Acta Geophysica最新文献

This article provides a comprehensive analysis of CO₂ injection monitoring in the Sleipner Field. Ensuring the safe storage and containment of CO₂ in geological formations or assigned storage sites, especially in the carbon capture and storage (CCS) projects. In this study, a seismic inversion method incorporating linear programming sparse spike inversion was employed to observe and analyze the CO₂ plume in the Sleipner field, Norway. This approach enhances the understanding of the dynamics and behavior of the CO₂ injection, providing valuable insights into the monitoring and assessment of CCS operations in the Sleipner field. The foundational dataset includes 3D post-stack seismic data from the year 1994, with special emphasis on the monitoring data collected in 1999, following four years of CO₂ sequestration. The analysis utilized synthetic data to investigate alterations in seismic amplitude, highlighting that amplitude variations were more prominent compared to variations in velocity and density. The findings highlight noticeable shifts in P-wave velocity, signifying a significant 29% reduction, with the most substantial decrease occurring within the 0 to 30% CO₂ saturation range. Correspondingly, density changes align with trace variations, demonstrating only a 2–3% reduction in density as gas saturation increases from 0 to 30%. Beyond 30% saturation, density exhibits a further decrease of 30%. The traces collectively reveal a consistent trend, showcasing a 32% reduction in impedance as CO₂ saturation levels rise. Through the cross-equalization process, it was observed that the initial data repeatability was low, indicated by a normalized root mean square (NRMS) value of 0.6508. However, significant improvement was achieved, bringing the NRMS value to a more satisfactory level of 0.5581. This improvement underscored the alignment of features both above and below the reservoir, underscoring the efficacy of the cross-equalization technique. The outcomes of the 4D inversion provided insights into the distribution of CO₂ within the reservoir, revealing upward migration. Importantly, the results confirmed the secure storage of CO₂ within the reservoir, affirming the integrity of the overlying cap layer.

Climate change is one of the most important global challenges of this century, with significant impacts on water resources, economic development and ecological health. This study aimed to investigate the effect of climate change on streamflow in Joumine watershed, upstream the Ichkeul Lake, a RAMSAR wetland and the most productive ecosystems in Tunisia and the Mediterranean. The hydrologic response of the basin was simulated based on Hydrologic Modelling System HEC-HMS. Climate data were generated from the emission scenarios RCP4.5 and RCP8.5 from the Irish Regional Climate Model (RCM) for the periods 2030–2060 and 2061–2100. The statistical analysis showed that model performance is satisfactory, with Nash–Sutcliffe efficiency of 0.7 and 0.64 for calibration and validation, respectively. The climate projections exhibited a declining trend in precipitation during the two future periods with more frequent extreme rainfall events in dry season and a rise in temperature which is more accentuated during the period 2061–2100. Climate change is expected to have profound impacts on water resources and resilience of ecosystems. Results showed that Joumine basin is projected to experience reduction in streamflow which is more pronounced under RCP8.5. The frequency and magnitude of hydrological extremes are expected to be intensified, notably during the far future period, leading to pressure on water availability in the end of the twenty-first century. Hence, sustainable water resources management is needed to close the water demand and supply gap in the Joumine river basin.

Seismic data analysis often faces the challenge of random noise contamination from various sources. To overcome this, innovative noise attenuation methods utilizing seismic signal properties are needed. This study focuses on efficiently suppressing random noise in the domain of time and frequency by accurately estimating instantaneous frequency using the single-valued group delay characteristic of seismic signals. The time-reassigned synchrosqueezing transform (TSST) and its second-order variant (TSST2) offer high-resolution time-frequency representations (TFRs) for noise suppression. Expanding on these advancements, we propose an efficient noise suppression method that integrates the adaptive thresholding model into the TSST2 framework and employs sparse representation of the TFR through low-rank estimation. This method effectively attenuates noise while preserving essential signal information. The proposed approach operates trace by trace on recorded data, initially transforming it into a sparse subspace using TSST2. The adaptive thresholding model then decomposes the resulting TFR into sparse and semi-low-rank components, achieving a high-resolution and sparse TFR for efficient separation of noise and signal. After noise suppression, the seismic data can be fully reconstructed by inversely transforming the semi-low-rank component data into the time domain. This method addresses previous limitations in noise attenuation techniques and provides a practical solution for enhancing seismic data quality.

Using the earthquake catalog provided by the Sichuan Earthquake Network Center, spatial and temporal b-value variations were calculated for in regional and local scales based on assessing the completeness of the earthquake catalog and declustering. The results show that (1) b-value temporal variations in regional scale ranged from 0.689 to 1.169, with a mean value of 0.928; while, the local-scale temporal variations ranged from 0.694 to 1.223, with a mean value of 0.925. The b-values in the study area were below the mean value before the moderate and large earthquakes occurrence, and all b-values exhibited the anomalous feature of a sudden decrease before the earthquake low peak rise after the earthquake. (2) The seismotectonic characteristic of the area is the higher value of slip rate of the NW section of Xianshui River Fault Zone; therefore, a large amount of stress was accumulated in the Moxi section of the SE section, leading to a M = 6.8 earthquake in Luding. Before the earthquake, the study area has a low b-value area. The b-value decreased within a short period after the earthquake, dividing the area into asperity. This area still has a future risk of moderate to strong earthquakes. (3) The error in the b-values for most of the earthquakes in the regional and local scales regions is between 0.05 and 0.15, and only individual grid points have larger b-value errors (> 0.2), indicating high confidence in the information. In addition, when conducting a b-value study, choosing a suitable study area is important to avoid missing the b-value anomaly area.

Graphical abstract

Talcher Coalfield is one of the most important coalfields considering thermal grade coal reserves in India; nevertheless, hardly any published geophysical study is available for mapping the subsurface coal, in-crop zone, fault location, formation boundary, etc. In the present study, a combined analysis of electrical resistivity tomography (ERT) in five profiles and high-resolution shallow seismic (HRSS) survey in two profiles was carried out in Goribandh at the northern–eastern part of the Talcher Coalfield, Odisha, India, to study the structural control of coal seams and to delineate the coal potential zone and non-coal zone. Geological core data from three boreholes were utilized to validate the ERT and HRSS results. Three ERT profiles (ERT_P1, ERT_P2, and ERT_P3) data were acquired in perpendicular to the strike direction, and two ERT profiles (ERT_P4 and ERT_P5) data were collected in the strike direction. The purpose of the acquisition of ERT data in the strike direction is to correlate the resistivity values at the cross point of dip lines and strike lines. Two HRSS profiles (HRSS_P1 and HRSS_P2) data were collected along the same two corresponding dip lines of the ERT profiles (ERT_P1 and ERT_P2). The ERT data were collected using Wenner–Schlumberger array at 10 m electrode spacing with multiple roll-along sequences to cover the desired profile length with an approximate profile line spacing of 200 m. The Res2Dinv program was used to execute the inversion of the combined data set. The HRSS data were acquired by ‘End-on-Shooting’ method using 24-fold common depth point survey at 4 m geophone spacing with multiple roll-along sequences to cover the desired profile length with approximate profile line spacing of 200 m, where near trace and far offsets trace were 88 and 276 m, respectively. HRSS data were analyzed using Paradigm 19 seismic processing software. Comprehensive analysis of five numbers of 2D ERT sections (ERT_P1-ERT_P5) and two numbers of HRSS sections (HRSS_P1 and HRSS_P2) indicates that the southern part of the study area is characterized by relatively low to moderate high resistivity (100–500 Ωm) distribution while seismic sections demonstrate multiple strong reflecting horizons, due to carbonaceous beds as identified in the boreholes, indicating Barakar formation. The northern part is characterized by high resistivity (200–1000 Ωm) distribution, while seismic sections exhibit multiple distributed minor reflectors due to boulder beds and or compact sandstone. The combined study of ERT and HRSS data delineates a prominent fault zone F4, indicating a contact boundary between the Talchir and Barakar formations.

Soil salinization has become a global environmental issue, and soil cracking can lead to preferential flows and destabilize the developments of plant-soil system. However, little is known about saline soil cracking, especially under external drying-wetting (D-W) alternations. This study explored how soil salt and continuous D-W cycles affected water evaporation and crack development responding to soil salinity (0, 0.3, 0.6, 1.0, and 2.0%, w/w) and three D-W cycles. Observed findings showed that saline soil water evaporation was smaller than nonsaline soil. Besides, the water evaporation decreased and increased as the soil salinity increased and the D-W cycles progressed, respectively. In addition, soil salt and D-W cycle inhibited and promoted soil cracking, respectively; specifically, the crack area density decreased and increased with increasing soil salinity and number of D-W cycles, respectively. Correlations indicated that the soil salt had overall larger contributions than the D-W cycle to the variations of water evaporation and crack development. Soil salt was negatively correlated with cumulative evaporation, evaporation rate, and crack length density, but was positively correlated with soil moisture; besides, D-W cycle was negatively correlated with soil moisture, but was positively correlated with cumulative evaporation, evaporation rate, crack area density, and crack length density. Mechanism exploration suggested that the salts inhibit surface cracking by promoting inter-microaggregate cementation and clay flocculation and blocking soil macropores; and the D-W cycle promotes surface cracking through the swelling-induced crack healing in the case of hydrophilic clay minerals in contact with water.