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The evolving roles of geophysical test sites in engineering, science and technology

Alao Joseph Omeiza, Lawal Kola Muyideen, Dewu Bala Bello Muhammad, Raimi Jimoh

Acta Geophysica

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2024

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Vol. 72, no. 1

161--176

EN

Understanding the anomalies generated by various subsurface targets and their responses to different geophysical techniques in various subsoil types is critical to near-surface geophysical investigations. Geophysical test site (GTS) plays a vital role in near-surface geophysical investigations and related Earth sciences to adequately predict the geometries and anomalies generated by the subsurface targets. Therefore, developing a GTS on a site requires some technical efficiencies, mechanical procedures, engineering concepts and scientific approach, depending on the operating environment and the purpose of construction. This paper reviews the evolving roles of GTS in engineering, sciences, and technology via remarkable pedagogical and scientific research. The procedures for designing and installing GTS were also discussed. Every constructed GTS is unique and has its operating environment and sets of scientific requirements. As a result, the execution of GTS should be subjected to numerous factors that invariably affect the overall long time usage and performance. Comparative studies of GTS activities indicate that GTS is a vital geophysical research and academic platform to enrich the outcomes of the geophysical modelling for near-surface geophysical applications in engineering, science and technology. The evolving application of GTS has greatly impacted the field of science and engineering by enhancing the knowledge and understanding of the earth’s interior, which invariably affects the engineers, geophysicists, archaeologists and geologists to be critical in the analysis, interpretation, and providing precise and accurate information of subsurface anomalies underlying the uppermost soil of the earth’s crust. After a critical investigation, it was noted that the installation of GTSs is usually conceived to replicate situations often encountered in field investigation contexts. Examination shows that GTS can provide an ideal platform for young geoscientists, engineers and archaeologists to acquire the requisite skills, knowledge, technical know-how, and professional techniques for resolving near-surface challenges in real-life work situations. More also, a well-developed and equipped GTS could be a watershed in technological advancement, research development, and new scientific ideas. The GTS platform also indicates a promising pedagogical approach to geophysical educational usage, research mobilization, and development of new shallow geophysical techniques for various near-surface investigation and calibrating/testing geophysical equipment, which invariably catalyzed engineering designs, scientific concepts and technological advancement.

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Near-surface geophysical characterization of gully erosion hazard-prone area in Calabar, southern Nigeria

Ebong Ebong Dickson, Urang Job Gideon, Melouah Oualid, Ugi Anthony Ukpongnukpon, Sule Andebutop

Acta Geophysica

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2024

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Vol. 72, no. 1

85--96

EN

The electrical resistivity, i.e. electrical resistivity tomography (ERT) and direct current-resistivity sounding (DC-ERS), and ground penetrating radar (GPR) methods were deployed to assess a gully erosion site in Bacoco area of Calabar, Nigeria. The study aims to assess the mechanism and dynamics of the gully erosion conditions in the area based on shallow lithostrati-graphic evaluations. The results revealed good contrast in the operative properties (i.e. electrical resistivity and dielectric permittivity) between competent and weak zones along the profiles close to the gully head. The joint interpretations provided reliable shallow subsurface models and lithologies that consist predominantly of lateritic top cover and sands. However, the ERT model delineates the contrast between lithologies and demarcates the weak zones from the relatively competent zones, in contrast to the responses generated by the GPR technique. This joint interpretation approach minimizes the uncertainty due to the non-uniqueness problems common to the geophysical technique. Also, the geophysical interpretations were constrained using lithologic information from the gully walls and one-dimensional (1-D) DC-ERS inverted model to provide additional validity. Our findings suggest the influence of structural control on gully formation and demonstrate its contribution to the complex interactions with other drivers, such as seepages through porous media and high-energy runoff due to intense rainfall. The rapid, non-invasive and environmentally friendly characteristics of ERT and GPR techniques favour their applicability in assessing shallow subsurface environmental problems.

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Near-surface study of a hot spring site in Fiji

Lal A., Deo R. N., Kumar A.

Acta Geophysica

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2018

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Vol. 66, no. 4

659--672

EN

A geophysical investigation of a hot spring system located in Rabulu, Fiji, was carried out from October 2014 to March 2015. The investigation covered a survey area of 6075 m2. Self-potential (SP), ground temperature and soil carbon dioxide (CO2) concentrations were measured and investigated for their distribution characteristics and inter-linkages. Results indicated obvious anomalous zone at the hot spring discharge site. The SP profile analysis highlighted thermal water upwelling zones and elevation-driven subsurface groundwater pathways. Measurement of subsurface temperatures up to 1 m depths revealed increasing temperatures, indicating potentially high thermal gradients in the area. Surface soil CO2 distributions also agreed with SP and ground temperature results. The overall result of the study demonstrated that synchronised measurements of SP, ground temperature and soil CO2 can be instrumental in identifying anomalous zones near the hot spring sites. Other parameters such as spring water temperature, discharge rate and energy flux estimates from the spring were calculated and analysed. The high-dense multi-parameter data coverage allowed interpretation of geothermal features at a scale never conducted in Fiji before. The near-surface investigations reported in this study corroborate previously suggested steady geothermal activity in the region, deserving further detailed investigation.

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Near-surface Structure of the Carpathian Foredeep Marginal Zone in the Roztocze Hills Area

Majdański M., Grzyb J., Owoc B., Krogulec T., Wysocka A.

Acta Geophysica

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2018

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Vol. 66, no. 2

179--189

EN

Shallow seismic survey was made along 1280 m profile in the marginal zone of the Carpathian Foredeep. Measurements performed with standalone wireless stations and especially designed accelerated weight drop system resulted in high fold (up to 60), long offset seismic data. The acquisition has been designed to gather both high-resolution reflection and wide-angle refraction data at long offsets. Seismic processing has been realised separately in two paths with focus on the shallow and deep structures. Data processing for the shallow part combines the travel time tomography and the wide angle reflection imaging. This difficult analysis shows that a careful manual front mute combined with correct statics leads to detailed recognition of structures between 30 and 200 m. For those depths, we recognised several SW dipping tectonic displacements and a main fault zone that probably is the main fault limiting the Roztocze Hills area, and at the same time constitutes the border of the Carpathian Forebulge. The deep interpretation clearly shows a NE dipping evaporate layer at a depth of about 500-700 m. We also show limitations of our survey that leads to unclear recognition of the first 30 m, concluding with the need of joint interpretation with other geophysical methods.

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Very Low Frequency Electromagnetic Induction Surveys in Hydrogeological Investigations; Case Study from Poland

Oryński S., Okoń M., Klityński W.

Acta Geophysica

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2016

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Vol. 64, no. 6

2322--2336

EN

In 2011, a geophysical survey was carried out in the surroundings of the Jagiellonian University in Cracow, using a Very Low Frequency method. The measurements were designed to determine the reason of frequent flooding of the lowest level of the building. The main objective of the study was to find out from where and in which way the rainwater seeps into the building and how this problem can be solved in the least invasive manner. The aim of geophysical methods was also to provide necessary information that will enable the construction of a hydrogeological model of the local environment. The interpretation revealed the presence of a sandy gutter surrounded by impermeable clay. There is a big resistivity contrast between those layers. Their location and approximate dimensions were determined.

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Characterization of near-surface sediments based on Electrical Resistivity Tomography measurements in the vicinity of the Wawel Hill (Krakow, Poland)

Ćwiklik M.

Geology, Geophysics and Environment

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2013

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Vol. 39, no. 4

351--361

EN

The Electrical Resistivity Tomography (ERT) method was applied at the SW foot of the Wawel Hill was applied. The survey was carried out along five survey lines (P1-P5), 50 m long each. The Wenner alpha array with spacing a = 0.5 m, 1.0 m, 1.5 m, 2.0 m, 2.5 m, 4.0 m, 5.5 m, 7.5 m, and 10.0 m was used. The basic electrode spacing was 0.5 m. In apparent resistivity contours and sections we can distinguish two zones, which have noticeably different resistivity values. The low resistivity zone dominates in the deeper part of the section on all survey lines, especially on the profiles located in the close neighbourhood of the Vistula River. The relative high resistivity zone is probably the effect of complex local geology, as well as the influence of the limestone of the Wawel Hill. Based on ERT inversion results, three resistivity zones were distinguished. Then the probable lithological or/and anthropogenic character was assigned to them. The shallowest zone has the thickness of about 0.5 m and results probably from accumulation of weathered limestone fragments derived from the Wawel Hill. It may be that high resistivity zones have anthropogenic character. Below, a zone of water-bearing sands was recorded, which may result from redevelopment and reclamation of this area. Thickness of this zone increases towards the Vistula River. Another zone, which can be identified with limestone, was identified on survey lines P4 and P5. This could also be result of accumulation of the calcareous debris for the purpose of planation of the area. In order to generalize and simplify the characterization of the quaternary sediments, ID interpretation was made. The method allows us to estimate the depth of groundwater, which in that place is about 5 m.

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Application of first-arrival tomography to characterize a quick clay landslide site in southwest Sweden

Adamczyk A., Malinowski M., Malehmir A.

Acta Geophysica

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2013

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Vol. 61, no. 5

1057--1073

EN

First-arrival traveltime tomography was applied to high-resolution seismic data acquired over a known quick-clay landslide scar near the Göta River in southwest Sweden in order to reveal the geometry and physical properties of clay-related normally consolidated sediments. Investigated area proved to be a challenging environment for tomographic imaging because of large P-wave velocity variations, ranging from 500 to 6000 m/s, and relatively steeply-dipping bedrock. Despite these challenges, P-wave velocity models were obtained down to ca. 150 m for two key 2D seismic profiles (each about 500-m long) intersecting over the landslide scar. The models portrait the sandwich-like structure of marine clays and coarse-grained consolidated sediments, but the estimated resolution (20 m) is too small to distinguish thin layers within this structure. Modelled velocity structures match well the results of reflection seismic processing and resistivity tomography available along the same profiles.