Geophysical Results Research Articles

Lithofacies variability of the Yarakta horizon as a complex result of geodynamic processes of tectonogenesis and sedimentogenesis

The purpose of the research is to analyze the lithological and facies conditions of formation and the causes of lithological composition variability of the Yarakta horizon deposits as well as formation and distribution features of reservoir rocks in the horizon. The paper uses the data on drilling and geophysical work results and research materials from the public sources. The Yarakta horizon is commercially productive in the deposits of the southeastern slope and the central part of the Nepa-Botuoba anteclise: Dulisminskoe, Yaraktinskoe, Ayanskoe, Danilovskoe deposits, etc. The deposits of the Yarakta horizon were formed during the initial transgressive stage of the Vendian sedimentation cycle and are characterized by extreme lithological irregularity of rock composition and thickness. Investigations of a number of scientists testify that in the early formation of the Yarakta horizon its territory in geomorphological terms was predominantly presented by a coastal plain, which was occasionally flooded by the sea. The rocks in the area are represented by the facies of temporary proluvial-deluvial flows of the coastal plain replaced by coastal shallow sediments. The change in the lithological composition of rocks and thicknesses of the Yarakta horizon is a result of changes in the nature of oscillatory movements, while its structural and textural features are determined mainly by the dynamics of water flows of the sedimentation medium and the paleorelief nature of the underlying surface. The conducted research allows to conclude that lithological heterogeneity of the Yarakta horizon in sections (vertically) and along the strike (laterally) is determined by the frequent alternation of various lithotypes, the formation of which is determined by the complex nature of tectonic movements and irregularity features of sedimentary layer facies.

Characteristics of the foundation rocks using geophysical techniques: A case study for the Egyptian solar plant site, Aswan, Egypt

The main target of the present study is to investigate the foundation layers and the subsurface structures in an Egyptian solar plant site using geophysical techniques including the seismic refraction and Multichannel Analysis of Surface Waves (MASW). The studied solar park is situated at about 40 km to the north of Aswan city on the Aswan-Cairo highway road and is classified as the largest solar plant in Africa and worldwide. Due to its location in the vicinity of the most prone earthquake area in Egypt (Aswan seismic zone); it is imperative to mitigate the earthquake hazard in this region. The geophysical results show that the subsurface foundation in this site is primarily composed of two layers. The upper one is loose and incompetent soil sediments that extend down to about 10 m depth with P-wave velocity ranging from 400 to 1000 m/s and shear-wave velocity ranging from 260 to 550 m/s. The deeper section is considered the main foundation layer with velocities ranging between 650 and 1900 m/s and from 350 to 950 m/s for P-wave and shear-wave, respectively. The average shear-wave velocities calculated for the topmost 30 m (Vs30) vary almost between 319 and 834 m/s; thereby the studied site is primarily ranked into classes C&D (180-360 m/s & 360-760 m/s, respectively) according to the National Earthquake Hazards Reduction Program (NEHRP) soil classification. Additionally, the southwestern and southeastern zones of the site area are characterized by maximum velocity values, relative high values of rock densities, rigidity or shear modulus “μ”, Standard Penetration Test (N-Value), ultimate bearing capacity and allowable bearing capacity, while the low values are observed through the northern and middle sectors across the area. This study an integral part of many works being carried out delineating the subsurface foundation structures around the solar plant and allows the most appropriate sites for constructing the renewable energy plants to be sited away from the highly hazards prone areas.

Microgeophysics and geomatics data integration reveals the internal fracturing conditions of the statue of Ramses II (Museo Egizio, Torino, Italy)

The combined acquisition of 3D ultrasonic tomography and radar scans is growing for cultural heritage diagnostics. Both methods proved to be efficient in the detection and location of fractures and weaknesses within the investigated artefacts. Although the two techniques are widely applied together, an integrated approach for data interpretation is still missing. We present the results of radar and ultrasonic prospections carried out on the statue of the young Ramses II, an absolute masterpiece of the Egyptian art preserved in the collection of the Museo Egizio of Torino (Italy). Geophysical results are incorporated within the 3D model of the statue retrieved from total station measurements, ground-based and handheld laser scanning. A data integration approach is then proposed for the joint interpretation of the geophysical results, exploiting the final ultrasonic velocity model and radar attribute analysis (i.e. local dissimilarity computation) to define a combined damage index. The proposed methodology is efficient in fracture detection and location and improves the readability of the final results also for non-expert geophysical interpreters, offering guidance to the museum for preservation and restoration of the masterpiece.

Lower oceanic crust formed by in situ melt crystallization revealed by seismic layering

Oceanic crust forms at mid-ocean spreading centres through a combination of magmatic and tectonic processes, with the magmatic processes creating two distinct layers: the upper and the lower crust. While the upper crust is known to form from lava flows and basaltic dykes based on geophysical and drilling results, the formation of the gabbroic lower crust is still debated. Here we perform a full waveform inversion of wide-angle seismic data from relatively young (7–12-Myr-old) crust formed at the slow-spreading Mid-Atlantic Ridge. The seismic velocity model reveals alternating, 400–500 m thick, high- and low-velocity layers with ±200 m s−1 velocity variations, below ~2 km from the oceanic basement. The uppermost low-velocity layer is consistent with hydrothermal alteration, defining the base of extensive hydrothermal circulation near the ridge axis. The underlying layering supports that the lower crust is formed through the intrusion of melt as sills at different depths, which cool and crystallize in situ. The layering extends up to 5–15 km distance along the seismic profile, covering 300,000–800,000 years, suggesting that this form of lower crustal accretion is a stable process.

Evidential belief functions modeling of geophysical and multi-element geochemical data for Pb-Zn mineral potential targeting

The Evidential Belief Functions model was used for investigating the geochemical and geophysical anomalies and delineating the Pb–Zn mineralization zones in the Chichakloo area, east of Takab, Iran. In addition, we evaluated the uncertainty of geochemical and geophysical results in the detection of mineralization zones. For this purpose, the individual belief, disbelief, plausibility, and uncertainty functions of geophysical and geochemical predictor maps were assigned and then integrated using belief function equations. The obtained belief map reveals a remarkable potential for Pb–Zn mineralization in the east part of the study area with a conservative estimation of more than 50% and uncertainty of less than 10%. An increase in conservative estimate and a decrease in the uncertainty rate in this zone, compared to any of the other individual exploration predictor maps, indicate remarkable overlapping anomalies. The results of drilled boreholes proved the existence of the Pb–Zn mineralization and confirmed the obtained mineral potential map.

Integrated Resistivity, Index, and Strength Characteristics of Subgrade Soils: Implication for Highway Pavement Failure Studies in North-Central Nigeria

Integrated geophysical and geotechnical studies have been carried out to determine the geological cause(s) of the failure of sections of Ajaokuta – Anyigba Highway, North-central Nigeria. Forty-eight (48) Vertical Electrical Soundings (VES) were conducted on failed and stable sections of the highway. Also, twenty-one (21) subgrade soil samples close to VES stations from the unstable and stable sections of the highway were subjected to laboratory geotechnical analyses which include grain size distribution, Atterberg limits, compaction (Optimum Moisture Content, OMC, and Maximum Dry Density, MDD) and California bearing ratio (CBR) at soaked and unsoaked states following American Society for Testing and Material (ASTM) standards as appropriate. The geophysical results show that low resistivity (10–100 Ohms-m) inferred as clay/silt of low competence characterizes the subgrade soils of the unstable segment. While higher resistivity (148–272 Ohms-m) interpreted as sandy-clay/silt with moderate competence was obtained for the subgrade soils of the stable segment. Results of Geotechnical tests show that the subgrade soils of the unstable segment have geotechnical properties that generally fall below required standard specifications. Strong correlations of R = 0.86, 0.9, and –0.88 were obtained between CBR and sand, resistivity, and the amounts of fines, while a fairly strong correlation of R = –0.67 was obtained for the plasticity index. The high level of correlation implies that CBR can be predicted from geophysical data and other geotechnical parameters. The study has revealed that the advanced weathering of the underlying Mica-Schist to clayey/silty subgrades with unsuitable geophysical and geotechnical properties is a major contributor to the instability of the highway. Keywords: Atterberg limit; CBR; Grain size distribution; Resistivity; Subgrade soil.

A Multidisciplinary Approach for Groundwater Potential Mapping in a Fractured Semi-Arid Terrain (Kerdous Inlier, Western Anti-Atlas, Morocco)

This study is focused on developing an approach for spatial mapping of groundwater by considering four types of factors (geological, topographical, hydrological, and climatic factors), and by using different bivariate statistical models, such as frequency ratio (FR) and Shannon’s entropy (SE). The developed approach was applied in a fractured aquifer basin (Ameln Basin, Western Anti-Atlas, Morocco), to map the spatial variation of groundwater potential. Fifteen factors (15) influencing groundwater were considered in this study, including slope degree, slope aspect, elevation, topographic wetness index (TWI), slope length (LS), topographic position index (TPI), plane curvature, profile curvature, drainage density, lineament density, distance to rivers and fault network, normalized difference vegetation index (NDVI), lithology, and land surface temperature (LST). The potential maps produced were then classified into five classes to illustrate the spatial view of each potential class obtained. The predictive capacity of the frequency ratio and Shannon’s entropy models was determined using two different methods, the first one based on the use of flow data from 49 boreholes drilled in the study area, to test and statistically calibrate the predictive capacity of each model. The results show that the percentage of positive water points corresponds to the most productive areas (high water flow) (42.86% and 30.61% for the FR and SE models, respectively). On the other hand, the low water flows are consistent with the predicted unfavorable areas for hydrogeological prospecting (4.08% for the FR model and 6.12% for the SE model). Additionally, the second validation method involves the integration of 7200 Hz apparent resistivity data to identify conductive zones that are groundwater circulation zones. The interpretation of the geophysical results shows that the high-potential zones match with low apparent resistivity zones, and therefore promising targets for hydrogeological investigation. The FR and SE models have proved very efficient for hydrogeological mapping at a fractured basement area and suggest that the northern and southern part of the study area, specifically the two major fault zones (Ameln Valley in the north, and the Tighmi-Tifermit Valley in the south) has an adequate availability of groundwater, whereas the central part, covering the localities of Tarçouat, Boutabi, Tililan, and Ighalen, presents a scarcity of groundwater. The trend histogram of the evolution of positive water points according to each potentiality class obtained suggests that the FR model was more accurate than the SE model in predicting the potential groundwater areas. The results suggest that the proposed approach is very important for hydrogeological mapping of fractured aquifers, and the resulting maps can be helpful to managers and planners to generate groundwater development plans and attenuate the consequences of future drought.

Characrerization Of Arba Minch University General Hospital, Construction Site, Using Seismic Refraction Method In Arba Minch Town Of Southern Ehiopia

Geophysical investigation using seismic refraction method was conducted for engineering characterization of the foundation conditions of Arba Minch University General Hospital, Construction Site located in Arba Minch town, Sothern Ethiopia. The principal objective of the research was studying the suitability of the foundation earth materials underlying the site, where hospital is established. The seven refraction seismic spreads, seismic velocity models interpretation have provided valuable geotechnical information incorporated with available geologic information in the study area. Interpretation of geophysical data revealed that the subsurface geology of the area is composed of three layers. The topsoil consisted of clay, silt and sand mixtures having a 1-4 m thickness and 255-510 m/s p-wave velocity ranges are mapped over the whole area. The second layer attributed to the highly weathered and fractured vesicular basalt is characterized by 948-1802 m/s P-wave velocity range and revealed somewhat undulating morphology. The depth extent of this layer varies from about 10m on the North West end and southeastern parts and to about 27m around the central part. The third layer occurred in the depth range of 10-27m is characterized by greater than 2550m/s average high p-wave velocity and it is due to moderately weathered and fractured basaltic bedrock, which is deeper near to the center of the profiles and gets shallower towards North West end and southeastern portions. Besides, analyses of collected data have suggested the possible locations of minor structural discontinuities (maybe local fractures).The geophysical results show that the bedrock is found at shallow depth in the northwestern end and southeastern part of the study area, whereas in the central part of the survey area the bedrock is found relatively at high depth. Therefore, setting the building foundation is more recommended in the southeastern part of the construction site.

Characteristics and formation mechanism of the Yangjiazhuang-Maguduo ground fissure, western Linfen Basin, Northern China

• An integrated method was used to examine the ground fissure. • The strike of the YJZ-MGD ground fissure was parallel to the basin edge. • The YJZ-MGD ground fissure showing a synsedimentary structure feature. • Tectonic activity and groundwater exploitation jointly drive of the ground fissure. The Yangjiazhuang-Maguduo ground fissure, which is in front of the Luoyun Mountain on the western margin of the Linfen Basin, is a typical ground fissure that developed in the transition zone between the basin and mountain. In this paper, the developmental characteristics and mechanisms of the ground fissure in the transition zone between the basin and mountain under the action of fault activity and pumping were studied and analyzed through ground investigation, engineering geological mapping , trenching and geophysical exploration. The investigation and research confirmed that the strike of the ground fissure is parallel to the Luoyun Mountain piedmont fault and the ground surface has both horizontal extension and vertical offset. Trench result shows that the plane of the superficial part of the ground fissure is rough, which is typical tensile failure; the plane of the ground fissure under the bottom of the trench is smooth and mainly displaying shear deformation, and meanwhile the vertical offset of the stratum increases with depth showing synsedimentary structural characteristics. Shallow geophysical results reveal that the ground fissure is a manifestation of the Luoyun Mountain piedmont fault. Research suggests that deep tectonic activity caused pre-existing faults in the Luoyun Mountain piedmont to be in a continuous tensile shear state, which enhanced their activity and caused the pre-existing faults to extend to the surface, forming the ground fissure in the hanging wall of the fault. Continuous groundwater overexploitation led to the consolidation and settlement of the hanging wall of the Luoyun Mountain piedmont fault, which increased the differential settlement on both sides of the Luoyun Mountain piedmont fault, thus intensifying the movement speed of the Yangjiazhuang-Maguduo ground fissure and forming the present ground fissure. The development characteristics and formation mechanism of the Yangjiazhuang-Maguduo ground fissure provide not only an important reference for studying ground fissures in basin-mountain transition zones, but also guidance for the prevention and mitigation of such geological disasters .

Geophysical Studies of Wells in the Settlements of Konoplyanka 1 and Konoplyanka 2 (Bronze Age)

In the South Urals, numerous wells have been found inside dwellings in settlements of the Bronze Age. These features are of great interest, not only because of the artifacts found inside the wells, but also as the first hydrotechnical structures within the territory of northern Eurasia. Geophysical studies were carried out over the area of two Bronze Age settlements: the fortified settlement of Konoplyanka and the unfortified settlement of Konoplyanka 2. A gradient magnetic survey was carried out and settlement plans reconstructed, which formed the basis for the selection of sites for the archaeological excavations. Comparison of geophysical and archaeological results showed that, using magnetic maps, it was possible to accurately reconstruct the plans of ancient settlements and localize the positions of wells. At the excavation site of the settlement of Konoplyanka 1, as a result of the magnetic susceptibility survey, it was established that the edges of the wells were reinforced with a special soil that has higher magnetic properties than the subsoils present. At the excavation site at the settlement of Konoplyanka 2, ground penetrating radar (GPR) prospection of the four wells was carried out, the depth and structural features of these wells being determined. Excavations at two of the wells confirmed the results of the geophysical studies.

Tectono-Thermal Evolution and its Significance of Hydrocarbon Exploration in the Fuyang Sag, Southern North China Basin: A Case Study of Well WFD-1

The study of tectono-thermal evolution of sedimentary basins reveals both geothermal field characteristics and hydrocarbon generation and expulsion in the basin. However, there are only a few studies on the tectono-thermal evolution of the Fuyang Sag. This means the hydrocarbon exploration in the study area is restricted and unable to be effectively supported. Based on the geophysical exploration and drilling results, the tectono-thermal evolution of the Fuyang Sag has been studied for the first time in this paper. Using the organic geochemical data of the source rocks, the influence of tectono-thermal evolution on hydrocarbon exploration in the Fuyang Sag was discussed. The burial history of the Fuyang Sag since the late Paleozoic falls into four stages: stable sedimentation, rapid subsidence and deposition, long-term continuous uplift and denudation, and sedimentation. The heat flow evolution history of the Fuyang Sag since the late Paleozoic is characterized by ascending first and descending afterward. The main source rocks in the sag increased rapidly during the Permian and was gradually finalized in the Yanshanian period. The Fuyang Sag was reformed after the early hydrocarbon generation. The main source rocks with deeper burial depth, weaker uplift, and denudation reformation have greater potential for hydrocarbon exploration in the sag. The results of this study provide not only a scientific basis and important guidance for hydrocarbon exploration in the Fuyang Sag, and but also effective geothermal constraints for further geodynamics research in the Southern North China Basin.

Lithospheric-mantle modification beneath the thick sedimentary fan of Bay of Bengal: Inference from the 3D gravity model

A lithospheric density structure of the Bay of Bengal (BoB), which includes the thickest sedimentary layers deposited after continental rifting, is determined from constrained 3D/2D gravity modeling, to understand intricate tectonics processes of the region. The results suggest lateral density variation in the sub-crustal lithospheric mantle and high-density upper mantle is found beneath the thick sedimentary region of BoB. The present density model also predicts the thick lithosphere beneath the huge pile of sediments. The dense and thick lithospheric mantle results are supported by global tomographic and other geophysical results. It is also noticed that the dense mantle and thick sedimentary region have high elastic strength. We propose that the density and strength of the lithospheric mantle in the northern BoB are increased with age and sedimentation since rifting. The cause of density changes in the mantle is indistinct and could occur due to numerous reasons such as the transformation of mantle material catalyzed by a change in pressure and temperature conditions, or mantle flow.

Geophysical and Geochemical Characterization of Solidwaste Dumpsite: A Case Study of Chowa Gujar, Peshawar (Part of Indus Basin)

Open and non-engineered dumping is a typical method for solid waste disposal in most cities of Pakistan. This practice of waste dumping poses a serious threat to the surrounding ecosystem and human population due to the release and transport of decomposed organic matter, i.e., leachate from dumpsite into the groundwater. The present study was conducted over a non-engineered and open dumpsite (Chowa Gujar), located in the outskirts of the highly populated city of Peshawar by using integrated geophysical techniques such as electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) and geochemical techniques. The main goal was to delineate the characterization and depth of buried waste, to map the subsurface extension of contaminant plumes towards agricultural land and groundwater table and the concentration of heavy metals (HMs) in dump and agricultural soil. Geophysical results showed that the thickness of buried waste (predominantly composed of domestic waste) was around 4 m and the leachate plumes have percolated to the adjacent agricultural land. A range of heavy metals (mg/kg) such as Cr (20.5–26.6), Cd (2.6–5.7), Pb (0.35–21.25), Ni (2.5–53.05), Cu (29–68.3), Zn (45.7–77), and Co (18.9–23.2) have been found in the agricultural land adjacent to the dumpsite. The findings demonstrated that combined use of ERT and GPR successfully characterize the buried waste and spread of pollutant plumes spatially and vertically from Chowa Gujar dumpsite. The anomalous geophysical signatures were confirmed by geochemical characterization. The movement of leachate plumes towards agricultural land and groundwater table and the concentration of HMs in soil show that Chowa Gujar dumpsite is a potential source of contamination not only to the surrounding population but also to the agricultural land, surface (Bara River), and subsurface water bodies. In the study region, there is an urgency to take remediation and mitigation measures to reduce the level of pollution created by the dumpsite.

Ground truth validated 3D electrical resistivity imaging of the archaeological deposits at Arma Veirana cave (northern Italy)

ABSTRACTWe present 3D electrical resistivity tomography (ERT) imaging of the archaeological deposits at Arma Veirana cave (northern Italy), to date only partially explored. The archaeological importance of the cave is due to the presence of a rich Mousterian layer, traces of Late Upper Palaeolithic (Epigravettian) temporary occupations and an Early Mesolithic burial of a female newborn. ERT is rarely employed in Palaeolithic cave contexts because Palaeolithic remains are typically disseminated in loose deposits and either do not possess high electrical resistivity contrasts or are too small to be detected. Furthermore, some issues can derive from the confined environment in caves. In this view, our study represents an opportunity to assess the capability of this geophysical method to retrieve subsurface information of Palaeolithic cave deposits and create a framework for the improvement of ERT applications in such a peculiar cave context. The aim of this study was to define the features of the deposits (i.e. geometry, thickness and sediment distribution) and to map the morphology of the underlying bedrock. Results reveal that the thickness of the deposits varies both along the primary axis of the cave and transverse to it. This study allowed the recognition of shallow, meter‐sized, fine‐grained sediment‐filled structures with a longitudinal orientation with respect to the primary axis of the cave, as well as a possible erosional‐like structure. The cross‐validation of geophysical results with the archaeological evidence (the Early Mesolithic newborn burial and Epigravettian artefacts) confirms that the low‐resistivity unit could be the most promising from an archaeological point of view.

Geophysical survey in archaeological context: A review from Cyprus

AbstractCyprus, the third largest Mediterranean island, is located at an exceptional crossroad in the eastern Mediterranean, where cultures from the Middle East, Africa and Europe have interacted for more than 10 000 years. The aim of this paper is to present an exhaustive review of the past archaeological geophysical surveys on the island. The result of our research indicates that to date, more than 30 archaeological sites spanning from the Pre‐Pottery Neolithic (ca. 10 000 BC) to the Venetian period (up to 1571 AD) have been investigated through noninvasive ground‐based techniques. The investigations concern the mapping of the extent of ancient occupation (settlements and cemeteries), the study of the internal organization of settlements (domestic architecture, palaces and fortifications), the investigation of funerary structures (tombs) and the use of space within buildings. The methods implemented are multiple and often used in combination. Emphasis has been given to ground penetrating radar (GPR), electromagnetic induction (EMI) and magnetic and electrical resistance techniques. Most surveys have been targeted towards the production of maps representing the spatial distribution of the subsurface architectural residues, and sometimes these have been accompanied by soundings, tomographies, as well as 3D reconstructions of the ancient structures. Very few sites have been subjected to the measurements of the chemical or magnetic properties of the soils in relation to the results of geophysical prospection. Further discussion concerns (i) the targets of the archaeo‐geophysical surveys in Cyprus, (ii) the limitations of the application of the specific techniques in relation to the Cypriot archaeological and geological context, (iii) the geophysical signatures of archaeological remains and (iv) the metadata accompanying the geophysical results.

МЕТОДИКА ГЕОФІЗИЧНОГО КАРТУВАННЯ ТА МОНІТОРИНГУ МІСЦЬ ЗАХОРОНЕННЯ РАДІОАКТИВНИХ ВІДХОДІВ

Sites of radioactive waste disposal in Chernobyl exclusion zone still contain significant amounts of fissile materials. At the same time, the information on the amount of radioactive material buried during the accident cannot be called satisfactory. Within the strengthening international safety and environmental requirements, special activities were initiated to survey the radioactive waste disposals created during the liquidation of the accident at the Chernobyl nuclear power plant. The work involved the following combination of non-invasive geophysical methods: 1) high-resolution magnetometry; 2) ground penetrating radar (GPR) 3) direct current electrical resistivity tomography (ERT). Magnetometry provided the detailed map of facilities, and highlighted the sites where containers with fissile substances had been buried. ERT models revealed variations in the resistivity across the disposal site, which is associated with different water content, and may indicate flooding. Ground water level was determined from GPR mesurements. The combined interpretation of geophysical results served a basis for designing the geometric model of the "Chernobyl 3rd stage" radioactive waste disposal facility. It was used to determine the places for subsequent applying direct radioactive methods for investigation and monitoring of this disposal site.

The lithospheric effective elastic thickness and its tectonic implications in the Ordos Block and adjacent areas

The Ordos Block, located at the western edge of the North China Block, is a stable rigid block. It is characterized by inactive tectonic activity and rare earthquakes, while the south‐west margin of this block and adjacent areas present the opposite features. There is still considerable ambiguity with regard to the lithospheric mechanical strength in these areas. The effective elastic thickness (Te), widely used for comprehending the mechanism of cratonic deformation and lithospheric dynamics, is a proxy of the lithospheric strength. This study provided detailed two‐dimensional lithospheric Te spatial variations in the Ordos and adjacent areas by using coherence analysis of the topography and Bouguer anomaly. The result showed that the higher Te values in the Ordos Block varied from 80 to 100 km and implied that it is capable of strong rigidity. The lower Te values were distributed over the Qinling Block (20–45 km), the Qilian Block and Haiyuan arcuate tectonic region (20–40 km), as well as the Baryan‐Har Block (15–30 km). By comparing the Te values with the geophysical results, we believe that the higher Te value in the Ordos Block was supported not only by the crust, but also by the upper mantle. In contrast, the mechanical strength of the south‐west margin, especially the Baryan‐Har Block and western Qinling Block, was mainly borne by the brittle upper crust, but the tectonic activity and brittle failure likely resulted in a lower Te. Furthermore, we found that a large number of shallow earthquakes were located above low‐velocity and low‐resistivity layers, most of which probably occurred in the brittle upper crust with small mechanical strength.

Ore-controlling structures of sandstone-hosted uranium deposit in the southwestern Ordos Basin: Revealed from seismic and gravity data

We present the seismic and 3-D gravity study to define the ore-controlling structures of sandstone-hosted uranium deposits in the southwestern Ordos Basin, the second largest sedimentary basin in China. The instantaneous amplitude and frequency are extracted from seismic reflection data, and the seismic impedance is obtained by joint inversion of well-log and post-stack seismic data. Results of the seismic attributes and inversion show that the uranium-bearing deposits exhibit low instantaneous frequencies, low instantaneous amplitudes and medium–low seismic impedances. The scratch analysis method is employed on the residual gravity anomaly generated from the gravity bouguer anomaly by using the potential field separation. The edge coefficient image of the residual gravity anomaly shows that the fault structures are composed of NE-trending faults in the west and EW-trending faults in the east of the study area. The 3-D gravity inversion constrained by the seismic data was performed to reveal that uranium-bearing deposits are characterized by low gravity anomaly, which is related to the larger porosity of the uranium-bearing sandstones. Geophysical results show that the uranium-bearing deposits are controlled by flower structures, EW-trending normal faults and NW-trending thrust faults. Flower structures are produced by the tectonic inversion as a result of the uplift and NE-directed growth of the Tibetan Plateau. Ore-controlling faults cut crossing the floor of the ore-bearing strata as channels, along which the ore-forming fluids move upward and are enriched in the sandstone strata with high permeability and porosity in Luohe Formation. In addition, the roof and floor of the ore-bearing strata in Luohe Formation are characterized by high impedance and gravity anomaly, which has a sealing effect on uranium deposits. Then we predicted the thickness of the sandstones in Luohe Formation, as the sandstone is a prerequisite for mineralization.

Preserving Holocaust history: Geophysical investigations at the Ponary (Paneriai) extermination site

Holocaust mass grave sites in eastern Europe can be difficult to investigate due to a paucity of historical documentation relating to the events and because the use of traditional invasive archaeology methods raises concerns around the disturbance of the remains of Jewish people. When combined with other lines of evidence, including historic photos and eyewitness testimony, noninvasive geophysical methods help to effectively identify and demarcate buried features at Holocaust sites, limiting unnecessary excavations. Between 1941 and 1944, as many as 100,000 people were murdered at the Ponary (Paneriai) extermination site in Lithuania, but many critical details of the site layout during this period are still to be resolved, including the location of some of the mass graves and confirmation of an escape tunnel that was used by slave laborers to escape captivity and certain death at the site. At Ponary, a combination of electrical resistivity tomography (ERT) profiling, limited ground-penetrating radar data, and bare-earth elevation data (from a light and distance ranging data set) was used to confirm the location of a large unmarked mass grave with a diameter of approximately 25 m and depth of approximately 4 m. Additional ERT profiling at a second location imaged the entrance to an escape tunnel previously uncovered by an archaeological excavation in 2004, and it detected an approximately 5 m section of the continuation of the tunnel, approximately 33 m away from the tunnel entrance. The geophysical results are supported by evidence from limited archaeological excavations, historical photographs, eyewitness descriptions of the site layout, and testimonies from the few survivors who managed to escape Ponary.

When faults diverge – High resolution imaging of an intra-fault zone in an urban environment. A case study from the city of Tiberias, Israel

The presence of active faults or potentially active faults in urban settings is of great concern to city planners and developers. The high value of property within cities means that it is not always possible to avoid construction in such areas. Thus, building codes exist in order to regulate where and how to build in the vicinity of such faults. The Israeli National Building Code defines a zone of active faulting as a 200-m wide area on each side of an active or potentially active fault trace. In this area, there is a high potential for repeated activity of undetected branches or secondary faults and construction should be avoided or built with extreme safety measures in place. The current study examines an area located between two fault strands – an active and a potentially active one - in the city of Tiberias, northern Israel. The area lies outside the active fault zones defined for each strand (i.e., at a distance of more than 200 m from each fault). Eight high-resolution ground penetrating radar (GPR) profiles were collected along the streets that crisscross this area. Results show a dense series of potential fault strands that reach the base of the artificial fill that was laid down for the construction of the roads, indicating potential seismic hazard in this seemingly “safe” zone, thus raising a “red flag” for construction plans in the area. A geological study should be conducted to validate the geophysical results. This study shows the importance in conducting a geophysical site survey in tectonically active settings, even in areas that lie outside well defined zones of active faulting.