Summary The preliminary results of a new proposed technique for the data acquisition of the 2D MASW method is discussed in this extended abstract. This technique aims at increasing the fieldwork productivity of the 2D MASW data acquisition significantly. It is estimated that this technique may increase the productivity of the filed work of more than 70% than the traditional land-streamer towed by truck technique. The basic idea is to perform two 2D MASW profiles simultaneously for each run of the truck, employing two land streamers, two seismic recording instruments, but only one seismic source for both receiver arrays, located in the middle of the two profiles. This work aims to investigate the applicability of the proposed acquisition technique and the accuracy of the acquired data, using real data taken from two different sites as well as synthetic seismic data. The dispersion curves and S-wave profile comparison between the traditional and the proposed technique for the real and synthetic data was found to be quite encouraging. The proposed technique manages to reproduce the S-wave profiles resulted from the conventional MASW deployment, in the framework of an acceptable, for the engineers, error. Further basic research concerning the MASW-DS assumptions is considered necessary.

Summary The application of seismic reflection and electrical resistivity methods (2D and 3D) in geotechnical investigations is explored through a case study in Northern Greece. These methods were employed to Mavropigi lignite open pit mine and the surveyed area is the next step in mining expansion. The main aim of the geophysical survey was to map the bedrock, the contact between the Neogene and Schist/Carbonate formations as well as to estimate the thickness of the carbonate rocks on top of the Schist formations in order to study the stability of the final mine slopes. These geophysical data provides a geotechnical model which will be used in mine planning from Greek Public Power Corporation.

Summary Several researchers have utilized the multipath summation method, for the focusing of GPR diffracted sections. This method is based on using weighted stacking of constant-velocity migrated sections over a predefined velocity range. It has the advantage of enhancing the lateral and the temporal resolution of such GPR sections without the need to fully build a migration velocity model. In this extended abstract, we propose an improvement on the multipath summation method in order to reduce the user interference in its implementation. We have employed a “divide and conquer technique” for estimating the range of velocities to be used in the constant-velocity migration. We have also employed a modified spectral scaling scheme for the spectral whitening of the resulted migrated GPR sections. Here we present initial results of this methodology for synthetic and real data.

The needs for water supply in the western coastal zone of Kavala (N. Greece) have been rapidly increased during the last decades because of the high tourist and agricultural development. This resulted to a number of wells that drilled along the coastline. During summer period, when human and irrigation consumptions are maximized, phenomena of groundwater salinization are observed. Although restrictions to new drillings have been taken, salinization in some aquatic systems of the area tends to become a major environmental and economical issue. The only available information till now was a timeseries of groundwater electrical conductivity measurements, in some of the wells of the area. This information is useful but not adequate for the study of the salt intrusion mechanism. Geophysical investigation was carried out and electrical resistivity tomography (ERT) was chosen as the most appropriate technique for the case. The geophysical survey was set in a site between the coastline and an existing borehole. The 2D ERT profiles gave a clear image of geoelectrical heterogeneities, associated with seawater intrusion in the coastal aquifers, contributing to future measures towards a rational management of ground water resources in the area.

The needs for water supply in the western coastal zone of Kavala (N. Greece) have been rapidly increased during the last decades because of the high tourist and agricultural development. This resulted to a number of wells that drilled along the coastline. During summer period, when human and irrigation consumptions are maximized, phenomena of groundwater salinization are observed. Although restrictions to new drillings have been taken, salinization in some aquatic systems of the area tends to become a major environmental and economical issue. The only available information till now was a timeseries of groundwater electrical conductivity measurements, in some of the wells of the area. This information is useful but not adequate for the study of the salt intrusion mechanism. Geophysical investigation was carried out and electrical resistivity tomography (ERT) was chosen as the most appropriate technique for the case. The geophysical survey was set in a site between the coastline and an existing borehole. The 2D ERT profiles gave a clear image of geoelectrical heterogeneities, associated with seawater intrusion in the coastal aquifers, contributing to future measures towards a rational management of ground water resources in the area.

In this work, we present the results of a geophysical survey at Malia, Crete, Greece. This survey combines VES, electrical tomography and seismic refraction at two sites where equal number of water reservoirs is planned to be constructed for the needs of a hybrid power station using wind-hydro pumping renewable energy. The geophysical sections are interpreted using geological and borehole data. This survey determines the thickness of the overburden, defines the quality of the carbonate bedrock, detects faults and weathered zones in carbonates. One major very low resistivity anomaly was detected at the northern investigated area, which corresponds to completely fractured or weathered limestone, while a 25m deep fracture zone, was detected at the southern investigated area.

One of the most important environmental problems in coastal areas is the salinization of ground water. The groundwater contamination due to seawater intrusion is usually caused by a violation of a delicate hydrogeological balance that exists between freshwater and seawater in coastal aquifers. The development of a methodology for the prediction of the systematic sea water intrusion can contribute to the planning of effective prevention measures in the coastal areas. The geophysical techniques offer a suitable non-invasive method for determining the geometric characteristics of an aquifer and monitoring the saline water intrusion. Among all geophysical techniques, the most successful methods, concerning the detection of salinization in the coastal areas, are the electric resistivity and electromagnetic methods. Seismic methods can also help in providing further geological information for the stratigraphy. In this work, we present the preliminary results from the geoelectrical survey conducted in Tympaki basin (Herakleio, Greece) within the framework of the project “geophysiCaL basEd hydrogeologicAl modeling to pRevent pollution from sea WATER intrusion at coastal areas”

Summary 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.

Summary 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.

SUMMARY 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.

A. Vafidis, P. Soupios, N. Economou, H. Hamdan, N. Andronikidis, G Kritikakis, G. Panagopoulos, E. Manoutsoglou, M. Steiakakis, E. Candansayar and M. Schafmeister present the processing and interpretation of data to show seawater intrusion imaging. Coastal areas are densely populated, since they provide the best conditions for both economic development and quality of life. One of the most important environmental problems in coastal areas is the salinization of ground water. The dynamic hydrogeological balance between freshwater and seawater in coastal aquifers is subverted by groundwater over-pumping that lowers the groundwater level and causes seawater movement into the coastal aquifers (Abdalla et al., 2010). In arid or semi-arid areas, where the rainfall is the main source of freshwater and the groundwater is inadequate, the problem of seawater intrusion is irreversible leading to the conclusion that effective prediction tools are of vital importance for the prevention of aquifer contamination.

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.

Geophysical methods are useful for mapping the boundary between fresh and saline water in coastal areas. However, the existence of karstic formations increases the uncertainty on geophysical sections and complicates the interpretation of geophysical data. In this paper, a systematic geophysical methodology for imaging saline water intrusion, in complex geological structure is being presented. We applied three methods for the inversion of resistivity data, as well as multi array data joint inversion and time lapse tomography. For the interpretation of the geophysical data we combined seismic velocity and resistivity sections. This integrated geophysical survey revealed saline water zones in the investigated area and verified that a major normal NE-SW fault zone is mainly responsible for the groundwater salinization in the Stylos area.

The complexity of karstic structures causes major problems in the processing and interpretation of 2D resistivity data. This paper investigates the optimum inversion method to be applied in such cases. Three inversion methods (combined, smoothness constrained and robust inversion) are applied on real data set and their results are compared. In addition, joint inversion of two electrode arrays, namely Wenner-Schlumberger and dipole-dipole, has been employed to achieve the maximum reliability of the 2D resistivity model. The resistivity data have been collected from a strongly karstic site where saline water intrusion is present.