pure and applied geophysics最新文献

This study systematically investigates the mechanical degradation mechanisms of pre-fractured samples subjected to freezing and thawing cycles through a combined experimental–numerical methodology. Utilizing systematic triaxial compression testing synchronized with ANSYS-based finite element simulations, the strain-dependent evolution of damage models of samples, stress fields and fracture propagation mechanisms in specimens containing artificial discontinuities with angular orientations ranging from 0° to 90° were calculated and analyzed. Results indicate that the freezing and thawing cycles markedly intensified internal structural deterioration of the cracked samples, leading to a certain degree of decrease in peak strength, cohesion and internal friction angle. The initial internal crack damage significantly impacts the mechanical properties of the samples. As the crack angle increases, the peak strength decreases and then increases, with the minimum value occurring at α = 45°. The mechanical properties of samples with 30° and 60° crack angles are intermediate, while those with 0° and 90° crack angles are the most significant. And stress triaxiality is introduced as a stress state parameter to describe the degree of tension and compression at each stress field point. It explores how stress triaxiality, maximum tensile stress, and maximum tensile strain affect crack initiation position, direction. With the increase of crack angle, the crack initiation position gradually shifts from the center of the crack surface to the crack tip, aligning with the shift in the stress triaxiality maximum position. The final damage surface direction is consistent with the direction of axial compression, corresponding to the far-field principal stress or strain direction, and crack propagation follows the maximum stress triaxiality gradient, and the crack extension follows the maximum stress triaxiality gradient.

This study systematically investigates the pressure dependence of P-wave velocity anisotropy in stressed shale through water injection experiments. A modified single-plug method (MSPM) based on iterative reweighted least squares is proposed to accurately determine orthorhombically anisotropic velocities and parameters under anisotropic stress conditions. Triaxial compression tests with water injection on Longmaxi shale (Sichuan Basin) reveal that both isotropic and differential stress fields significantly influence velocity anisotropy, exhibiting nonlinear relationships with stress and pore pressure. Due to anisotropic Biot coefficients, water injection induces asymmetric pore pressure gradients, leading to distinct mechanical responses such as stress hysteresis and secondary failure during unloading. Results highlight that anisotropy parameters like δy are highly sensitive to stress changes, while velocity in the direction parallel to bedding(Vz) shows pronounced hysteresis. Adsorption of injected water at clay particle interfaces is identified as an additional factor enhancing anisotropy beyond stress effects. This study deepens the understanding of stress-dependent shale anisotropy, emphasizing the critical role of pore pressure dynamics in reservoir characterization and hydraulic fracturing design for unconventional oil and gas development.

Low-velocity fault zones, predominantly located in the shallow crust (0–5 km depth), amplify localized earthquake-triggered ground shaking, thereby exacerbating the vulnerability of surface structures. Understanding the influences of fault zones on seismic wave propagation, including their effects on both translational and rotational ground motions, is necessary for seismic hazard assessment. We first establish a 2D model based on the Binhai fault zone in the Taiwan Strait and a Hualien M_W 6.1 earthquake and then use the staggered-grid finite difference method to simulate seismic wavefields of translational (X, Z) and rotational Y (Ry) components in models with and without a normal fault zone. By evaluating amplitude and spectral characteristics of ground motion across observation positions along the fault, we investigate the responses of translational and rotational component motions to the fault zone. Results demonstrate spatially heterogeneous amplification and attenuation effects and differential responses between seismic rotational and translational motions: (i) The fault zone amplifies ground motions asymmetrically on its northwestern (NW) and southeastern (SE) sides (up to 300% and 100% amplification, respectively), while attenuating amplitudes (40–70% reduction) in its overlying central region. (ii) Near the fault (≤ 10 km), Ry-component amplitudes exceed translational components by 20–80%, but this enhancement diminishes, becoming 20–120% weaker at farther distances (~ 10–30 km). (iii) High-frequency Ry signals exhibit stronger amplification and weaker attenuation compared to translational components, highlighting frequency-dependent fault-zone dynamics. These findings underscore the necessity of incorporating rotational ground motions into seismic risk evaluations, particularly for structures near fault zones.

Morelia City stands in central México, within the Trans-Mexican Volcanic Belt and the Michoacán-Guanajuato volcanic field. With a population of about 850,000, it is the largest and most populated city in the state of Michoacán. In 1991, UNESCO designated its historic center as a World Heritage Site, attracting millions of tourists yearly. However, the city is vulnerable to regional intraplate and inter-plate earthquakes and the municipality’s outdated building regulations. Recently, the strong shaking experienced in the metropolitan area due to the November 19th, 2022 (Mw7.7) subduction earthquake on November 19th, 2022 (Mw 7.7), emphasizes the need to understand the site's effects and to update the municipality’s building regulations. This study presents a comprehensive seismic microzonation of Morelia, using the ambient noise horizontal-to-vertical spectral ratio (HV) technique as an initial step toward mitigating seismic risk. Because of several peaks in the HV, we presented the HV amplification at several frequencies and not only at the dominant frequency, as is usually the case. We identified amplification levels of up to 6.0. We also inverted the HVs, considering the thicknesses identified by geological data, to create a velocity model of the subsurface extending to a depth of 400 m. The results indicate the existence of a local half-graben where the sediment thickness ranges from 50 to 110 m and define the regions with the most significant amplification. Furthermore, we reported the existence of long-period ground vibrations that could affect high-rise buildings, long-span bridges, and historical buildings. Since HV ambient noise amplification maps do not always effectively predict earthquake responses, we also compared these maps with acceleration maps from two recorded earthquakes at similar frequencies. One of these earthquakes was a subduction event, while the other originated from a local source. They exhibited low and high central frequency sources, respectively, as recorded by the accelerograph network of the Universidad Michoacana. The excellent correspondence between all the output results indicates the reliability of the used approach.

Mining operations are essential for various industrial sectors, requiring a comprehensive approach to exploration, extraction, processing, and waste management. In uranium mining, waste management is particularly critical due to the presence of radioactive materials in tailings, posing environmental and public health risks. Geotechnical characterization of rock masses supporting tailings dams is fundamental to ensuring structural integrity and safety. This study aimed to correlate compressional wave velocities with geomechanical rock quality parameters in the foundation of a radionuclide storage dam. While the initial analysis suggested a reasonable correlation, the application of this relationship to new seismic tests during the mine’s decommissioning phase did not yield a significant predictive capability. Despite this limitation, the consistency between rock quality designation values obtained via photogrammetry and geophysical methods underscores the potential of integrated approaches for rock mass assessment. These findings contribute to geotechnical, mining, civil engineering, and geophysical applications, reinforcing the need for multi-method validation in subsurface investigations.

The CSIR-NGRI, Hyderabad, conducted seismic imaging of the crust and lithosphere structures of the Hyderabad region during the period 2020–21 by installing a 10-station broadband seismic network. The data from this network was used to perform a joint inversion of P-radial receiver functions (PRFs) and fundamental mode group velocity dispersion data of Rayleigh waves to estimate the crustal and lithospheric thicknesses beneath the eastern Dharwar Craton (EDC), India. Modelled Moho depths range from 35.5 to 37.6 km, with a mean of (36.7 ± 0.7) km, while modelled lithospheric thicknesses range from 134.0 to 154.0 km, with a mean of (139.6 ± 6.7) km. The modelled Moho depths reveal an NW–SE trending crustal thinning in the southwestern part of the Hyderabad region while the modelled lithospheric thicknesses show an NNE-SSW trending elongated region of down-warping below the central part of the study region, which is bounded by thinning of the lithosphere on both the eastern and western sides. A stacking of radial PRFs using the common conversion point (CCP) indicates three seismic discontinuities, namely the Moho discontinuity (an increase in positive PRF amplitude at 30.0–35.0 km depth), the Hales discontinuity (an increase in positive PRF amplitude at 90.0–115.0 km depth), and the Lithosphere-Asthenosphere Boundary (an increase in negative PRF amplitude at 140.0–160.0 km depth). Our modelling reveals a (36.7 ± 0.7) km thick Archean crust and a (139.6 ± 6.7) km thick lithosphere beneath the Hyderabad region, indicating the absence of a thick cratonic root beneath the EDC.

The Banda Islands is a sub-district within the Province of Maluku. As outlined in the Regional Spatial Plan for the period 2011–2031, Banda Island is specifically delineated as the Provincial Strategic Activity Center, with a primary focus on tourism as the key strategic activity. However, it is imperative to note that the Banda Islands are highly susceptible to earthquakes and tsunamis. Majority tsunamis occuring in Banda Islands classified as near-field tsunamis, so the rapid execution of data collection, processing, modelling, and analysis is crucial. But, the technical data available for tsunamis in this area is notably limited. This study endeavours to address this gap by constructing a comprehensive tsunami database through simulations and numerical modelling of various scenarios. The TUNAMI F1 model, a simulation methodology grounded in linear equations for tsunami wave propagation, is employed in this research. By leveraging historical earthquake source data, the model generated tsunami data amounting to 1,647 instances from 234 earthquake epicentres. Notably, the magnitude of an earthquake and its proximity directly correlate with the resultant maximum wave height and arrival time; higher magnitudes and closer proximity lead to increased wave height and swifter arrival times. The computed maximum tsunami height at the Banda Islands is estimated to reach 13 m. Furthermore, the arrival time for a tsunami exceeding 2 m in height ranges from 0 to 46 min at two designated observation points within the Banda Islands. This dataset is anticipated to serve as a valuable addition to the existing database managed by the Meteorology, Climatology, and Geophysical Agency (BMKG), enhancing its comprehensiveness. This database is intended to support tsunami early warning systems (TEWS) through rapid scenario retrieval in coastal areas. Additionally, it is poised to fortify the efficacy of the tsunami early warning system, thereby contributing to the development of a disaster-resilient tourism sector in the Banda Islands.

Using the dimensional analysis a novel model for shock wave generation during explosive volcanic eruptions is proposed. An analytical derivation of the dependence of the shock wave’s peak pressure on the initial energy and the distance from the epicenter in the case of a volcanic explosion has been obtained, whose predictions agree with the results of numerical modeling within the margin of error. A relationship between the parameters of the shock wave in the vicinity of the source and those of the atmospheric Lamb wave is established, offering an explanation for the phenomenon of longer-than-expected periods in volcanic Lamb waves, first observed following the 1980 eruption of Mount St. Helen’s. Differences between atmospheric Lamb waves generated by volcanic explosive eruptions and thermonuclear tests are studied. Additionally, based on the introduced model, a method for estimating the composition of volcanic gases based solely on observational data from points distant from the epicenter is proposed. The model’s consistency with observational data is demonstrated through a comparison with barographic measurements from the January 15, 2022, Hunga-Tonga eruption, provided by Albuquerque Seismological Laboratory, where the Lamb wave was recorded at 50 stations worldwide. The evolution of Lamb wave parameters with distance and its attenuation characteristics were investigated using observational data.

Numerous rockfalls occur along the southern foothills of the Alborz mountain range, particularly affecting the Chalus highway. This study aims to identify the key factors influencing rockfall events and to produce a susceptibility zoning map using GIS-based modeling techniques. A high-resolution 10-m DEM, geological maps, and field data were integrated to simulate rockfall frequency, velocity, height, and energy. The analysis identified nine high-risk zones along the highway corridor. Results indicate that while tectonic activity plays a role in rock fragmentation, climatic conditions particularly freeze–thaw cycles during winter are the main trigger for rockfalls. The generated susceptibility map provides essential information for road management and risk mitigation strategies.