New Achievements in Geoscience, 2012

2016

The rapid development of industrial and urban areas in the last decades caused a significant amount of environmental degradation with serious consequences to human life, ecosystems, natural resources, land utilization, as well as to human and natural heritage. Thus, the role of site restoration and rehabilitation projects, in the context of the Management Environmental degradation, is crucial for the modern society. Environmental Geophysics comprises a relative modern part of the Geophysics discipline, aimed at determining the physical properties of the shallow sub-surface by using non invasive high-resolution geophysical techniques. The detailed knowledge of the subsurface structure is valuable for a variety of disciplines involved in the study of the shallow earth's crust, which is directly related with human activities. In particular, Environmental Geophysics efficiently deals with technical problems arising during construction works such as karst collapse, evaporite sinkholes, landslides, mine subsidence and fault zones. Furthermore, it is involved in investigations concerning the detection of buried or abandoned waste, the location of the aquifer and part of its related properties to identify the possible presence of contaminants in the subsurface and finally, the mapping of archaeological sites. The aim of this work is to present the most familiar and robust techniques used in environmental geophysics and new methodologies of data processing and interpretation. Extensive literature research and examples from case studies are presented and analyzed. Special emphasis is given to the limitations of all applied techniques.

The present survey aimed to image the subsurface structure, including karstic voids, and to evaluate the extent of the heterogeneities that can result in potentially dangerous collapse of road segments overlying these features. A multidisciplinary geophysical approach (seismic refraction, frequency domain electromagnetic and ground penetrating radar) in combination with a detailed geological survey indicated the presence of tectonic faults as well as velocity and conductivity anomalies along an old road within the area of Akrotiri at Chania (Crete). Due to the presence of subsurface fuel pipes, perpendicular to the direction of the road, 2D resistivity imaging was excluded from the applied geophysical methods. Interpretation of the geophysical data revealed that the section of the road investigated overlies prominent voids attributed mostly to karst features. The conductivity and velocity anomalies are interpreted to indicate an area where the host limestone rock has been downthrown by faulting and associated karstification. The continuation of this fault zone was observed in the slope of the road during later excavations. Interpretation, using geographic information systems (GIS) to integrate data, allowed these controls and relationships to be understood and monitored. The above methodology was proved successful for areas where the application of resistivity method is not possible.

Geophysics can briefly be described as investigation methods that aim towards investigating the earth's physical characteristics as e.g density, electrical conductivity, and elastic properties, which can then be developed into geological models. Contrary to sampling, geophysical measurements may provide a continuous cross section of the sub-surface. On the other hand the interpretation of geophysics to geological and hydrological information is seldom one-sided. The non-uniquess of the result is most often reduced by using a combination of several geophysical methods (Aaltonen, 2000). This chapter deals with the geoelectric resistivity tools and Ground Penetrating Radar (GPR)which we used it at a New Cairo City. The electric resistivity technique is based essentially on the quantitative estimation of the conductivity properties of the subsurface, while the Ground Penetrating Radar (GPR) is a high-resolution technique of imaging shallow soil and ground structures using electromagnetic waves(EM).

Applied Sciences

The Athenet network is the network of the Seismological Laboratory of the National and Kapodistrian University of Athens. We present the geophysical investigation that has been carried out at six seismological stations of the Athenet network for their site characterization. More specifically, at the location of each seismological station, four geophysical methods have been carried out: Seismic Refraction Tomography (SRT), Multichannel Analysis of Surface Waves (MASW), the Horizontal to Vertical Spectral Ratio (HVSR) technique, and Electrical Resistivity Tomography (ERT). The applied geophysical survey provided important information regarding the site characterization at the selected seismological stations, including key parameters such as the fundamental frequency fo, the shear-wave velocity VS, the average shear-wave velocity for the upper 30 m depth (VS30), the seismic bedrock depth, the soil type, and the subsurface geology. Moreover, selected elastic moduli (Poisson’s ratio, she...

The shallow subsurface structure of the Earth is important to understand for many economic and safety reasons. The problem is usually difficult due to complexity of the earth's subsurface processes especially near the surface. A number of geophysical methods are used for this purpose using different physical characteristics of the Earth materials. A particular geophysical method illuminates part of the problem, but a reliable solution can only be found by combining results of different methods. In order to synthesize information from different geophysical methods, it is important to understand their similarities and differences. The aim of this study is to correlate the basic principles of geophysical methods side-by-side starting from fundamental equations. This study reveals that many analogies exist among these methods both in their mathematical formulation, and sometimes, in ways they are used in the geophysical applications.

Several integrated geophysical surveys are performed by OGS in different sites located in the Friuli Venezia-Giulia region (North-East of Italy) to characterise the near surface subsoil for seismological applications. For this purpose, we used seismic, geoelectric, and ground penetrating radar (GPR) methods. The first meters are described in details by GPR measurements, the fifty meters by electric data and the layers until the basement are illuminated by seismic surveys. The results obtained at different resolution are in very good agreement and the direct measurements (downhole and cross-hole data) confirmed the models obtained by our indirect metodologies.