Electrical Resistivity Tomography Investigations Research Articles

Confirmation of Nature of Palaeo-course of Assi River, India: Some Significant Revelations from Electrical Resistivity Tomography

ABSTRACT A long and continuous palaeo-course of Assi River, in between Prayagraj and Varanasi, in the Ganga River plains with indications of good groundwater potential had been traced from remote sensing data. Electrical Resistivity Tomography (ERT) has been conducted along eight lines for confirmation of the same palaeo-course in general and to specifically ascertain the nature of the course—the past flow conditions and the type of deposits. The variation in the thickness of channel deposits along the concave and convex banks and the middle parts is an indication of lean flow. The mixed fractions of channel deposits are an indication of dumping of sediments in the dying stages of a river. The ERT investigation has further helped in delineating the high resistive palaeo-channels (20 to 50 Ohm.m), the low resistivity aquiclude clay layer (<15 Ohm.m) and the deeper and relatively higher resistivity sandy layer (>50 Ohm.m), which could be the principal aquifer in the area.

Electrical resistivity tomography: A reliable tool to monitor the efficiency of different irrigation systems in horticulture field

Water management in agricultural systems is essential for optimal crop yields without incurring excessive water costs and wastage. The choice of irrigation method is crucial for better water management and distribution. The drip system appears to be among the best methods in the field of precision agriculture. In addition to the irrigation system, mulching with ridge plastic film to drain excess water is widely used to increase crop yields in terms of plant water availability. In this study, the time-lapse Electrical Resistivity Tomography (ERT), a not-invasive geophysical technique, is proposed as a simple and reliable method to evaluate the effectiveness of the irrigation systems and to monitor the changes in water content over time and over a volume of soil. ERTs data were compared to moisture ones retrieved from sensors that record continuously over time, but punctually. The ERT investigations were conducted in melon-growing lands in southern Tuscany (Italy). Measurements were carried out on two different fields in two periods: spring and summer. The aim of the work was to evaluate, by means of volumetric measures of the soil conductivity, the effectiveness of three different drip systems and of the mulch ridge. In both the monitored fields the ridge was created in a half portion of the field itself, while the other part of the land was left plat. Geoelectrical investigations associated with humidity sensors have shown that in the summer a too high mulch ridge quickly drains the irrigation water, bringing the root zone into a water deficit. The ERTs also provided good results relating to the irrigation system, demonstrating that a three-lines drip irrigation system, compared to a two-lines one, manages to distribute the irrigation water homogeneously, guaranteeing a constant water content for the plants over time.

Electrical resistivity tomography (ERT) exploration data in drought prone areas case study: Buriram Province, Thailand

An electrical resistivity tomography (ERT) investigation was conducted across four drought-prone districts in the Buriram Province, Thailand. The primary objective was to evaluate and map the potential of groundwater reservoirs as sources of water for household and agricultural purposes during the dry season. It was accomplished through the implementation of the Schlumberger array configuration. An electrical resistivity survey instrument was used to generate a 2D resistivity model of the electrical resistance profiles, or pseudo section profiles. The survey instrument included more than 50 electrodes, enabling the investigation of the profile to a depth of up to 50 m from the ground surface. The resistivity values obtained from the field data were recorded and converted or interpreted using RES2DINV software. The data were analysed by comparing them with the geological information about the site and referencing the geological borehole data as at 50 m depth from the surface. The results of the ERT survey indicated that groundwater in the arid areas of the Buriram Province can be found at shallow depths around 10–20 m from the surface and it is deposited in sedimentary and clay layers, and it has remained relatively stable over a 2-year period with the water level measured by an electric probe in the summer, winter and rainy seasons in Thailand.

Electrical Resistivity Tomography (ERT) Investigation for Landslides: Case Study in the Hunan Province, China

Electrical resistivity tomography is a non-destructive and efficient geophysical exploration method that can effectively reveal the geological structure and sliding surface characteristics inside landslide bodies. This is crucial for analyzing the stability of landslides and managing associated risks. This study focuses on the Lijiazu landslide in Zhuzhou City, Hunan Province, employing the electrical resistivity tomography method to detect effectively the surrounding area of the landslide. The resistivity data of the deep strata were obtained, and the corresponding geophysical characteristics are inverted. At the same time, combined with the existing drilling data, the electrical structure of the landslide body is discussed in detail. The inversion results reveal significant vertical variations in the landslide body’s resistivity, reflecting changes in rock and soil physical properties. Combined with geological data analysis, it can be concluded that the sliding surface is located in the sandy shale formation. Meanwhile, by integrating various geological data, we can conclude that the landslide is currently in a creeping stage. During the rainy season, with rainfall infiltration, the landslide will further develop, posing a risk of instability. It should be promptly addressed through appropriate remediation measures. Finally, based on the results of two-dimensional inversion, this article constructs a three-dimensional surface morphology of the landslide body, which can more intuitively compare and observe the internal structure and material composition of the landslide body. This also serves as a foundation for the subsequent management and stability assessment of landslides, while also paving the way for exploring new perspectives on the formation mechanisms and theories of landslides.

Depth estimation of buried targets using integrated geophysical methods: comparative studies at Ahmadu bello university geophysics test site

Accurate prediction of depth and position of underground structures is a critical step in structural foundation surveys such as civil engineering excavations to adequately maintain the existing underground utilities. The study presents the results of comparative studies conducted to evaluate the performance of electrical resistivity tomography (ERT) alongside the VLF-EM method regarding depth estimation and location of buried targets of known materials, properties and dimensions. A laboratory test was carried out on the buried targets to determine the electrical properties of the buried targets before burial. The pre-burial geophysical investigation indicates no major anomaly within the site that could influence the geophysical response of the buried objects significantly. The results of the post-burial geophysical investigation indicate high variations in electrical resistivity values varying from 47 Ωm – 1081 Ωm (before) and 0.113 Ωm – 19,879 Ωm (after) the buried targets, while the VLF-EM data indicates that the current density values within the site were significantly influenced due to the presence of buried materials, confirming major influence or distortion of geophysical signature of the site. In post-burial ERT investigation, the Wenner and dipole-dipole (DD) arrays registered 67 % and 80 % degrees of alignment with the actual depth of the buried targets, respectively. Both Wenner and DD arrays show strength in depth estimation. However, the DD array indicates higher strength in terms of depth estimation and it is potentially suitable for near-surface utilities investigation due to its high precision in depth estimation. In comparison, VLF-EM captured six (6) out of eight (8) buried targets with a 47 % degree of alignment with the actual depth of the buried targets, which is far lower than the ER method, and may not be considered the most preferable method for geophysical prospecting where depth estimation of targets is of prime interest. However, the depth of targets varies from one method to another and one array to another.

The use of non-invasive ERT method to diagnose karst in roadengineering in the Lublin Upland (Poland)

Appropriate design in linear construction depends on many factors, including detailed geological conditions. One of the biggest problems are unrecognized erosion forms, in particular karst ones, which have a huge impact on the design and subsequent operation of roads. For this purpose, in addition to conventional methods such as drilling or geotechnical probing, which are point-based, non-invasive spatial geophysical methods are used. This article presents an example of the use of geoelectrical surveys, Electrical Resistivity Tomography (ERT) for the recognition of karst zones for linear investments. The article describes ERT investigations, which to some extent allows to identify dangerous karst phenomena occurring in the Lublin Upland (Poland), which are of great importance at the design stage of roads and in their further safe operation. Non-invasive geophysical research has been verified and confirmed by traditional geotechnical research, which confirms the effectiveness of their use. The Electrical Resistivity Tomography was used as a method providing a broader spectrum of knowledge on the spatial arrangement of soil layers in the subgrade of the planned road investments. It also enabled a more accurate, more detailed interpretation of geotechnical studies. The described geophysical investigations opens wide possibilities for their application to researchers. In the future, non-invasive methods have a chance to become as reliable as geotechnical methods, but this requires a lot of research to improve the effectiveness and accuracy of the interpretation of the obtained results.

Electrical Resistivity Tomography Investigation of Permafrost Conditions in a Thermokarst Site in Fairbanks, Alaska

<abstract> <p>The degradation of permafrost poses severe environmental threats to communities in cold regions. As near-surface permafrost warms, extensive topographic variability is prevalent in the Arctic and Sub-Arctic communities. Geologic hazards such as thermokarst are formed due to varying rates of permafrost degradation, resulting in ground subsidence. This gradual subsidence or abrupt collapse of the earth causes a danger to existing infrastructure and the economic activities of communities in cold regions. Understanding the causes of thermokarst development and its dynamics requires imaging its underground morpho-structures and characterizing the surface and subsurface controls. In this study, we conducted a two-dimensional (2D) electrical resistivity tomography (ERT) survey to characterize the permafrost conditions in a thermokarst prone site located in Fairbanks, Alaska. To increase the reliability in the interpretability of the ERT data, borehole data and the depth-of-investigation (DOI) methods were applied. By using the 2D and three-dimensional (3D) ERT methods, we gained valuable information on the spatial variability of transient processes, such as the movement of freezing and thawing fronts. Resistivity imaging across the site exhibited distinct variations in permafrost conditions, with both low and high resistive anomalies observed along the transects. These anomalies, representing taliks and ice wedges, were characterized by resistivity values ranging from 50 Ωm and above 700 Ωm, respectively. The results from this study showed the effectiveness of ERT to characterize permafrost conditions and thermokarst subsurface morpho-structures. The insights gained from this research contribute to a better understanding of the causes and dynamics of thermokarst, which can be instrumental for engineers in developing feasible remedial measures.</p> </abstract>

ERT investigation of mud volcanoes: detection of mud fluid migration pathways from 2D and 3D synthetic modelling

Mud volcanoes are geological structures observed throughout the world that arise from the upwelling of deep fluids along discontinuities in the subsoil. The detection of mud fluid migration pathways can be challenging, even when using Electrical Resistivity Tomography (ERT) as detectability issues may arise from complex geological settings. This paper presents new results from 2D and 3D ERT synthetic modelling for the investigation of the shallow, internal structure of terrestrial mud volcanoes. This study revealed the internal structure of the ‘Cenerone-Pineto’ mud volcano (Central Italy) and provided further clues as to its internal structure. The main results of the study are: the presence of a mud chamber, which represents the last phase of mud accumulation before final emission, not located beneath the crater but laterally offset, as well as the presence of a narrow, shallow feeder channel; these findings represent evidence of a much more complex structure than one would expect. This means that the mud volcano is not supplied with mud fluids directly from below as would be the case with an uprising of deep fluid along a near-vertical open fracture and that the shallow mud fluid reservoir is not correlated to the distribution of any mud volcano observed on the surface. Findings from this study are consistent with the observed structural features already noted in ERT and seismic field data collected at the ‘Cenerone-Pineto’ mud volcano and may be helpful in explaining the mechanisms and processes involved in mud volcanism in similar geological settings.

Cavity detection using a pseudo-3D electric resistivity tomography at the Palaeolithic/Neolithic site of Scaloria Cave, Apulia, Italy: integrated assessment of synthetic and field data sets

A pseudo-3D electrical resistivity tomography (ERT) survey has been carried out to detect cavities at the Neolithic/Palaeolithic site of Grotta Scaloria, close to Manfredonia, Apulia, Italy. Scaloria Cave has a rich history of archaeological research of more than 80 years and is one of the most important Neolithic complexes in the Mediterranean. Synthetic data modelling allowed to check the adequacy of the geophysical method and to develop a proper experimental setup at the survey design stage. Indeed, the results of the field data inversion revealed high resistivity anomalies which can be related to cavities and provided a good definition of the main geological structures and boundaries. Moreover, the results suggest that unknown and speleological unexplored cavities are still present at the Scaloria Cave study site. These findings may provide further insights on pseudo-3D ERT applicability, particularly for cavity detection. Furthermore, the approach used in this study yields fruitful information for further archaeological survey design and for the interpretation of ERT investigations targeting similar geological features and structures.

Landslide Investigation through Emerging Technology of Electrical Resistivity Tomography

A landslide is an event of a disaster and has adverse effects on every country with varying degrees of impact. The lithology's complex nature, the vast slide area and the landslide's topography make the direct investigation challenging. In depth landslide investigation demands multidisciplinary knowledge, skilled human power and costly testing equipment, making direct investigation tedious and time-consuming. However, an alternative for the direct investigation is needed to cover all the aspects of landslide mechanism. Recently advanced geophysical methods have an excellent potential for collecting landslide mechanism-related information without disturbing them. One such method is effectively used to investigate the soil's subsurface properties as one of the significant threats to stability is rainfall in a landslide-prone area and its resolve is effectively called Electrical Resistivity Tomography (ERT). The present study endeavors to display cutting-edge research on the applications of Electrical Resistivity Tomography (ERT) in the field of landslide investigation. The foremost objective of the study is to present the outcomes of geophysical surveys conducted through ERT, which encompass 1D, 2D, 3D and time-lapse investigations. The study also highlights the advantages and limitations of these ERT investigations and identifies potential challenges that need to be addressed for the optimum utilization of ERT in future research.

Monitoring of soil contamination from olive mill wastewater (OMW) using physico-chemical, geotechnical analysis and electrical resistivity tomography (ERT) investigation

Monitoring of soil contamination from olive mill wastewater (OMW) using physico-chemical, geotechnical analysis and electrical resistivity tomography (ERT) investigation

Multidisciplinary Research of Thermal Springs Area in Topusko (Croatia)

Topusko is the second warmest natural thermal water spring area in Croatia, located at the southwest edge of the Pannonian Basin System. Due to favourable geothermal properties, these waters have been used for heating and health and recreational tourism since the 1980s. Thermal springs with temperatures up to 50 °C are the final part of an intermediate-scale hydrothermal system. However, systematic research on the Topusko spring area has not been conducted to lay the foundation for sustainable resource utilisation. Multidisciplinary research including the hydrogeochemical characterisation of naturally emerging thermal water, an electrical resistivity tomography (ERT) investigation conducted to reconstruct the subsurface geology, and hydrogeological parametrisation of the geothermal aquifer was carried out to refine the existing local conceptual model. The results show Ca-HCO3 facies of Topusko thermal waters, which get heated in a Mesozoic carbonate aquifer. The water equilibrium temperature in the geothermal aquifer is estimated to be 78 °C based on the SiO2-quartz geothermometer. The fault damage zone, which enables the upwelling of thermal water, was identified by ERT investigations. The transmissivity values of the aquifer derived from the results of step-drawdown tests range from 1.8 × 10−2 to 2.3 × 10−2 m2/s. Further multidisciplinary research is necessary to improve the existing conceptual model of the Topusko hydrothermal system.

2D electrical resistivity tomography (ERT) investigation of a landslide: A case study from Ali Mendjeli, Constantine, North-East of Algeria

ABSTRACT Constantine is city characterised by a very rugged relief in which frequently happened the collapse of buildings as a result of landslide hazards. The aims of this study are to determine the depth of the surface landslide and to evaluate the landslide mass in the new city of Ali Mendjeli, which is nearby Constantine in Northeastern Algeria, using a geophysical method, namely the electrical resistivity tomography (ERT). Five two-dimensional (2D) ERT profiles were performed along and across the landslide using Wenner electrode array. Two parallel profiles to the sliding direction of 69 m length of each profile and three other perpendicular profiles, each with a length of 115 m, were conducted with inter-electrode spacing of 3 and 5 m, respectively. The resistivity data processing was carried out using Res2Dinv software. The inverted pseudo-section models presented formations characterised by low resistivities which can be summarised in two sets ranging from 1.38 to 6.20 Ωm and from 6.20 to 19 Ωm. The inverted resistivity data were correlated and calibrated with respect to the subsoil lithology obtained by well drilling and inclinometer tests. According to the inclinometer displacements, the measurements were of the order of 2–3 mm for a depth of 10 m and between 17.5 and 19.5 m for a depth of 13 m. The combined measurements of ERT and the geotechnical testing not only have shown a good agreement in the results obtained but also have successfully detected the depth of probable rupture surfaces and displaced materials likely to slip. This concordance of the obtained results. The estimated volume of the sliding material was around 20.000 m3. According to the obtained results of this study, ERT can be applied to detect sliding surfaces in landslides.

Insights on the active Southern Matese Fault system through geological, geochemical, and geophysical investigations of the CO2 gas vent in the Solopaca area (southern Apennines, Italy)

The south-eastern sector of the Matese Massif (southern Apennines, Italy) includes several nonvolcanic gas (mainly CO2) vents. The gas emissions in the northern part (Ciorlano-Ailano sector) have been associated with the Southern Matese Fault system, whereas a similar relationship is not evident in the southern part (Telese-Solopaca sector). Hence, we investigated the latter area (hills north of Solopaca town) through a multidisciplinary study of the principal CO2-degassing vent (Santantuono spring). The main goal is to reconstruct the structural architecture of the area and study the role of the fault array in conveying the gas migration to the surface. In particular, an integrated approach that combines structural and stratigraphic investigations with CO2 flux and geoelectrical surveys is proposed to shed light on the relationships between near-surface faults and gas rising. The main results from the geological-structural investigation suggest that thrust faults are the oldest structures, mainly verging to NNW, crosscut by high-angle N-S and younger NW-SE normal faults. This understanding is supported by the results of the CO2 flux survey, which records the highest flux values in correspondence with the mapped young normal faults, especially at their intersections. Moreover, the hypothesized tectonic and stratigraphic structure at depth is entirely consistent with the 3D geoelectrical model of the survey area provided by a 3D electrical resistivity tomography investigation, which also identifies the main NW-SE striking fault as the preferential pathway for gas migration. Finally, we suggest that the reconstructed NW-SE faults are the prolongation of the active Southern Matese Fault system bounding the SW Matese Massif margin defined by different segments with dominant normal kinematics and several gas vents.

Detection of Groundwater Pathways to Monitor Their Level Rise in Osirion at Abydos Archaeological Site for Reducing Deterioration Hazards, Sohag, Egypt Using Electrical Resistivity Tomography Technique

Climatic changes because of groundwater levels rising near the archaeological sites became a fundamental issue in Egypt. The problem will affect the deterioration of the stone foundations of the temples and any archaeological features, which will affect their deformation, changing their features, and their archaeological and architectural importance. Osirion in Abydos archaeological place, west of Sohag Governorate, undergoes this problem where the level of ground water increases west of this site in the spring season. Solving this problem will help to preserve the antiques at the Abydos site and, in particular, the Osirion and its surrounding area. It is important to understand the hydrostratigraphic conditions of the Abydos site and its surroundings. The main objectives of the work are: (1) characterizing the subsurface succession and lithology; (2) identifying the sources responsible for the groundwater level rising near the Osirion, and groundwater assessment distribution and water table depth; and (3) evaluating the subsurface location and geometry of any paleochannels that may represent conduits for groundwater flow pathways to join the water to the studied site. All this information will aid the officials to decide and make future solutions to solve these problems. To achieve these goals, the authors implemented an advanced geophysical technique, namely electrical resistivity tomography (ERT) investigations in conjunction with the existing boreholes data. The main outcomes of this work are 2D and 3D representations of the resistivity distributions, which reflect a full picture about the subsurface engineering layers, including details of the lithology of the study site. The subsurface succession includes four geoelectrical zones that were recognized. The water table level in the study site varies from 5 m to 14 m as confirmed from all the ERT profiles together with the available borehole data. A three-dimensional visual representation of the water-bearing muddy sand formation shows the presence of a potential channel in the north-east direction and its location, which is responsible for delivering the groundwater from the Nile River to the Osirion site. This result is in consistent with archaeological studies conducted in the Osirion site, where there are ancient archaeological text and drawings on the temple walls and columns. By defining the direction of the groundwater pathways, the authors recommend the decision-makers to take the engineering precautions to try to prevent the groundwater from reaching the important archaeological sites by establishing the dams and partitions. In addition, they should monitor and control the groundwater level changes around the archaeological foundations by implementing all the necessary measurements to prevent the soil subsidence and foundation collapse, and establishing a dewatering system network.

Geophysical investigations to search for the remains of sister Chiara Isabella D'Amato

This paper reports the results of the integrated geophysical surveys performed inside the Monastery of St Chiara in Nardó in southern Italy. Ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) investigations were carried out to find the tomb of Sister Chiara D’Amato, whose location has been lost over the centuries. Sister Chiara Isabella D'Amato was a charismatic and holy figure. She died in 1693. She was buried inside the monastery but her body has never been found. The data acquisition was performed along with a series of closely spaced lines for GPR and using a non-standard array for ERT. Data were processed and visualised as two-dimensional vertical sections and depth slices or three-dimensional volumes (GPR and ERT) to allow an integrated interpretation of the geophysical results. The analysis of the geophysical data sets revealed a series of anomalies that could be ascribed possible archaeological structures, probably related to the earliest ages of the sacred building as well as other anomalies (bedrock, fractures) of presumable natural origin. In particular, one geophysical anomaly was suspected of being connected to burial and consequently further investigated with the use of a video endoscope. The results reveal the presence of a void but it has not yet been clarified whether it is the burial of Sister Chiara or not as it is awaiting the excavation.

Surface Deformations Resulting from Abandoned Mining Excavations

The occurrence of surface discontinuous deformations in post-mining areas is currently a significant and important problem, due to both the frequency of their occurrence and the threat they pose to public safety. This paper presents the results of research concerning the possibility of sinkhole formation in the areas of abandoned mining excavations. For the purpose of assessing the condition of the rock mass disturbed by the existence of numerous mining excavations, electrical resistivity tomography investigations were carried out for the selected area where mining was undertaken in the past at shallow depths and many underground workings accessing the deposit exist. The sinkhole hazard was also analysed theoretically with a new original model based on the solution of A. Sałustowicz’s pressure arch theory.

Geophysical investigations for the identification of active seismic faults below alluvium for seismic hazard assessment

ABSTRACTThe existence of active faults hidden below Quaternary alluvium is a common geological scenario for intermontane basins, such as the areas struck by the recent earthquakes in Central Italy, and is of great importance for seismic hazard evaluation. Finding hidden faults is a challenging task from the geophysicist's point of view since the goal is twofold: to identify the seismic bedrock at a certain depth; and to detect lateral variations or dislocations that may indicate the presence of a fault. We propose a mixed approach encompassing at first single‐station seismic noise measurements, to detect sudden lateral variations in the bedrock surface in a fast and cost‐effective way, which might serve as a proxy for the potential identification of fault zones. Then, more accurate electrical resistivity tomography investigations are carried out only at selected sites as indicated by the preliminary noise analysis, as electrical methods cannot effectively be employed at a large scale for time and economic limitations. Surface‐wave dispersion analysis is jointly interpreted together with ambient noise data to improve the seismic characterization of the alluvium, giving further insight on the assessment of the depth to bedrock. The proposed approach can be an effective way to manage and investigate a large portion of the territory within a sensible budget, as commonly needed in seismic hazard assessment and microzonation studies. We present a real‐world application to the San Vittorino Plain (Central Italy) close to the epicentre of the 24 August 2016 Amatrice earthquake, where the geological faulted bedrock is covered by alluvial sediments of the Velino River up to a maximum estimated thickness of 150–200 m. Although engineered for the post‐earthquake reconstruction emergency, the approach employed in our study can be adopted in other areas of similar geology, to ease the application of seismic microzonation in time of seismic silence as a tool for long‐term land planning and management.

Interpretation on water seepage and degree of weathering in a landslide based on pre‐ and post‐monsoon electrical resistivity tomography

ABSTRACTThe influence of rainfall on the Pakhi landslide has been examined using a pre‐ and post‐monsoon timelapse electrical resistivity imaging technique. The results obtained have been used to characterize the subsurface based on the depth and degree of water seepage and degree of weathering. The combined interpretation of pre‐ and post‐monsoon electrical resistivity tomography is not very common in landslide characterization. This study focuses on post‐monsoon electrical resistivity tomography investigation and its interpretation in conjunction with earlier research on pre‐monsoon investigations. The advancing water seepage across depth was reflected in the sharp decrease in the post‐monsoon resistivity value of the top (near‐surface) colluvial layer, mostly at the crown and toe portions of the investigated slope, as compared to that of weathered dolomites and fresh dolomites. Hence, the water‐saturated colluvium deposits could easily be delineated using a timelapse pre‐ and post‐monsoon electrical resistivity tomography technique. On the basis of degree of saturation, the materials were classified into four zones, namely: a highly saturated zone with resistivity values <600 Ωm; a fairly saturated zone with resistivity values 600–2500 Ωm; a low saturated zone with resistivity values 2500–4500 Ωm; and an unsaturated zone with resistivity values >4500 Ωm. Further, a twofold classification of dolomites based on the degree of weathering, namely highly weathered dolomites with resistivity values 1000–2500 Ωm and low weathered dolomites with resistivity values 2500–4500 Ωm, is presented. This type of information will add value to the design of landslide‐monitoring programmes and also for landslide stability analysis. Therefore, the method can be highly recommended as a cost‐ and time‐effective as well as an efficient way for characterization of potential landslide slopes.

Ground penetrating radar and electrical resistivity tomography investigations in the southern sector of the Roman Forum: First results on the pre‐Augustan phases of the Basilica Julia

AbstractA research project aimed at the study of the archaeological context of the Basilica Julia in the Roman Forum (Rome, Italy) and the transformation phases of the building involved the use of different techniques of geophysical prospecting. In particular, Ground‐penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) surveys were carried out in order to record the buried structures of the Basilica and the previous buildings laying in the southern part of the Forum. These geophysical methods have been chosen in order to guarantee a good compromise between resolution (GPR in the shallow subsurface) and depth of investigation (ERT in the deeper subsurface), with the aim of investigating up to a depth of about 10 m in a very conductive subsoil. In particular, GPR surveys were conducted in the five aisles of the monument, while ERT measurements were performed with nonstandard acquisition mode in order to include the entire perimeter of the building. These techniques allowed us to acquire new data on the structures buried in the sectors of the monumental complex that have never been excavated and on the paleosoil till a depth of about 10 m from the surface. Interesting data were acquired on the Basilica Julia itself, built during the late Republican period (54–46 BC) and rebuilt at the beginning of the first century AD, such as the technical features of the caementicium and travertine foundations, their relationship with the Cloaca Maxima and the traces of a design change occurred during the construction in the central aisle of the building; other buried remains of the previous Basilica Sempronia, constructed in 169 BC in the same area, were identified. Moreover, the investigations documented the paleosoil in the area between the Forum and the Velabrum to the south, between 7.5–8.5 and 5.5 m a.s.l. These data confirmed the general geological setting of the area, obtained from previous coring, but significantly specified the geomorphology of this border sector of the Roman Forum, which slopes down towards the south and the west.