pure and applied geophysics最新文献

Estimating earthquake source parameters is important for understanding seismic characteristics and potential hazards in intraplate regions, where seismic activity often deviates from the pattern observed in interplate regions. This study focuses on Mainland Gujarat, India, which hosts a large and densely distributed population. The region has previously experienced earthquakes of up to M ~ 6.0 and remains vulnerable to similar events. We used spectral analysis techniques to quantify the key source parameters viz. stress drop, corner frequency, source radius, and seismic moment for earthquakes in this region. We have analyzed 122 local earthquakes in the Mainland Gujarat region that occurred between 2007 and 2022, with magnitudes ranging from 2.5 to 4.4. We applied a method based on the source term of the displacement spectra from observed S-wave spectra. The estimated stress drop values range from 0.08 to 28.32 MPa, with a median value of 7.18 ± 0.24 MPa, which remains nearly constant with the moment, indicating self-similarity in local earthquake behaviors. The corner frequency varies between 2.27 to 13.2 Hz, and the source radius ranges from 68.7 to 897.2 m. The seismic moment spans from 6.31 × 10¹² to 5.02 × 10¹⁵ N-m. We found the scaling relationship between corner frequency and seismic moment to be M₀f_c³ = 2.13 × 10¹⁶ Nm/s³. This study contributes to a deeper understanding of earthquake mechanics in Mainland Gujarat and provides valuable insights into proper seismic hazards in the Gujarat region.

The Songliao Basin, a major Meso-Cenozoic sedimentary basin in Northeast Asia, is well known for its significant hydrocarbon resources. The sediments beneath the Central Depression have been extensively investigated, but the western basin, including the Western Slope and Southwestern Uplift, remains relatively under-explored. For a better understanding of the sediments in the western Songliao Basin, we conducted a frequency-dependent P-wave delay analysis using waveforms from 26 temporary broadband seismic stations of a north–south linear array across the western basin from 2021 to 2023. Our results reveal a pronounced variation in the thickness of the Quaternary and Cretaceous sedimentary cover, ranging from ~ 1.5 km in the axial part of the Western Slope to 0.5 km at the basin margin. The thicknesses also exhibit obvious variations around the Chifeng–Kaiyuan Fault and the Jiamatu Uplift, highlighting a significant relationship between sedimentation and tectonics. The resulting S-wave velocity profiles show that the sediments between the Solonker–Xar Moron Suture and the Jiamatu Uplift can be represented by a single layer, while those in the central part of the Western Slope and Southwestern Uplift exhibit a pronounced vertical negative velocity gradient. These results imply that beneath the basin-wide Nenjiang Formation, the low-velocity Qingshankou Formation, being rich in hydrocarbon resources, is likely developed in such areas with a negative velocity gradient. Consequently, the central part of the Western Slope and Southwestern Uplift may have more favorable hydrocarbon resource potential compared to other regions of the western basin, but its potential is modest compared to the Central Depression.

A meteorological drought is an unusually long period without rainfall that causes problems in nature and for humans. This study compared four meteorological drought indices: the Standardized Precipitation Index (SPI), the Percent of Normal Precipitation Index (PN), the Decile Index (DI), and the Rainfall Anomaly Index (RAI) computed for the annual (12-month) rainfall time series. The four indices were calculated for eight rainfall stations in the Mae Klong River Basin, Thailand during 1971–2015. Comparison between the drought indices was done using Pearson’s correlation coefficient (r) and Cohen’s Kappa test. The correlation coefficient between the four drought indices varied from 0.948 to 1. The values of the unweighted Cohen’s Kappa ranged from 0.104 (‘Slight’ agreement) to 1 (‘Almost perfect’ agreement) while the weighted Cohen’s Kappa varied from 0.215 (‘Fair’ agreement) to 1 (‘Almost perfect’ agreement) between the indices for all the stations. For the whole Mae Klong River Basin, the Cohen’s Kappa test indicated a lesser degree of agreement (fair to moderate) between the majority of the drought indices pairs, despite the generally very high correlation coefficient values (0.977 ≤ r ≤ 1). The results indicated that the Cohen’s Kappa test can be more effective in determining the strength of agreement or disagreement between the drought indices as compared to the correlation analysis. The Mann–Kendall test was used to calculate the trends in the drought indices while the magnitude of the trends was determined by the Sen’s slope test. All the four drought indices showed statistically non-significant increasing trends for the mean annual rainfall in the basin.

A global increase in sea surface temperature (SST) is anticipated under a warming climate, thus implying that natural hazards associated with SST, such as typhoons are projected to pose greater risks, particularly to nuclear power plants in Korea. Due to their limitations in both spatial and temporal resolutions, existing climate models remain posing challenges in quantifying the strength of typhoons approaching the Korean Peninsula (KP). This study investigated how changes in the future environment can influence the intensity of typhoons approaching Korea. Using the statistical approach, we estimated the location and strength of the future Lifetime Maximum Intensity (LMI) of typhoons based on the environment-derived Maximum Potential Intensity (MPI). Along with other environmental factors such as SST and vertical wind shear, we propose a multilinear regression model to predict the rate of change in intensity of typhoons approaching the nuclear power plants. Our result shows that under the different climate change scenarios, the maximum intensities of typhoons approaching KP can increase from 5.36% in SSP126 to 15.17% in SSP585. Furthermore, the maximum typhoon intensities in the four major nuclear power plants in Korea namely, Gori, Wolsong, Hanul, and Hanbit are projected to face an increase of up to 16.36%, 16.36%, 17.48%, and 16.23% from their present values under the SSP585 scenario, respectively. Considering the risk of typhoons to the said power plants, our study can serve as an input for mitigating the potential damages and impacts of typhoons on the future operations of these power plants.

Complete and continuous flow data provides contributions to the water resources projects appropriate design. However, both financial and technical factors prevent the regular collection of data and such a situation leads to missing data problems. Input variables are from five stations in the Çoruh Basin in the northeast province of Türkiye, and output variables are from one station. In the study, 75% (171 months of data) of the 228 months flow data between the years 1993–2011 are used in the training phase and 25% (57 months of data) in the testing phase. In the ANFIS models, Decision Tree (DT) and K-means (KM) methods are used in selecting the input variables and determining the number of membership functions. In addition, artificial neural network (ANN), multiple linear regression (MLR), and ANFIS models with randomly determined cluster numbers are also used to compare the model performance of these methods. The results show that using DT and KM methods, the ANFIS models generate more reliable results than other models. During the study, the regression coefficient (R²), weighted mean square error (WMSE), and Wilcoxon (Z) values are taken into account for reliability measure. The DT–K-means–ANFIS model achieved the highest accuracy with R² = 0.98 and WMSE = 5.89 during the testing phase, demonstrating superior performance to the ANN and MLR models. It is shown that the most successful models can be determined in a shorter time by using DT and KM methods before generating ANFIS models.

The threat of surface discontinuous deformations–sinkholes is a frequent serious problem in many places all over the world. In polish conditions deformations are connected with shallow galleries mined a long time ago. Forecasting sinkhole formation is difficult because of randomness of the phenomenon frequent lack of data necessary for prediction. Credible forecasts should include the mechanism of sinkhole formation. As the existing forecast methods have limitations resulting from assumptions, a procedure for preparing forecasts that uses methods known in literature is proposed. The procedure is illustrated by an example. A way of determining expected sinkhole size based on statistical data is also proposed.

In underground engineering projects such as subway systems, tunnel networks, and mining operations, the interaction between rock creep behavior and thermal stability poses significant challenges to structural integrity and construction efficiency. This study comprehensively investigates the creep behavior of sandstone at elevated temperatures (300–800 °C) by integrating macroscopic mechanical testing with microscopic analysis. By comparing two loading methods—staged loading and step loading—the research demonstrates that, under identical temperature and stress conditions, staged loading results in significantly greater creep strains than step loading, with a maximum difference of 0.416% observed at 500 °C. Both loading methods exhibit temperature-dependent increases in the transient and steady-state creep phases, consistent with progressive microstructural degradation. Detailed microstructural examinations reveal thermally activated processes such as intergranular dehydration and the development of fracture networks, which become increasingly pronounced as temperatures approach 800 °C. A modified Nishihara constitutive model incorporating thermal-damage factors is developed to characterize creep behavior under both loading modes. Furthermore, the study quantitatively analyzes the thermal evolution of the Nishihara model parameters under these two distinct creep conditions.

This paper presents a study focused on near-surface geophysical exploration in a region characterized by significant karst features, specifically the Cenote Ring, located at the outer edge of the Chicxulub impact crater. The high density of near-surface sinkholes, locally known as ‘cenotes’, and cavities in the area introduces complex groundwater flow patterns and varying degrees of geological risk. To address these challenges, we propose a gravity inversion method to estimate the spatial distribution and geometry of near-surface karst features. Although gravity data acquisition is rapid and cost-effective, interpretation in karst terrains is complex due to the gravity response of such features typically being in the range of a few tenths of a milligal. To mitigate nonuniqueness and uncertainty in gravity inversion, we integrate interpretations from Electrical Resistivity Tomography (ERT), Ground-Penetrating Radar (GPR), and LiDAR data. The inversion process, using the Simulated Annealing (SA) method, incorporates these constraints to build a comprehensive model. The resulting model is analyzed to identify geological patterns and structures associated with karstification, providing information on the dynamics of the subsurface groundwater flow of the region and enhancing the assessment of geological risk.

As conventional structural traps become increasingly overexploited, hydrocarbon exploration has shifted toward underexplored stratigraphic traps, which often remain underexplored despite their significant potential. These traps pose significant challenges due to subtle lateral and vertical facies variations—particularly in complex deltaic environments. Recent progress in petroleum exploration increasingly relies on advanced approaches such as seismic inversion, which enables the extraction of quantitative subsurface information, thereby enhancing delineation of stratigraphic traps and reservoir property predictions. This study demonstrates the integration of seismic inversion within a sequence stratigraphic framework to delineate stratigraphic traps and characterize the spatial distribution and reservoir quality of sandstone bodies in the Acacus Formation of the Ghadames Basin, southern Tunisia. High-resolution 3D post-stack seismic and borehole data were used to derive acoustic impedance and density volumes. These volumes supported the construction of a 3D lithofacies model and enabled the establishment of a relationship between acoustic impedance and porosity, from which a porosity model was computed. The results reveal porous sandstone bodies (15–20% porosity) within the lowstand and transgressive systems tracts of sequences S10 and S11, sealed by compact clay-rich layers (> 2.55 g/cm³). The integrated models illuminate multiple stratigraphic trap configurations, including pinch-outs, and lens-shaped sandstone bodies encased within marine claystone. These features constitute important stratigraphic traps with clear lateral facies terminations and well-defined trap–seal configurations. Integrated interpretation of density, lithofacies, and porosity models within a sequence stratigraphic framework significantly refines reservoir distribution, enhances the identification of trap–seal pairs, and improves the prediction of thin, heterogeneous clastic reservoirs in the basins. This integrated workflow offers a robust methodology for reducing exploration uncertainty and supports near-field exploration strategies in the Ghadames Basin and similar siliciclastic settings across North Africa.

We investigate a miniaturized prototype of gravimeter named B-grav to overview different metrological questions to resolve for a system as part of a geophysical instrument package set-up on an asteroid lander. It must meter with 1% tentative accuracy of a weak 50 µm/sec² gravity field in a harsh environment with very strict limitations of inclusion in a CubeSat. With its 3D orthogonal components, our system allows to determine gravity in amplitude and in angular position without levelling. B-grav in-situ calibrations are based on centrifugal torques and electrostatic forcing. Simulation of asteroid gravity field in laboratory is applied to the pendulum set-up in a vertical position to reject the Earth gravity field. Expertise gained with the design of B-grav was applied for the development at the Royal Observatory of Belgium of the gravimeter GRASS.