glycogen content was significantly reduced (3.70 ± 1.05 vs. 26.87 ± 2.87; p < 0.05). SWE revealed consistently higher liver shear wave velocities in diabetic rats compared with controls at both examination sessions. Although liver stiffness increased over time in both groups, these changes did not reach statistical significance. Conclusions: HFD/STZ-induced diabetes was associated with increased liver stiffness and histopathological evidence of hepatic injury and fibrosis. SWE may represent a feasible non-invasive approach for assessing diabetes-related changes in liver mechanical properties. Full article

Deep lower-crustal detachments may control the development of fold-and-thrust belts, but their seismic expression and role in upper–lower-crustal deformation partitioning remain poorly constrained. Here, we present a 2-D deep seismic reflection profile across the thick-skinned segment of the eastern Sichuan fold-and-thrust belt near the Enshi fault, integrated with regional shear-wave velocity, Vp/Vs, and magnetotelluric resistivity constraints. The profile images a segmented upper-crustal fold–fault system above a continuous, high-amplitude laminated reflective zone in the lower crust. This zone, consisting of closely spaced, subhorizontal to gently dipping reflections, broadly coincides with reduced Vs, elevated Vp/Vs, and low resistivity along the Qiyueshan–Zhangjiajie structural corridor. We interpret this zone as a fluid-bearing ductile shear zone that likely acted as the main lower-crustal décollement during regional shortening, enabling rheological decoupling between fault-related folding in the brittle upper crust and ductile shearing in the lower crust. From an exploration perspective, this décollement and its associated anomalies define a deep structural corridor that may have controlled long-distance fluid transport and upward fluid focusing, providing a critical framework for regional mineral exploration along the eastern Sichuan fold-and-thrust belt. Full article

Integrating geophysical techniques at two contrasting locations—fractured young lavas in southwestern Iceland and older layered basalts in eastern Iceland—constrains the structure and shear-wave velocity of the volcanic subsurface. The results show that relying on a single geophysical method often yields non-unique solutions that can obscure velocity profiles and overlook sharp structural contrasts. Findings from southwestern Iceland reveal that young, faulted ‘a‘ā flows have a complex architecture with shallow, eroded layers, resulting in a reduced V_s30. Conversely, older Miocene bedrock in eastern Iceland shows a well-layered, consolidated structure with a higher V_s30. We demonstrate that modelling Scholte waves from legacy marine seismic data can generate regional velocity models consistent with onshore measurements. Full article

Improvement of the engineering properties of soils by reinforcing them with fibers, at an appropriate percentage of the weight of dry soil, is frequently selected to ensure the safe construction and operation of many structures. However, the published information regarding the investigation of the dynamic properties of fiber-reinforced soils at very small strains is very limited. Toward this end, the dynamic behavior of fiber-reinforced soils is investigated experimentally by conducting Bender Element tests under different confining pressures. The effect of polypropylene fiber reinforcement on the shear wave velocity (V_s), the velocity of the primary wave (V_p), the initial Young’s modulus (E₀) and the initial shear modulus (G₀) of sand and sand–clay mixtures with varying compositions is examined in this study. The soils were reinforced with five different types of polypropylene fibers having lengths from 9 mm to 50 mm, at fiber contents from 0.5% to 2% by weight of dry soil. The results indicate that the dynamic and the small-strain stiffness parameters of fiber-reinforced soils increase with increasing confining pressure, while also being affected by the soil type, the fiber type, and content. Although fiber inclusion resulted generally in a reduction of the dynamic properties of soils, increases ranging from 5% to 55% were observed in certain soil–fiber combinations in comparison with the unreinforced soils. Full article

Shear-wave velocity (V_s) estimation from the Standard Penetration Test (SPT) can support preliminary site characterization when direct geophysical data are limited, but empirical correlations require validation schemes that reflect transferability between sites. This study evaluates V_s prediction using an interval-paired dataset derived from geotechnical investigations of school foundations in Piura, Peru. Its novelty lies in comparing the raw SPT blow count (NSPT) and the overburden- and energy-corrected SPT blow count ((N₁)₆₀) on the same strict common sample, using grouped cross-validation by school, thereby emphasizing transferability across sites rather than only internal fit. Five predictive scenarios were tested, from penetration-only formulations to geotechnically enriched specifications. The lowest grouped out-of-fold error among the evaluated models was obtained by a generalized power baseline using (N₁)₆₀ and the integral geotechnical predictor set, yielding root mean square error (RMSE) = 80.48 m/s, mean absolute error (MAE) = 60.15 m/s, and coefficient of determination (R²) = 0.338. This moderate R² indicates limited standalone predictive capacity under transfer to unseen schools; therefore, the model is interpreted as a preliminary transfer-oriented correlation rather than as a substitute for direct V_s measurements or as an independent design equation. In the complementary full-data analysis, the strongest descriptive fit was obtained with Hist Gradient Boosting, whereas the strongest explicit equation corresponded to the log-semi baseline. Overall, the findings show that externally validated transferability, descriptive full-data fit, and equation-based interpretability represent different analytical roles in V_s-SPT modeling. Full article

Accurate estimation of shear-wave velocity (Vs) is fundamental for reservoir geomechanics, as it directly influences the calculation of elastic properties used in Mechanical Earth Models (MEMs). However, shear-wave sonic logs are frequently unavailable in legacy or data-limited wells due to high operational costs and technical constraints. Therefore, reliable prediction of Vs has become essential. This study proposes a physically guided porosity-compensated compressional-wave predictor, Vp (1 − PHIT), derived from the Wyllie time-average equation, to mitigate porosity-induced variability and enhance sensitivity to rock-frame stiffness. The proposed model was evaluated using a multi-well sandstone and shaly sand dataset comprising 29,426 data points from 19 wells in the Sirte Basin, Libya. Its performance was benchmarked against five widely used global correlations using statistical metrics including R², RMSE, MAE, and MAPE. The results demonstrate that the proposed model achieves superior predictive performance: R² = 0.908, root-mean-square error (RMSE) = 0.00047 ft/µs, mean absolute error (MAE) = 0.00037 ft/µs, and mean absolute percentage error (MAPE) = 4.05%, outperforming conventional empirical correlations. The developed correlation provides a simple, physically interpretable, and field-applicable solution for predicting Vs in sandstone reservoirs and similar formations where shear-wave measurements are unavailable. Full article

Shear wave velocity (V_S) measurements are widely used to characterize geomaterials, evaluate small-strain stiffness, and develop indirect approaches for estimating the liquefaction resistance of various soil types. In this study, the bender element method was employed to investigate the V_S characteristics of sand–gravel mixtures (SGMs), with the aim of clarifying the combined effect of key factors such as gravel content (G_C), relative density (D_r), packing state, and soil fabric. Laboratory tests were performed on reconstituted specimens composed of two sandy soils and pea gravel with G_C of 0, 10, 25, 40, 60, 80 and 100% and D_r of 20, 30, 45 and 60%. Specimens were prepared using wet tamping (WT) and air pluviation (AP) techniques. V_S measurements were conducted under effective confining stresses (${{\sigma }^{\prime }}_0$) of 50, 100, 150 and 200 kPa. The results show that the V_S of SGMs increases with increasing D_r and ${p^{\prime }}_0$, whereas the influence of G_C depends on the limiting and threshold sand contents. The effect of soil fabric was found to be marginal. Furthermore, the combined effects of G_C and D_r on V_S can be uniquely captured using the equivalent void ratio approach for SGMs with sand-dominated microstructures, while the skeleton void ratio approach is more appropriate for SGMs with gravel-dominated microstructures. Full article

Understanding dry-out-induced weakening of reservoir and caprock rocks driven by gas displacement is critical for ensuring the operational safety and efficiency of underground gas storage (UGS). Using core samples from the Xiangguosi UGS collected from different regions and stratigraphic intervals, we quantify the evolution of dynamic elastic parameters during simulated downhole dry-out with a joint ultrasonic and nuclear magnetic resonance (NMR) monitoring system. The results show that as water saturation (S_w) decreases, the dynamic bulk modulus (K_d) and P-wave velocity (V_p) decline by varying degrees across specimens, with reductions ranging from 3.0% to 50.48% and from 1.34% to 17.56%, respectively, whereas the dynamic shear modulus (G_d) and S-wave velocity (V_s) show only minor variations throughout the process. These findings demonstrate that the sensitivity of dynamic parameters to dry-out is strongly specimen-dependent. Further analysis indicates that the dry-out response is highly variable and depends on a combination of petrophysical properties. Among these, the heterogeneity of the initial pore structure acts as an important factor, with its influence shaped by mineralogy and bulk frame rigidity. Cores with multimodal pore size distributions and well-developed macropores (long T₂ components) respond more strongly to dry-out, whereas higher clay mineral contents tend to mitigate modulus degradation by retaining water under stronger capillary confinement. Based on these observations, we propose a conceptual model of pore support and skeleton constraint. The model suggests that dry-out weakening arises from a progressive loss of pore fluid volumetric support to the rock skeleton as free water is preferentially displaced from meso- and macropores. These findings provide key experimental evidence and mechanistic insights for using geophysical methods to monitor dry-out zone expansion and to assess long-term formation stability in UGS. Full article

This study investigates the combined effects of partial saturation and aligned fractures on P- and S-wave velocities and anisotropy in tight sandstones. Ultrasonic measurements (0.5 MHz) were conducted on three synthetic samples with a matrix porosity of 11.7% ± 1.2% and controlled fracture densities (0%, 3.12%, and 6.24%) under a full range of water saturation rate (S_w), from dry to fully water-saturated. Experimental results reveal that for fractured samples, the P-wave anisotropy parameter ε increases sharply as S_w decreases from 100% to approximately 60%, followed by a gentler variation at lower saturation. In contrast, fracture-induced shear-wave splitting (SWS) is predominantly governed by fracture density and exhibits weak dependence on S_w. To interpret these observations, we developed a coupled rock physics framework by integrating the MJGW partial saturation model with the Galvin fracture model, introducing a distribution coefficient to account for the non-uniform water distribution between the matrix and fractures. The coupled model accurately explains the V_p and SWS trends, while the overestimation of V_s and ε is attributed to near-dry surface effects at grain contacts and mutual interaction between fractures. This work provides experimental data and modeling insights for seismic-based characterization of multiphase-fluid-saturated fractured reservoirs. Full article

Objectives: We aimed to evaluate Achilles tendon stiffness characteristics in asymptomatic patients with psoriatic arthritis (PsA) using shear wave elastography (SWE). Methods: In this prospective case–control study, 34 asymptomatic PsA patients and 34 age- and sex-matched healthy controls underwent bilateral Achilles tendon evaluation with grayscale ultrasonography and SWE. Tendon thickness was measured 3 cm proximal to the calcaneal insertion. Shear-wave velocity (m/s) and Young’s modulus (kPa) were obtained under standardized acquisition conditions, including five-star motion stability and ≥90% reliability. Results: Achilles tendon morphology and thickness did not differ between PsA patients and controls (p > 0.05). In contrast, SWE demonstrated higher tendon stiffness in the PsA group. Mean shear-wave velocity was significantly greater in PsA patients for both the left (4.89 ± 2.52 m/s vs. 3.23 ± 0.41 m/s; p < 0.001) and right tendons (4.88 ± 1.94 m/s vs. 3.12 ± 0.30 m/s; p < 0.001), with corresponding increases in Young’s modulus (all p < 0.001). SWE demonstrated good group discrimination, with shear-wave velocity achieving AUC values of up to 0.90 in differentiating PsA patients from healthy controls. Conclusions: SWE may reflect biomechanical tendon alterations in PsA, even in the absence of clinical symptoms, and may serve as a complementary imaging tool in the assessment of tendon involvement. Full article

Mexicali, capital of Baja California, has 1,049,792 inhabitants and lies in a high-seismic-hazard zone in northwestern Mexico, according to CENAPRED, the MDOC-CFE-2015 seismic regionalization, and the ASCE 7-22 “Hazard Toolkit”. This study develops a probabilistic seismic hazard map to estimate peak ground accelerations with a 2% probability of exceedance in 50 years, using the OpenQuake platform. The study area coincides with the 2025 urban development plan polygon for the central population area defined by the Municipal Institute for Research and Urban Planning of Mexicali. The Imperial and Cerro Prieto faults, the Pescaderos–Indiviso fault system, and the Laguna Salada fault were modeled as seismic sources. Four PEER-NGA ground motion prediction equations and regional geophysical and geotechnical data were employed to characterize shear-wave velocity (Vs30). Design response spectra were generated for each grid point for the 21 periods specified in ASCE 7-22. A representative Vs30 of 236 m/s was obtained, and the a, b, and Mc parameters were derived for the seismic catalog. Resulting peak ground accelerations range from 0.842 g to 1.221 g, with a maximum spectral pseudo-acceleration of 2.23 g at 0.30 s. Full article

This study presents an integrated framework that couples three-dimensional geotechnical ground modeling with a HAZUS-based urban seismic vulnerability assessment for Seoul, Korea. Over 63,000 boreholes, in situ seismic tests, and building inventory records were compiled into a unified relational database following rigorous multi-stage quality control. A multi-parameter N–Vs regression model was calibrated to supplement missing shear-wave velocity (Vs) data, reducing prediction errors by more than 20% relative to conventional empirical equations. Based on the quality-controlled Vs dataset, a high-resolution three-dimensional Vs–ground model was constructed to represent subsurface heterogeneity and associated uncertainty across the metropolitan area. The building inventory, comprising approximately 700,000 structures, was standardized according to the HAZUS structural taxonomy and mapped to Korean seismic design eras, enabling a Seoul-adapted vulnerability assessment in which exposure characterization and seismic demand are localized. Site-specific ground-motion amplification and response spectra derived from the 3D ground model were used to modify the spectral acceleration input to the HAZUS fragility functions. Results reveal pronounced spatial variability in site conditions, with northern mountainous zones corresponding primarily to NEHRP Site Class B, central districts to Class C, and southern alluvial basins to Classes D–E, producing amplification differences of up to 1.7 under identical input spectral accelerations. High-risk zones such as Gangnam, Songpa, and Yeouido exhibit concentrated expected damage where thick alluvial deposits coincide with dense stocks of mid-rise reinforced-concrete buildings. Overall, the study demonstrates that integrating high-resolution 3D geotechnical ground models with HAZUS-based fragility analysis provides a physically consistent and data-driven basis for urban-scale seismic risk assessment and resilience planning. Full article

Background: Elastography is a non-invasive technique used to assess tissue stiffness. There are two main types of elastography: shear-wave elastography and strain imaging. Both are useful for evaluating the degree of liver fibrosis (LF). Shear-wave imaging is influenced by fibrosis and hepatic congestion, whereas strain imaging primarily reflects fibrosis progression and is less affected by congestion. We previously reported the clinical usefulness of combinational elastography in patients with heart failure (HF). However, its prognostic significance in this population remains unclear. Accordingly, in this prospective study, we aimed to evaluate the prognostic impact of combinational elastography in patients with HF. Methods: We included 77 patients with HF (median age: 79 years). Shear-wave imaging was used to obtain shear-wave velocity (Vs), whereas the liver fibrosis index (LF index) was derived from strain imaging. The Vs/LF index (V/L) was used as a prognostic indicator based on combinational elastography. Cardiac events were defined as cardiac death or hospitalization due to HF. Results: During a median follow-up of 716 days, 17 cardiac deaths or hospitalizations for HF were observed. The V/L demonstrated a cut-off value of 1.2 for predicting cardiac death or hospitalization for HF, with an area under the curve of 0.80, sensitivity of 0.82, and specificity of 0.68. Kaplan–Meier analysis demonstrated that patients with a high V/L (≥1.2) had significantly higher rates of hospitalization for HF than those with a low V/L (<1.2; log-rank test, p < 0.001). Conclusions: Combinational elastography demonstrated prognostic utility in patients with HF and may serve as a novel, non-invasive tool for assessing hepatic congestion. Full article

Background: Accurate intraoperative assessment of sentinel lymph node (SLN) status is critical for staging and guiding surgical management in gynaecological malignancies. Frozen-section histopathology remains the gold standard, but it is time-consuming and resource-intensive. Shear-wave elastography (SWE) quantifies tissue stiffness in real time and may offer a rapid alternative. Methods: In this prospective single-centre study, 63 women (median age 62 years) undergoing primary surgery with sentinel lymph node biopsy (SLNB) for endometrial, cervical, vulvar, or early ovarian carcinoma were enrolled. A total of 172 SLNs were excised, submerged in coupling gel, and scanned ex vivo using a 9 MHz linear probe. Results: A total of 172 SLNs underwent SWE (mean 2.7 nodes/patient). Endometrial primaries accounted for 58% of nodes, mostly retrieved by robotic-assisted surgery (71.8%). Node dimensions were significantly larger in malignant lesions for sonographic (long-axis: 13.02 ± 3.31 mm vs. 10.80 ± 3.28 mm; p = 0.002) and pathological long-axis measurements (11.45 ± 2.83 mm vs. 9.75 ± 2.61 mm; p = 0.004). Mean SWE velocities were similar between groups (1.381 ± 0.307 vs. 1.343 ± 0.236 m/s; p = 0.541). Histopathology identified metastases in 18% of SLNs, comprising macrometastases (7%), micrometastases (5%), and isolated tumour cells (6%). Conclusions: Although ex vivo SWE is rapid, reproducible, and integrates seamlessly into the sterile field, stiffness measurements alone lack sufficient discriminatory power for SLN staging in gynaecological cancers. Future research should focus on three-dimensional SWE, advanced radiomic analyses, and machine-learning algorithms to improve the detection of low-volume metastatic disease. Full article