Exploring Through Cover - The Integrated Interpretation of High Resolution Aeromagnetic, Airborne Electromagnetic and Ground Gravity Data from the Grant’s Patch Area, Eastern Goldfields Province, Archaean Yilgarn Craton Part C: Combining Geophysical Methods for a Holistic Exploration Model.

Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection for the fast, large–scale characterization of hydrogeological potential using the Ain El Beidha plain (central Tunisia) as an analogue. Extending the values of vintage petroleum seismic reflection profiles and gravity data, in conjunction with available geological and hydrogeological information, we performed an advanced analysis to characterize the geometry of deep tertiary (Oligocene and Eocene) aquifers in this arid area. Residual and tilt angle gravity maps revealed that most gravity anomalies have a short wavelength. The study area was mainly composed of three major areas: the Oued Ben Zitoun and Ain El Beidha basins, which are both related to negative gravity trends corresponding to low–density subsiding depocenters. These basins are separated by an important NE–SW trend called “El Gonna–J. El Mguataa–Kroumet Zemla” gravity high. Evaluation of the superposition of detected lineaments and Euler deconvolution solutions’ maps showed several NE–SW and N–S relay system faults. The 3D density inversion model using a lateral and vertical cutting plane suggested the presence of two different tectonic styles (thin VS thick). Results from the gravity analysis were in concordance with the seismic analysis. The deep Oligocene and Eocene seismic horizons were calibrated to the hydraulic wells and surrounding outcrops. Oligocene and Eocene geological reservoirs appear very fractured and compartmented. The faulting network also plays an important role in enhancing groundwater recharge process of the Oligocene and Eocene aquifers. Finally, generated isochron maps provided an excellent opportunity to develop future comprehensive exploration surveys over smaller and more favorable areas’ sub–basins.

Download Full-text

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.

Download Full-text

Integrated Geophysical Methods Approach to Subsurface Geologic Mapping Utilizing High‐Resolution Transient Electromagnetic Surveys

Journal of Environmental and Engineering Geophysics ◽

10.4133/jeeg4.1.57 ◽

1999 ◽

Vol 4 (1) ◽

pp. 57-70 ◽

Cited By ~ 5

Author(s):

Michael K. Sharp ◽

Dwain K. Butler ◽

Keith J. Sjostrom

Keyword(s):

High Resolution ◽

Geophysical Methods ◽

Geologic Mapping ◽

Transient Electromagnetic ◽

Electromagnetic Surveys

Download Full-text

P-wave velocity and density structure beneath Mt. Vesuvius: a magma body in the upper edifice?

Annals of Geophysics ◽

10.4401/ag-6443 ◽

2013 ◽

Vol 56 (4) ◽

Author(s):

Paolo Capuano ◽

Guido Russo ◽

Roberto Scarpa

Keyword(s):

High Resolution ◽

Wave Velocity ◽

Gravity Data ◽

High Energy ◽

P Wave ◽

Gravity Inversion ◽

Density Structure ◽

Resolution Image ◽

High Resolution Image ◽

P Wave Velocity

<p>A high-resolution image of the compressional wave velocity and density structure in the shallow edifice of Mount Vesuvius has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes and from gravity inversion. The robustness of the tomography solution has been improved by adding to the earthquake data a set of land based shots, used for constraining the travel time residuals. The results give a high resolution image of the P-wave velocity structure with details down to 300-500 m. The relocated local seismicity appears to extend down to 5 km depth below the central crater, distributed into two clusters, and separated by an anomalously high Vp region positioned at around 1 km depth. A zone with high Vp/Vs ratio in the upper layers is interpreted as produced by the presence of intense fluid circulation alternatively to the interpretation in terms of a small magma chamber inferred by petrologic studies. In this shallower zone the seismicity has the minimum energy, whilst most of the high-energy quakes (up to Magnitude 3.6) occur in the cluster located at greater depth. The seismicity appears to be located along almost vertical cracks, delimited by a high velocity body located along past intrusive body, corresponding to remnants of Mt. Somma. In this framework a gravity data inversion has been performed to study the shallower part of the volcano. Gravity data have been inverted using a method suitable for the application to scattered data in presence of relevant topography based on a discretization of the investigated medium performed by establishing an approximation of the topography by a triangular mesh. The tomography results, the retrieved density distribution, and the pattern of relocated seismicity exclude the presence of significant shallow magma reservoirs close to the central conduit. These should be located at depth higher than that of the base of the hypocenter volume, as evidenced by previous studies.</p>

Download Full-text