CONTRIBUTION OF GEOPHYSICAL METHODS TO THE INVESTIGATION OF GEOTHERMAL CONDITIONS IN THE SOUTHWESTERN PART OF THE STRYMON BASIN (MACEDONIA, NORTHERN GREECE)

The Strymon basin is one of the most important sedimentary basins in Northern Greece where significant geothermal fields are located. The SW part of the Strymon basin manifests geothermal interest. Available geophysical data (seismic, gravity, magnetic and electrical data) contributed to the identification of major faults that control the fluid-flow paths of the geothermal field and the estimation of depth to the metamorphic basement. The former is of great importance because the geothermal aquifer is expected to be at the contact of the basal conglomerate with the metamorphic basement. The highest thermal gradient values (10-15o C/100 m) were observed in the western part of the study area near the known geothermal field of Therma – Nigrita. Other important geothermal anomalies (>6o C/100 m) occur in the Patriki area, north of the village of Ivira and in the area between the villages of Patriki and Achinos. Geothermal interest manifests itself in the following areas: north of Mavrothalassa (>4o C/100 m), southwest of Ivira and east of Agios Dimitrios. It appears furthermore that the main thermal anomaly is associated with two NW-SE fault systems that affect the basement in the areas of Patriki and north of Achinos - Ivira correspondingly. These faults have been detected by the use of geophysical surveys. The presence of NE-SW faults extends the anomaly southwestwards.

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Investigations in groundwater flow toward a spring in the Saphire area, Soufriere, Saint Lucia, West Indies

The Leading Edge ◽

10.1190/tle38060460.1 ◽

2019 ◽

Vol 38 (6) ◽

pp. 460-464

Author(s):

Frank Dale Morgan ◽

Saleh Al Nasser ◽

Ruel Jerry ◽

Ananias Verneuil

Keyword(s):

Groundwater Flow ◽

Geophysical Methods ◽

Housing Development ◽

Tree Cover ◽

Flow Paths ◽

Biological Contamination ◽

Geophysical Surveys ◽

Saint Lucia ◽

Area Of Concern ◽

Underground Flow

The Cocoa Grove Group is planning a housing development on approximately 5.5 acres in the area of Saphire, Diamond, Saint Lucia. Directly downhill of the property is a Water and Sewage Company (WASCO) spring that supplies drinking water to the town of Soufriere. This potable water is of high purity. Concern was expressed by WASCO as to the advisability of implementing development directly above the emanation of the spring. The obvious concerns were the possible change in flow volumes and chemical and biological contamination if a housing development was completed. F. D. Morgan and the Saint Lucia Water Resources personnel representing the Cocoa Grove Group discussed whether geophysical methods could be used to map the direction of groundwater flow into the spring. The group agreed that geophysical methods could be used in an attempt to delineate the underground flow paths into the spring. It was made clear that investigations could produce results that could be either favorable or unfavorable to the proposed development. Consequently, geophysical surveys were planned and executed in the area of concern to measure resistivity and self potentials. The geophysics did not indicate evidence of substantial fluid flow into the spring. However, we were able to locate the main water supply from the top of Terre Blanche down toward the spring. The flow comes downhill via a significant geologic fracture that is hidden from sight in the dense tree cover. Recommendations were made that it is relatively safe to develop the site as intended with respect to possible water contamination. In conclusion, we also recommended that WASCO take water from another point of a topographic step on Terre Blanche. Doing so would reduce the contamination risk essentially to zero from the planned housing development area.

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Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

Journal of Environmental and Engineering Geophysics ◽

10.32389/jeeg9-067 ◽

2020 ◽

Vol 25 (3) ◽

pp. 415-423

Author(s):

Ahmed Lachhab ◽

El Mehdi Benyassine ◽

Mohamed Rouai ◽

Abdelilah Dekayir ◽

Jean C. Parisot ◽

...

Keyword(s):

Heavy Metals ◽

Seismic Velocity ◽

Seismic Refraction ◽

Geophysical Methods ◽

Low Frequency ◽

Electrical Current ◽

P Wave ◽

Low Resistivity ◽

Refraction Tomography ◽

Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

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Application of geophysical methods for the investigation of the large gravitational mass movement of Séchilienne, France

Canadian Geotechnical Journal ◽

10.1139/t05-034 ◽

2005 ◽

Vol 42 (4) ◽

pp. 1105-1115 ◽

Cited By ~ 66

Author(s):

O Meric ◽

S Garambois ◽

D Jongmans ◽

M Wathelet ◽

J L Chatelain ◽

...

Keyword(s):

Rock Mass ◽

Mass Movement ◽

Seismic Refraction ◽

Geophysical Methods ◽

Time Lapse ◽

Gravitational Mass ◽

Electrical Tomography ◽

Refraction Tomography ◽

Geophysical Surveys ◽

Geophysical Techniques

Several geophysical techniques (electromagnetic profiling, electrical tomography, seismic refraction tomography, and spontaneous potential and seismic noise measurement) were applied in the investigation of the large gravitational mass movement of Séchilienne. France. The aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists, whose lateral and vertical limits are still uncertain. A major observation of this study is that all the zones strongly deformed (previously and at present) by the movement are characterized by high electrical resistivity values (>3 kΩ·m), in contrast to the undisturbed mass, which exhibits resistivity values between a few hundred and 1 kΩ·m. As shown by the surface observations and the seismic results, this resistivity increase is due to a high degree of fracturing associated with the creation of air-filled voids inside the mass. Other geophysical techniques were tested along a horizontal transect through the movement, and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve. These preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass involved in the movement. Results also suggest that monitoring the evolution of the rock mass movement with time-lapse geophysical surveys could be beneficial.Key words: gravitational movement, geophysical methods, Séchilienne.

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The use of geophysical prospecting for imaging active faults in the Roer Graben, Belgium

Geophysics ◽

10.1190/1.1444925 ◽

2001 ◽

Vol 66 (1) ◽

pp. 78-89 ◽

Cited By ~ 62

Author(s):

Donat Demanet ◽

François Renardy ◽

Kris Vanneste ◽

Denis Jongmans ◽

Thierry Camelbeeck ◽

...

Keyword(s):

High Resolution ◽

Physical Properties ◽

Fault Zone ◽

Geophysical Methods ◽

Depth Range ◽

Electrical Tomography ◽

Reflection Seismic ◽

Refraction Seismic ◽

Geophysical Surveys ◽

Geophysical Techniques

As part of a paleoseismological investigation along the Bree fault scarp (western border of the Roer Graben), various geophysical methods [electrical profiling, electromagnetic (EM) profiling, refraction seismic tests, electrical tomography, ground‐penetrating radar (GPR), and high‐resolution reflection seismic profiles] were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters. These geophysical investigations, in parallel with geomorphological and geological analyses, helped in the decision to locate trench excavations exposing the fault surfaces. The results could then be checked with the observations in four trenches excavated across the scarp. Geophysical methods pointed out anomalies at all sites of the fault position. The contrast of physical properties (electrical resistivity and permittivity, seismic velocity) observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change in the water table depth across the fault. Extremely fast techniques like electrical and EM profiling or seismic refraction profiles localized the fault position within an accuracy of a few meters. In a second step, more detailed methods (electrical tomography and GPR) more precisely imaged the fault zone and revealed some structures that were observed in the trenches. Finally, one high‐resolution reflection seismic profile imaged the displacement of the fault at depths as large as 120 m and filled the gap between classical seismic reflection profiles and the shallow geophysical techniques. Like all geophysical surveys, the quality of the data is strongly dependent on the geologic environment and on the contrast of the physical properties between the juxtaposed formations. The combined use of various geophysical techniques is thus recommended for fault mapping, particularly for a preliminary investigation when the geological context is poorly defined.

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Verification of geophysical models in Alpine permafrost using borehole information

Annals of Glaciology ◽

10.3189/172756400781820057 ◽

2000 ◽

Vol 31 ◽

pp. 300-306 ◽

Cited By ~ 39

Author(s):

Daniel S. Vonder Mühll ◽

Christian Hauck ◽

Frank Lehmann

Keyword(s):

Geophysical Methods ◽

Swiss Alps ◽

Rock Glacier ◽

Surface Microtopography ◽

Refraction Seismics ◽

Geophysical Surveys ◽

Ground Conditions ◽

Lateral Extent ◽

Ice Content ◽

Difficult Terrain

AbstractAt two permafrost sites in the Swiss Alps a range of geophysical methods were applied to model the structure of the subsurface. At both sites, borehole information was used to verify the quality of the model results. On the Murtèl-Corvatsch rock glacier (2700 m a.s.L; upper Engadine) a 58 m deep core drilling was performed in 1987. D. c resistivity measurements, refraction seismics, ground-penetrating radar (GPR) and gravimetric surveys allowed the shape of the permafrost table beneath the marked surface microtopography to be determined and the lateral extent of a deeper shear horizon to be established The validity of each method was verified by the borehole information (cores, density log and temperature). A coherent model of the rock-glacier structure was developed. At the Schilthorn (2970 m a.s.L; Bernese Oberland), it was not clear whether permafrost is in fact present. Various geophysical surveys (d.c. resistivity tomography, refraction seismics, GPR and EM-31) gave results that were not typical of permafrost environments. A 14 m percussion drilling revealed warm permafrost and a very low ice content. These geotechnical and geothermal data allowed reinterpretation of the geophysical results, improving modelling of ground conditions. The paper demonstrates that in the difficult terrain of Alpine permafrost, boreholes may be critical in calibration and verification of the results of geophysical methods. The most useful combinations of geophysical techniques proved to be (a) seismics with d.c. resistivity, and (b) gravimetry with GPR.

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Metamorphic consequences of Neogene thermal anomaly in the northern Apennines (Radicondoli-Travale area, Larderello geothermal field – Italy)

Geodinamica Acta ◽

10.1080/09853111.2000.11105379 ◽

2000 ◽

Vol 13 (6) ◽

pp. 345-366 ◽

Cited By ~ 3

Author(s):

Marilisa Carella ◽

Paolo Fulignati ◽

Giovanni Musumeci ◽

Alessandro Sbrana

Keyword(s):

Thermal Anomaly ◽

Geothermal Field ◽

Northern Apennines

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Fluid activity detection in geothermal areas using a single seismic station by monitoring horizontal-to-vertical spectral ratios

Scientific Reports ◽

10.1038/s41598-021-86775-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Kyosuke Okamoto ◽

Hiroshi Asanuma ◽

Hiro Nimiya

Keyword(s):

Carbon Capture ◽

Seismic Station ◽

Carbon Capture And Storage ◽

Fluid Flows ◽

Temporal Variations ◽

Geothermal Field ◽

Spectral Ratios ◽

Subsurface Structures ◽

Geothermal Fields ◽

Single Station

AbstractSubsurface structure survey based on horizontal-to-vertical (H/V) spectral ratios is widely conducted. The major merit of this survey is its convenience to obtain a stable result using a single station. Spatial variations of H/V spectral ratios are well-known phenomena, and it has been used to estimate the spatial fluctuation in subsurface structures. It is reasonable to anticipate temporal variations in H/V spectral ratios, especially in areas like geothermal fields, carbon capture and storage fields, etc., where rich fluid flows are expected, although there are few reports about the temporal changes. In Okuaizu Geothermal Field (OGF), Japan, dense seismic monitoring was deployed in 2015, and continuous monitoring has been consistent. We observed the H/V spectral ratios in OGF and found their repeated temporary drops. These drops seemed to be derived from local fluid activities according to a numerical calculation. Based on this finding, we examined a coherency between the H/V spectral ratios and fluid activities in OGF and found a significance. In conclusion, monitoring H/V spectral ratios can enable us to grasp fluid activities that sometimes could lead to a relatively large seismic event.

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Investigating the Effective Resistivity of Reinforced Concrete Waste Storage Tanks at the Hanford Site

Geophysics ◽

10.1190/geo2021-0187.1 ◽

2021 ◽

pp. 1-50

Author(s):

Allan Haas ◽

Dale F. Rucker ◽

Marc T. Levitt

Keyword(s):

Electrical Resistivity ◽

Reinforced Concrete ◽

Geophysical Methods ◽

Underground Storage ◽

Storage Tanks ◽

Hanford Site ◽

Underground Storage Tanks ◽

Effective Resistivity ◽

Geophysical Surveys ◽

Wide Range

Industrialized sites pose challenges for conducting electrical resistivity geophysical surveys, as the sites typically contain metallic infrastructure that can mask electrolytic-based soil and groundwater contamination. The Hanford site in eastern Washington State, USA, is an industrialized site with underground storage tanks, piping networks, steel fencing, and other potentially interfering infrastructure that could inhibit the effectiveness of electrical resistivity tomography (ERT) to map historical and monitor current waste releases. The underground storage tanks are the largest contributor by volume to subsurface infrastructure and can be classified as reinforced concrete structures with an internal steel liner. Directly measuring the effective value for the electrical resistivity of the tank, i.e., the combination of individual components that comprise the tanks shell, is not reasonably possible because they are buried and dangerously radioactive. Therefore, we indirectly assess the general resistivity of the tanks and surrounding infrastructure by developing synthetic ERT models with a parametric forward modeling study using a wide range of resistivity values from 1×10−6 to 1×104 ohm-m, which are equivalent to steel and dry rock, respectively. The synthetic models used the long-electrode ERT method (LE-ERT), whereby steel cased metallic wells surrounding the tanks are used as electrodes. The patterns and values of the synthetic tomographic models were then compared to LE-ERT field data from the AX tank farm at the Hanford site. This indirect method of assessing the effective resistivity revealed that the reinforced concrete tanks are electrically resistive and the accompanying piping infrastructure has little influence on the overall resistivity distribution when using electrically based geophysical methods for characterizing or monitoring waste releases. Our findings are consistent with nondestructive testing literature that also shows reinforced concrete to be generally resistive.

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Tectonic state and oil-gas prospects of Khidirly-Bandovan structure according to the new gravimetric data

Azerbaijan Oil Industry ◽

10.37474/0365-8554/2020-6-7-11-18 ◽

2020 ◽

pp. 11-18

Author(s):

A.S. Hasanov ◽

◽

Keyword(s):

Geophysical Methods ◽

Geological Mapping ◽

Seismic Exploration ◽

Huge Amount ◽

Ray Method ◽

Common Depth Point ◽

Geophysical Surveys ◽

Gravimetric Data ◽

Exploration Drilling ◽

Oil Gas

Khidirly-Bandovan structures have been studied through geological mapping, structural exploration drilling, geophysical methods (gravimetric, magnetic, electrical, seismic exploration methods) since the 1930s. Small amount of oil from different wells in the upper part of Productive Series (PS) and huge amount of gas fountain from Middle Absheron sediments have been obtained. As the interest to these areas had not decreased, the geophysical surveys continued during further years. Seismic exploration surveys were executed in Bandovan structure via Common Depth Point (CDP) method in 2004, refracted ray method and gravimetric exploration complex in 2006 and 3D seismic exploration works and gravimetric investigations with “Scintrex CG-5 Autograv” devices in 2016, correspondingly. In the result of analysis of distribution characteristics for local gravimetric anomalies, as well as 3D descriptions of new gravimetric data, up-to-date logs on tectonic state of Khidirly-Bandovan structure have been obtained and as the new oil-gas exploration objects, the west and south-west wings of these structures highlighted.

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Scale dependency of fractional flow dimension in a fractured formation

Hydrology and Earth System Sciences ◽

10.5194/hess-15-2165-2011 ◽

2011 ◽

Vol 15 (7) ◽

pp. 2165-2178 ◽

Cited By ~ 6

Author(s):

Y.-C. Chang ◽

H.-D. Yeh ◽

K.-F. Liang ◽

M.-C. T. Kuo

Keyword(s):

Field Data ◽

Geothermal Field ◽

Fractured Media ◽

Fractional Flow ◽

Hydraulic Test ◽

Flow Paths ◽

Flow Dimension ◽

Flow Geometry ◽

Flow Dimensions ◽

Observation Wells

Abstract. The flow dimensions of fractured media were usually predefined before the determination of the hydraulic parameters from the analysis of field data in the past. However, it would be improper to make assumption about the flow geometry of fractured media before site characterization because the hydraulic structures and flow paths are complex in the fractured media. An appropriate way to investigate the hydrodynamic behavior of a fracture system is to determine the flow dimension and aquifer parameters simultaneously. The objective of this study is to analyze a set of field data obtained from four observation wells during an 11-day hydraulic test at Chingshui geothermal field (CGF) in Taiwan in determining the hydrogeologic properties of the fractured formation. Based on the generalized radial flow (GRF) model and the optimization scheme, simulated annealing, an approach is therefore developed for the data analyses. The GRF model allows the flow dimension to be integer or fractional. We found that the fractional flow dimension of CGF increases near linearly with the distance between the pumping well and observation well, i.e. the flow dimension of CGF exhibits scale-dependent phenomenon. This study provides insights into interpretation of fracture flow at CGF and gives a reference for characterizing the hydrogeologic properties of fractured media.

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