Combined Ground Deformation Study Of Broader Area Of Patras Gulf (W. Greece) Using PSI-WAP, DGPS And Seismicity Analyses

Long-term ground deformation monitoring using the Persistent Scatterer Interferometry Wide Area Product (PSI-WAP) technique for the period 1992-2003, combined with Differential GPS measurements and seismicity analysis has provided useful information about the tectonic motions of the tectonically complex area of Patras Gulf (Western Greece), and lead to new insights on the geotectonic regime of this region. Descending ERS radar images were used to compile the PSI-WAP product that has been calibrated using the absolute velocity field of available GPS stations in the area. It has been found that the deformation of the southern part of Patras Gulf near the coastline has been characterized by considerable subsidence (>-5mm/yr), where unconsolidated sediments usually prevail, compared to the northern part of the gulf. Significant subsidence has also been identified in areas along the down-throw side of possible faults, as well as areas where extensive ground water pumping has occurred for irrigation. These results correlate well with local GPS and seismicity data

Ground deformation detection of the greater area of Thessaloniki (Northern Greece) using radar interferometry techniques

In the present study SAR interferometric techniques (stacking of conventional interferograms and Permanent Scatterers), using images from satellites ERS-1 and 2, have been applied to the region of Thessaloniki (northern Greece). The period covered by the images is 1992–2000. Both techniques gave good quantitative and qualitative results. The interferometric products were used to study ground surface deformation phenomena that could be related to the local tectonic context, the exploitation of underground water and sediments compaction. <br><br> The city of Thessaloniki shows relatively stable ground conditions. Subsidence in four locations, mainly in the area surrounding the city of Thessaloniki, has been detected and assessed. Two of the sites (Sindos-Kalochori and Langadhas) were already known from previous studies as subsiding areas, using ground base measurements. On the contrary the other two sites in the northern suburbs of Thessaloniki (Oreokastro) and in the south-east (airport area) were unknown as areas of subsidence. A further investigation based on fieldwork is needed in these two areas. Finally, an attempt to interpret the observed deformation, according to the geological regime of the area and its anthropogenic activities, has been carried out

Deformation in Nisyros volcano (Greece) using differential radar interferometry

Nisyros Volcano located at the southeastern Aegean Sea (Greece) has recently shown (1996-97) a high seismic activity, associated with a significant deformation has determined by DGPS measurements. The determination of the overall deformation of the island was also attempted by Differential Radar Interferometry (DInSAR). The DInSAR analysis has been applied using the ERS-2 satellite data, covering the period 1996-1999. The removal of the interferometric phase related to the topography has been done using an external high resolution DEM. Two areas of the island show a good coherence, the southwestern and the eastern part. Almost two interferometric fringes were respectively recognized and evaluated. These two zones coincide with the main tectonic fractures of the island. The time separation and resolution, which consist important factors, for the extraction of the effective information and the quality of the finally produced differential interferogram, seem however that influence very slight its accuracy. The deformation outlined by the interferogram is compatible with the existing differential GPS observations

Structure of the Marathon basin (NE Attica, Greece) based on gravity measurements

Η παρούσα εργασία παρουσιάζει τα αποτελέσματα μίας βαρυτομετρικής διασκόπησης που διεξήχθη στην περιοχή της Λεκάνης Μαραθώνος, (ΒΑ. Αττική), προκειμένου να προσδιορίσει την δομή του υποβάθρου. Έγιναν συνολικά 120 μετρήσεις και εφαρμόσθηκαν τυπικές διαδικασίες αναγωγής δεδομένων, αν και με χρήση σύγχρονων τεχνικών υψηλής ακρίβειας. Η αντιστροφή της προκύπτουσας ανωμαλίας Bouguer προσέφερε μία μάλλον λεπτομερή απεικόνιση του υποβάθρου, η οποία συμπλήρωσε την πληροφορία διαθέσιμη από γεωλογικές και μορφολογικές μελέτες. Τα κύρια δομικά χαρακτηριστικά της Λεκάνης Μαραθώνος φαίνεται να ελέγχονται από ένα σύστημα ΒΑ-ΝΔ νεοτεκτονικών ρηγμάτων προκαλούντων κλιμακωτή πτώση του υποβάθρου κατά ΝΑ φορά, μέχρι του μέγιστου ανιχνεύσιμου βάθους των ~450m. Αυτά, μαζί με ένα σύστημα ΒΛ-ΝΑ ρηγμάτων και χορεία ελασσόνων ρηξιγενών χαρακτήρων, προσδίδουν στην Λεκάνη χαρακτηριστικά δομής Riedel, προκύπτουσας από κυρίως εφελκυστικό πεδίο Β-Ν διεύθυνσης που επιφέρει και δεξιόστροφη περιστροφή περί κατακόρυφο άξονα. Η παραμόρφωση αυτού του τύπου φαίνεται να διευκολύνει τον σχηματισμό τοπικών αντικλινικών/ συγκλινικών δομών, οι οποίες καθορίζουν την μάλλον περίπλοκη μορφολογία της περιοχής. Τέλος,, τα πολλαπλά διασταυρούμενα ρήγματα φαίνεται να σχηματίζουν υδροπερατό ιστό, πιθανότατα υπεύθυνο για την υφαλμύρινση των υδροφορέων της περιοχής. Τα ΒΑ-ΝΔ κανονικά ρήγματα πιθανόν να έχουν την σημαντικότερη συμβολή στο φαινόμενο αυτόThis work presents the results of a high resolution gravity survey conducted in the area of Marathon Basin to asses the structure of the basement. A total of 120 gravity stations were measured. Standard data reduction procedures were followed, albeit based on modern, high precision techniques. The inversion of the Bouguer anomaly map provided a rather detailed image of the basement topography completing the information available from surface geological and morphological surveys. The major structural features of the Marathon Basin appear to be controlled by a system of NE-SW neotectonic faults causing stepwise NW-SE deepening of the basement to a maximum detectable depth of~450m. These faults, together with a system of NW-SE major, and a host of minor faulting features, lend to the Basin characteristics of a Riedel structure formed by a predominantly N-S extensional field effecting clockwise block rotation. This mode of deformation may also have facilitated the formation of local anticlinal/ synclinal structures, which endow the area with its rather complicated morphology. Finally, the multiple intersecting faults appear to form a permeable network, presumably responsible for the salination of the local aquifer system; the NE-SW major normal faults may the most significant contributor to this effect

DIFFERENTIAL INTERFEROMETRY AS A TOOL OF AN EARLY WARNING SYSTEM IN REDUCING THE VOLCANO RISK: THE CASE OF NISYROS VOLCANO

In this study an attempt to evaluate the possibility to use the interferometric (InSAR) technique as an operational tool in an early warning system concerning the volcanic hazard, is presented. The InSAR techniques was appied in Nisyros volcanic island which during 1996-1998 show an intensive seismic unrest. Two interferometric images were created covering the period before the seismic activity (1995-1996). In the two interferometric images fringe patterns of deformation were recognized related to the ground deformation occured before the seismic unrest period. The operational capabilities of the technique is mainly restricted by the low repetitevily of the image aquisitions and the parameters to take in consideration like perpendicular baseline, atmospheric conditions et

Foucauldian Genealogy and Maoism

If we look at the historical and social presuppositions of Foucault's methodology, we find out that Nietzsche's work cannot be the only root of the shift from archaeology to genealogy. In fact, a whole range of political activist practices after May '68 until the dissolution of the Groupe d'information sur les prisons (GIP) played an important role in inciting a politicization-in-motion that clearly left its traces in Foucault's thought and work