Ground Penetrating Radar Sections Research Articles

Geologic and Geophysical Evidence of Repeated Normal Faulting on the Itozawa Fault—the Source of the Mw 6.6 Iwaki Earthquake Triggered by the Mw 9.0 Tohoku-Oki Megathrust Earthquake, Northeast Japan

ABSTRACT The 2011 Mw 9.0 Tohoku-Oki earthquake ruptured the 500 km long and 200 km wide convergent plate margin between the North American and Pacific plates, and changed the crustal stress field and triggered widespread seismic activity in northeast Japan. In particular, many crustal earthquakes struck the southern Fukushima area. The largest inland normal-faulting earthquake with Mw 6.6 occurred on the northwest-trending Yunodake fault and the north-northwest-trending Itozawa fault on 11 April 2011. The coseismic surface ruptures appeared along the previously identified active and presumed active faults. To investigate the near-surface structure of the Itozawa fault, we conducted ground-penetrating radar (GPR) profiling across the fault, and two drilling surveys on its hanging-wall and footwall blocks. The GPR survey line about 50 m long was located near the previous trenching site. The GPR two-way travel-time sections were collected by common-offset modes by 50 and 100 MHz GPR systems. We acquired common midpoint ensembles on both sides of the surface rupture for depth conversion of the time sections. The resulting GPR sections show detailed subsurface structures to a depth of about 7 m. We identified event horizons for the 2011, penultimate, antepenultimate, and preantepenultimate earthquakes, indicating that the Itozawa fault has ruptured repeatedly as a normal fault. The vertical displacements during these earthquake events, obtained from the GPR sections, were about 0.8, 0.3, 0.4, and 0.7 m, respectively. These observations suggest that the coseismic surface offset amount on the Itozawa fault varies greatly. The recurrence intervals of surface-rupturing earthquakes on the Itozawa fault, calculated from the previous research and this study, are much longer than those of giant interplate earthquakes along the Japan trench, such as the 2011 Tohoku-Oki earthquake. We conclude that not every giant earthquake along the Japan trench triggers a rupture of the Itozawa fault.

Surface-Related Multiples Elimination for Waterborne GPR Data

Ground-penetrating radar (GPR) is a well-respected, effective, and efficient geophysical technique. However, for underwater engineering detection and underwater archaeology, the measured B-scan profiles typically contain surface-related multiple waves, which can reduce the signal to noise ratio and interfere with the interpretation of results. SRME is a feedback iteration method based on wave equation, which is frequently utilized in marine seismic explorations but very rarely in GPR underwater engineering detection. To fill this gap, we applied SRME to suppress multiples that appear in GPR underwater images. When we compared the effectiveness of the underwater horizontal layered model and the underwater undulating interface model, we found a high match rate between the predicted and the real-world multiples. In addition, the addition of the Gaussian random noise level with a 4% maximum amplitude to the B-scan profile of the horizontal stratified model yielded satisfactory multiple suppression results. Finally, we applied this method to the B-scan GPR section of actual underwater archaeological images to achieve multiple suppression, which can more effectively weaken and inhibit the surface-related multiples. Both numerical simulations and actual field data show that the SRME method is highly suitable for interpreting waterborne GPR data, and more accurate interpretation can be obtained from the GPR profile after multiples suppression.

Groundwater Level Variation Analysis Using Hydrogeophysical Methods in an Area of Campo Sujo in Cerrado, Chapada dos Veadeiros Region, Goiás

Cerrado’s campo sujo areas have been one of the main focuses of anthropic occupation in the Chapada dos Veadeiros region, Brazil’s Central Plateau, as they are easily accessible flattened areas with less dense vegetation. They are usually associated with wetlands representing excellent water reservoirs and groundwater recharge zones. The environmental characterization and analysis of water level variation are essential to investigate the impacts of human occupation. Hydrogeophysics represents one of the main subsurface research tools due to its easy application and efficiency in identifying the water level, with emphasis on Ground-penetrating radar (GPR), and electrical resistivity tomography (ERT). An analysis of GPR sections with 200, 400, and 900 MHz frequency antennas associated with the resistivity model was carried out to identify structures, and map the groundwater level. The overlapping data compose a hydrogeophysical model with good correlation to direct measurements of water level in a monitoring well, and soil horizons mapped in a trench. The GPR proved to be efficient in mapping the water level, mainly about to the survey with a 400 MHz antenna, shown as a horizontal reflector associated with attenuation portions of the reflection signal, registering in profile the lowering of the water level from 1.68 m in May to 3.35 m in August. The resistivity model showed a good correlation with the variations between the mapped soil horizons. The analysis shows that constructing a hydrogeophysical model is an excellent alternative for identifying the water level, and characterizing the shallow subsurface by applying non-invasive techniques. The study area represents a preserved area of campo sujo, and the research data can be used for comparison with future surveys, in addition to representing a base hydrogeophysics methodology that showed promising results for the physiographic characteristics of the area, which can be replicated in regions of similar geoenvironmental aspects.

Assessment of zones prone to sinkhole using ground penetrating radar and soil properties in Central Iran

Land subsidence and sinkhole, natural and anthropogenic events, occur globally especially in arid and semi-arid regions. The major problem of this phenomenon is over exploitation of ground water. Identification of important factors in the soils as soil properties were prone to sinkholes detection of subsurface holes as soil texture essentially. For detecting subsurface layers were used Ground Penetrating Radar (GPR) in the study area. The study area is Abarkooh alluvial plain of about 250 km2 is part of the Eghlid-Abarkooh watershed. For assessment potential zones prone to sinkhole, eight routs were determined in two different regions for the measurement of GPR and soil chemical, physical and mechanical properties. In GPR sections around the sinkholes, there were some breaks in subsoil layers and found subsurface cavities and on the side of the mountain slopes, the subsoil layers were uniform and there was no sign of breaks in subsoil layers and cavities. Regarding soil characteristics, soil texture near sinkholes was silt loam, sandy loam and loamy sand and on the side of mountain slope was Skeletal sandy loam, Skeletal loamy sand and Skeletal sand because of the existence of gravel on the slopes of the mountain. For evaluating soil parameters in two selected regions, some differences were observed such as Ca2+/Mg2+ in lime, COLE and Atterberg limits. Mg2+ in lime is more than to Ca2+ near sinkholes and the limes of the soils were dolomitic type and unstable. The amount of COLE and Atterberg limits as divergence index were high near sinkholes but on the side of mountain slopes were low. An increase in Mg2+ in lime, COLE and Atterberg limits near sinkholes proved the activity of clays and their movement underground and the GPR results confirmed the clay activity as breaks in stratigraphy traces to depth of 5 m and these soils are prone to sinkhole phenomenon. It has been concluded that GPR and Soil properties is the best way to determine areas that prone to sinkhole and also to detect the safe area for construction and contracting works. It is suggested that land conservation be introduced as the best alternative near sinkholes and redrawing the plan of urban development, construction of electric tower and railway from lowlands to the piedmonts as detected the safe area.

THE CAESAREA GERMANICIA (?) OF ARCHEOGEOPHYSICAL INVESTIGATIONS

The remains unearthed in the Dulkadiroğlu district, one of the central districts of Kahramanmaraş, are thought to belong to Caesarea Germanicia, which was founded in the Roman Period. Research and excavations carried out by the Kahramanmaraş Museum and us in the region have revealed that the spread of archaeological cultural remains is more than 150 hectares. Although the concentration of Roman Period cultural remains in the research and excavations was remarkable, the discovery of Byzantine, Seljuk, and Ottoman Period ceramic pieces indicates an uninterrupted settlement in the research area for centuries. However, as can be seen in the images, the dense residential texture in the region is one of the biggest obstacles to archaeological research and excavations. Because, in order to carry out archaeological excavations of the identified structures, expropriations are required. However, the expropriation period covers an average of 2-4 years, which makes it difficult to conduct scientific research. Archeogeophysical methods provide information about the location, depth, and dimensions of the archaeological remains by applying them from the surface, without causing any damage to the archaeological remains sought. In this context, Ground Penetrating Radar (GPR) measurements were carried out to determine the quality of the mosaic-based structure on 445 layout, which were previously unearthed through illegal excavations in 2019, and the parcels on which it extends. GPR was carried out along 6 profiles. The obtained results were compared both with each other and with the existing surface conditions, and GPR depth maps were created. When the GPR depth sections were examined, 4 important reflections were found. It has been interpreted that 3 of these reflections belong to the archaeological building remains and 1 of them originates from a metal material (pipe). It was determined that the depth of the archaeological remains identified in the GPR sections started at a depth of approximately 20 cm. As a result of the excavation, it was seen that the reflections determined in the GPR sections belonged to the wall remains and metal pipe. As a result of archaeological excavations, it was determined that the GPR reflections belong to the remains of the walls of the Villa Rustica of the Early Byzantine Period or a Roman bath, as well as a metal pipe. In the measurements of the ground radar, it was determined that other walls cut the building walls in parallel. As a result of archaeological excavations, it was understood that these walls were made of rubble stone with mud additives. It was discovered during archaeological excavations and was discovered in the 11th-13th centuries AD. One of the ceramic fragments indicates that this structure was used again in the Middle Byzantine Period.

GPR ringing suppression using lateral outliers' swap filter

Recent advances in automatic target recognition in ground penetrating radar (GPR) data dictates the need for an effective ringing noise removal tool that does not degrade features of interest. While there are many techniques to attenuate this persistent type of noise, each technique has its own limitations and drawbacks. In the current study, a new method is introduced to efficiently attenuate ringing noise while maintaining the integrity of hyperbolic features of interest. The new method uses a laterally sliding filter that detects potential outliers and replaces them with interpolated values from neighboring samples. This filter imposes minimal or no changes to majority of ringing noise and manipulates only those in the proximity of hyperbolic features. This approach guarantees that subtracting the estimated ringing noise matrix from the original data leaves a smooth and clear GPR section in which hyperbolic features are significantly preserved. Tests conducted on both synthetic and real field data show that the new method produces clearer and more accurate results than other ringing noise removal methods. Moreover, the flexibility of the user-defined parameters, such as operator length, operator step, and outlier detection limits, makes the new method applicable to the wide range of GPR data available today.

Combining ground-penetrating radar sections with different antenna frequencies including time-frequency domain noise suppression filters

Ground-penetrating radar (GPR) is one of the most useful geophysical methods that rapidly and efficiently provide high-resolution subsurface images depending on antenna frequencies and target depth. Recently, to enrich the interpretation of GPR sections, multifrequency sections have been combined at deeper and shallower levels in a profile. In this context, the techniques of combination and image quality improving processes of GPR data also have gained importance. For this, simple summation (SS) and time-shifted balanced summation (TSBS) techniques, frequency-domain local mean notch filter (FDLMNF), frequency-space ( f- x) filter, and automatic gain control (AGC) processes are sequentially applied within a workflow. Although the FDLMNF is used to effectively remove single-frequency spike-like noises without distortion around the notch frequency, the f- x filter is applied to suppress the random noise and improve the lateral traceability of the section, and AGC provides a statistically based gain recovery. In the proposed workflow, after generating synthetic and field GPR data with 100 and 250 MHz frequencies, data were combined using SS and TSBS techniques. Finally, FDLMNF, f- x, and AGC were applied to increase the image quality of this combined section. The result sections were evaluated and compared using the Fourier average amplitude and f- k spectra. According to the spectra, the TSBS technique provides good spectral balancing and offers wider spectral content. At the same time, it was observed that the image quality of the combined GPR sections increased significantly after applying FDLMNF, f- x, and AGC processes. As a result, when the sections resulting from SS and TSBS techniques are examined, the image enhancement processes that protect and strengthen the spectral bandwidth of the data are successful. Thus, the temporal resolution and spatial continuity of GPR sections also will be increased, and a better quality interpretation will be provided.

GPR application for the characterization of sinkholes in Teresina, Brazil

The town of Teresina, in the state of Piauí, Brazil, presents a history of land sinking processes. Two sinking events deserve to be highlighted, the first occurred in 1999 at Simplício Mendes Street and the other occurred on July 31, 2008, at Francisco Mendes Street. To identify possible shallow caves and associated structures, the Geological Survey of Brazil/CPRM developed a Ground Penetrating Radar (GPR) study to verify the occurrence of reflection patterns characteristic of these dissolution structures. In the field, the team conducted GPR sections along streets with a history of collapse. The GPR results obtained with shielded antennas of 200 MHz allowed the identification of old areas of collapse of the terrain, to a maximum depth of 3 m. In addition, the results obtained by this study show the potential of applying the GPR method in the characterization of the subsoil of paved streets, making it possible to identify various layers: asphalt, actual pavement, subgrade pavement, soil, saprolite, and mixed material. The high clay content of the subsoil does not allow the GPR to investigate further depths in the research area. The interpretation of aero-magnetometric data shows that the occurrence of sinkholes is associated with magnetic lineaments mainly in the NW–SE direction and enhances the understanding of the structural framework of the study area.

Right-lateral offset associated with the most recent earthquake on the Ikeda fault of the Median Tectonic Line, southwest Japan, revealed by ground-penetrating radar profiling

The Median Tectonic Line (MTL) is an arc-parallel strike-slip fault that accommodates much of the arc-parallel component of the oblique convergence of the Philippine Sea and Eurasian plates at the Nankai Trough. The MTL in Shikoku is one of the fastest-slipping faults in Japan, with a late Quaternary right-lateral slip rate of 5–10 mm/yr. To estimate the right-lateral slip amounts of the past faulting events on the MTL, we acquired 2D and pseudo-3D ground-penetrating radar (GPR) sections across the ENE-trending Ikeda fault of the MTL in eastern Shikoku. We conducted the GPR surveys at the Higashi-Miyoshi site, where two terrace riser offsets mark the active fault trace. The 2D lines were about 28–64 m long, and the pseudo-3D data were sized 20 m × 30 m with a 0.5-m inline spacing. We used 50 MHz GPR antennas and conducted wide-angle measurements to estimate the electromagnetic wave velocity. We identified three paleochannels on the final depth-converted GPR sections, and two of them are deflected by the fault. A paleochannel at 0.6–1.4 m depth is observed on all inline sections of the pseudo-3D GPR data. We built a 3D model of this paleochannel and estimated the right-lateral and vertical displacements of ~ 3.5 m and ~ 0.5 m, respectively. This paleochannel offset is probably caused by the most recent surface-rupturing earthquake on the Ikeda fault, which may be the 1596 Keicho-Fushimi earthquake. This study demonstrates the usefulness of the GPR surveys to identify geological features displaced laterally and vertically by the most recent surface-rupturing earthquake.

Stratigraphy and petrophysical characteristics of Lower Paleocene cool-water carbonates, Faxe quarry, Denmark

The Faxe limestone quarry in eastern Denmark exposes Danian (Lower Paleocene) cool-water carbonate deposits. They constitute remnants of an apparent build-up that covers about 12 km2 today. The Danian deposits at Faxe are conspicuous due to their pronounced thickness of coral limestone relative to the regional carbonate system. In the Faxe quarry, scleractinian corals are uniquely exposed in up to 30 m high mounds. The rapid accumulation of scleractinians combined with induration of the mounds may locally have protected the limestone from Quaternary glacial erosion and created a Danian thickness anomaly at Faxe. The position of Faxe above a local fault-bounded basement high and the extent of coral limestone has been better defined by new mapping. A mapped lithostratigraphic surface in the quarry reveals the large-scale organisation of nested bryozoan mounds on three elongated ridges striking NW–SE. The main scleractinian coral mounds are located above this horizon. Data for reservoir characterisation, mainly of the bryozoan mounds, were collected as photographs of the outcrop, petrophysical and petrographical data from cored boreholes, and as ground-penetrating radar sections. Old boreholes and measured sections were used to reconstruct the build-up, and new nannofossil data allow a discussion of stratigraphy and accumulation rate. The petrophysical data show that common mound-building bryozoan packstone has higher permeability and lower capillary entry pressure than chalk, whereas less commonly occurring grain-dominated packstone and grainstone deposits from local higher-energy sites of the mound complex were found to have reduced amounts of coccolith mud, significantly higher permeability and a higher degree of lithification. Based on biostratigraphic age constraints, correlation of flint – limestone couplets and recog-nised hierarchical patterns, we develop a cyclostratigraphy for the middle Danian and suggest that cyclicity in lithology and petrophysical characteristics of bryozoan limestone are controlled by precession and eccentricity of the orbit of the Earth.

Development of a model of a ground-penetrating radar section of a frozen rock massif with a crack

Revelance of the work. The presence of cracks significantly affects the physical and mechanical properties of rocks, which should be taken into account when planning mining operations and building mining facilities. In the conditions of the spread of permafrost rocks, characteristic of northeastern Russia, the study of fracturing is possible by the GPR method, which is used to assess the structure of rock massifs in placer deposits. The criteria for detecting cracks based on the features of wave georadar fields are currently known, and the main problem that prevents the full use of the georadar method for studying cracks in subsurface layers of rocks is the labour-consuming nature of processing and interpreting data from georadar measurements. Purpose of the work – to determine the patterns of cracks occurrence in frozen rocks in GPR wave fields. Methodology of the work. Based on the results of longstanding field work at the developed areas of alluvial diamond deposits in the Anabar region of the Republic of Sakha (Yakutia), the main elements of the radarogram structure were determined and presented in the form of a single formula. The developed formula is implemented in programs in the SCM Matlab and the results of its execution are compared with the results of modeling in the gprMax system. Results of the work and the scope of their application. The resultant formula describes the main elements of GPR radarograms quite correctly, which confirmed their comparison with the obtained model data. The correlation coefficient between the obtained matrices (Matlab and gprMax) without the low-amplitude values of multiple reflections was 0.91, which shows the identity of the structure of GPR wave fields. Conclusions. The studies carried out have confirmed the possibility of a mathematical description of the ground penetrating radar wave field obtained by sounding a mass of frozen rocks with a crack. The high correlation coefficient showed the adequacy of the developed radarogram model, which will be finalized taking into account the directional diagrams of existing georadars.

An integrated GPR and geoinformatics approach for assessing potential risks of flash floods on high-voltage towers, Makkah, Saudi Arabia

Makkah city is considered as a geologically transitional region that combines topographic and terrain features of the Sarawat Mountains to the east and the coastal plain of the Red Sea to the west and it is consisted of a semi-circular plateau cut by several structural valleys that were defined by faults and cracks. The surface runoff resulting from the rainstorms over the mountainous areas lead to the occurrence of flashfloods that debouch into the tributaries of valleys towards estuaries that encompass residential areas and municipal infrastructures. The present study assesses the negative impacts of flash floods on under-construction high-voltage towers in the valleys surrounding Makkah city using topographic analysis, Ground Penetrating Radar (GPR) surveys and field checks. Topographic modeling was implemented to delineate risky zones that are vulnerable to flash floods at the intersections between major valleys in Wadi Numan and Wadi Al Sharaya Basins and high voltage power lines. The GPR results showed the presence of three geological layers of sedimentary rocks: the first surface layer (A) is composed of alluvial sediments of fine to coarse sand with a thickness of 2 m. Followed by the second layer (B) of sand and gravel, which attains 3 m thickness. The third layer (C) consists of alluvial sediments mixed with rock fragments (diorite and quartzite diorite) and extend to a depth of more than 10 m. The GPR sections indicated that the concrete tower bases are different in thickness and depth from site to other. Different protection measures for the tower bases were suggested to avoid the adverse impacts of the flash flood. The measures varied from site to site and included the establishment of soil barriers, implementation of rocky hills, the defensive collision nets system and the concrete walls system.

A challenging archaeo-geophysical exploration through GPR and ERT surveys on the Keber Tepe, City Hill of Doliche, Commagene (Gaziantep, SE Turkey)

Doliche is an ancient city located at the northern fringe of Gaziantep in SE Turkey. The settlement spreads over a shallow hill called Keber Tepe. However, the lack of visible remains on the surface severely limits the comprehension of the spatial organization of the site. To understand the ancient city layout, but also to identify promising starting points of archaeological investigations, geophysical exploration plays a substantial role. In 2019 and 2020 campaigns, ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) surveys were conducted to determine anthropogenic structures in selected three study areas (SA) of the hill. Among them, SA-1 is adjacent to an excavation area on the south slope of the hill, where a large three-aisled Christian basilica had been discovered. SA-2 is in the eastern part of the city area, next to a sizeable civic bath building of the Roman period. Lastly, SA-3 covers the mosaic floor of the central nave and the terrace of the basilica where archaeological excavations were carried out in 2020 compaign. Archaeo-geophysical survey presented a challenging task as Keber Tepe is mainly composed of clayish-limestone and the same material had been used for architectural construction. Despite the disadvantages, GPR provided partial traces of the nave walls conforming with the existing basilica structures. The archaeological trenchs conducted in SA-3 confirm the partial reflection properties observed in the GPR sections. ERT surveys in this area provided subsurface models containing traces of anthropogenic structures unearthed. Since the findings obtained from both methods support each other very well in SA-2, we assumed that the field condition in this region of the hill is different or buried materials have lesser clay content in comparison to SA-1 and SA-3. As a result, the archaeo-geophysical survey contributed to the understanding of the archaeological structures and help to identify promising areas for further archaeological excavations.

Understanding Polydirectional Aeolian Cross-Strata Architecture in a Coastal Unidirectional Wind Regime

Carvalho, A.M.; Lima Jr., S.B.; Maia, L.P.; Claudino-Sales, V.; Gastão, F.G.C.; Eduardo, L.M.; Pinheiro, L.S., and Silva, M.V.C., 2021. Understanding polydirectional aeolian cross-strata architecture in a coastal unidirectional wind regime. Journal of Coastal Research, 37(2), 364–379. Coconut Creek (Florida), ISSN 0749-0208.Crescentic dune fields along the NE coast of Brazil were analyzed to justify processes associated with the wide range of cross-strata dip directions in aeolian deposits found in a unidirectional wind regime. Multiple spatial and temporal field-based methodologies were employed, including trenching, ground penetrating radar (GPR), and photogrammetry. Wind dynamics, coastline morphology, bounding surface developing processes, and dune migration patterns were also considered. Analysis revealed a relationship between small- and large-scale morphologies of the crescentic dune field. The interactions of crescentic dune crests, in association with the superposition of multiple superposed dunes, explain the majority of cross strata and dip directions found in dune trenches and GPR sections. This study provides convincing evidence that microscale structures observed within trenches and GPR sections are compatible with the macroscale slipface position observed within the dune field. Small-scale changes in wind direction, caused by the dune crest morphologies themselves, explain much of the supposedly unexpected strata dip directions that arc through from 90° to 180°. The presence of near-surface water tables supports the formation and preservation of aeolian cross-strata sequences.

Ground-penetrating radar data diffraction focusing without a velocity model

Ground-penetrating Radar (GPR) sections commonly suffer from strong scattered energy and weak reflectors with distorted lateral continuity. This is mainly due to the gradual variation of moisture with depth, dense lateral sampling of common-offset GPR traces (which are considered as zero-offset data), along with the small wavelength of the electromagnetic waves that is comparable to the size of the shallow subsurface dielectric heterogeneities. Focusing of the diffractions requires efficient migration that, in the presence of highly heterogeneous subsurface formations, can be improved by a detailed migration velocity model. Such a velocity model is difficult to develop because the common-offset antenna array is mostly used for its reduced time and cost in the data acquisition and processing stages. In such cases, migration processes are based on limited information from velocity analysis of clear diffractions, cores, or other ground truth knowledge, often leading to insufficient imaging. We have developed a methodology to obtain GPR sections with focused diffractions that is based on multipath summation, using weighted stacking (summation) of constant-velocity migrated sections over a predefined velocity range. The success of this method depends on the assignment of an appropriate weight, for each constant-velocity migrated section to contribute to the final stack, and the optimal width of the velocity range used. Additionally, we develop a postmultipath summation processing step, which consists of time-varying spectral whitening, to deal with the decrease of the dominant frequency due to attenuation effects and the additional degraded resolution expected by the constant migration summed images. This imaging strategy leads to GPR sections with sufficiently focused diffractions, enhancing the lateral and the temporal resolution, without the need to explicitly build a migration velocity model.

Ground penetrating radar investigations of the geological structure of loose sediments at solid mineral deposits

For effective commercial development of deposits, an increase in the information content of operational exploration is required. In recent years, the range of methods used to obtain complete and reliable information about the structure and properties of the rock mass of a developed field include remote methods of high-frequency electrical prospecting, in particular, the ground penetrating radar (GPR) method. The paper presents a methodological experience in the interpretation of GPR data of sandy river sediments based on the identification of radar facies. In the considered area, four types of radar facies have been identified that characterize the structure of sandy deposits and the morphology of the river bed. The criteria for identifying radar facies were used to analyze wave patterns of loose sediments in a sand and gravel pit and a placer gold deposit. Experimental GPR investigations are presented by data from a sandy-gravel pit (Warsaw, Poland) and from a placer gold deposit (Yakutia, Russia). As an example, a GPR section along the Paplin quarry and its interpretation, with the identification of GPR facies, is presented. A cross-sectional GPR profile of the dredging landfill is considered for the placer gold deposit. The analysis of the wave pattern was carried out, geological boundaries were highlighted. Based on the interpretation results, the characteristics of the rocks were given. It was noted that according to the GPR data, it is possible to identify zones of uplift of bedrock, which can affect the course of the dredge. As a result of using GPR in a swampy area where drilling was impossible, a deep three-layer section was obtained. The presented results of the successful use of GPR investigations and methodological approaches in the interpretation of data, show the promise of using the GPR method in assessing mining and geological conditions, in particular, placer deposits. At the same time, the efficiency of obtaining data can further contribute to the optimization of technology and increase the efficiency of field development.

Integrated use of electrical resistivity tomography and ground penetration radar for identifying subsurface sinkholes in Rufa Graben, Central Riyadh

Two-dimensional electric resistivity tomography and ground-penetrating radar (GPR) study was carried out in the eastern Rufa Graben, Riyadh area. Dipole–dipole configuration was used with a total length of 360 m and an electrode spacing of 5 m. In addition, the same number of ground-penetrating radar profiles was conducted in the same location of the electrical resistivity tomography (ERT) profiles. The goal of this study was to map and delineate the subsurface karstic features in the study area such as sinkholes, cavities, and fractured zones. The two methods showed the efficiency to detect the near-surface cavities and their distribution in the study area. The detected cavities were of different sizes. The air-filled cavities have appeared in ERT sections as anomalies that have high resistivity values while the cavities filled with wet clay were characterized with low-resistivity values. In GPR sections, the karstic features were seen by either hyperbola diffractions or uplift and discontinuity in horizontal reflection events. The results obtained from this study will contribute in solving the geotechnical problems for any expected future constructions planned to be done in the study area.

Reservoir deltas and their role in pollutant distribution in valley-type dam reservoirs: Les Království Dam, Elbe River, Czech Republic

Interpretation of catchment pollution history from sediment cores is a common approach for dam reservoirs, but relatively little is known about the spatial distribution of pollutants in the lithologically diverse depositional subsystems. We studied the depositional system of a hundred-year-old valley-type reservoir of the Les Království Dam built in 1919 on the upper reaches of the Elbe River, Czechia. Based on the analysis of pre-dam river valley morphology using historical topography maps with 1 m vertical resolution, 30 ground-penetrating radar sections on the lake and 137Cs dating of four cores, we described a deltaic sediment body with maximum thickness of ~11 m, accumulation rates ranging from 3.6 to 9.7 cm/yr, and an annual loss in reservoir capacity of 0.8%. The sediment body has a distinct delta shape in the longitudinal section, with a delta platform dissected by a channel (topsets) and delta slope (foresets) and a ponded basin (bottomsets) located near the dam. The upstream sections of the channels are prone to erosion and sediment redistribution into downstream parts of the reservoir, as indicated by ground-penetrating radar sections and distribution of 137Cs in younger sediment strata.We retrieved four cores 1.0 to 1.6 m long from different parts of the delta and analysed the sediment grain size using laser granulometry, geochemical composition (X-ray fluorescence, ICP-MS lithogeochemistry, total organic carbon (TOC)) and concentrations of polycyclic aromatic hydrocarbons (PAH). The grain size variation between the delta platform (sandy silts and silty sands) and prodelta (clayey silts) sediments strongly controls the concentrations of lithogenic elements (Al, Fe, K and Ti) but it has a relatively little effect on distribution of toxic metals (Zn, Cu, Pb) and TOC concentrations. The toxic metals show strong affinity to TOC and PAH show a distinct sawtooth vertical distribution suggesting that they were deposited from depositional events during hyperpycnal flows induced by river floods. This study shows that a hyperpycnal delta may serve as a good predicable model for toxic metal- and organic pollutant distribution in dam reservoirs. The role of hyperpycnal flows should not be overlooked in contamination studies of dam reservoirs.

Reduction of conceptual model uncertainty using ground-penetrating radar profiles: Field-demonstration for a braided-river aquifer

Hydrogeological flow and transport strongly depend on the connectivity of subsurface properties. Uncertainty concerning the underlying geological setting, due to a lack of field data and prior knowledge, calls for an evaluation of alternative geological conceptual models. To reduce the computational costs associated with inversions (parameter estimation for a given conceptual model), it is beneficial to rank and discard unlikely conceptual models prior to inversion. Here, we demonstrate an approach based on a quantitative comparison of ground-penetrating radar (GPR) sections obtained from field data with corresponding simulation results arising from various geological scenarios. The comparison is based on three global distance measures related to wavelet decomposition, multiple-point histograms, and connectivity that capture geometrical characteristics of geophysical reflection images. Using field data from the Tagliamento braided river system, Italy, we demonstrate that seven out of nine considered geological scenarios can be discarded as they produce GPR sections that are incompatible with those observed in the field. The retained scenarios reproduce important features such as cross-stratified deposits and irregular property interfaces. The most convenient distance measure of those considered is the one based on wavelet-decomposition. Direct analysis of the distances is the most intuitive and fastest way to compare scenarios.

Determination of unstable tectonic zones in C–North deposit, Sangan, NE Iran using GPR method: importance of structural geology

Ground Penetrating Radar (GPR) is an effective and practical geophysical imaging tool, with a wide set of applications in geological mapping of subsurface information. This research study aims at determination of the geophysical parameter differences in the subsurface geological structures and construction of a 3D fracture model. GPR and resistivity methods were applied to detect the unstable tectonic zones in the C-North deposit. Structural geology investigations were, first, surveyed to detect the faults and fractures in the study area. Based on the structural features, the survey was conducted over an area of 1 km2 with a total of 30 profiles and low-resistivity zones in the C-North deposit which is a great help in reducing their impacts in slope stability studies. GPR sections were, then, obtained from low and high frequency antennas (10 and 50 MHz) to detect fractures and water content zones. The obtained data results demonstrated that the major structural trends in the study area were W–E, NE–SW, and NW–SE while fault zones that can create pathways for groundwater inflow into the deposit in the future. Information obtained from geological and GPR studies were also integrated with drill hole data. The geological information from structures are in good agreement with the actual geological situation. Method and results of this study could be useful in solving problems related to subsurface structures in mining engineering.