N. Andronikidis

Time-varying deconvolution of GPR data in civil engineering

Ground Penetrating Radar (GPR) profiles are often used in civil engineering problems. Overlapping reflections from thin subgrade layers are observed when a relatively low frequency antenna is used. An efficient GPR data processing method, which increases the dominant frequency of GPR data and the temporal resolution, is proposed. It is implemented in the t–f domain. The proposed time-varying deconvolution technique avoids the need for both the calculation of an inverse zero-phase whitening operator and subsequently the application of a band-pass filtering. The user must select the dominant frequency of the Ricker wavelet and use the phase of a reference electromagnetic wavelet, which is acquired experimentally, for stationary dephasing. Apart from delineating thin layers, this method reduces the number of antennas for imaging both shallow and deeper layers in civil engineering. The effectiveness of the proposed method is demonstrated through four civil engineering applications.

Contribution of electrical tomography methods in geotechnical investigations at Mavropigi lignite open pit mine, Northern Greece

In this paper, the application of 2D and 3D electrical resistivity methods in geotechnical investigations is explored through a case study in Northern Greece. These two methods were employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonate formations near the southern limits of the pit, as well as to estimate the thickness of the carbonate rocks on top of the Schist formations to evaluate the stability of the southern slopes. Synthetic data were initially generated to help plan an efficient electrical tomography survey, in a region with complex geology and irregular terrain. Three configurations (Wenner–Schlumberger and dipole–dipole or pole–dipole) proved essential in such conditions and helped improving the resolution of the resistivity section. The sections were then calibrated by boreholes. Finally, the geophysical survey provided invaluable data regarding the geometry of the bedrock and possible faults, which was essential for the slope stability calculations.

Mapping the Bedrock Using ERT for Slope Stability Studies at Mavropigi Lignite Open Pit Mine, Northern Greece

The application of the electrical resistivity method in geotechnical investigations is explored through a case study in Northern Greece. This method was employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonates formations south of the pit. Two configuration arrays proved essential in such conditions, and helped improving the resolution of the geoelectrical section. The geoelectrical sections were then calibrated by boreholes indicating that the bedrock is dipping to the Northeast. Furthermore, the geophysical survey provided invaluable data regarding the geometry of the bedrock which was essential for the slope stability calculations.

Imaging Folegandros Basin by Using Seismic Reflection Data from a Part of Seismic Line AEG-1

Seismic reflection data of the part of seismic line AEG-1 which crosses Folegandros basin in the south-central Aegean has been processed in order to image structures within this basin. The processing sequence included band-pass filtering for noise suppression, velocity analysis, tau-p filtering for multiple attenuation, zero phase deconvolution and post stack migration techniques. The seismic reflection method at Folegandros basin provided information about the geological structures at intermediate depths which is possibly related to tectonic elements and structures at greater depth. The evolution of Folegandros basin is explained by the action of wrench tectonics which can contribute to the understanding of multi - direction crustal- extension in the area.

Geophysical Survey at the Area of the Ancient Theater of Aptera

In this paper we present the latest results of the geophysical surveys performed during the autumn 2013 in Ancient Aptera, Chania, Crete, Greece. It is part of the continuous collaboration of the Applied Geophysics Lab, Technical University of Crete and the local Ephorate of Antiquities. The main scope of the geophysical studies is to detect buried structures in the area of the ancient theater. We managed to detect walls, pavements and a well utilizing GPR, magnetics, ERT and EM profiler.

Two Dimensional Joint Inversion of Seismic refraction, Radiomagnetotelluric and DC Resistivity Data: an example from Bafra plain, Turkey

A new two dimensional joint inversion algorithm for Seismic refraction, Radio-magnetotelluric and DC Resistivity data was developed. We used synthetic data to show advantage of the algorithm. The developed joint inversion algorithm found resistivity and velocity model better than the individual inversion of each data set if one compare with the real models. We also tested the algorithm with the field data collected in the Bafra basin to image the saltwater intrusion at this area. The field data inversion is also showed that the joint inversion recovered the resistivity and velocity model better than the individual inversion of each data set.

Imaging the Saline/Fresh Water Interface at Bafra, Turkey Using Joint Inversion of Seismic Refraction and ERT Data

A geophysical survey was conducted at Bafra, Samsun, Turkey, Greece in order to support the geological and hydrogeological studies of the existing phenomenon of seawater intrusion. This survey employed seismic refraction tomography (ST), time domain electromagnetic (TDEM) and geoelectrical methods. The later, consisted of Electrical Resistivity Tomography (ERT). The objective of this survey was to image the saltwater intrusion at this area and map possible favorable sea water pathways. We present the interpretation of geophysical data obtained under the research project ClearWater project. We applied both individual and joint inversion of electric and seismic data from Bafra. At Bafra, the geophysical survey provided images of the saltwater intrusion which is present at the north eastern of the study area. These geophysical methods proved useful as prediction and prevention tools in qualitative characterization of water bearing formations for an optimum groundwater management plan for the Bafra basin.

Imaging of Alpine and Post-Alpine Formations Using ERT at Loutsa- Remeri Open Pit Mine, Scourta, Viotia, Greece

A geophysical survey carried out at Scourta plateau in Central Greece employed the electrical tomography method in order to image the interface between Alpine and Post-Alpine formations and estimate the thickness of Terra Rossa deposits. The later are crucial for TITAN-SA cement company open pit mine. This mine provides row materials for cement production. This survey is related with future extension plan of the existing Loutsa-Remeri open pit mine. Scourta is an active polje and is filled with a thick Terra Rossa deposit which is a row material for cement industry. The geophysical survey revealed two distinct layers, the upper is characterized by lower resistivity values (less than 20 Ωm), minimum thickness to the east (25 m) and maximum thickness at least 50 m and is attributed to Terra Rossa deposits. The underlying layer exhibits higher resistivity values (more than 70 Ωm) and is attributed to karstified carbonate relief. The variation of the polje depth is accosiated with tectonokarstic processes. The E-W direction fault system delineates the karstic structure and the N-S ridge in the east part of the survey area is delineated by N-S direction faults.

Salt Water Intrusion Imaging at Tybaki (Greece) Using Geophysical Methods

A geophysical survey was conducted at Tybaki, Crete, Greece in order to support the geological and hydrogeological studies of the existing phenomenon of seawater intrusion. This survey employed seismic refraction, transient electromagnetic (TEM) and geoelectrical methods. The later, consisted of Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT). The objective of this survey was to image the saltwater intrusion at this area and map possible favorable sea water pathways. We present the combined interpretation of vintage geophysical data obtained under the research project MEDIS and the ClearWater project data. At Tybaki, the geophysical survey provided images of the saltwater intrusion which is present at the north west of the basin.

Imaging of Karstic Carbonates Using Electrical Resistivity Data at Malia, Crete, Greece

This work involves the use of resistivity and borehole data for the delineation of weak zones in karstic carbonates at Malia, Crete, Greece, where two water reservoirs will be constructed. Site M mostly consists of cretaceous carbonates belonging to the Tripolis zone while Site K consists of upper triassic carbonates of the Tripolis zone. Electrical tomography data were combined with seismic refraction and borehole data. Electrical tomography imaged karstic structures of the Tripolis carbonates at sites M and K. A 3D resistivity image was generated by inverting resistivity data collected along parallel lines on a grid at site M. At this site, electrical resistivity imaging delineated fractured and weathered limestone zones whose thickness ranges from 20 to 40 m. 2D ERT images of the northern part of site M indicate a major low resistivity anomaly. The formations at site K are mostly characterized as slightly weathered limestone (H) with higher RQD values (more than 60). The existing voids are small and the fractured zones exhibit limited extent at site K.