Use Of Geophysical Techniques Research Articles

Geophysical methods help to assess potential groundwater extraction sites

Complex geology in glacial terrain makes groundwater exploration challenging for water supply companies. Abrupt lateral changes of geological conditions, for example, raise the risk of unsuccessful exploration drilling. At some locations, local water supply companies experience a large number of dry wells, raising the need for better exploration approaches. The use of geophysical techniques enables the detection and characterization of subsurface structures in terms of aquifers and aquitards.We present two examples in which seismic and resistivity methods are combined for subsurface characterization. A thrust structure is detected in the Varde study area in Denmark and a channel structure is mapped in the Hamburg-Sülldorf study area in Germany. The different imaging characteristics of seismic P‑ and S‑waves are demonstrated. The combination of seismic and resistivity methods enables delineating groundwater-bearing and groundwater-barrier layers down to a depth of 150 m.

Delineation of Groundwater Potential Zones using Integrated Approach in Semi-Arid Hard Rock Terrain, Kanavi Halla Sub-Basin, Belagavi District, Karnataka

Water scarcity has become a major problem especially in arid and semi-arid regions due to insufficient rainfall throughout the globe. This has led in serious search for groundwater resources. Kanavi Halla Sub Basin (KHSB) of Ghataprabha River basin drained by Ghataprabha River, Belagavi District of Karnataka state in India has been considered for present study. Electrical resistivity survey was carried out at selected sites using Schlumberger method with four electrode configuration. A total of 22 Vertical Electrical Sounding (VES) were conducted throughout KHSB and representative of different litho units were considered. Data obtained were then interpreted using curve matching technique with IPI2Win software. The interpreted graphs show three to six layers. The various interpreted curve types are of AAK-type, HA-type, A-type, KH-type, HAA-type, KQH-type, AK-type, K-type, HQH-type, H-type and AKQH-type. From the results it shows that the maximum number of curves are associated with A type which refers to hard rock terrain, whereas curve associated with H type indicates water potential site. The expected subsurface strata are interpreted on the basis of observed bore well drilling data. Borewell log reveals soil formation followed by moderately weathered formation, weathered jointed formation, jointed formation, hard formation from top to bottom. Further deep, the formation is devoid of joints and fractures. Therefore, the weathered, jointed formation may be interpreted as water bearing zone. 2-D geo-electric section has been drawn using IPI2WIN over eight selected trends to understand the geometry of the aquifer formed. The investigation was meant to characterize the aquifer in KHSB along with the risk assessment for contaminants through seepage in terms of protective capacity with the help of Dar-Zarrouk (D-Z) parameters such as longitudinal unit conductance (S), longitudinal resitivity (ρ1), transverse unit resistance (T), transverse resistivity (ρt), Electrical anisotropy(λ) and root mean square resistivity (ρm). These were evaluated to know the aquifer conditions in order to demarcate the freshwater bearing zones. South eastern part of KHSB might be contaminated and 30% of the area is weak to poor capacity protective zone for contaminants. The work adequately highlights the practical use of geophysical techniques, combination of geo-electrical modelling, D-Z parameters, borehole log in the groundwater resource assessment process. This technique is highly recommended for the area with similar geological setup.

Defining groundwater resource protection zones in aquifers using stable isotope analysis: a case study from the Namazgah Dam Basin in Turkey

Understanding mechanisms of groundwater recharge in karst aquifers that are used as a source of drinking water is vital for sustainable water management. In this study, 18O, 2H and 3H isotopes were used to understand the physical processes which affect water flow in a karstic region and for determining the locations of groundwater recharge areas and residence time in the Namazgah Dam Basin in Turkey. Overlay analysis was carried out with a geographic information system platform using residence time, recharge altitude and type and the hydraulic conductivity of geologic formations to identify protection zones of springs used for water supply. This assessment was supported by dye-tracer tests and the use of geophysical techniques. The methodologies used in this study could be used to develop water resource protection zones in other karstic regions where limited data are available.

A Regional Approach to Ancient Urban Studies in Greece Through Multi-Settlement Geophysical Survey

ABSTRACTThe systematic exploration of large archaeological sites in the Mediterranean has evolved considerably since the “big dig” excavations. Pedestrian field surveying and remote sensing applications, including satellite and airborne image analysis, are now practical and relatively cost-efficient methods of characterizing large and diachronically diverse landscapes on regional scales. However, the use of geophysical techniques as a means for exploring manifold archaeological contexts is still in its infancy. In this paper, we highlight the advantages of archaeological geophysics to conduct regional surveys in the Mediterranean. Through a multi-site geophysical fieldwork campaign to investigate the patterns and dynamics of ancient cities in Greece, we show how geophysics offer new opportunities for characterizing the spatial attributes and regional dynamics of urban landscapes, and, in doing so, we make an argument for its wider adoption on regional survey projects.

+40 years of Geophysics in Pilbara and Beyond Sponsor paper

The Pilbara region of North West Australia is one of the world’s major iron ore provinces. Geophysical techniques have been applied routinely for exploration of iron ore. The first known application of a geophysical technique in mineral exploration was, in fact, the use of a magnetic method in the search for iron.This presentation summarises the use of geophysical techniques in iron ore exploration over the last half century. Magnetic methods have been the most favoured, followed by gravity. EM has been applied in niche areas, such as in the exploration for CID. However it is time to venture beyond conventional techniques and start focusing on future developments in geophysics that promise yet greater benefits to mining generally and iron ore exploration in particular.

Use of Geophysical Techniques for the Localization of the Restricting Zones of Permeability in the Bottom of Basin: Forecasting the Zones of Clogging

Use of Geophysical Techniques for the Localization of the Restricting Zones of Permeability in the Bottom of Basin: Forecasting the Zones of Clogging

Geophysical techniques for low enthalpy geothermal exploration in New Zealand

Shallow warm water resources associated with low enthalpy geothermal systems are often difficult to explore using geophysical techniques, mainly because the warm water creates an insufficient physical change from the host rocks to be easily detectable. In addition, often the system also has a limited or narrow size. However, appropriate use of geophysical techniques can still help the exploration and further investigation of low enthalpy geothermal resources. We present case studies on the use of geophysical techniques for shallow warm water explorations over a variety of settings in New Zealand (mostly in the North Island) with variable degrees of success.A simple and direct method for the exploration of warm water systems is shallow temperature measurements. In some New Zealand examples, measurements of near surface temperatures helped to trace the extent of deeper thermal water.The gravity method was utilised as a structural technique for the exploration of some warm water systems in New Zealand. Our case studies show the technique can be useful in identifying basement depths and tracing fault systems associated with the occurrence of hot springs.Direct current (DC) ground resistivity measurements using a variety of electrode arrays have been the most common method for the exploration of low enthalpy geothermal resources in New Zealand. The technique can be used to detect the extent of shallow warm waters that are more electrically conductive than the surrounding cold groundwater. Ground resistivity investigations using the electromagnetic (EM) techniques of audio magnetotellurics (AMT or shallow MT), controlled source audio magnetotellurics (CSAMT) and transient electromagnetic (TEM) methods have also been used. Highly conductive clays of thermal or sedimentary origin often limit the penetration depth of the resistivity techniques and can create some interpretation difficulties. Interpretation of resistivity anomalies needs to be treated in a site specific manner.

Review Of Geophysical Applications in Australian archaeology

Multidisciplinary approaches are now commonplace in the investigation of archaeological sites worldwide. Consequently, geophysics has become an increasingly important tool for reconstructing past landscapes and investigating research questions. However, despite their acceptance internationally, in Australia the use of geophysical techniques on archaeological sites has been underutilised. This paper examines the history of archaeological geophysics in Australia and seeks to understand, given their potential advantages, the role that factors such as costs, time, instrument availability and lack of theoretical knowledge have played in the underrepresentation of these methods in local archaeological investigations to date. With the recent introduction of short courses in archaeological geophysics to at least one Australian tertiary institution, this review is a timely overview of where this discipline has been, what it has to offer and whether there is potential for Australian archaeologists to develop the skills necessary to conduct archaeological geophysic investigations, as their international counterparts do already, in the future.

Use of geophysical methods for soil profile evaluation

A geophysical investigation was performed to evaluate the effectiveness of three geophysical methods (electrical resistivity imaging (ERI), seismic refraction (SR), and multiple-channel analysis of surface waves (MASW)) for geotechnical site characterization in swamps and environmentally sensitive wetland areas. The geophysical test results were verified against the results from borehole and cone penetrometer test logs. The ERI results were best for determining the depth to the glacial till. However, the resolution of the ERI survey was not sufficient to accurately predict the upper lithologies. The electrode spacing (4 m) was instead selected to reliably predict the depth to the till, which in this case varied between 4.6 and 10.7 m. The SR results overestimated the depth to the till because of the presence of a stiffness reversal. The MASW results predicted the depth to the refusal till layer less accurately than the ERI method. However, this method was able to detect the three distinct layers above the till, even though the layer thicknesses were consistently underestimated. The complementary use of geophysical techniques was a successful approach in determining the main soil units and the depth to the competent layer (till) at the site. These methods can be used as a basis for further development to optimize a procedure to reduce the number of boreholes required for conventional site investigations in areas that are environmentally sensitive or where access is restricted.

Geophysical Techniques for Low Enthalpy Geothermal Exploration in New Zealand

Shallow warm water resources associated with low enthalpy geothermal systems are often difficult to explore usinggeophysicaltechniques,mainlybecausethewarmwatercreatesaninsufficientphysicalchangefromthehostrockstobe easily detectable. In addition, often the system also has a limited or narrow size. However, appropriate use of geophysical techniques can still help the exploration and further investigation of low enthalpy geothermal resources. We present case studies on the use of geophysical techniques for shallow warm water explorations over a variety of settings in New Zealand (mostly in the North Island) with variable degrees of success. Asimpleanddirectmethodfortheexplorationofwarmwatersystemsisshallowtemperaturemeasurements.InsomeNew Zealand examples, measurements of near surface temperatures helped to trace the extent of deeper thermal water. ThegravitymethodwasutilisedasastructuraltechniquefortheexplorationofsomewarmwatersystemsinNewZealand. Ourcasestudiesshowthetechniquecanbeusefulinidentifyingbasementdepthsandtracingfaultsystemsassociatedwiththe occurrence of hot springs. Direct current (DC) ground resistivity measurements using a variety of electrode arrays have been the most common method for the exploration of low enthalpy geothermal resources in New Zealand. The technique can be used to detect the extentofshallowwarmwatersthataremoreelectricallyconductivethanthesurroundingcoldgroundwater.Groundresistivity investigationsusingtheelectromagnetic(EM)techniquesofaudiomagnetotellurics(AMTorshallowMT),controlledsource audio magnetotellurics (CSAMT) and transient electromagnetic (TEM) methods have also been used. Highly conductive clays of thermal or sedimentary origin often limit the penetration depth of the resistivity techniques and can create some interpretation difficulties. Interpretation of resistivity anomalies needs to be treated in a site specific manner.

Comparisons of magnetic and electrical resistivity surveys over simulated clandestine graves in contrasting burial environments

ABSTRACTDetermining the effectiveness and limitations of near‐surface, non‐invasive geophysical techniques is imperative when attempting to locate clandestine burials. Unlike in archaeology, there has been limited forensic research with regard to optimum methodologies, with most emphasis to date being on metal detectors and ground‐penetrating radar. However, these techniques may not be suitable in certain soil types (e.g., conductive or highly magnetic) or for certain non‐metallic targets. Therefore, in this study, magnetic and electrical resistivity detection techniques have been utilized over different aged (0.25–1 year) simulated clandestine burials with no buried metal, in contrasting depositional environments. These environments included semi‐rural, urban, woodland and a parkland medieval grave site acting as an archaeological analogue.The magnetic surveys showed mixed success in detecting clandestine burials. Elevated magnetic gradient readings, with respect to background values, were observed over very shallow burials, whereas deeper burials displayed a reduction in gradient and/or no associated magnetic anomalies. Magnetic anomalies were observed over surface‐burials and validated by simple 2D forward modelling. Magnetic anomalies were also observed in the control data set. Electrical resistivity surveys produced anomalies over all the simulated burial positions, including surface burials but did not produce anomalies at the archaeological analogue site.Laboratory analysis of fluid retrieved from simulated graves showed an overall increase in iron levels over a year post‐burial, which may account for the observed magnetic anomaly variation. There was also a corresponding increase in grave ‘fluid’ conductivity, which was interpreted to be the cause of the observed low resistivity anomalies.This research suggests that, as a technique for locating clandestine burials, bulk ground resistivity is more successful than the tested magnetic methods. Moreover, magnetic techniques are more effective when used as part of a multi‐technique study over rural and semi‐rural sites that are relatively low in magnetic and electrical ‘noise’. These results have important implications for the use of geophysical techniques when searching for clandestine burials. We emphasize that local depositional environment, soil type, likely style of burial and search area size should all be considered when choosing forensic geophysical detection techniques. We also provide evidence to show that geophysical data can assist in locating a primary deposition site even when no physical evidence remains.

Use of geophysical techniques to conceptualise groundwater connectivity and sub-surface nutrient (NO3) fluxes in hydrogeologically complex terrain

Use of geophysical techniques to conceptualise groundwater connectivity and sub-surface nutrient (NO3) fluxes in hydrogeologically complex terrain

DETECTING TRENDS IN THE PREDICTION OF THE BURIED PAST: A REVIEW OF GEOPHYSICAL TECHNIQUES IN ARCHAEOLOGY*

Geophysical survey techniques are a highly visible part of the scientific toolkit that is now used by archaeologists. In this paper, the history of the use of geophysical techniques in archaeology will be discussed, as will significant research themes associated with the most widely used prospecting devices. It is apparent that while the use of geophysical techniques is at an all‐time high, there are many key areas where prospecting is rapidly developing. Some of the advances relate to fundamental aspects of the techniques, while others dictate how we undertake survey in the future. There is a movement away from pre‐gridded survey areas towards real‐time GPS for navigation. This allows greater integration, or fusion, of disparate data sources using visualization techniques derived from associated disciplines. The analysis of landscapes has become a major component of the application of new technology and there are many challenges to be tackled, including how to analyse and interpret significant archaeology within large‐scale, data‐rich, multi‐technique investigations. The reflective nature of the review acknowledges the important role of Archaeometry in the development of archaeological geophysics.

Application of field geophysics in geomorphology: Advances and limitations exemplified by case studies

During the last decade, the use of geophysical techniques has become popular in many geomorphological studies. However, the correct handling of geophysical instruments and the subsequent processing of the data they yield are difficult tasks. Furthermore, the description and interpretation of geomorphological settings to which they apply can significantly influence the data gathering and subsequent modelling procedure ( e.g. achieving a maximum depth of 30 m requires a certain profile length and geophone spacing or a particular frequency of antenna). For more than three decades geophysical techniques have been successfully applied, for example, in permafrost studies. However, in many cases complex or more heterogeneous subsurface structures could not be adequately interpreted due to limited computer facilities and time consuming calculations. As a result of recent technical improvements, geophysical techniques have been applied to a wider spectrum of geomorphological and geological settings. This paper aims to present some examples of geomorphological studies that demonstrate the powerful integration of geophysical techniques and highlight some of the limitations of these techniques. A focus has been given to the three most frequently used techniques in geomorphology to date, namely ground-penetrating radar, seismic refraction and DC resistivity. Promising applications are reported for a broad range of landforms and environments, such as talus slopes, block fields, landslides, complex valley fill deposits, karst and loess covered landforms. A qualitative assessment highlights suitable landforms and environments. The techniques can help to answer yet unsolved questions in geomorphological research regarding for example sediment thickness and internal structures. However, based on case studies it can be shown that the use of a single geophysical technique or a single interpretation tool is not recommended for many geomorphological surface and subsurface conditions as this may lead to significant errors in interpretation. Because of changing physical properties of the subsurface material ( e.g. sediment, water content) in many cases only a combination of two or sometimes even three geophysical methods gives sufficient insight to avoid serious misinterpretation. A “good practice guide” has been framed that provides recommendations to enable the successful application of three important geophysical methods in geomorphology and to help users avoid making serious mistakes.

Geophysical Investigations at the Pulemelei Mound

ABSTRACT To obtain further information concerning the internal structure of the mound Pulemelei mound and its temporal and spatial relation to structures and habitation areas in the vicinity, investigations using remote sensing methods ground penetrating radar and a magnetometer have been employed. The use of geophysical techniques at Pulemelei was a pilot project to evaluate if they might be applied more broadly to monumental sites in the Pacific.

Advances in Geophysics

There has always been a gap between the disciplines geophysics and geology with people working in these fields commonly situated in different departments within companies and in different faculties at Universities. However, the goals that these two solitudes are trying to achieve are ultimately the same whether it is exploring for an economic deposit, mapping geology or understanding the processes of the earth. When geologists work in heavily vegetated and weathered terrains and areas with younger cover, the use of geophysical techniques is no longer an option. Similarly, without a good understanding of the causative geology an interpretation of a geophysicist is at best devalued and at worse erroneous. Whatever our core discipline, to gain advantage advance we must integrate and employ the main strengths of both geophysics and geology. This issue of the South African Journal of Geology contains a selection of geophysical papers from authors in South Africa and demonstrates the excellence of geophysical endeavours in the region. The standard definition …

GeoPASS: a decision support system for selecting the optimal geophysical technique for shallow surveys

In this paper we present a decision support system for selecting the optimal geophysical technique to detect shallow land targets (< 80 m-bs, i.e. less than 80 m below the surface). The system is freely available on the Internet. The aim of the decision support system is to stimulate geophysicists and end-users to assess the applicability of geophysical techniques prior to a survey in order to increase the chance of a satisfactory outcome. In the long term this will hopefully lead to enhanced recognition of the value of geophysics. The use of geophysical techniques for investigating environmental problems is less then it could be. In our view an important reason for this is that, in the Netherlands at least, geophysics in quite a number of cases does not supply the information expected by the end-user. The information is often vaguer or more ambiguous than environmental managers are used to, and/or the performance of the geophysical technique is poor due to the characteristics of the site and/or soil. The poor performance may also be caused by the application of a less suitable technique or the use of a non-optimal field-design. Applying geophysical methods without satisfactory results for end-users is, in the long term, bad for geophysics in general. Often these unsatisfactory results are due to a lack of assessment of the applicability of the geophysical techniques at specific sites prior to the survey. Such assessments hardly cost any time, especially when site characteristics are known and are backed by a geophysical decision support system. As geophysicists, we think that geophysical measurements can, if used properly, become more and more important for subsurface investigations for environmental and infrastructure projects. The well-known advantages of geophysical techniques are that a lateral continuous image of the subsurface is obtained and that geophysics is generally less destructive for the subsoil than, for example, drilling. To overcome the problem of applying non-optimal techniques, a decision support system was designed within the framework of the European HYGEIA Project (Hybrid Geophysical technology for the Evaluation of Insidious contaminated Areas). The system is called GeoPASS. In the past, several organizations developed tools for selecting a geophysical technique for a specific problem. Crosstables indicating which technique(s) could be applied to certain problems have been prepared by several organizations and companies. These tables are mostly general and do not indicate whether the technique will be successful for a specific site. A good example can be found at the website of the Swiss Geophysical Commission (www.aug.geophys.ethz.ch/gpmapping). One other geophysical decision support system asking the user more detailed information about the site characteristics is known to the authors. This system, called GAES, was specifically designed for detecting pollutants (Geophysics Advisor Expert System, Gary R. Aloft, USGS Open-File Report 92- 526). However, the system is not very user-friendly, rather old (1992), and the outcome is a set of rather general remarks about the applicability of geophysical techniques. GeoPASS is designed to provide the user with an estimate of the chance of success of several geophysical techniques. The target may be either a pollutant or a relevant subsurface feature (e.g. sealing clay layer, fracture). The outcome of GeoPASS may even be that none of the assessed geophysical techniques can detect the target given the site conditions. The aims of GeoPASS are to: ■ Provide an estimate of the success chance of geophysical techniques at a specific site and therefore avoid the application of geophysical techniques that are not appropriate ■ Make the end-user aware of the chance of success expected of the geophysical technique(s) to be applied and the factors that influence that chance ■ Give an initial estimation of the costs of a geophysical survey on the site GeoPASS also serves as a checklist. If no information about the site and target parameters is available, it is difficult to predict whether a geophysical technique is capable of supplying the required results. This situation is prone to mis-use by some enthusiastic geophysicists and geophysical companies, often resulting in disappointed end-users. Hopefully the use of GeoPASS will lead to more 'happy faces' among the end-users of shallow geophysical techniques and therefore enhance recognition of the value of geophysical techniques in general.

Electrical and magnetic response of archaeological features at the early neolithic site of Movila lui Deciov, western Romania

AbstractAn archaeological geophysics survey was conducted on the early neolithic site of Movila lui Deciov, in the Province of Banat, Romania. Magnetometry and electromagnetic terrain conductivity were used for the main prospection effort, and a test of electrical resistivity imaging was conducted on a selected profile. In addition, magnetic susceptibility measurements were obtained from excavation pit samples.The magnetic survey was successful in determining the extent of the site, in delimiting zones rich in structures and artefacts, and in confirming the presence of a ditched enclosure that could be the earliest known in the region. The electromagnetic survey was limited by a lack of resolution of electrical property contrast. Detailed joint modelling of the magnetic and electrical response of the subsurface was used to confirm that electrical resistivity imaging can provide depth information to complement magnetic mapping.One of very few reported in Romania, this survey paves the way for an increased use of geophysical techniques in the cultural heritage management of this country. From a methodological viewpoint, this work further demonstrates the potential of electrical resistivity imaging in archaeology Copyright © 2004 John Wiley & Sons, Ltd.

Sandstone-type uranium deposits in South Australia and North America: A comparison of their geophysical characteristics

The sandstone-type uranium deposits in the Frome Embayment and Eucla Basin, South Australia, are characterised by uranium oxide mineralisation in the form of roll-fronts at redox boundaries. The host rocks are Tertiary clastic sediments deposited in palaeochannels, but now covered by up to 150 m of cover. None of the deposits are associated with surface radiometric anomalies. These deposits were discovered in the 1970s, but Government policy prevented exploitation at that time. With mining now permitted, there is renewed interest in these deposits and exploitation is underway, or imminent, and new resources are being sought. The comparatively low cost of drilling restricted the use of geophysical techniques during initial exploration, with downhole logging being the most extensively used method. Nevertheless, reconnaissance geophysical surveys were used to locate the prospective palaeochannels, with resistivity soundings proving most useful. Recent TEMPEST airborne EM surveys over the Billeroo/Curnamona and Yarramba palaeochannels, located in the Frome Embayment, have demonstrated that this method allows detailed mapping of the palaeochannels, despite the thickness of the cover. The electromagnetic response is attributed to the conductivity of contained saline groundwater. Once the palaeochannel sequence had been located, alteration zoning within the host sandstones, associated with characteristic responses on downhole logs, was used to locate the redox interface. An understanding of the channel stratigraphy and sedimentary environment, specifically the likely location of prospective permeable formations, was also largely based on downhole logs. Attempts to use electrical methods to detect areas of increased pyrite content, associated with the redox boundary, and to determine the redox state of the host sandstones, met with mixed success. A comparison of the use of geophysics in South Australia with exploration for similar deposits in the United States shows some aspects in common, in particular the use of downhole logging to map alteration. However, care must be taken when making comparisons, since variations in the type of deposit can significantly affect their geophysical signatures.

Evaluation of multifrequency airborne EM for opal prospect definition at Lightning Ridge, NSW

The NSW Department of Mineral Resources has been evaluating the use of geophysical techniques as a tool to better understand controls on opal formation in the Lightning Ridge district of New South Wales. A detailed study over the Gurley Ridge, approximately 25km southwest of the Lightning Ridge township, commenced in June 2001. This Cretaceous sedimentary ridge hosts the Coocoran Opal Field and includes the productive Allahs and Natelies Dream prospects. Current geological understanding predicts opal occurrence at the interface of clay and sandstone horizons within the sedimentary package. The study included a compilation of historic drill records, detailed surface geological mapping, lithofacies mapping, and acquisition of detailed airborne electromagnetic data. An electrical model of the subsurface generated from previous ground work was used to guide selection of the transmit?receive frequencies employed in the airborne survey. The acquired multifrequency airborne data were inverted and conductivity depth images for each flight and tieline produced. The CDI sections revealed the existence of an ubiquitous conductor located between 10m and 20m below the surface, covering the majority of the ridge area. A ground follow-up program was instigated to investigate the identified conductive zone. Eight high-resolution, detailed transient EM ground lines were acquired coincident with various conductive signatures identified in the airborne data. A small drill program was conducted to ground truth both the airborne and TEM subsurface conductive features. Drill results, downhole geophysical logs, and the detailed ground TEM data have been used to validate and refine inversion of the airborne data.