Geophysical Assessment Research Articles

Effectiveness of geophysical assessment of boreholes drilled in basement complex terrain at Afe Babalola University, using Electromagnetic (E.M.) method

In this research, an Electromagnetic (E.M) method of groundwater investigations was used as an on-spot assessment tool to test the integrity of the developed borehole in Afe Babalola University, Ado-Ekiti. Some randomly selected functional and abandoned boreholes developed by the Vertical Electrical Sounding (VES) methods were chosen for this study, with the aim to know the potential of the boreholes. Four transverses were established across the institution consisting of two functional and two abandoned boreholes selected from the existing forty boreholes. These weresubjected to E.M method of groundwater investigation using a PQWT S500 series machines. The results obtained from this study produced curve graphs and subsurface profile maps of each transverse location. It was observed that boreholes TR 1 and TR 3, were accurately sited on vertical fractures and weathered formations while TR 2 and TR 4 were wrongly sited at the locations of poor groundwater yielding zone.
 Keywords: Electromagnetic, Vertical electrical Sounding, transverse, Groundwater.

Groundwater Aquifer Vulnerability Assessment using a Dar-Zarrouk Parameter in a Proposed Aboru Residential Estate, Lagos State, Nigeria

The need to build an automobile mechanic settlement, abattoir and a proposed meat processing factory at Aboru residential estate necessitated a geophysical assessment (using a Dar-Zarrouk parameter – longitudinal unit conductance, S) of the vulnerability of the subsurface aquifers in the study area against the expected long-term anthropogenic impacts of these facilities on the groundwater system. Thirteen (13) Vertical Electrical Sounding (VES) points and four (4) Dipole-Dipole resistivity profile lines were occupied on four traverse lines across the study area. Isoresistivity and Isopach maps were generated and Total Longitudinal Unit Conductance, S of the earth materials overlying the aquifer was computed and the aquifer protective capacity (APC) map was generated. The VES delineated four (4) geo-electric layers namely; topsoil, pebbly/lateritic sand, clay/clayey/silty sand and sandstone. The depth to the sandstone aquifer ranges from 30.6 – 39.4 m with resistivity values ranging from 851 – 1437 Ωm. The iso-resistivity and isopach maps reveal that the near surface lateritic materials with resistivity values ranging from 350 – 1150 Ωm and thicknesses ranging from 2 – 29 m are pervious. The Total Longitudinal Unit Conductance, S varies from 0.0164 - 0.1168 mhos indicating a poor to weak protective capacity rating across the study area and the APC map reveals that the north-eastern and western parts of the study area show areas with weak protective capacity ratings while other areas are characterized by poor protective capacity rating. As such, the establishment of the proposed service facilities in the study area is strongly discouraged as the nature of their operations has a high potential to contaminate and eventually pollute the sub-surface aquifers on the long-run. If however the inevitability of their establishment cannot be set-aside, then secondary measures must be taken to forestall a direct impact of their operations on the subsurface. Keywords : Aquifer, Dar-Zarrouk, Vulnerability, Longitudinal Unit Conductance

Time‐lapse geophysical assessment of agricultural practices on soil moisture dynamics

AbstractGeophysical surveys are now commonly used in agriculture for mapping applications. High‐throughput collection of geophysical properties such as electrical conductivity (inverse of resistivity) can be used as a proxy for soil properties of interest (e.g., moisture, texture, salinity). Most applications only rely on a single geophysical survey at a given time. However, time‐lapse geophysical surveys have greater capabilities to characterize the dynamics of the system, which is the focus of this work. Assessing the impact of agricultural practices through the growth season can reveal important information for the crop production. In this work, we demonstrate the use of time‐lapse electrical resistivity tomography (ERT) and electromagnetic induction (EMI) surveys through a series of three case studies illustrating common agricultural practices (cover crops, compaction with irrigation, and tillage with N fertilization). In the first case study, time‐lapse EMI reveals the initial effect of cover crops on soil drying and the absence of effect on the subsequent main crop. In the second case study, compaction leading to a shallower drying depth for potatoes (Solanum tuberosum L.) was imaged by time‐lapse ERT. In the third case study, larger changes in electrical conductivity over time were observed in conventional tillage compared with direct drill using time‐lapse EMI. In addition, different N application rates had a significant effect on the yield and leaf area index but only ephemeral effects on the dynamics of electrical conductivity, mainly after the first application. Overall, time‐lapse geophysical surveys show great potential for monitoring the impact of different agricultural practices that can influence crop yield.

Geophysical assessment of aquifer vulnerability and management: a case study of University of Nigeria, Nsukka, Enugu State

Seventeen vertical electrical soundings and seven electrical resistivity tomography profiles were carried out at the University of Nigeria, Nsukka, Enugu State, Nigeria. The study involves the use of Schlumberger and Wenner electrodes configuration. The thrust of this work is on determining the vulnerability of the hydrogeological units by employing the aquifer vulnerability index (AVI) method. The resistivity data measured were interpreted manually and with computer software packages, which gave the resistivity, depth and thickness for each layer within the maximum current electrodes separation. The hydraulic conductivity (K) and hydraulic resistance (C) of the protective layers estimated from the primary parameters estimated have values ranging from 0.0434 to 0.4890 m day−1 and 38.37 to 1005.84 day−1, respectively. AVI of the study shows that the study area is characterised by low to high AVI with moderate AVI as dominant. This is to help in delineating aquifer protective zones and also possible locations, which further helps in groundwater resource exploration and management.

Correlation of P-wave Velocity with Rock Quality Designation (RQD) in Volcanic Rocks

One important part of rock mass investigation is the geomechanical assessment in terms of rock mass classification systems. Rock mass classification is one of themost efficient methods in rock mechanics to provide a basic understanding of rock masscharacterization. Rock mass properties can be determined by a seismic refraction surveyas an indirect geophysical assessment. In this study, the P-wave velocity from seismicrefraction was compared with the Rock Quality Designation (RQD) from the boreholes.The empirical correlation between the RQD and the P-wave velocity was found by usingthe linear regression analysis. The RQD value estimated from the P-wave velocity can beapplied for tropical environment study with geological conditions of volcanic rocks. This study helps to estimate and predict the subsurface rock quality, to reduce investigation costs, and to improve understanding of subsurface rock quality.

Geophysical Assessment of a Proposed Landfill Site in Fredericktown, Missouri.

In cooperation with the U.S. Environmental Protection Agency (EPA), the U.S. Geological Survey (USGS) collected numerous types of geophysical data at a site in Fredericktown, Missouri, in June 2018. Various geophysical surveys were collectively used to help evaluate the overall suitability of the site for use as a mine waste-soil and sediment repository, and to evaluate the suite of geophysical methods for rapid collection and preliminary assessment of sites with shallow sediments. Land-based geophysical methods, which included frequency-domain electromagnetic induction (FDEM), electrical resistivity tomography (ERT), horizontal-to-vertical spectral ratio passive seismic (HVSR), and shear-wave refraction, were used to determine the depths to crystalline bedrock and characterize the overlying unconsolidated sediments (or regolith). Water-borne FDEM profiles and forward-looking infrared (FLIR) thermal image surveys were conducted along the Fredericktown City Lake shoreline to identify locations of potential interactions between groundwater and surface water. Sediment temperature profilers were installed at two locations along the shoreline to characterize shallow unconsolidated sediment thermal properties and support the interpretation of the other geophysical surveys. Geophysical reconnaissance methods including the FDEM and HVSR methods, were used to rapidly evaluate the vertical and lateral extent of overburden, or unconsolidated sediments, overlying the bedrock at the site. The results of these methods were compared to reference geophysical methods of ERT and shear-wave refraction surveys that have greater accuracy and are more labor intensive and time-consuming. A goal of the project was the evaluation of the validity and reliability of this suite of reconnaissance geophysical methods as a means by which shallow (less than 3 meters (m)) sediments can be rapidly assessed. Two orthogonal ERT survey profiles, which used 28 electrodes spaced 1 m apart in dipole-dipole and combined Wenner-Schlumberger configurations, were collected to determine the subsurface resistivity. The results were inverted to produce electrical resistivity profiles that were compared to the FDEM and HVSR survey results. The FDEM data were collected along cleared paths through the proposed disposal cell locations. The data were inverted to generate depth-dependent estimates of electrical conductivity along the transects. An analysis of the depth of investigation (DOI) indicated the FDEM imaged to depths of about 3 m below land surface. The ERT, FDEM, and HVSR indicated the depth to crystalline bedrock was approximately 1.5 m below land surface with shallower and deeper areas. Results from this investigation indicate this suite of methods will likely perform well at sites with shallow depths to bedrock and strong conductivity and acoustic impedance contrasts, where the FDEM and HVSR methods can provide estimates of the depth to bedrock, and ERT and shear-wave refraction surveys might not be worth the added time and expense.

Crustal lithology vs. thermal state and Moho heat flow across the NE part of the European Variscan orogen: a case study from SW Poland

Geotherms of four crustal profiles across the Variscan orogen in SW Poland have been constructed to better understand the variation in thermal state of the region. Seismic and drilling data as well as rock sequences in exposed parts of the orogen were used for Wilcza Góra (Sudetic Block), Polkowice–Rudna (Middle Odra Horst), Święciechowa (Wolsztyn–Leszno Horst) and Września (Szczecin–Miechów Synclinorium within TESZ) profiles. The palaeoclimate-corrected surface heat flow map and the heat-production calculations based on literature data enabled the construction of geotherms and estimation of Moho heat flow. Exception is the Polkowice–Rudna profile, where the surface heat flow was calculated using temperature measurements in underground copper mines, and K, U and Th contents and density/heat conductivity measurements in rocks drilled in the Middle Odra Horst were used to calculate geotherm. The basaltic lava migration through the lithospheric mantle and its effect on crustal geotherm in Wilcza Góra (area of Cenozoic alkaline volcanism at ca. 30–18 Ma) was shown to increase slightly both current surface and current Moho heat flow (by ca. 4 mW/m2). The presented approach couples geological and geophysical information and thus differs from standard purely geophysical assessment of lithosphere thermal state. It shows that surface heat flow is enlarged to 84 mW/m2 by granitic plutons in the upper crust in the Lubin–Polkowice site. Heat flow on the Moho varies from 28 to 34 mW/m2 in sites located in the Sudetic- /Fore-Sudetic Blocks, Middle Odra Horst and Wolsztyn–Leszno Horst. Locally it may slightly increase because of extraneous heat input by Cenozoic basaltic volcanism, but the values close to 30 mW/m2 are specific for mantle root of Saxothuringian Zone in SW Poland. Mantle heat flow is 36 mW/m2 in Września site and supposedly is a manifestation of different nature of lithospheric mantle underlying TESZ.

Geophysical assessment of illegally buried toxic waste for a legal enquiry: A case study in Northern Ireland (UK)

Buried illegal waste and uncontrolled legal waste dumps are a major problem throughout the world, both in developing and more economically developed countries. Criminal investigations can effectively use geoscience techniques to better understand how to locate and characterize such waste. When a case is brought to the courts, the volume, areal extent of the likely waste and land ownership needs to be estimated. This article presents a brief overview of how the investigative process currently occurs and evidences the estimation of waste volume and land owner areas by a case study. The case study illustrates how a combination of geodetic topographic and near-surface geophysics surveys were used to both determine the amount of illegal waste present on a site and assess whose land (in this case, above or below High Tide Mark) the material had been buried on.

Geophysical Assessment of Subsurface Conditions at Proposed Building Sites: Implications for Foundation Failure and Building Collapse

Abstract Building collapse has been a recurrent environmental hazard in Nigeria in the last two decades. This is a corollary of inadequate foundation investigation prior to construction, poor government policies, and general lack of awareness on the importance of geophysical and geotechnical investigations. In this study, geological mapping and detailed geophysical investigation using Electrical Resistivity Imaging (ERI) and Vertical Electrical Sounding (VES) were carried out to understand the suitability of proposed building sites at the main campus of the Olabisi Onabanjo University (OOU), Ago-Iwoye, Nigeria for construction. Both Wenner array and dipole-dipole were used for profiling and Schlumberger for sounding. Four transverses and VES were used in each of the three areas investigated. Our results show that the subsurface of the study areas is underlain by Precambrian basement rock of Nigeria. Rocks in the study area include banded gneiss, porphyroblastic gneiss, biotite-hornblende granite and quartzite schist. The sounding stations across the three areas and 2D resistivity imaging revealed three principal geoelectric layers, the topsoil, the weathered layer and the fractured/fresh basement with varied resistivity values for each layers. At the VES stations, the three geoelectric layers have resistivity values of 62 to 1182 Ωm, 3.2 to 1360Ωm and 87 to 4680 Ωm. On the 2D resistivity imaging profiles, the resistivity of the three layers varies from 2 to 1182 Ωm, 30to 1360 Ωm, and 40 to 2904 Ωm for the topsoil, the weathered basement, and fractured/fresh bedrock. Our work demonstrates that some of the proposed sites are structurally incompetent for engineering or foundation purposes. Excavation of the topsoil and reinforcement are required to sustain the proposed structures.

Geophysical assessment for vertical leachate migration profile and physicochemical study of groundwater around the Olusosun dumpsite Lagos, south-west Nigeria

The study was aimed at assessing the vertical movement of leachate from 2001 through 2015, and groundwater physicochemical parameters analysis around the Olusosun dumpsite, through a time-lapse study.Tracking the leachate vertical migration profile was achieved through analysis of VES time-lapse data obtained from previous investigations on the dumpsite between 2001 and 2006, and 2D resistivity data acquired from this study in 2014 and 2015. Seventeen borehole and hand-dug well water samples were obtained randomly from 17 sampling locations around the dumpsite, first, in August 2014 (wet season) and then a repeat in December 2015 (dry season). The results of the VES data and 2D resistivity analysis showed that there is a constant and progressive increase in the depth of migration of the contaminants generated on this site into the subsurface environment over the years. It also showed that the contaminated zones are characterised by resistivity values ranging from 0.63 to 12.5 Ωm, and a maximum depth of 120 m has been impacted by the contaminants. The results of the water sample analysis showed clear variations for the various elemental constituents analysed for. Most of the physicochemical parameters analysed fell within the World Health Organisation (WHO) and the Nigerian Standard for Drinking Water Quality (NSDWQ) standard limit. Comparing the wet and dry season results, there was generally an increase in the mean concentrations of TDS, EC, temperature, hardness, Ca2+, Mg2+, K+, Na+, {text{Cl}}^{ - } , {text{NO}}_{3}^{ - } , Zn, Cu, Pb and Cr from the dry season study, particularly the samples with close proximity to the dumpsite. On the other hand, there was reduction in the mean concentrations of {text{SO}}_{4}^{2 - } , {text{PO}}_{4}^{3 - } , Fe, pH, and Ni from the dry season study when compared with the wet season. This trend could be attributed to the fact that in the absence of rainfall during the dry season period, contaminant accumulation in groundwater continued undiluted due to continuous breakdown of the biodegradables units with time, and this led to the generally high concentration of the physicochemical properties during the dry season. The implication is that the water around the study area has lower quality in the drier season when compared to the quality of water during the wet season, and so water treatment should be given more priority during the dry season before consumption and usage for other domestic purposes to avoid waterborne diseases. Generally, the information obtained from the geophysical study will facilitate decisions on improving protection for groundwater resources around the study area.

Geophysical assessment for contaminant hydrology in Ujevwu, Nigeria

Indiscriminate dumping of both domestic and industrial waste has been increasing since the beginning of the exploration and exploitation of hydrocarbon in the Niger Delta area of Nigeria and has impacted the groundwater quality. Therefore, this study seeks to evaluate contaminant hydrology from dumpsite around Ujevwu area in relation to a Control site. Three Electrical methods, which include the spontaneous potential, dipole-dipole and the vertical electrical sounding were adopted. Also laboratory water analysis and groundwater/contaminant modelling using VISTA, version 4 were used to evaluate groundwater quality and flow direction/velocity. The low values of 11–515 Ωm and 10 to −160 mV for resistivity and spontaneous potential respectively around the dumpsite area to a depth of about 20 m is a reflection of the redox phenomenon occurring at depth in the contaminated groundwater. Hydrogeochemical parameters from water analysis showed values that are higher around the dumpsites when compared to the control site. Results for conductivity, lead and total viable bacteria count are higher than the permissible limits of the World Health Organisation (WHO) and they range from 380 to 440 μs/cm, 0.2–0.3 mg/l and 4.2–15.8 cfu/mL respectively. The steady state groundwater distribution model of the dumpsite and control site gives an approximate head gradient of about 0.00036 and 0.0007 respectively, and the flow direction in the south west. It is observed that the water level indicates that there is no significant change of the hydraulic gradient with time and therefore, the groundwater flow is assumed to be in steady state with the flow direction in the NE-SW, and a flow rate of 0.0093 m/d or 3.3 m/year, and 0.0197 m/d or 7.0 m/year respectively. From these results, immediate evacuation of the dumps in the area and remediation program should be carried out, as there is a risk of outbreak of water borne diseases in the area.

Geophysical Assessment of Groundwater Potential: A Case Study from Mian Channu Area, Pakistan.

An integrated study using geophysical method in combination with pumping tests and geochemical method was carried out to delineate groundwater potential zones in Mian Channu area of Pakistan. Vertical electrical soundings (VES) using Schlumberger configuration with maximum current electrode spacing (AB/2 = 200 m) were conducted at 50 stations and 10 pumping tests at borehole sites were performed in close proximity to 10 of the VES stations. The aim of this study is to establish a correlation between the hydraulic parameters obtained from geophysical method and pumping tests so that the aquifer potential can be estimated from the geoelectrical surface measurements where no pumping tests exist. The aquifer parameters, namely, transmissivity and hydraulic conductivity were estimated from Dar Zarrouyk parameters by interpreting the layer parameters such as true resistivities and thicknesses. Geoelectrical succession of five-layer strata (i.e., topsoil, clay, clay sand, sand, and sand gravel) with sand as a dominant lithology was found in the study area. Physicochemical parameters interpreted by World Health Organization and Food and Agriculture Organization were well correlated with the aquifer parameters obtained by geoelectrical method and pumping tests. The aquifer potential zones identified by modeled resistivity, Dar Zarrouk parameters, pumped aquifer parameters, and physicochemical parameters reveal that sand and gravel sand with high values of transmissivity and hydraulic conductivity are highly promising water bearing layers in northwest of the study area. Strong correlation between estimated and pumped aquifer parameters suggest that, in case of sparse well data, geophysical technique is useful to estimate the hydraulic potential of the aquifer with varying lithology.

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria

The geophysical assessment of groundwater in Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is predominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very low frequency electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES) methods. The VLF-EM survey was at 10 m interval along eight traverses ranging between 290 and 700 m in length using ABEM WADI VLF-EM unit. The VLF-EM survey was used to delineate areas with conductive/fractured zones. Twenty-three VES surveys were carried out with the use of Campus Ohmega resistivity meter at different location and at locations areas delineated as high conductive areas by VLF-EM survey. The result of VLF-EM survey along its traverse was used in delineating high conductive/fractured zones, it is, however, in agreement with the delineation of the VES survey. The VES results showed 3–4 geoelectric layers inferred as sandy topsoil, sandy clay, clayey and fractured/fresh basement. The combination of these two methods, therefore, helped in resolving the prospecting location for the groundwater yield in the study area.

The geochemical and petrological characteristics of prenatal caldera volcano: a case of the\xa0newly formed small dacitic caldera, Hijiori, Northeast Japan

Evaluating the magma depth and its physical properties is critical to conduct a better geophysical assessment of magma chambers of caldera volcanoes that may potentially cause future volcanic hazards. To understand pre-eruptive conditions of a magma chamber before its first appearance at the surface, this paper describes the case of Hijiori caldera volcano in northeastern Japan, which emerged approximately 12,000 years ago at a place where no volcano ever existed. We estimated the depth, density, bulk modulus, vesicularity, crystal content, and bulk H_2O content of the magma chamber using petrographic interpretations, bulk and microchemical compositions, and thermodynamic calculations. The chemical mass balance calculations and thermodynamic modeling of the erupted magmas indicate that the upper portion of the Hijiori magmatic plumbing system was located at depths between 2 and 4 km, and had the following characteristics: (1) pre-eruptive temperature: about 780 ^{circ }C; (2) bulk magma composition: 66 ± 1.5 wt% SiO_{2}; (3) bulk magmatic H_2O: approximately 2.5 wt%, and variable characteristics that depend on depth; (4) crystal content: le57 vol%; (5) bulk modulus of magma: 0.1–0.8 GPa; (6) magma density: 1.8–2.3 g/cm3; and (7) amount of excess magmatic H_2O: 11–32 vol% or 48–81 mol%. The range of melt water contents found in quartz-hosted melt inclusions (2–9 wt%) suggests the range of depth phenocrysts growth to be wide (2sim13 km). Our data suggest the presence of a vertically elongated magma chamber whose top is nearly solidified but highly vesiculated; this chamber has probably grown and re-mobilized by repeated injections of a small amount of hot dacitic magma originated from the depth.

Geophysical Assessment of Vulnerability of Surficial Aquifer in the Oil Producing Localities and Riverine Areas in the Coastal Region of Akwa Ibom State, Southern Nigeria

Geophysical Assessment of Vulnerability of Surficial Aquifer in the Oil Producing Localities and Riverine Areas in the Coastal Region of Akwa Ibom State, Southern Nigeria

Geophysical Assessment of the Upper Dja Series Using Electrical Resistivity Data

The upper Dja series consists of carbonates and shales deposits that date 580 ± 150 Ma. Petrography and mineral chemistry studies helped to differentiate this series into many sequences including massive limestone layers with calcite (CaO3) contents of about 30 to 42%. In order to determine the subsurface distribution of these sequences, a geophysical prospection campaign was carried out in which a total of 24 vertical resistivity soundings were recorded over a surface area of 9 km2. The processing and interpretation of data using the IX1D and OpendTect modeling tools permitted the distinction of two massive limestone layers in the upper Dja series. The first layer of about 10 to 35 m thick and outcrop in few places is characterized by resistivity ranging between 1110 and 2377 Ωm, while the second layer located beyond 50 m deep is separated by a very conductive clay stone layer with a capped thickness of 15 to 35 m. 3D modeling of the top and base of these formations indicates that, the whole Upper Dja series of about 190 m thick presents folded structure. These results can constitute a useful base of information in regards to a large scale economic study of the Upper Dja limestone series.

Hydrogeologic and Geophysical Assessment of Groundwater Prospects and Aquifer Vulnerability in Alade Idanre, Southwestern Nigeria

Hydrogeologic and Geophysical Assessment of Groundwater Prospects and Aquifer Vulnerability in Alade Idanre, Southwestern Nigeria

Geophysical assessment of potential hydrological units in hydrologically challenged geomaterials of Makurdi, Benue State, Nigeria

A geo-electric survey employing the Vertical Electrical Sounding (VES) was carried out in order to access the distributions of electrical and hydraulic parameters of hydro-geologic units in some locations of Makurdi where groundwater resources are difficult to tap. A total of fifteen geo-electric soundings were acquired. The contour maps were generated using the results. From the bulk aquifer resistivity and water resistivity values, the formation factor was calculated and it ranges from 4.12 to 10.07. The porosity with a range of 24.58 to 39.36% and hydraulic conductivity with a range of 0.85 to 45.1 m/day were estimated. The porosity values confirm that hydro-geologic units in the study area consist mainly of sandstone. The high resistivity in the northern part of the study area is due to high water quality while the southern part has lower resistivity due to the presence of argillaceous materials. It is also observed that the areas with low resistivity have high porosity. The observed low resistivity zone with high porosity is believed to have poor interconnected pores, the condition for high total or absolute porosity in argillaceous materials. The analyses of the geophysical data constrained by geological and borehole information revealed that potable water can be extracted within the depth of 35 to 50 m in the study area. Key words: Porosity, formation factor, hydraulic conductivity, aquifer resistivity, Makurdi, geo-electric survey.

Geophysical assessment of contamination due to explosives in an abandoned facility towards its hydrogeological characterization

This paper discusses a case study concerning the application of geophysical methods in long-term contaminated areas with explosive compounds and their input to the environmental assessment and hydrogeological characterization. The study is focused on the old factory of Sociedade Portuguesa de Explosivos, located in Seixal, Portugal, that produced explosives for almost 50 years and was closed about 15 years ago. The remains of the activity consist on the production of poly-nitroaromatic compounds that were deposited inside the facilities perimeter and caused negative environmental impacts in the soils and groundwater of the area. Although several studies have been conducted in the Sociedade Portuguesa de Explosivos facilities area and focused on the aquifers to assess the environmental impact of contaminated areas, they were mostly restricted to borehole studies and hydrochemical organic and inorganic compounds analysis of groundwater sampled in the numerous boreholes existing in the area. In the present study, this information is complemented with geophysical surveys that comprised several methods, namely electrical resistivity tomography and both time and frequency domains electromagnetics. Geoelectrical parameters determined with the geophysical surveys and laboratory determinations were related with physical and chemical parameters from soil samples collected in two shallow investigation boreholes located in a poly-nitroaromatic deposition area. These surveys allowed not only an important input to the general assessment of the Sociedade Portuguesa de Explosivos environmental situation but also the evaluation of its effects in the surrounding area and constitute an important input towards its hydrogeological and environmental characterization. They also give information about in situ geoelectrical characteristics of poly-nitroaromatic compounds in long-term attenuation process.

Geophysical assessment of migration and storage conditions of fluids in subduction zones

By enhancing mass transfer and energy release, the cycle of volatiles and melt is a major component of subduction. Investigating this fluid cycle is therefore critical to understand the past and current activity of subduction zones. Fluids can significantly affect rock electrical conductivity and elastic parameters that are measured using electromagnetic and seismic methods, respectively. This letter emphasizes how these geophysical methods complement each other to provide information about the storage of fluids in subduction systems. By compiling electromagnetic and seismic results from various subduction zones, a possible correlation between electrical conductivity and seismic wave attenuation anomalies in the mantle wedge is observed, consistent with fluid accumulation. A possible relationship between geophysical properties and the slab age is also suggested, whereas no significant trend is observed between electrical conductivity or seismic wave attenuation and estimates of water flux in the mantle wedge. These field-based relationships require further constrains, emphasizing the need for new measurements in the laboratory.