Quantitative Integration Of Multiple Near-Surface Geophysical Techniques For Improved Subsurface Imaging And Reduced Uncertainty In Discrete Anomaly Detection

2010 ◽  
Author(s):  
Megan E. Carr ◽  
Gregory S. Baker
Keyword(s):  
Anomaly Detection ◽  
Subsurface Imaging ◽  
Near Surface ◽  
Geophysical Techniques ◽  
Quantitative Integration

Subsurface Investigation

2015 ◽  
pp. 744-795
Keyword(s):  
Field Tests ◽  
Field Investigation ◽  
Soil Parameters ◽  
Near Surface ◽  
Ground Investigation ◽  
Geophysical Techniques ◽  
Vertical Profiling ◽  
Sample Recovery ◽  
Subsurface Investigation ◽  
A Site

A good knowledge about a site including its subsurface conditions is very important in its safe and economical development. It is therefore an essential preliminary to the construction of any civil engineering work. This chapter outlines the objectives of site characterization and the general objectives of geotechnical investigation. It discusses the phases of field investigation and the stages of a full exploratory program including methods of sample recovery and field tests and sampling methods. Geophysical techniques can contribute very greatly to the process of ground investigation by allowing an assessment, in qualitative terms, of the lateral variability and vertical profiling of the near-surface materials beneath a site. Some of these geophysical techniques are discussed in the chapter. Laboratory examination/verification and testing should be made of representative portions of the samples to establish appropriate soil parameters. Some soil parameters may be estimated by correlations. The results of the subsurface investigation and related testing, together with interpretations, discussions, and foundation recommendations, are usually presented in the form of a detailed soil report.

Geophysical approach to the environmental study of a coastal plain

Geophysics ◽  
2003 ◽  
Vol 68 (5) ◽  
pp. 1446-1459 ◽  
Author(s):  
Roberto Balia ◽  
Enrico Gavaudò ◽  
Federica Ardau ◽  
Giorgio Ghiglieri
Keyword(s):  
Coastal Plain ◽  
Seismic Reflection ◽  
Gravity Data ◽  
Environmental Study ◽  
Specific Situation ◽  
Near Surface ◽  
Paleozoic Basement ◽  
Phreatic Aquifer ◽  
Geophysical Techniques ◽  
Soil And Water

In the study of coastal plains affected by soil and water salination, a knowledge of several geological aspects, such as structural features, depth to basement, stratigraphy of sedimentary cover, relationships between the phreatic aquifer and underlying aquifers, and the latter's structure, is basic to gaining an adequate understanding of both the causes and possible evolution of salination. In this framework, geophysical techniques can play a very important role. To improve the available geophysical information about the Muravera coastal plain, Sardinia, Italy, which is affected by severe soil and water salination, previously acquired electrical resistivity, reflection seismic and gravity data have been reprocessed, and a new seismic reflection survey has been conducted. Moreover, in order to give better support to the geological and hydrogeological interpretation of geophysical data, three boreholes were drilled. Reprocessed electrical data indicate the presence of a wide, electrically homogeneous low‐resistivity zone associated with salination phenomena. Reprocessed reflection data provide useful information on the near‐surface stratigraphy. The combined interpretation of resistivity and seismic results, supported by one calibration borehole, elucidates the relationships between the phreatic aquifer and the underlying confined aquifer. A new seismic reflection survey gives information on the depth to, and structure of, the Paleozoic basement, as well as on stratigraphic conditions of Pleistocene‐Holocene sediments. Finally, the combined interpretation of seismic, gravity, and well data results in a geological section containing most of the information considered essential, such as the interface between Holocene alluvium and Pleistocene alluvium, the thickness of the latter, and the structure and composition of the Paleozoic basement. The work as a whole shows how the combined application of geophysical techniques can in this specific situation provide wide‐ranging and high‐quality information that is essential for the realistic mathematical modeling of aquifer contamination, and can enable the rational planning of exploratory drillings.

Quantification of groundwater storage heterogeneity in a hard rock aquifer using near-surface ERT and IP geophysical techniques

2021 ◽  
Author(s):  
Jesús Alberto Mézquita González ◽  
Jean-Christophe Comte
Keyword(s):  
Water Content ◽  
Hard Rock ◽  
Geophysical Data ◽  
Specific Yield ◽  
Groundwater Storage ◽  
Near Surface ◽  
Magnetic Resonance Sounding ◽  
Geophysical Techniques ◽  
Hard Rock Aquifers ◽  
Storage Properties

<p>Characterization of groundwater aquifers plays an important role in addressing the increasing demand for freshwater and low carbon energy. Specifically, hard rock aquifers that have been neglected in the past due to their overall low productivity, are increasingly recognised as important aquifers for local water supplies, sustaining environmental flows, and low enthalpy geothermal resources. Groundwater flow and, more so storage, in these aquifers are still poorly understood creating a necessity to quantify their properties and role in sustaining human and ecosystem needs. This study aims to quantify groundwater storage properties, and their spatial variability, in weathered/fractured hard rock aquifers using near-surface geophysical techniques and further evaluate the associated uncertainties. To do so, we analysed 2D electrical resistivity tomography (ERT) and induced polarization (IP) data in combination with 1D magnetic resonance sounding (MRS) and borehole geophysical logging from a metamorphic rock catchment in Gortinlieve, Ireland. The geophysical data comprised a challenging dataset that includes information at different resolution scales: a low-resolution ERT profile of 1,3 km of length, a high-resolution ERT+IP profile of 70 m of length, 8 MRS logs distributed along the study area, borehole logs (gamma ray, temperature and caliper) and petrological analysis at borehole locations. Aquifers storativity data derived from application of petrophysical model to the geophysical data showed good accuracy and reasonable uncertainty of estimated properties. ERT porosities derived from Archie´s model revealed that this model overestimates the porosity for the study site whereas estimates derived from the Waxman & Smits (WS) model, which accounts for the influence of the cation exchange capacity (CEC) of clay minerals on the ERT measurements, were closer to specific yield values obtained from pumping test in boreholes, MRS water content estimates and the typical ranges of hard rock aquifers. The superiority of WS over Archie demonstrated that the clay content cannot be neglected when characterizing storage properties in weathered/fractured basement rock aquifers. Water content profiles from MRS corroborated the results with a particularly good match at three locations across the study area characterised by deep weathering/fracturing associated with regional fracture zones. Results demonstrated that the methodology provides a reasonable estimate of storage heterogeneity which is consistent with weathering/fracturing patterns as described in accepted conceptual models of hard rock aquifers. To further challenge the ERT porosity models, we tested an alternative approach based on the differential effective medium (DEM) theory applied to time-domain IP data to recover CEC and porosity tomograms. Preliminary results show promise, through yielding porosity values close to both 2D WS porosities and 1D MRS water contents and, importantly, the approach may provide a mean to bypass the requirement for having direct clay data of the study site. Taken together, the results confirmed that near-surface geophysical techniques are key instruments to assess groundwater conditions in hard rock aquifers and quantify the spatial heterogeneity of their storage properties at larger scales. The approach can be applied in similar hard rock environments affected by weathering and fracturing.</p>

Seismic Soundoff: Exploring land seismic case studies

2021 ◽  
Vol 40 (10) ◽  
pp. 784-784
Author(s):  
Andrew Geary
Keyword(s):  
Data Acquisition ◽  
Case Studies ◽  
Seismic Data ◽  
Surface Modeling ◽  
Subsurface Imaging ◽  
Near Surface ◽  
Seismic Data Acquisition ◽  
Data Acquisition And Processing

In this episode, Öz Yilmaz discusses his latest book, Land Seismic Case Studies for Near-Surface Modeling and Subsurface Imaging. Written for practicing geophysicists, the book is the culmination of land seismic data acquisition and processing projects conducted by Yilmaz over the last two decades. His expertise and experience are highlighted in detail in this revealing and essential conversation. Hear the full episode at https://seg.org/podcast/post/12564 .

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