Acta Geophysica最新文献

We estimated the source parameters for local earthquakes near the Idukki reservoir, Kerala. The region falls under seismic zone III, indicating moderate seismicity, and is reported to have witnessed several small to moderate size magnitude earthquakes. Eight local earthquakes with magnitudes ranging between 2 and 3.6 were used during the data analysis of this study. Four key parameters were primarily estimated from the earthquake signals, providing an overall idea about the source characteristics, i.e., seismic moment, stress drop, corner frequency, and source radius. Our estimated moment magnitudes (M_w) range between 2 and 3.4, which are consistent with the reported local magnitude (M_L) scale, indicating a minor difference between M_W and M_L scale. The estimated variations in seismic moment align well with the global model of micro-earthquakes, ranging between 1.2E + 15 and 1.1E + 17 dyn-cm. The source radius mostly varies between 110 and 220 m, with seismic moment exhibiting a linear increase as source size grows. This suggests a clear dependence of seismic moment on the radius of the source. It is likely that the brittle shear-failure mechanism on the fault segment and/or the presence of weak zones would contribute to local earthquakes with smaller source radius. Stress drops for most of the events are relatively low in the study region, ranging from 0.3 to 4.5 bars. The initiation of rupture is evident along an existing fault plane, potentially acting as a contributing factor to the observed lower stress drop values. The stress drop variable with a positive correlation to the seismic moment of the event might indicate a wide range of strength of the crustal rock in the region. Interestingly, both the corner frequency (f_c) and maximum frequency (f_max) decrease as seismic moment increases, indicating that both are related to the source process and possibly influenced by the site effects. Finally, we can suggest that the derived source parameters can be utilized to simulate ground motion parameters of historical events, thereby enhancing seismic hazard assessment and facilitating earthquake engineering analyses in future research initiatives.

To study how the soils, respond to an earthquake, seismic waves are frequently utilized. The purpose of this work is to build the porosity graphs based on the geotechnical parameters of the soils and forecast the porosity of shallow clay soils using seismic wave velocities that analyze the dynamic features of the soil. Compressional (P) and shear (S) wave velocities, seismic velocity ratio, Poisson ratio, bulk modulus, and shear modulus are the factors used to calculate porosity. In this work, porosity values are calculated using grain and dry densities of core samples taken from different boreholes within the study region, and bulk modulus, shear modulus, and Poisson ratio are calculated using P- and S-wave velocities obtained by utilizing the seismic-refraction method, as well as porosity values. The research region is in Iran; Isfahan Metro Line 2 and mostly consists of clay, silt, sand, and gravel deposits. Based on the values of the Poisson ratio, seismic P-wave velocity, seismic velocity ratio (V_p/V_s), and the stiffness of the clay soils, the data of the clay soils in the region were individually sorted. These characteristics were used to create novel multi-parameter relationships between clay soil porosity, seismic velocities, shear modulus, and the Poisson ratio. Using the error norm approach, the errors in the parameters utilized for each relationship were identified. The error norm technique's findings show that the shear wave velocity and shear module have the lowest error when calculating porosity. Therefore, it is advised to estimate porosity of shallow clay soils using the given correlations. These relationships can be used to assess the porosity of clay soil and to determine if the soil's pores are saturated with liquid.

The research on the effect of calcareous cementation on rock resistivity has been limited to qualitative analysis, while quantitative research has been lacking. Therefore, a quantitative study on the effect of calcium on rock resistivity is carried out based on the effective medium H-B theory; then, a new electrical conduction model suitable for the evaluation on oil–gas potential of calcium-bearing shaly formations is established accordingly. First, the repeatability of two parallel artificial cores is analyzed with petrophysical parameters to insure the accuracy of the artificial core technology. Then, 51 artificial rock samples with different calcium and clay content but basically with consistent quartz particle size distribution are made using artificial core technology, and the resistivity of these artificial rock samples saturated with different salinity water is measured experimentally. Next, considering the salt exclusion effect of clay pore water and its dispersion distribution, the effective medium Hanai-Bruggeman resistivity model is improved by treating the clay pore water as a dispersed phase. The improved model is more accurate and reasonable when compared with the oil testing results and the sealed coring results. Then, based on the improved effective medium Hanai-Bruggeman resistivity model, the relationship between the cementation exponent and calcium content and that between the cementation exponent with clay content was established. Meanwhile, the relationship among the cementation exponent, calcium content and clay content was established. These were done using the resistivity experimental data of the artificial cores with different clay and calcium contents, while being saturated with water of different salinities. Finally, treating the calcareous particles as a dispersed phase, the established relationship among the cementation exponent, calcium content and clay content was added to the improved model, after which a new electrical conduction model suitable for calcium-bearing shaly sandstone formation was formed.

Understanding the impact of hydroelectric development in the Brazilian Amazon is critical for maintaining ecological balance. This research evaluates the impact of the Balbina Dam on the Uatumã River's flow and landscape. We employ a method to measure flow regime changes, scoring these changes from 0 to 1. Additionally, we analyze landscape changes through satellite imagery. Results indicate a significant dam-induced alteration in downstream water flow, with a score of 0.638. However, the river's in-stream shape has not notably changed since the dam construction. Assessing lateral water movement in the adjacent forested areas is challenging with satellite data, necessitating on-ground studies for accurate mapping. By integrating flow measurement techniques with landscape analysis, this study provides insights into sustainable water management and ecosystem rehabilitation in the Amazon.

The processing of potential field datasets requires many steps; one of them is the inverse modeling of potential field data. Using a measurement dataset, the purpose is to evaluate the physical and geometric properties of an unidentified model in the subsurface. Because of the ill-posedness of the inverse problem, the determination of an acceptable solution requires the imposition of a regularization term to stabilize the inversion process. We also need a regularization parameter that determines the comparative weights of the stabilization and data fit terms. This work offers an evaluation of automated strategies for the estimation of the regularization parameter for underdetermined linear inverse problems. We look at the methods of generalized cross validation, active constraint balancing (ACB), the discrepancy principle, and the unbiased predictive risk estimator. It has been shown that the ACB technique is superior by applying the algorithms to both synthetic data and field data, which produces density models that are representative of real structures and demonstrate the method’s supremacy. Data acquired over the chromite deposit in Camaguey, Cuba, are utilized to corroborate the procedures for the inversion of experimental data. The findings gathered from the three-dimensional inversion of gravity data from this region demonstrate that the ACB approach gives appropriate estimations of anomalous density structures and depth resolution inside the subsurface.

With the escalating demand for underground mining and infrastructure construction, the optimization of tunnel construction has emerged as a primary concern for researchers. The geological conditions encountered during the excavation of hard rock tunnels using tunnel boring machines (TBM) significantly impact construction efficiency and cost-effectiveness. The existing lithology testing methods need to be more efficient in aligning with TBM operational efficiency. In recent years, the rapid advancement of artificial intelligence has paved the way for its integration into numerous domains, including tunnel engineering. To address this issue, this study proposes three innovative hybrid RF-based intelligent models, namely PSO-RF, ALO-RF, and GWO-RF, for the precise prediction of lithology in hard rock tunnels using TBM working parameters. The TBM operating parameters of the Jilin Yinsong Water Supply Project serve as the basis for this investigation. Twelve distinct characteristic parameters relevant to the lithology of the tunnel working face were carefully selected as input parameters for lithology prediction. Comparative analysis of the three hybrid models reveals that GWO-RF demonstrates exceptional lithology prediction performance (ACC = 0.999924; PRE_A = 0.0.9999976; REC_A = 0.999775; F1_A = 0.999876; Kappa = 0.999911), whereas PSO-RF and ALO-RF exhibit slightly inferior performance. Nonetheless, all three hybrid models exhibit a significant improvement in prediction accuracy compared to the unoptimized RF model. The research findings presented herein facilitate the swift determination of TBM working surface lithology, enabling timely adjustment of TBM working parameters, reducing equipment wear and tear, and enhancing construction efficiency.

Given the shortcomings of inadequate vacuum transfer effectiveness, susceptibility to clogging, and environmental impact, i.e., white pollution, associated with standard plastic drainage boards, this paper introduces an innovative solution termed combined vertical drain (CVD). This CVD is composed of biodegradable straw materials and tailings sand. Through controlled indoor model experiments, the drainage and consolidation performance of the CVD is investigated across varying proportions of straw content. The findings indicate that increasing the concentration of straw within the mixture of straw particles and tailings sand (referred to as MST) within the drain distinctly mitigates the diminishment of the vacuum condition during the vertical drainage transfer. Optimal elevation of the straw component in MST can notably reduce the duration required for vacuum preloading and enhance displacement up to a certain value. Nonetheless, an excessive increase in the straw composition not only fails to enhance drainage effectiveness but also raises the organic matter level within the soil. Furthermore, compared with the average water content difference of soil in different model box test units after vacuum preloading, the average divergence in vane shear strength of test soil exhibits a more pronounced variation.

To enhance the seismicity analysis within a given seismic region, it is crucial to establish a unified earthquake catalog with minimized uncertainties. The preparation of such a unified catalog needs scaling relationships to convert different magnitude types to a homogeneous magnitude. Among the plethora of magnitude types, the moment magnitude (M_w) stands out as a widely utilized metric in modern earthquake risk and recurrence analysis. Hence, the key objective of this study is to expand the M_w earthquake dataset specifically for the Northern Algeria region and its surrounding areas, providing a valuable resource for researchers investigating seismicity in this region and for earthquake magnitudes homogenization. To achieve this objective, surface wave (M_s) and body wave (m_b) magnitudes obtained from international agencies were standardized to M_w using newly developed regional empirical relationships based on the general orthogonal regression method (GOR). The use of GOR for magnitude conversions has gained popularity in recent years. However, a critical aspect when employing the GOR method is estimating the standard deviations associated with different magnitude types and subsequently determining the error variance ratio. To address this, the present study leverages recent research works to approximate the standard deviations associated with various magnitudes. By calculating the error variance ratio, derived from the estimation of magnitude uncertainties, the general orthogonal regression method was effectively applied to achieve the desired earthquake magnitude homogenization. Notably, this study fills a significant gap in research conducted in Algeria by developing regional empirical relationships using GOR with appropriate values of the error variance ratio. The expanded M_w dataset serves as a dependable resource used for other earthquake magnitudes homogenization, hence the preparation of a more extensive and unified M_w earthquake catalog for Northern Algeria and its neighboring areas.

The flow regime in geology is critical to the underground activity. In this study, axial seepage tests within a wide range of grain sizes were conducted to better understand the influence of pore size distribution and pore structure evolution on hydraulic characteristics in porous media. The effect of pore size distribution and evolution on flow regime transition was quantitatively analyzed. The pore size distribution was controlled by varying uniformity coefficient (Cu) (4 < Cu < 24) and curvature coefficient (Cc) (0.2 < Cc < 14). The results show that coefficient size appears to have a positive correlation with the permeability of the granular materials, but cannot impact the transition of flow regime that is mainly dominated by the heterogeneity of the pore structure. Compared to the pore space and the effect of medium, the heterogeneity of pore structure significantly impacts on the occurrence of pre-Darcy flow and directly correlates with the magnitude of inertial forces or fluid velocity. It demonstrates that the curvature coefficient (Cc) is an important characteristic parameter in flow transition. The particle size ratio (left( {frac{{d_{60} }}{{d_{30} }}} right)) could be considered as one of the reference characteristic particle sizes for assessing non-Darcy flow characteristics. Subjected to the axial stress, the critical hydraulic gradient for the transition from pre-Darcy to post-Darcy flow was reduced, and even the pre-Darcy flow disappeared. These findings will contribute to the identification of non-Darcy flow transition in groundwater and promote a better understanding of the nonlinear evolution behavior of fluids under underground extraction conditions.

Great attention has been focused on uncovering the physics of seismic wave attenuation in rocks in the past few decades. However, the contribution of different attenuation mechanisms on attenuation is not completely clear in coal. We use the fractal viscoelastic model to describe the P-wave attenuation in coal, and the model has a good approximation to the constant-Q model when choosing lower fractional order (alpha). We experimentally measured attenuation in dry and water-saturated coal samples in the frequency range of 10–250 Hz, at room temperature, and approximately room pressure. Attenuation in the dry sample is frequency independent and the fractal viscoelastic model curves fit well with the data when (alpha =0.056). For the partial water saturation cases, attenuation is frequency dependent, and the simple viscoelastic attenuation theory cannot describe the strong attenuation in seismic band; when water saturation is high ((ge 80%)), we need wave-induced fluid flow mechanism to explain the high (Q^{-1}) values. The final contribution of viscoelasticity to attenuation is about 63%, while the final contribution of wave-induced fluid flow mechanism to attenuation is about 37% in the test.