Results in Geophysical Sciences最新文献

This research emphasizes the significance of groundwater for human activities and the challenges of prospecting in complex basement terrain. The study suggests using the Audiomagnetotelluric (AMT) method to explore the subsurface conductivity structure as an indicator of potential groundwater resources. The AMT method, preferred for its deep penetration and sensitivity to resistivity changes, is analyzed using the Audiomagnetotelluric Data Management Tool (ADMT) software for data interpretation. The research demonstrates the effectiveness of AMT in mapping groundwater and characterizing geological materials up to a depth of 200 m.The analysis reveals distinct layers with varying resistivity values, primarily composed of Pegmatite and Migmatite gneiss. Pegmatite, with its lower resistivity, acts as a water-bearing zone when weathered, while Migmatite gneiss's higher resistivity suggests reliance on fracture zones within the bedrock for groundwater exploration. Shallow potential groundwater zones are identified at 10–30 m depth in certain profiles, while deeper zones are detected at 40 m and beyond across the study area. The prevailing aquifer systems are influenced by fractures and weathered zones. The saprock region, located between fresh bedrock and regolith at 40 m depth and above, is deemed most promising for drilling purposes. Overall, this study underscores the effectiveness of the Audiomagnetotelluric technique in delineating zones with high groundwater potential. The research concludes that combining the AMT method with ADMT software provides valuable tools for groundwater prospecting in complex basement terrain, offering detailed data on the subsurface resistivity structure and facilitating the identification of potential groundwater resources.

Qualitative interpretation of aeromagnetic maps involves the visual inspection and pattern analyses of produced maps to identify potential geological structures in the magnetic field by processing the dataset to characterize the Earth's magnetic variations and map subsurface geological structure which is important to tackle the challenges of resource management, environmental assessment and infrastructure design in the study area. This technique has been employed to a part of Abeokuta metropolis of Ogun state, Southwestern Nigeria, using high resolution aeromagnetic dataset acquired from the Nigerian Geological Survey Agency (NGSA). Pre-processing analyses such as data transformation, map re-projection and power spectrum plot were performed on the dataset to minimize noises and remove unwanted variations. The application of Reduction to Magnetic Equator (RTE) filter was to remove asymmetries in the data and position the peaks of magnetic anomalies over their sources while the Gaussian (low pass) filter was aimed at improving the signal-to-noise ratio. Low magnetic zones indicated by blue colours from the total magnetic fields possibly reveal the sedimentary intrusions into the area, intermediate magnetic regions having green, yellow and red colourations suggest transition zones and the Northeastern portion of the maps indicated with pink colours correlate to the core basement regions. Derivative filters are applied as enhancement techniques to accentuate the inferred linear subsurface structures interpreted as cracks, fractures, lineaments, etc. These structures are predicted mineral entrapments or fault lines whose NE-SW orientation conforms to the Pan African Orogeny and they can aid environmental assessments generally.

This research paper explores the effective utilization of 2-D Resistivity and Induced Polarization (IP) techniques for identifying sulfide deposits in complex geological settings. To enhance the accuracy of the findings, the geophysical data were complemented with geological information, petrophysical data, Digital Elevation Model (DEM), and Electromagnetic data Versatile Time Domain Electro-Magnetics (VTEM) and Total Magnetic Intensity (TMI) Reduced-To-Pole (RTP).

The analysis of DEM, magnetic susceptibility, and magnetic intensity revealed a lack of correlation with the DEM, indicating that these parameters alone were insufficient to confirm the presence of sulfide deposits. Consequently, five regions exhibiting high to moderate conductivity were chosen for conducting six survey lines using the Wenner array with a 10 m electrode spacing. The objective was to map sulfide zones in Restigouche County, located in northeast New Brunswick.

Geophysical measurements were acquired using a RESECS instrument, and the field data were processed using the Res2Dinv software after removing erroneous data points. Since the study area was characterized by thick overburdened glacial sediments and lacked surface exposure, information from numerous boreholes and core samples from the western part of the study area were utilized.

The study achieved successful mapping of the shallow alteration zone containing pyrite mineralization in most of the survey lines. Specifically, resistivity responses below 50 Ω⋅m, coupled with high chargeability, likely corresponded to the alteration zone containing pyrite. Additionally, resistivity responses above 50 Ω⋅m, combined with chargeability and RTP readings, were indicative of the alteration zone with pyrite.

Negative abnormal changes of atmospheric electric field have been monitored many times before large earthquakes. However, its mechanism has not yet been clearly concluded. Based on the comparative analysis of the positive anomaly characteristics of atmospheric electric field before lightning and geoelectric field before earthquakes in earthquake areas, this paper concludes that the negative anomalies of atmospheric electric field before earthquakes are caused by the rise of the geoelectric potential in the ground in earthquake areas. Thus the areas with an abnormal rise of the geoelectric potential are potential earthquake areas. Based on the inference above, an earthquake early warning method under ideal conditions is proposed with station network layout of geoelectric field instruments in combination with the atmospheric electric field data monitored by Electric Field Mills (EFMs).

This study uses deconvolution of earthquakes registered at the SMNH01 station of KiK-net, which is located in Japan, to identify the presence of: (a) anisotropic layers and (b) waves which could have been induced by motion of fluid, crack propagation and local fault activation. The SMNH01 station has a borehole which is equipped with triaxial accelerometers installed at surface and at 100 m of depth. By deconvolving seismic events registered at surface and at 100 m of depth, anisotropic layers are identified. To interpret interferograms, the following tools are utilized: (a) a one dimensional (1D) isotropic layered medium, (b) empirical mode decomposition and (c) an orthorhombic model. From the empirical mode decomposition, genuine resonances or tremors are identified along directions that are subparallel to the horizontal stress orientations that seem to bisect an effective orthogonal-conjugate fracture set. The strong changes in the amplitude of the main descending deconvolved wave could be mainly due to the combined influence of: motion of fluids through fractures on the spatial scale of meters, recurrent seismic events, evolving anisotropy, dilation and temperature variations. This wave travels from the surface of the earth to the receiver located at 100 m of depth. The detected anisotropy could be associated with the presence of layers constituted by naturally fractured basalt, which are situated beneath the soil. Such anisotropic layers could have orthorhombic symmetry or lower. This study has implications in the exploration and production of natural resources.

The Pirmam and Bana Bawi anticlines are two elongated anticlines located in the central northern part of the Kurdistan Region of north Iraq (KRI), in the northeastern part of the Arabian Plate. We have used satellite images and geological maps to interpret the presented data and to calculate the rates of uplift and down wards (subsidence) amounts, besides estimating the rates of deposition and incision of some alluvial fans and stream terraces. Most of the achieved data were checked in the field. In the Pirmam anticline the rate of the uplift and subsidence is 8.613 mm/ 100 year and 7.962 mm/ 100 year, respectively, whereas in the Bana Bawi anticline the rates are 3.036 mm/ 100 year and 4.365 mm/100 year, respectively. The indications of the lateral growth are the presence of water gaps, wind gaps, en-echelon plunging, whale-back shape and different types of valleys. We have calculated the depositional and incision rates in the Kori and Bastoora streams. They are 5.204 mm/ 100 year and 5.555 mm/ 100 year, respectively in the former, whereas in the latter are 3.469 mm/100 year and 8.731 mm/ 100 year, respectively. Moreover, we have calculated the depositional and incision rates in old and recent alluvial fans. In the former, they are 1.665 mm/ 100 year and 0.722 mm/ 100 year, respectively, whereas in the latter are 3.036 and 4.365 mm/ 100 years, respectively.

The analytical signal method and its derivatives can be explicitly calculated and assessed for analyzing and estimating the boundary of geological structures, such as faults or dikes, from potential field anomalies. Gravity field of the east of Qeshm Island and its north coast from Sarkhun to Latidan in SE Iran has been measured in one-kilometer regular network. The regional anomaly effects are deducted from the Bouguer anomaly, where it can get the residual anomalies which is the considered dataset used in this study. The Bouguer range is -297 to -330 milligals (mGal) applying filters and modeling. It was revealed that there are five negative anomalies caused by salt penetration in the region. Regional anomalies expectedly have a low spatial frequency and long wavelengths, while the residual anomalies associated with shallow sub-surface potentials have high spatial frequencies and short-wave wavelengths.Two different fault trends were observed comparing the artificial model using MATLAB coding, the real one, and the filtered residual anomaly map of the Qeshm region. Also, another fault trend is suggested in the east height of Oman, which is a possible place of salt penetration. Due to the limited dimensions (120 * 100 km) and the information obtained from the existing drillings, the depth of the anomaly resources can be examined up to 8 km. Due to the gravitational condition between the two domes of Qeshm saline and the bridge located in the Hara saline area, it is suggested to be considered as an area for further oil exploration routines.

Relatively cheap and non-intrusive magnetic geophysical technique has been employed to reduce the hydrocarbon exploration uncertainty in the Middle Benue Basin which straddles the northeastern and southeastern parts of Nigeria. Various derivatives and magnetic attributes extracted from the filtered, transformed and enhanced aeromagnetic data of the basin highlighted valuable information employed to appraise the hydrocarbon generating and preservation potentials of the basin, thus delineating the prospective regions where further search light of expensive and intrusive geophysical exploration tools could be focused. The trough delineated from the analyzed aeromagnetic data comprised of a massive 350 km NE-SW trending fan shaped sedimentary body bounded to the northwest and southeast by Basement Complex rocks. Active structural framework with dominant NE-SW fault systems which appeared to be the landward extension of the Chain and Charcot offshore fractures characterize the basement rocks that underlay the sediments. Sedimentary thickness of up to 3.68 km in some parts of the basin obtained from depth weighting analyses, indicate the possibility of hydrocarbon generation through the maturation of organic matter from available source rock(s). Analytic signal grids confirmed the occurrence of already documented volcanic intrusions in addition to newly delineated ones. These volcanics which are often renowned for compromising the hydrocarbon potential of a sedimentary basin are widespread in the western and southern parts the basin. Combination of adequately thick sedimentary units which overly structurally active basement rocks in regions of limited (very few/non) occurrence of volcanic intrusions delineate the north central region for further petroleum exploration prospect evaluation.

Enhanced hydrocarbon recovery processes coupled with CO₂ storage are, by far, the cheapest carbon capture and storage (CCS) options in geological structures. However, reservoirs are also being explored for CO₂ storage in regions without producing/depleted hydrocarbon reservoirs, such as the Irati and Rio Bonito Formations in the southwestern part of São Paulo. Therefore, the study involves petrophysics-based flow unit factors to predict the reservoirs’ quality, primarily focusing on hydrocarbon viability with CO₂ storage possibilities based on the shale, carbonate, sandstone and siltstone rock units. The methodology involving the models for the research objective is uncommon for the Irati and Rio Bonito Formations. The porosity range is 0.02 to 0.15 in shales, 0.028 to 0.18 in siltstones, 0.03 to 0.21 in carbonates, and 0.10 to 0.31 in sandstones based on the sonic-density porosity (Ф_S-D) approach. Permeability (k) is 0.00005mD to 36.6mD in shales, 0.0008mD to 132mD in siltstones, 0.025mD to 786mD in carbonates and 8mD to 10000mD in sandstones. The results show more significant fluid transmission indices for the sandstone based on Ф, k, free fluid index-FFI, reservoir quality index-RQI, and flow zone indicator-FZI. Also, the parameters are considerably significant for carbonates in some instances, less effective for siltstone and comparatively insignificant for shale. However, shales` total organic content (TOC) values are up to 10.5%, suggesting their hydrocarbon generation potentials. Significant values (e.g., Ф ≥25% and FFI ≥20%) in sandstones indicate reservoirs with the potential for hydrocarbon accumulation. Considerable physical qualities, as presented for the sandstone, suggest reservoir rock units with reasonable fluid (e.g., gas) recovery and CO₂ injection rates. Therefore, based on the research results, the Irati Formation shales are viable hydrocarbon source rocks, and the Rio Bonito Formation sandstones are potential hydrocarbon reservoirs. Subsequently, future hydrocarbon production events will enhance CO₂ storage options in the region. Furthermore, the research results may serve as input data in related hydrocarbon exploration studies. However, if further research indicates non-commercially viable hydrocarbon reserves, the findings will also aid in delineating dedicated geological reservoirs for CO₂ storage when needed.

We estimated a long-term velocity field for Mount Etna volcano by taking into account a dense GNSS dataset collected during the 2004.42 - 2018.95 period. To properly isolate the volcanic deformation from the background tectonic one, we defined a new local reference frame (termed MERF23) by using 32 stations mainly located in north-western and south-eastern Sicily. The computed long-term velocity field well highlights contrasting patterns between the north-western flank and the eastern one. The north-western flank was characterized by a general radial pattern with small deformations, mainly related to inflation and deflation episodes occurred during the investigated period. The eastern flank was characterized by a vigorous seaward motion, with rates ranging from ∼60 mm/yr on the Pernicana fault (northern boundary) to ∼29 mm/yr along the Aci Trezza fault (southern boundary), clearly evidencing as flank instability remains by far the predominant type of deformation at Mount Etna. A small contraction along the peripheral base of the volcano, coupled with a small uplift has been also detected; both patterns lend credit to the concurrent action of different processes as local and regional tectonics as well as long-term magmatic doming.