Geophysical and geochemical study of geropotamos aquifer in the north-central coast of crete

The geological setting of Geropotamos aquifer on the north-central coast of Crete, Greece, is considered complex, while the local tectonic regime of the study area is characterized by two sets of faults orientated NW-SE and NE-SW. Investigation of the aquifer using the Transient ElectroMagnetic method (TEM) has resulted initially in 1D models of geoelectric structures and a final 3D geoelectrical model was constructed, depicting the zones of salination of groundwater in the aquifer. Groundwater samples were analysed and the most important chemical parameters were determined to provide an independent dataset for comparison with the TEM results, while Groundwater Quality Maps were produced. TEM and geochemical data correspond and provide verification of the TEM approach. As a result, saline intrusion is likely to occur along fractures in a fault zone through bedrock, and this work emphasises the critical role of fracture pathways in salination problems of coastal aquifers

Groundwater resources assessment using integrated geophysical techniques in the southwestern region of Peninsular Malaysia.

Combined geophysical techniques such as multi-electrode resistivity, induced polarization, and borehole geophysical techniques were carried out on volcano-sedimentary rocks in the north of Gemas as part of the groundwater resource’s investigations. The result identifies four resistivity units: the tuffaceous mudstone, tuffaceous sandstone, the tuff bed, and the shale layer. Two types of aquifer systems in terms of storage were identified within the area: one within a fracture system (tuff), which is the leaky area through which vertical flow of groundwater occurs, and an intergranular property of the sandy material of the aquifer which includes sandstone and tuffaceous sandstone. The result also reveals that the aquifer occupies a surface area of about 3,250,555 m2 with a mean depth of 43.71 m and a net volume of 9.798 × 107 m3. From the approximate volume of the porous zone (28 %) and the total aquifer volume, a usable capacity of (274.339 ± 30.177) × 107 m3 of water in the study area can be deduced. This study provides useful information that can be used to develop a much broader understanding of the nature of groundwater potential in the area and their relationship with the local geology

Reconstructing concealed cultural remains through integrated geophysical tomographic methods.

Σκοπός της εργασίας είναι να συγκρίνει τα αποτελέσματα της χαρτογράφησης θαμμένων αρχαιολογικών δομών από μία περιοχή στους Δελφούς με τις μεθόδους της ηλεκτρικής και σεισμικής τομογραφίας και τη μέθοδο του Γεωραντάρ. Για την συλλογή των περίπου 1752 χρόνων διαδρομής των επιμήκων κυμάτων, τοποθετήθηκαν 24 γεώφωνα σε μία περιοχή που κάλυπτε μία έκταση 50x40 μέτρα και πραγματοποιήθηκαν 73 κρούσεις μέ ένα σφυρί πάνω σε μεταλλική επιφάνεια. Τα δεδομένα της τρισδιάστατης ηλεκτρικής τομογραφίας συλλέχθηκαν κατά μήκος πυκνών παράλληλων γραμμών με την διάταξη πόλου-διπόλου όπου η απόσταση μεταξύ των τομών ήταν 1 μέτρο. Η χωρική ανάλυση παράλληλων τομών για τα δεδομένα του γεωραντάρ ήταν 0,5 μέτρα. Τα γεωηλεκτρικά και σεισμικά δεδομένα επεξεργάστηκαν με αλγόριθμους τρισδιάστατης μη-γραμμικής αντιστροφής με σκοπό την ανακατασκευή τρισδιάστατων μοντέλων αντίστασης και ταχύτητας. Τα μοντέλα αυτά περιγράφουν την χωρική κατανομή των αρχαιολογικών λειψάνων μέσα στο υπέδαφος αλλά και τα επιφανειακά γεωλογικά στρώματα μέχρι το βάθος των 5 μέτρων από την επιφάνεια. Επιπλέον τα σήματα του γεωραντάρ ενισχύθηκαν με την εφαρμογή συγκεκριμένων φίλτρων με σκοπό την ενίσχυση της αρχαιολογικής πληροφορίας μέχρι το βάθος των δύο μέτρων από την επιφάνεια του εδάφους. Η συνδυαστική ερμηνεία των γεωφυσικών αποτελεσμάτων δείχνει την ύπαρξη αρχιτεκτονικών δομών μέσα σε ένα αργιλικό περιβάλλον. Τα αποτελέσματα δείχνουν γενικά τη σημασία των τομογραφικών γεωφυσικών μεθόδων προς την κατεύθυνση της πιο ολοκληρωμένης αποτύπωσης των φυσικών ιδιοτήτων του υπεδάφους στο πλαίσιο αρχαιολογικών προσεγγίσεων και της διατήρησης της πολιτισμικής κληρονομιάς . Λέξεις κλειδιά: Ηλεκτρική τομογραφία, σεισμική τομογραφία, γεωραντάρ, 3D, Δελφοί.The purpose of this work was to compare the mapping of shallow subsurface archaeological structures through Seismic Refraction Tomography (SRT), Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) methods. For achieving the goals of the project, a specific section of the archaeological site in Delphi has been surveyed through the employment of the above techniques. For the SRT survey, twenty four P-wave geophones were installed randomly in a 50 by 40 m area. Totally seventy three (73) shots were made by striking a metal plate with a sledgehammer to collect about 1752 travel-times. The pole-dipole array was employed to capture the ERT data along twenty densely spaced parallel profiles. The GPR data were collected along parallel sections with a resolution of 50 cm between the lines. The SRT and ERT field data were processed with modern tomographic inversion algorithms for the reconstruction of the 3-D velocity and resistivity models describing the buried archaeological remains and the subsurface matrix up to the depth of 5 meters below the ground surface. GPR signals were enhanced with specific filters signifying the shallow structures up to 2 meters below the ground surface. The integrated processing results indicate the existence of walls buried in a relatively uniform background soil. The outcome of this approach signifies that SRT, ERT and GPR methods can be used as a validation tool in any archaeological investigation by providing accurate tomographic subsurface models and contribute in cultural resources management.

Simulation of ERT surface-to-tunnel measurements.

Στην παρούσα εργασία με τη χρήση μίας δεξαμενής προσομοίωσης πραγματικών συνθηκών πραγματοποιήθηκαν μία σειρά πειραμάτων ώστε να μελετηθεί η εφαρμογή της διάταξης επιφανειακών-τούνελ ηλεκτροδίων. Στη δεξαμενή τοποθετήθηκε ειδικά κατασκευασμένη διάταξη για την τέλεση των πειραμάτων. Χρησιμοποιήθηκαν μίασειρά από ετερογενείς στόχους (αντιστατικούς και αγώγιμους) και η δεξαμενή πληρώθηκε με ομογενές μέσο (νερό). Για τη λήψη των μετρήσεων χρησιμοποιήθηκε πολυκάναλο όργανο. Ο αρχικός σκοπός των πειραμάτων ήταν να επιβεβαιωθεί η ορθότητα του κώδικα, ο οποίος προσμαρμόσθηκε ώστε να είναι εφικτές αυτού του είδους οι μετρήσεις. Επιπλέον εφαρμόσθηκαν καινούρια πρωτόκολλα, όπως επίσης και έγινε χρήση βέλτιστων μετρήσεων. Τέλος, μελετήθηκε η επίδραση των λανθασμένης θέσης των ηλεκτροδίων και η επίδραση του μεγέθους του τούνελ στα δεδομένα. The applicability of surface-to-tunnel electrical resistance tomography (ERT) measurements using a simulation tank for imaging subsurface targets is studied in this work. The tank was filled with water and inside of it was placed firmly a plastic construction where all targets were placed. Some of the targets that used were: a void plastic cylinder (resistive target) and metal plates (conductive target). Data were collected with a multichannel resistivity meter. The initial scope for these tests was to verify the reliability of developed inversionsoftware which was modified to cope with the specific measurements (surface-totunnel). Furthermore, during several experiments different electrode arrays (standard as well as new optimized) were validated. In our attempt to show the advantages of surface-to-tunnel measurements we analyzed the resolution for each configurationof traditional (surface) and surface-to-tunnel arrays. Studies also included testing the electrode displacement effect and also the effect of the tunnel size into the measurements

SEDIMENTOLOGICAL AND GEOPHYSICAL OBSERVATIONS IN THE DELTA PLAIN OF SELINOUS RIVER, ANCIENT HELIKE, NORTHERN PELOPONNESUS GREECE

Fine and coarse grained lithofacies and depositional environments were distinguished in Selinous River delta plain, from sediment cores using an Eijkelkamp percussion corer with barrel windows. The sedimentary sequence of deltaic plain deposits of Selinous River mostly consists of fine lithofacies interbedded occasionally with conglomerate facies. Fine grained lithofacies based on sediment types, structure, color, as well as contact depths and bed characteristics were interpreted as floodplain, crevasse splay, back swamp / fresh water swamp, permanent shallow fresh water lake and ephemeral fresh water lake facies. The coarse grained lithofacies consists of pebble - conglomerates and were interpreted as paleochannels. The Time-Domain Electromagnetic technique, (TEM) was applied in order to define the spatial distribution of lenses of conglomerates, palaeochannels and fine grained sedimentary material to be recognised, at a depth up to 35m. Both the sedimentological and geophysical approaches, in combination with the available geological and geomorphological data of the area, can provide information about the evolution, existence and the geometry of paleochannels of the Selinous River flood plain, and the paleoenvironment of the area of the ancient Helike

SEDIMENTOLOGICAL AND GEOPHYSICAL OBSERVATIONS IN THE DELTA PLAIN OF SELINOUS RIVER, ANCIENT HELIKE, NORTHERN PELOPONNESUS GREECE

Fine and coarse grained lithofacies and depositional environments were distinguished in Selinous River delta plain, from sediment cores using an Eijkelkamp percussion corer with barrel windows. The sedimentary sequence of deltaic plain deposits of Selinous River mostly consists of fine lithofacies interbedded occasionally with conglomerate facies. Fine grained lithofacies based on sediment types, structure, color, as well as contact depths and bed characteristics were interpreted as floodplain, crevasse splay, back swamp / fresh water swamp, permanent shallow fresh water lake and ephemeral fresh water lake facies. The coarse grained lithofacies consists of pebble - conglomerates and were interpreted as paleochannels. The Time-Domain Electromagnetic technique, (TEM) was applied in order to define the spatial distribution of lenses of conglomerates, palaeochannels and fine grained sedimentary material to be recognised, at a depth up to 35m. Both the sedimentological and geophysical approaches, in combination with the available geological and geomorphological data of the area, can provide information about the evolution, existence and the geometry of paleochannels of the Selinous River flood plain, and the paleoenvironment of the area of the ancient Helike

ESTIMATION OF SEISMIC RESPONSE OF HISTORICAL AND MONUMENTAL SITES USING MICROTREMORS: A CASE STUDY IN THE ANCIENT APTERA, CHANIA, (GREECE)

Main purpose of the present study is to investigate the dynamic characteristics of the remainings at the ancient city of Aptera (Chania) and identify the main damage mechanism, in order to evaluate the risk of structure damage or collapse in case of future events using microtremor recordings. Our study focuses on the application of HVSR method (Horizontal to Vertical Spectral Ratio) to microtremor measurements carried out in specific sites. Registrations have been performed by means of a tridirectional sensor Lennartz 3D-Lite (1 natural Hz frequency), connected with a 24-bit digital acquisition unit. A set of 10 time series of 800 second each, sampled at 125 Hz was recorded in several sites. The selected time windows of each time series were corrected for the base line and for anomalous trends, tapered with a cosine function to the first and last 5% of the signal, and band pass filtered from 0.5 to 20 Hz with cut off frequencies at 0.3 and 22 Hz. The same procedure performed for all sites and components and finally the H/V spectral ratios were computed. Most of the sites present significant amplification peaks in frequency around 2 Hz. Finally, electrical resistivity tomography was carried out. The extracted results clearly show a very complex subsurface geometry indicated by the presence of large-scale voids, which may possibly correspond to ancient reservoirs. In the present work we confirm that the archaeological site of Aptera in Chania consists of a very complex subsurface structure and that the results obtained by HVSR method and by resistivity method are very well correlated