Pub Date : 2022-01-09DOI: 10.1080/20909977.2021.2021001
Mostafa A. Teama, Mohamed A. Kassab, Moataz M. Gomaa, Abdelrahman B. Moussa
ABSTRACT Rock strength is an essential and effective property in the rock drilling, excavation, and cost evaluation. This work aims to examine a practical approach to evaluate the geomechanical properties that control rock drillability, such as uniaxial compressive strength (UCS) by utilising some petrophysical parameters (porosity and bulk density) and elastic properties (Young’s modulus, bulk modulus, and slowness). To achieve this aim, the study was conducted on some Jurassic rock samples that were cored from different localities in Gebel El-Maghara, North Sinai, Egypt. The uniaxial compressive strength (UCS) was calculated from the measured porosity of 28 sandstone and 89 carbonate plug samples. Empirical equations that relate the uniaxial compressive strength of sandstone and carbonate rocks to physical properties and elastic properties are represented. The physical and elastic parameters that were measured from logging data (sonic, density, neutron, and gamma-ray logs) can be utilised in other future studies to predict the strength of the rock by using these empirical equations that were inferred in this study. The comparison between the relationships of calculated results of UCS in this study with the relationships of laboratory rock strength of different types of sedimentary rocks collected from different places around the worldfrom the previous studies shows high compatibility. The estimated equations from regression analysis of sandstone are more recommended than carbonate.
{"title":"The assessment of rock drillability from elastic and petrophysical parameters","authors":"Mostafa A. Teama, Mohamed A. Kassab, Moataz M. Gomaa, Abdelrahman B. Moussa","doi":"10.1080/20909977.2021.2021001","DOIUrl":"https://doi.org/10.1080/20909977.2021.2021001","url":null,"abstract":"ABSTRACT Rock strength is an essential and effective property in the rock drilling, excavation, and cost evaluation. This work aims to examine a practical approach to evaluate the geomechanical properties that control rock drillability, such as uniaxial compressive strength (UCS) by utilising some petrophysical parameters (porosity and bulk density) and elastic properties (Young’s modulus, bulk modulus, and slowness). To achieve this aim, the study was conducted on some Jurassic rock samples that were cored from different localities in Gebel El-Maghara, North Sinai, Egypt. The uniaxial compressive strength (UCS) was calculated from the measured porosity of 28 sandstone and 89 carbonate plug samples. Empirical equations that relate the uniaxial compressive strength of sandstone and carbonate rocks to physical properties and elastic properties are represented. The physical and elastic parameters that were measured from logging data (sonic, density, neutron, and gamma-ray logs) can be utilised in other future studies to predict the strength of the rock by using these empirical equations that were inferred in this study. The comparison between the relationships of calculated results of UCS in this study with the relationships of laboratory rock strength of different types of sedimentary rocks collected from different places around the worldfrom the previous studies shows high compatibility. The estimated equations from regression analysis of sandstone are more recommended than carbonate.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"1 1","pages":"48 - 57"},"PeriodicalIF":0.0,"publicationDate":"2022-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88275111","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-09DOI: 10.1080/20909977.2021.2020999
M. Olorunfemi, A. G. Oni, T. K. Fadare
ABSTRACT We utilised resisto-thermal effect of iron smelting to precisely locate concealed furnaces and slag trenches at an ancient iron smelting site situated within the estate of Obafemi Awolowo University, Ile-Ife, Southwest Nigeria. The methodology involved closely spaced, small electrode spacing (micro) Vertical Electrical Soundings across diagnostic dipolar magnetic anomaly closures. Both the furnace and the slag trench sites were characterised by thermal induced enhanced layer resistivity values and anomalously high depth extent of an index (second) resisto-archaeological geoelectric layer with higher influence beneath the furnace than the slag trench. The results showed that the location of the furnace is shifted from the centre of the magnetic low (negative), sometimes overlapping the transition zone towards the magnetic high (positive) while the slag trench is generally situated within the magnetic high zone. Preliminary archaeological excavation at one of the investigated sites (site 1) identified a furnace and the adjoining slag trench structures at the precise locations predicted from the geoelectric section. The study concluded that thermal-induced resistivity attribute is effective in precisely locating concealed ancient iron smelting furnace and slag trench structures.
{"title":"Geoelectric characterisation of furnace and slag trench structures: Case study Obafemi Awolowo University ancient iron smelting site, Ile-Ife, southwest Nigeria","authors":"M. Olorunfemi, A. G. Oni, T. K. Fadare","doi":"10.1080/20909977.2021.2020999","DOIUrl":"https://doi.org/10.1080/20909977.2021.2020999","url":null,"abstract":"ABSTRACT We utilised resisto-thermal effect of iron smelting to precisely locate concealed furnaces and slag trenches at an ancient iron smelting site situated within the estate of Obafemi Awolowo University, Ile-Ife, Southwest Nigeria. The methodology involved closely spaced, small electrode spacing (micro) Vertical Electrical Soundings across diagnostic dipolar magnetic anomaly closures. Both the furnace and the slag trench sites were characterised by thermal induced enhanced layer resistivity values and anomalously high depth extent of an index (second) resisto-archaeological geoelectric layer with higher influence beneath the furnace than the slag trench. The results showed that the location of the furnace is shifted from the centre of the magnetic low (negative), sometimes overlapping the transition zone towards the magnetic high (positive) while the slag trench is generally situated within the magnetic high zone. Preliminary archaeological excavation at one of the investigated sites (site 1) identified a furnace and the adjoining slag trench structures at the precise locations predicted from the geoelectric section. The study concluded that thermal-induced resistivity attribute is effective in precisely locating concealed ancient iron smelting furnace and slag trench structures.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"18 1","pages":"1 - 20"},"PeriodicalIF":0.0,"publicationDate":"2022-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84430395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-24DOI: 10.1080/20909977.2021.2005335
Adrija Banerjee, Amaresh Bej, T. N. Chatterjee, A. Majumdar
ABSTRACT Magnetosphere-ionosphere energy transfer and AE fluctuations are studied using a cellular automata model of terrestrial magnetosphere based on the concept of self-organised criticality (SOC). The model is a SOC-driven dissipative dynamical system with both spatial and temporal degrees of freedom. The input parameter to this model is derived from the real-time values of solar wind ion density and flow speed data. Both the direction and intensity of the real-time values of the BZ component of the interplanetary magnetic field (IMF) are the factors controlling the energy injection into the system. The model produces an output series which can be regarded as a mathematical representation of the AE index. The spectral response of the simulated output follows a 1/fβ power law, demonstrates a breakpoint at f0 = 0.050 mHz (5.5 hours) having slopes βA = 2.2–2.4 for f > f0 and βB = 0.9–1.0 for f < f0, the typical characteristics of the natural AE index. The entire 23rd solar cycle had been studied using the model. The parameter KA plays a significant role in the entire process. KA represents the remaining percentage of the released energy from the previous magnetosphere-ionosphere energy transfer, stored in the ionosphere.
{"title":"A SOC based avalanche model to study the magnetosphere-ionosphere energy transfer and AE index fluctuations","authors":"Adrija Banerjee, Amaresh Bej, T. N. Chatterjee, A. Majumdar","doi":"10.1080/20909977.2021.2005335","DOIUrl":"https://doi.org/10.1080/20909977.2021.2005335","url":null,"abstract":"ABSTRACT Magnetosphere-ionosphere energy transfer and AE fluctuations are studied using a cellular automata model of terrestrial magnetosphere based on the concept of self-organised criticality (SOC). The model is a SOC-driven dissipative dynamical system with both spatial and temporal degrees of freedom. The input parameter to this model is derived from the real-time values of solar wind ion density and flow speed data. Both the direction and intensity of the real-time values of the BZ component of the interplanetary magnetic field (IMF) are the factors controlling the energy injection into the system. The model produces an output series which can be regarded as a mathematical representation of the AE index. The spectral response of the simulated output follows a 1/fβ power law, demonstrates a breakpoint at f0 = 0.050 mHz (5.5 hours) having slopes βA = 2.2–2.4 for f > f0 and βB = 0.9–1.0 for f < f0, the typical characteristics of the natural AE index. The entire 23rd solar cycle had been studied using the model. The parameter KA plays a significant role in the entire process. KA represents the remaining percentage of the released energy from the previous magnetosphere-ionosphere energy transfer, stored in the ionosphere.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"30 1","pages":"33 - 47"},"PeriodicalIF":0.0,"publicationDate":"2021-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87540732","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-24DOI: 10.1080/20909977.2021.2005334
A. Awad, Esmat Abd El-Aal, Ahmed Amin Khashaba
ABSTRACT Several exposures of basaltic intrusions are distributed near Red Sea coast at Wadi Hodein Southern Egypt. There is some disagreement about the palaeomagnetic pole results of these basalts; some claim it is Tertiary in age, while others claim it is of Cretaceous age. To our knowledge, no Anisotropy of Magnetic Susceptibility (AMS) results have ever been published from these rocks. Therefore, palaeomagnetic and AMS studies were performed on these basalts in order to identify phases of magmatism, paleomagnetic pole position and types of magmatic intrusions. In the present study, eight sites (219 oriented core specimens) were sampled from eight location. Rock magnetic studies reflect the presence of magnetite as the chief mineral in these rocks. Alternating field technique in association with Thermal Demagnetisation process revealed presence of one magmatic phase took place in Cretaceous age with VGP (65°N, 250°E; A 95 = 5.3). AMS results showed that the basaltic intrusions in the study area are still holding their primary fabrics.
{"title":"Phases of Magmatic Activities in South Wadi Hodein-Shalatein, Egypt: Resolving controversy about their age using Paleomagnetism and AMS","authors":"A. Awad, Esmat Abd El-Aal, Ahmed Amin Khashaba","doi":"10.1080/20909977.2021.2005334","DOIUrl":"https://doi.org/10.1080/20909977.2021.2005334","url":null,"abstract":"ABSTRACT Several exposures of basaltic intrusions are distributed near Red Sea coast at Wadi Hodein Southern Egypt. There is some disagreement about the palaeomagnetic pole results of these basalts; some claim it is Tertiary in age, while others claim it is of Cretaceous age. To our knowledge, no Anisotropy of Magnetic Susceptibility (AMS) results have ever been published from these rocks. Therefore, palaeomagnetic and AMS studies were performed on these basalts in order to identify phases of magmatism, paleomagnetic pole position and types of magmatic intrusions. In the present study, eight sites (219 oriented core specimens) were sampled from eight location. Rock magnetic studies reflect the presence of magnetite as the chief mineral in these rocks. Alternating field technique in association with Thermal Demagnetisation process revealed presence of one magmatic phase took place in Cretaceous age with VGP (65°N, 250°E; A 95 = 5.3). AMS results showed that the basaltic intrusions in the study area are still holding their primary fabrics.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"34 1","pages":"21 - 32"},"PeriodicalIF":0.0,"publicationDate":"2021-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89823651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-07-28DOI: 10.1080/20909977.2022.2037817
W. Badawy, A. Tadross, Y. Hendy, I. A. Hassan, M. N. Ismail, A. Mouner
ABSTRACT The study of open star clusters makes us understand a lot about the composition and construction of the Milky Way Galaxy. Thanks to the Gaia DR2 database that helps us to get the genetic members of star clusters using their proper motions and parallaxes, and estimating their physical properties in a very accurate way. This study aims to detect the reasons that make clusters (within 2 kpc) have proper motions completely separated from the background field stars. We studied a large sample of open stellar clusters taken from Dias’s catalogue and drew the vector point diagrams using the astrometric data of Gaia DR2. By visual inspection, we specified 108 objects as separated clusters and 377 ones as melted clusters. We studied their mean parameters in the four galactic quadrants of the Milky Way Galaxy.
{"title":"Open clusters with proper motions fully separatedfrom the field stars using Gaia DR2","authors":"W. Badawy, A. Tadross, Y. Hendy, I. A. Hassan, M. N. Ismail, A. Mouner","doi":"10.1080/20909977.2022.2037817","DOIUrl":"https://doi.org/10.1080/20909977.2022.2037817","url":null,"abstract":"ABSTRACT The study of open star clusters makes us understand a lot about the composition and construction of the Milky Way Galaxy. Thanks to the Gaia DR2 database that helps us to get the genetic members of star clusters using their proper motions and parallaxes, and estimating their physical properties in a very accurate way. This study aims to detect the reasons that make clusters (within 2 kpc) have proper motions completely separated from the background field stars. We studied a large sample of open stellar clusters taken from Dias’s catalogue and drew the vector point diagrams using the astrometric data of Gaia DR2. By visual inspection, we specified 108 objects as separated clusters and 377 ones as melted clusters. We studied their mean parameters in the four galactic quadrants of the Milky Way Galaxy.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"152 1","pages":"142 - 146"},"PeriodicalIF":0.0,"publicationDate":"2021-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75294813","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1080/20909977.2021.1940742
A. Radwan, M. Magdy, M. Rabah, A. Saber, A. Zaki
ABSTRACT The current study focuses on the analysis of observed sea level in the northern delta coast, which is considered the most important region in Egypt. The used sea-level data are records of three tide gauge stations located on the north of the delta, on Alexandria, Damietta, and Port Said. Different periods of sea-level records had been used to be analyzed to get the astronomical tide and surge heights. Geotide software had been used to obtain the tidal harmonic constituents. The tidal cycle sort at the three locations of the tide gauges had been calculated and the results were as follows: a mixed semidiurnal tidal type in Alexandria and Damietta, and a semidiurnal tidal type in Port Said. The Mean Sea Level (MSL), referred to the Egyptian Survey Authority datum (ESA-1906), had been calculated, and the tidal datums of each station referred to the International Terrestrial Reference Frame (ITRF-2014) had been calculated else. Ten groups of tidal constituents had been obtained and two of them have the largest amplitudes and they are M2 (Principal lunar), S2 (Principal solar). The amplitudes and percentages of astronomical tide and surge, in the observed sea level data, will be shown in the results section.
{"title":"Sea level analysis using tide gauge observations at the northern delta coast, Egypt","authors":"A. Radwan, M. Magdy, M. Rabah, A. Saber, A. Zaki","doi":"10.1080/20909977.2021.1940742","DOIUrl":"https://doi.org/10.1080/20909977.2021.1940742","url":null,"abstract":"ABSTRACT The current study focuses on the analysis of observed sea level in the northern delta coast, which is considered the most important region in Egypt. The used sea-level data are records of three tide gauge stations located on the north of the delta, on Alexandria, Damietta, and Port Said. Different periods of sea-level records had been used to be analyzed to get the astronomical tide and surge heights. Geotide software had been used to obtain the tidal harmonic constituents. The tidal cycle sort at the three locations of the tide gauges had been calculated and the results were as follows: a mixed semidiurnal tidal type in Alexandria and Damietta, and a semidiurnal tidal type in Port Said. The Mean Sea Level (MSL), referred to the Egyptian Survey Authority datum (ESA-1906), had been calculated, and the tidal datums of each station referred to the International Terrestrial Reference Frame (ITRF-2014) had been calculated else. Ten groups of tidal constituents had been obtained and two of them have the largest amplitudes and they are M2 (Principal lunar), S2 (Principal solar). The amplitudes and percentages of astronomical tide and surge, in the observed sea level data, will be shown in the results section.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"34 1","pages":"361 - 371"},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78249243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1080/20909977.2021.1927427
C.C. Uwaezuoke, K.S. Ishola, E. A. Ayolabi
ABSTRACT Electrical resistivity imaging (ERI) and Multichannel Analysis of Surface Waves (MASW) surveys were carried out over a reclaimed wetland area of University of Lagos, Nigeria. The main purpose of the geophysical surveys was to characterise the site for better understanding of the subsurface conditions before building construction is carried out. For this purpose, seven traverses were established for electrical resistivity and surface waves measurements. The PASI resistivity metre was used for the ERI surveys with minimum electrode spacing of 5 m using the Wenner array. The MASW measurements were carried out using Terraloc seismograph with 24 channel 4.5 Hz vertical component geophones. The results of the ERI surveys show that the subsurface strata are composed of peat/organic materials with resistivity values of (0.7– 3) Ω-m, silty clay having resistivity values of (5– 50) Ω-m and sandy clay sediments of resistivity between (51– 105) Ω-m, all were mapped at different depths. Also, the shear wave velocity models from MASW measurements show that three zones were clearly mapped. These zones are the low shear strength strata of peat/organic materials with Vs between (25– 70) m/s, silty clay with Vs ranges between (70– 120) m/s and sandy clay of Vs ranging from (120– 150) m/s. The combined approach has helped to better define the interface between layers, their thicknesses and consistency of each stratum. Thus, moderate to very strong correlations between the measured resistivity and velocity and the boreholes drilled were achieved. The regression models obtained compared reasonably well for all the traverses. The engineering implication of the geological units mapped is that the site is characterised with weak/incompetent materials not suitable for hosting the foundation of especially massive engineering structures. Hence, deep foundation through pilling to the competent layer is to be giving consideration or soils improvement techniques can be employed for the stabilisation of the soils.
{"title":"Electrical resistivity imaging and multichannel analysis of surface waves for mapping the subsurface of a Wetland Area of Lagos, Nigeria","authors":"C.C. Uwaezuoke, K.S. Ishola, E. A. Ayolabi","doi":"10.1080/20909977.2021.1927427","DOIUrl":"https://doi.org/10.1080/20909977.2021.1927427","url":null,"abstract":"ABSTRACT Electrical resistivity imaging (ERI) and Multichannel Analysis of Surface Waves (MASW) surveys were carried out over a reclaimed wetland area of University of Lagos, Nigeria. The main purpose of the geophysical surveys was to characterise the site for better understanding of the subsurface conditions before building construction is carried out. For this purpose, seven traverses were established for electrical resistivity and surface waves measurements. The PASI resistivity metre was used for the ERI surveys with minimum electrode spacing of 5 m using the Wenner array. The MASW measurements were carried out using Terraloc seismograph with 24 channel 4.5 Hz vertical component geophones. The results of the ERI surveys show that the subsurface strata are composed of peat/organic materials with resistivity values of (0.7– 3) Ω-m, silty clay having resistivity values of (5– 50) Ω-m and sandy clay sediments of resistivity between (51– 105) Ω-m, all were mapped at different depths. Also, the shear wave velocity models from MASW measurements show that three zones were clearly mapped. These zones are the low shear strength strata of peat/organic materials with Vs between (25– 70) m/s, silty clay with Vs ranges between (70– 120) m/s and sandy clay of Vs ranging from (120– 150) m/s. The combined approach has helped to better define the interface between layers, their thicknesses and consistency of each stratum. Thus, moderate to very strong correlations between the measured resistivity and velocity and the boreholes drilled were achieved. The regression models obtained compared reasonably well for all the traverses. The engineering implication of the geological units mapped is that the site is characterised with weak/incompetent materials not suitable for hosting the foundation of especially massive engineering structures. Hence, deep foundation through pilling to the competent layer is to be giving consideration or soils improvement techniques can be employed for the stabilisation of the soils.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"18 1","pages":"300 - 319"},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81889153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1080/20909977.2021.1902111
M. Olorunfemi, A. G. Oni, T. K. Fadare, O. Bamidele
ABSTRACT This paper presents results of previous investigations involving 1D and 2D resistivity imaging of linear geological structures with varying traverse orientations relative to the structure azimuth with a view to determining the effect of such variation on the resolution of the structures. It observed that the orientation of 2D traverse relative to a fault azimuth significantly determines the resolution of the structure while the alignment of 1D vertical electrical sounding (VES) relative to the structure azimuth defines the form of the VES curve and leads to inconsistency in resistivity and thickness estimates and overall depth estimates at deep depth. 2D structures were best resolved with 2D resistivity images when the traverses were established normal (in-line) to the structure azimuth. Structures delineated by in-line 2D images are corroborated by in-line VES interpretation models and confirmed by drillers’ logs, whereas the resolution of such structure is impaired on parallel (cross-line) 2D resistivity images/maps with distorted and disjointed image of the investigated fault at deep depth. For two orthogonal VES alignments (in-line and cross-line) to the azimuth of an investigated fault, deviations in layer resistivity values were generally ˂17% while thickness/depth estimates deviated by as much as 30–78%, at deep depth.
{"title":"Linear geological structure, traverse orientation and structure resolution and characterisation using 1D and 2D resistivity images","authors":"M. Olorunfemi, A. G. Oni, T. K. Fadare, O. Bamidele","doi":"10.1080/20909977.2021.1902111","DOIUrl":"https://doi.org/10.1080/20909977.2021.1902111","url":null,"abstract":"ABSTRACT This paper presents results of previous investigations involving 1D and 2D resistivity imaging of linear geological structures with varying traverse orientations relative to the structure azimuth with a view to determining the effect of such variation on the resolution of the structures. It observed that the orientation of 2D traverse relative to a fault azimuth significantly determines the resolution of the structure while the alignment of 1D vertical electrical sounding (VES) relative to the structure azimuth defines the form of the VES curve and leads to inconsistency in resistivity and thickness estimates and overall depth estimates at deep depth. 2D structures were best resolved with 2D resistivity images when the traverses were established normal (in-line) to the structure azimuth. Structures delineated by in-line 2D images are corroborated by in-line VES interpretation models and confirmed by drillers’ logs, whereas the resolution of such structure is impaired on parallel (cross-line) 2D resistivity images/maps with distorted and disjointed image of the investigated fault at deep depth. For two orthogonal VES alignments (in-line and cross-line) to the azimuth of an investigated fault, deviations in layer resistivity values were generally ˂17% while thickness/depth estimates deviated by as much as 30–78%, at deep depth.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"54 1","pages":"168 - 182"},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85689007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1080/20909977.2021.1979889
G. El-Qady, H. Shaaban, M. Abdel Zaher, M. Atya
ABSTRACT The determination of groundwater potentiality is one of the most significant challenges in hydro-geophysical research, especially in arid areas with limited water resources. A geophysical survey was carried out in the northwest of El-Minya Governorate to investigate the groundwater aquifer. A total of 20 controlled source audio-magnetotelluric (CSAMT) and 20 time domain electromagnetic soundings (TEM) were surveyed along two parallel profiles with station spacing varying between 500 and 2000 m. The CSAMT data was acquired using a hybrid source of low frequency band (0.1 Hz – 1 KHz) and standard high frequency band (10 Hz- 100 KHz). For the TEM survey, a coincident loop of side length of 50 m was used. The results of the integrated interpretation of both data sets (TEM and CSAMT) show a good consistency in the conductivity distribution. However, inspection of the results of the cross section indicates that two to three geoelectrical layers can be recognised in the subsurface medium. The area’s water potentiality is divided into two levels: the first begins immediately beneath the rock cap at depths of over 50 m and reaches nearly 200 m in some spots. The second level begins at a depth of 250 m and continues to a depth of 500 m.
{"title":"Integrated electromagnetic survey for groundwater exploration: case study at El-Minya, western desert of Egypt","authors":"G. El-Qady, H. Shaaban, M. Abdel Zaher, M. Atya","doi":"10.1080/20909977.2021.1979889","DOIUrl":"https://doi.org/10.1080/20909977.2021.1979889","url":null,"abstract":"ABSTRACT The determination of groundwater potentiality is one of the most significant challenges in hydro-geophysical research, especially in arid areas with limited water resources. A geophysical survey was carried out in the northwest of El-Minya Governorate to investigate the groundwater aquifer. A total of 20 controlled source audio-magnetotelluric (CSAMT) and 20 time domain electromagnetic soundings (TEM) were surveyed along two parallel profiles with station spacing varying between 500 and 2000 m. The CSAMT data was acquired using a hybrid source of low frequency band (0.1 Hz – 1 KHz) and standard high frequency band (10 Hz- 100 KHz). For the TEM survey, a coincident loop of side length of 50 m was used. The results of the integrated interpretation of both data sets (TEM and CSAMT) show a good consistency in the conductivity distribution. However, inspection of the results of the cross section indicates that two to three geoelectrical layers can be recognised in the subsurface medium. The area’s water potentiality is divided into two levels: the first begins immediately beneath the rock cap at depths of over 50 m and reaches nearly 200 m in some spots. The second level begins at a depth of 250 m and continues to a depth of 500 m.","PeriodicalId":100964,"journal":{"name":"NRIAG Journal of Astronomy and Geophysics","volume":"27 1","pages":"387 - 396"},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84100670","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1080/20909977.2021.1880817
Okoro E. Martins, Onuoha K. Mosto, Oha A. Ifeanyi
ABSTRACT Significant yet untapped resources still abound in the Nigerian sector of the Dahomey Basin. Although the presence of an extensive Cretaceous Petroleum System has been confirmed following recent discoveries in Aje and Ogo Fields offshore Lagos, exploration outputs in the Dahomey Basin has so far not been encouraging. Proper understanding of the basement architectural framework and controls on tectonic development remains key to unlock the unrealised potentials in the basin. Hence, a geophysical interpretation of the basement structure and architecture of the Dahomey Basin southwestern Nigeria has been carried out in this study. Various edge enhancement techniques were applied to the high-resolution residual magnetic intensity (HRRMI) grid of the area. This includes first vertical derivative (FVD), total horizontal derivative (THDR), tilt derivative (TDR) and total horizontal derivative of upward continuation (10 km). Determination of the depth to magnetic sources and sedimentary thicknesses in the study area were achieved using standard Euler deconvolution and source parameter imaging (SPI) techniques, with depth range of 4.5–6.3 km attained in the two identified sub-basins located offshore of the study area. Lineament analysis gave insights on the tectonic trends and stress-field orientation in the basin with major trends in the NNE-SSW, NE-SW, NW-SE, and WNW-ESE directions. 2D forward modelling of some selected profiles was employed to characterise the basement pattern and architecture, which depicted a horst-graben architecture. The basement structure and architecture have a major control on the distribution of sub-basins, petroleum systems elements and trap styles in the basin. The study demonstrates the robust application of high-resolution aeromagnetic data in basin-wide mapping of regional subsurface geological features, basement architecture and determination of sedimentary thickness in a frontier basin.
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