Acta Geophysica最新文献

Shanxi Reservoir is one of the most seismically active areas in Zhejiang Province, Eastern China, making it a natural experimental site for reservoir earthquake research. We apply the fluid substitution method to the study of reservoir earthquakes. Firstly, we estimate the distribution of seismic wave velocity and wave velocity ratio around Shanxi Reservoir based on the seismic phase observation reports. Then, based on the rock physics models and techniques, we estimate the porosity and saturation distribution around the reservoir using wave velocity and velocity ratio results, and analyze the permeability conditions of underground rocks. Further, using the earthquake catalog, we estimate the spatial distribution of b-value and stress field characteristics in the area. Finally, we discuss the influence of reservoir impoundment and underground lithology on seismicity and speculate on the mechanism of earthquake occurrence. The main conclusions are as follows: (1) When earthquakes occur, the rocks that rupture are essentially saturated; the earthquake magnitude of the region, where the rocks rupture before they are fully saturated, is relatively small. (2) The porosity of the SE segment on seismogenic fault F₁₁ (Shuangxi–Jiaoxiyang fault) is greater than that of the NW segment. (3) After the reservoir impoundment, the water first infiltrates in the middle to SE segment of the F₁₁ fault, which has large porosity, causing the pores within the rock to reach water saturation and inducing initial seismicity. The occurrence of initial earthquakes creates new infiltration channels, which makes the reservoir water infiltrate northwest along the fault. Therefore, the NW segment began to become active, resulting in the 2014 earthquake sequence. (4) The 2014 sequence started in the region with large porosity differences and small b-values. Large differences in porosity tend to result in large differences in local water pressure, coinciding with the large stress reflected by the b-value; this region became the most unstable location on the NW segment, and the underground rocks were the first to reach the yield limit and rupture.

Landslides are a major natural hazard in mountainous regions, often resulting in thousands of deaths and billions of dollars in property damage. Climate change is increasing the frequency and severity of these events. Seismic network monitoring has made it possible to detect landslides in real time. However, distinguishing seismic signals caused by landslides from those generated by earthquakes and background noise remains a key challenge. This study investigates the reliability of power spectral density (PSD) trends in seismic waveforms for identifying landslide-generated signals. By analysing seismic data from multiple stations within a 150-km radius of the event, we find a consistent PSD decay pattern across different landslides, regardless of their size, duration, or distance from the stations. We use the slope of the seismic waveform PSD in the frequency band 0.01–5 Hz and skewness of the spectral power distribution as scalable entities for landslide detection. This confirms that landslides have unique spectral features, enabling them to be distinguished from other seismic sources. Our analysis suggests that the landslides show PSD slope values between − 3 and − 9. We have also noticed steeper slopes that match the slope of seismic waveforms of background noise when the station distances are above 200 km. Although this limits landslide detection using distance stations, this can be ruled out when using the local networks for landslide monitoring. The study demonstrates that PSD analysis of seismic waveforms offers a stable and innovative method for real-time landslide detection in continuous seismic data. Utilizing these spectral signatures could greatly enhance landslide monitoring and early warning systems in high-risk areas.

This research examines the methods of controlling the surface evaporation rate of water reservoirs in drought conditions. Using physical and chemical coatings is one of the new methods to prevent evaporation. In this research, the combination of octadecanol and hexadecanol, as well as hexadecanol dissolved in ethanol, has been used as a chemical method to control evaporation on the surface of three ponds designed with dimensions of 2 × 2 × 2 square meters in the hydrometeorological research station of the Faculty of Natural Resources of Lorestan University. Quantitative (evaporation rate reduction) and qualitative (possible changes in some chemical and microbial parameters) effects were investigated in a 3-month period from 7/23/2021 to 10/22/2021. The monolayer combination of octadecanol and hexadecanol showed the highest reduction in evaporation rate (23%) with a significant difference of 5% compared to the control group. Hexadecanol monolayer ranked second with 17% reduction in evaporation. The chemical parameters of alkalinity (pH), total dissolved solids (TDS) and the presence of microbial biomass (turbidity) were investigated. The acidification of the environment due to the release of CO2 in the treatment ponds led to a decrease in pH. The faster growth of algae, bacteria and solid particles has increased the turbidity in the control pond compared to the treatments.

The operation of the Three Gorges Dam (TGD) since 2003 has induced a 60–90% reduction in suspended sediment concentrations in the Middle Yangtze River (MYR), which led to significant channel degradation and riverbed coarsening, and further affects the flood control and riverbank protection in the Middle Yangtze River. However, the influence of the riverbed adjustment on the bedload transport process in the near-dam reaches remains unclear. Based on the measured data in the MYR, a bedload transport formula was proposed that considered the coupled effects of riverbed topography and entrainment probability. The results showed that: (i) The proposed formula in this study can reasonably reflect the impact of cross-sectional morphology and bedload transport on the riverbed erosion and deposition process, and it is consistent well with the observations; (ii) after the TGD operation, the bedload transport rate in the Jingjiang Reach significantly decreased, accompanied by a reduction in sediment entrainment probability; the transport rate at Zhicheng station decreased from 163.66 to 2.55 kg/s, and the entrainment probability decreased from 0.994 to 0.001, but the transport rate and entrainment probability remained relatively stable at Shashi and Jianli stations; (iii) riverbed scouring in the Jingjiang Reach intensified, with reduced bank slope angles leading to weakened bedload transport intensity; and the transport rate revealed a negative correlation with riverbed coarsening and longitudinal riverbed stability. The results of this research are an enrichment to the sediment movement theory and can be used in the prediction of riverbed evolution in the alluvial rivers.

Grade control structures (GCS) are hydraulic structures often used in river regulation in the steep slope basins. Prediction of local scour dimensions is crucial for managing control structures and foundation design in water resources engineering. The present research experimentally investigates the influence of tailwater depth on the dimensions of the scour hole downstream of the GCS under steady flow and sediment mobility. Experiments were carried out for different discharges and tailwater depths, including three free tailwater depths of 1.5 and 2 times the initial tailwater depth in three different bed slopes of 0.05%, 0.2%, and 0.4%. The results indicated that increasing the tailwater depth while maintaining a constant flow rate and bed slope leads to a decrease in the dimensions of the scour hole downstream. On average, establishing the maximum tailwater depth for different discharges caused a 25% and 20% reduction in the downstream scour hole depth and length, respectively. An increase in bed slope from 0.05 to 0.4% at the maximum tailwater depth resulted in a 9% and 19.4% increase in the length and depth of the scour hole, respectively. Conversely, when the tailwater depth was doubled at the maximum bed slope and discharge, a reduction of 18.8% in depth, and 38.54% in scour length was observed. Finally, a general empirical relationship has been proposed to predict the depth and length of the scour hole downstream of GCS, incorporating the influence of the tailwater depth and bed slope.

This study applies the persistent scatterer interferometric synthetic aperture radar (PS-InSAR) technique to investigate surface deformation in Makkah City, Saudi Arabia, a region undergoing rapid urbanization and characterized by complex geological conditions. The rationale for this research stems from the extensive anthropogenic activities in Makkah City, such as groundwater over-extraction, large-scale construction projects, and significant land-use changes, which may lead to surface deformation and pose potential risks to infrastructure and public safety. Utilizing 16 C-band Sentinel-1 satellite images acquired from the European Space Agency (ESA) between December 2017 and January 2019, we employ the StaMPS code within MATLAB to measure deformation velocity and visualize the results using R Studio. The findings reveal that the deformation velocity in Makkah City ranges from − 19.1 to + 19.1 mm/year, indicating areas of both subsidence and uplift. Notably, certain regions exhibit substantial subsidence, while others show upward movement or an uplift. This study demonstrates the effectiveness of the PS-InSAR technique in detecting surface deformation in Makkah City, offering a valuable and economical tool for creating risk maps and implementing disaster mitigation strategies. The results stress the importance of continuous monitoring in areas exhibiting deformation signals and provide crucial insights for urban planning and infrastructure development in Makkah City, helping to mitigate potential future hazards and enhance the city’s resilience to geological risks.

Seismo-acoustic and stratigraphic framework of the North İmralı Basin in the Eastern Marmara Sea has been investigated using high-resolution seismic reflection data, in order to reconstruct the evolution of the basin over the past 500 ka. Seismic data indicate that the right-lateral strike-slip İmralı Fault, which bounds the basin to the south, is the primary structural feature controlling the formation and development of the basin. The fault bends offshore of the Armutlu Peninsula and north of İmralı Island which induces a NE-SW oriented extensional regime within the basin. As a result, NW–SE trending normal faults with a right-lateral slip component have formed in the north operating as growth faults, demonstrating that the basin is actively subsiding with a counterclockwise rotational motion. Under this subsidence regime, the North İmralı Basin has developed over a negative flower structure associated with a releasing segment mechanism. Vertical displacement measurements along these faults suggest that the subsidence has persisted in a steady-state manner at a constant rate of approx. 60 cm/ka over the past 500,000 years. The four buried deltas observed in the seismic data were formed during marine regression and represent glacial-stage deltas, excluding Delta-2 which appears to be associated with sea-level rise. No delta has been observed in the past 74 ka due to an imbalance between sedimentation rates and the increasing accommodation space.

Graphical abstract

River flow is a crucial component in water resource management, environmental protection, and disaster mitigation. Also, the Mississippi River, one of the largest and most significant rivers in North America, plays an essential role in shaping the region’s infrastructure and economy. Moreover, reliable flow forecasting is essential for several key purposes, including flood prevention, optimal water resource allocation, and ecosystem preservation, all of which are critical to promoting sustainable development and enhancing disaster resilience in the region. This study aims to predict the discharge of the Mississippi River at the Memphis station for the period from 1990 to 2024 by employing hybrid models that integrate short-term long-term memory (LSTM) with random forest (RF) and neural network (CNN), considering lag intervals of 3–15 days. Various evaluation criteria were utilized to assess the accuracy of these models. The performance evaluation revealed that a three-day lag interval produced the most accurate results, with the CNN-LSTM model achieving the best performance, with NRMSE = 0.0165, at the Memphis station. Additionally, the RF-LSTM and CNN-RF-LSTM models demonstrated high accuracy in predicting daily discharge, with NRMSE = 0.0179, 0.0177, respectively. These findings have significant implications for water resource managers, providing enhanced efficiency in reducing labor costs and saving time in forecasting.

Soil improvement methods aim to enhance geotechnical properties such as strength, durability, and resistance to environmental loads. Among recent advances, microbially induced calcium carbonate precipitation (MICP) has emerged as a sustainable alternative to conventional chemical stabilizers. This study presents a novel application of Box–Behnken experimental design (BBD) for optimizing MICP parameters in sandy soils, focusing on the interaction between sand type, treatment solution molarity, and curing time. A total of 17 experimental runs were conducted under a structured response surface methodology to identify optimal conditions for maximizing unconfined compressive strength (UCS). The highest UCS value, 1297 kPa, was achieved using fine-grained sand treated with a 1.5 mol solution over 5 days. The key innovation of this research lies in the integration of statistical design techniques with microbial geotechnology, enabling efficient modeling of nonlinear interactions and minimizing experimental effort. Beyond laboratory findings, the results offer practical guidance for field-scale implementations by identifying critical parameter ranges that ensure microbial viability and performance stability. This integrated approach provides both methodological novelty and applied relevance, contributing to the advancement of bio-based soil improvement strategies in geotechnical engineering.

This study examines seismicity and deformation in New Zealand's North Island using data from 2014 to 2024. The North Island, shaped by the Hikurangi Subduction Zone (HSZ), the Taupo Volcanic Zone (TVZ), and the North Island Dextral Fault Belt (NIDFB), exhibits complex tectonic activity. Therefore, in this study, Global Navigation Satellite System (GNSS) data were processed to analyze the horizontal and vertical movements of the North Island relative to the Pacific and Australian plates. Additionally, earthquakes were examined based on their magnitudes, epicenters, and hypocenters. The analysis of M ≥ 4 earthquake distribution highlights a seismic quiescence in the northwestern part of the island, particularly around Auckland and the Northland Volcanic Field. According to hypocenter depths, earthquakes at 20–60 km and 60–300 km form two NE-SW trending seismic zones, suggesting distinct structural domains with a potential transition zone in the west. GNSS velocities relative to the Pacific-fixed frame are found to be consistent with the subduction rate of the HSZ, while velocities relative to the Australian-fixed frame reveal higher horizontal velocities in the north, which align with a greater subduction rate and rollback effect. In contrast, the western part of the island rotates significantly slower than the eastern part. Consequently, this study presents and evaluates deformation trends, potential transition and quiescent zones, and the recent movement of the North Island in conjunction with previous studies.