Acta Geophysica最新文献

Three major granite batholiths in west-central Saudi Arabia, namely Jeddah, Mecca, and Afar, are dissected by oblique shear zones; most conspicuous of them being the Ad Damm shear zone/fault that continues offshore to connect to the Red Sea fracture zone. Receiver function analysis (REF) results from 15 broadband seismic stations are used to investigate the rheological parameters (Vp/Vs, ρ, σ, λ, μ, AI) of the batholithic crust. The Moho-relief map prepared for the first time for the batholiths unravels two significant features: (i) a regional decrease in crustal thickness by ~ 38% (40 to 25 km) in NW–SE direction across the Asir to Jeddah–Mecca batholiths, and a Moho upwarp at the Red Sea margin underlying the rifted Arabian Shield edge. The transition between the UC and LC beneath the granite batholiths is defined by a strong jump in Vs velocity, as much as 0.60 km/s. 2D distribution of the rheological parameters corresponding to the lower crust (LC) demonstrates their lateral and vertical variations. The rheological parameters bear an inverse relationship with the thickness. The LC appears to exhibit two crustal domains: a thicker and rheologically stronger crust under the Asir terrane and a thinner and warmer crust under the batholiths. The rheological model thus identifies two layers: gabbro and mantle-derived mafic composition in the LC with a high-temperature shear zone in between. The granitic melt is supposedly sourced from the high-temperature shear zone, differentiated and emplaced in the low-strain areas in the UC as batholiths. The UC needs detailed gravity analyses to decipher its structure.

The decline in potable water sources due to climate change and pollution underscores the importance of monitoring potential water sources near major settlements for sustainable water management. Surface sediment quality serves as a key indicator of pollutants like heavy metals, which significantly affect environmental and human health. Effective watershed management requires identifying contamination sources and understanding the long-term ecological and health risks posed by these pollutants in sediment. This study examines heavy metal and metalloid (As) presence in surface sediments of the Goksu and Canakdere rivers, which are located within the same watershed and are potential water sources for Istanbul. A total of 24 sediment samples from both rivers, collected in dry and wet seasons, were analyzed for As, Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn. Sediment quality, human health risks (via hazard quotient (HQ) and hazard index (HI)), and pollution levels were assessed using ecological risk indices, including the geo-accumulation index, enrichment factor, and potential ecological risk index. Statistical analyses identified potential metal sources. Results showed high pollution, especially in agricultural areas, with average concentrations of As, Cu, Ni, and Pb in Goksu (16.90, 24.05, 18.72, and 27.96 mg/kg) and Canakdere (20.18, 30.02, 20.20, and 30.16 mg/kg). Surface runoff during the wet season intensified contamination. Ecological risk analyses confirmed severe pollution, and HQ and HI values indicate higher non-carcinogenic health risks for children. These findings highlight the need to prevent agricultural pollutants from contaminating the rivers and underscore the importance of monitoring sediment quality in watershed management.

The matrix inversion of seismic data for finite-fault source parameters is based on the formulation of the representation theorem as a linear inverse problem. The way the problem is parameterized involves substantial, and often subjective, decision-making. The inversion solution involves several levels of uncertainties and instabilities. In inversion solutions, the connection between model and data null spaces, solution uniqueness, and the ability to fit data is important. Therefore, these aspects are discussed in this research. We aim to reduce model space errors to arrive at more reliable and stable solutions. The Tikhonov method and the truncated singular value decomposition are used to explain the properties of rank-deficient and ill-conditioned linear inverse problems. The background of the essential trade-off between solution stability and data fitting. The 2004 M_w 6.1 Parkfield earthquake, a well-documented event, is chosen as our case study. The results show that the Tikhonov model with 0.15 m maximum slip and 5.8 moment magnitude produces the most stable model. By imposing a moment magnitude constraint on the Tikhonov solution, a maximum slip of 0.22 m is achieved.

This study presents a new way to predict bedforms in open-channel flows by analyzing 811 laboratory experiments. Previous methods by Van Rijn (J Hydraulic Eng 110:1431–1456, 1984), Engelund (J Fluid Mechan 42:225–244, 1970), Simons and Richardson (1966), and Kennedy (J Fluid Mechanics 16:521–544, 1963) had limited success, with prediction accuracies of 77%, 76%, 72%, and 70%, respectively. These methods struggled with transitional flow regimes and various channel shapes. To fix these problems, a new dimensionless parameter (Φ) is extracted, which combines the Froude number, Shields parameter, relative roughness, and channel aspect ratio. The analysis showed strong links, including 0.82 between the Froude number and Shields parameter (Fr > 0.8, τ* > 0.5). The Φ-method got better prediction rates: 92% for lower-regime plane beds, 89% for ripples, 87% for dunes, 84% for transitional forms, and up to 88% for upper-regime bedforms. It performed robustly across flow conditions, with 91% accuracy in low-flow, fine-sediment scenarios (d₅₀ < 0.2 mm) and 80% in high-flow, coarse-sediment conditions (d₅₀ > 0.5 mm). The method excelled in both subcritical (88%) and supercritical (84%) regimes, offering a reliable framework for predicting bedform transitions in alluvial channels, especially where traditional methods falter.

River systems like the Brahmaputra and its tributary Jia Bharali frequently shift course, making valley floors highly dynamic and flood-prone, posing recurring risks to agriculture, infrastructure, human lives, and habitats, and requiring careful monitoring and management each year. This study aims to assess the spatiotemporal morphological changes of the Jia Bharali–Brahmaputra River confluence from 1973 to 2023, focusing on channel dynamics and associated risks. Using multi-date Landsat imagery and GIS techniques, riverine parameters such as sinuosity index (SI), braid index (BI), fluvial corridor width (CW), and lateral channel shifting were quantified. Geoprocessing was done to identify unchanged areas and calculate river erosion and accretion. BI was derived through vectorization, CW from satellite-based spatial analysis, and shifting using the transect method. The SI showed a gradual increase from 1.18 in 1973 to 1.21 in 2023, indicating enhanced meandering of the river over five decades. Fluvial corridor width fluctuated from 2.54 km (1973) to 2.14 km (2023), with a peak of 3.17 km in 1978, showing frequent width fluctuations. The maximum lateral migration width recorded between 2003 and 2023 was 6.6 km, averaging 1.8 km, predominantly shifting toward the north bank. Geoprocessing revealed notable erosion and accretion patterns, with significant risk to nearby settlements. This study recommends building flood protection structures on the North Bank, away from the area where the river naturally curves and shifts over time, to reduce the risk of flooding and erosion. These findings highlight the need for strategically placed flood protection structures and offer practical insights for disaster mitigation, infrastructure planning, and sustainable river management.

The article presents horizontal-to-vertical (H/V) spectral ratios estimated for the rotated horizontal components of the registered signals. Estimations were performed for rotational and translational signals using waveforms from mining-induced seismic events. The amplification curves were estimated for each case of the axis rotation using the Fourier Spectrum Amplitude (FSA) and the Response Spectrum Analysis (RSA). Estimating the amplification spectrum for the rotated horizontal components is a method that allows determining the directional amplification effect, connected with the local anisotropy and fault occurrence. The Quaternary fault presence characterises the closest proximity of the station. Therefore, the surveys assumed analysis of the possibility and limitations of the directional amplification effect estimation by using records of rotational and translational motion as well as both approaches of the H/V estimation. The comparisons presented the limitation of the RSA approach in estimating the rotational H/V curve, which was an effect of the sensor settings on the pedestal. The directional amplification effect presented a perpendicular orientation to the close-distance fault, similar to rotational and translational motion analysis assuming the FSA approach.

Strong-motion recordings from the 2023 Türkiye earthquake doublets (the Pazarcık and Elbistan earthquakes) and the 2008 Wenchuan earthquake were used to reveal the characteristics of large shallow crustal earthquakes (e.g., the multi-segment rupture, source effects, and attenuation, duration, and velocity pulse of ground motions). A comparison of typical recordings showed that the multi-segment rupture could lead to multiple wave packets of acceleration waveforms at very near-field sites to the earthquake source. Ground motions at short periods observed in the Wenchuan earthquake were generally larger than those in the Türkiye earthquake doublets at mid- to far-field sites, while the intermediate-period amplitudes were similar, and the long-period amplitudes were smaller regardless of the distance. The analysis of within-event residuals indicated that, in contrast to the 2023 Türkiye earthquake region, the anelastic attenuation in the Wenchuan earthquake region was slower at short periods, similar at intermediate periods, and stronger at long periods. This study revealed that the different fault mechanisms and crustal structures could be two reasons for the period-dependent differences in amplitudes and attenuation of ground motions for large crustal earthquakes. The directivity effects and energy release process could explain the differences in ground motion durations. The pulse-like recordings in the Pazarcık earthquake are concentrated in Antakya city, exhibiting notably strong fling-step and forward-directivity effects. These near-fault effects, compounded by local site amplification and widespread structural vulnerabilities, likely contributed significantly to the severe damage observed in the region.

The direct current (DC) resistivity method is extensively employed in the investigation of challenging geological conditions. The inversion of resistivity model based on observed data represents a prevalent approach for geological interpretation. In recent years, significant strides have been made in this field through the application of deep learning techniques. Unsupervised learning methods that incorporate physics principles offer particular promise due to their independence from manual annotation. However, gradients derived from electric field propagation physics rules, often suffer from low quality and high computational complexity, thereby yielding suboptimal predictive results. In our study, we propose a gradient optimization approach for unsupervised deep learning (DL) inversion. Firstly, we perform multiple gradient calculations and aggregate them, thereby updating the resistivity model with the cumulative gradients to mitigate errors. Secondly, we introduce a novel method for rapidly solving sensitivity matrices by optimizing matrix computations and data storage, resulting in a significant enhancement in computational efficiency by several orders of magnitude. Finally, we validate the effectiveness of our gradient optimization approach through comprehensive experiments and field tests, accurately locating and depicting both boulder and karst zones.

Cementing is a critical operation in petroleum well drilling. It is important to have high-quality cement in the annulus to ensure casing protection and prevent fluid flow into the well. The cement quality in the annulus is often evaluated using the bonding index, derived from the cement bond log/variable density log (CBL/VDL) and the segmented bond tools log (SBT) logs. However, the reliability of these logs in assessing cement slurry quality remains uncertain due to influencing factors such as formation lithology. This study interprets SBT logs from eight wells. Log interpretation reveals that washouts are more frequent in sandstone formations than limestone, negatively impacting the bonding index between cement and casing. The aim of this paper is to investigate the reasons behind the weak bonding index. The hypothesis that sandstone cuttings contaminate cement, weakening the bond, was tested through experiments, including crush tests, ultrasonic cement analyzer (UCA), and CT scans. Three samples were prepared: pure cement, limestone-contaminated cement, and sandstone-contaminated cement. Surprisingly, sandstone-contaminated cement exhibited 523 psi higher compressive strength than limestone-contaminated samples. CT scans quantified impurity volumes, showing 14.6% for sandstone and 17.6% for limestone, correlating with stronger bonds in sandstone-contaminated cement. In contrast, UCA results indicated weaker bonding in sandstone samples, aligning with SBT log observations. UCA’s compressive strength results showed that ultrasonic waves encounter more difficulties in sandstone formations. These findings conclude that weak bonding indices through sandstone formations are more due to the sandstone’s nature, which affects ultrasonic and sonic waves, than the cement slurry quality.

Gujarat and adjacent regions, located along the western margin of the Indian plate, are among the most seismotectonically active areas in the Indian Peninsula and have experienced significant seismic events such as the 1819 Allah Bund (M_W 7.8) and the 2001 Kachchh (M_W 7.6) earthquakes. This study employed a maximum likelihood approach to quantitatively assess key earthquake hazard parameters in 15 identified seismogenic source zones. The targeted parameters are the maximum possible magnitude (m_max), seismic activity rate (λ), Gutenberg-Richter b-value, earthquake return periods, and probabilities of future seismic events. A unified, Poissonian and complete earthquake catalogue was compiled to facilitate this analysis from 1819 to 2021, with a magnitude range of M_W 2.0–7.8. The estimated maximum magnitudes (m_max) exhibited a range of M_W 4.61–8.25, with the lowest occurring in Zone 6 (northern Cambay rift) and the highest in Zone 1 (Allah Bund). The b-value range was found equal to 0.47–0.88, with the minimum value in Zone 7 (northern Mainland) and the maximum in Zone 3 (Gedi Fault) revealing a pronounced differential crustal stress regime. The range for the seismic activity rate (λ) for a threshold magnitude of M_W 3.6 was between 0.03 and 0.60 events per year, with the lowest rate in Zone 2 (northern Kachchh) and the highest in Zone 4 (the 2001 Kachchh earthquake). The shortest return periods are observed in zone 4 (e.g., 7.5 years for M_W 5.5 and 60 years for M_W 7.0) for a particular threshold magnitude, indicating a heightened frequency of substantial seismic events in this zone relative to that of other zones. The occurrence probabilities for different magnitudes over the next 20, 50, and 100 years indicate the highest likelihoods in Zone 4, with a 56% probability for a M_W 7.0 event within 50 years and 80% within 100 years. The combination of low return periods (< 50 years) and high probabilities of occurrence (> 75%) specified Zones 1 (Allah Bund), 4 (2001 Bhuj earthquake), and 12 (Rajkot-Paliyad) as the most hazardous areas in the study region. The spatial variability of the estimated earthquake hazard parameters elucidates the heterogeneous seismic hazard levels across various zones, providing essential insights for future seismic hazard assessments and developing risk mitigation strategies.