Vertical tectonic motion in Andaman Islands detected by multi-temporal satellite radar images

Στις 26 Δεκεμβρίου 2004 ένας από τους ισχυρότερους καταγεγραμμένους σεισμούς (Mw>9.0) έλαβε χώρα στην περιοχή Soumatra-Andaman. Η διάρρηξη έφτασε τα 1300km εκτεινόμενη από τη βόρεια Σουμάτρα έως το σύμπλεγμα νήσων του Andaman. Λόγω του περιορισμένου αριθμού των ενόργανων καταγραφών και της δυσκολίας υπαίθριων παρατηρήσεων, η συμβολή της τηL·πισκόπησης είναι ουσιαστική καθώς επιτρέπει τη συλλογή πληροφοριών σχετικά με την κατανομή της παραμόρφωσης στο χώρο και το χρόνο. Στην παρούσα εργασία, ASAR δεδομένα του δορυφορικού συστήματος ENVISAT υπέστησαν επεξεργασία προκειμένου να παραχθεί μια διαχρονική εικόνα, βάση της οποίας αναγνωρίσθηκαν κατακόρυφες τεκτονικές κινήσεις κατά μήκος της νήσου Andaman. Σύμφωνα με τα αποτελέσματα της ανάλυσης, φαίνεται ότι τα βόρεια τμήματα της νήσου υπέστησαν γενικότερη ανύψωση. Παρόλο που οι ενδείξεις ανύψωσης ήταν εκτεταμένες στις ΒΔ ακτές της νήσου, κατά μήκος των δυτικών ακτών των κεντρικών και νότιων τμημάτων της υπήρξαν περιορισμένες. Σε ορισμένες περιπτώσεις κυρίως στα ΝΑ περιθώρια των Andaman αναγνωρίστηκαν φαινόμενα βύθισης. Η χαρακτηριστική ζώνωση που παρατηρείται στην διαχρονική εικόνα πιθανό να οφείλεται είτε στη μετα-σεισμική επαναφορά, είτε σε παλιρροϊκά φαινόμενα. Παρά τον ποιοτικό χαρακτήρα των παρατηρήσεων, εφόσον αναγνωρίζεται αποκλειστικά και μόνο η φορά της κίνησης, τέτοιου είδους δεδομένα δύναται να χρησιμοποιηθούν ως πρόσθετη πληροφορία σε μελέτες προσομοιώσεων της παραμόρφωσηςOn 26 December 2004 one of the largest earthquakes ever recorded by modern seismology (Mw>9.0) occurred in Sumatra-Andaman region. About 1300km of seafloor were ruptured extending from northern Sumatra to Andaman Island complex. As instrumental data are sparse and in most of the cases field observations difficult to undertake, the role of remote sensing may be beneficial in providing information about the pattern of deformation in space and time. In the present study ENVISAT ASAR data are acquired and processed to generate a single multitemporal SAR image in order to detect vertical motion along Andaman Island. According to our analysis it seems that the northern parts of the island are generally uplifted. Though its north-western coasts show significant marL· of uplift, such indications become less evident along the western coasts of Middle Andaman. At some locations at the south-eastern margins of the island marks of downlift are recognized. Characteristic banding observed in the multi-temporal image could be attributed either to post-seismic relaxation, either to tidal phenomena. Although qualitative in nature, as just the sign of elevation change can be detected, results of such analysis could be used as constrains in deformation modelling research

SHORT PERIOD CHANGE DETECTION OF SPERCHIOS LOWER DELTA AREA USING SPACE RADAR IMAGES

Being highly dynamic by nature, due to their changing hydrological regime and to the encroachment of urbanization, industrialization and changing patterns in agriculture, reliable and timely information of coastal areas is a prerequisite for their effective management. The aim of this paper is to assess the use of ERS-2 SAR satellite data to detect short period changes in the case of the R. Sperchios coastal area that is located at the eastern part of the Maliakos Gulf (near the middle of the east coast of the Greek mainland). A Landsat 7 (ΕΤΜ+) image served as a reference for the interpretation of the ERS images. In order to highlight and detect the changes occurred in the study area two methods were applied. The first method is based on the creation of a Temporal Differentiate Image, consisted of the three ERS-2 images (Figure 1). The second method concerns the implementation of Principal Component Transform (PCT) on the three multitemporal scenes. The final images derived from the two different methods were compared and evaluated. Both methods didn't show any significant change along the coastline. PCT method illustrates more clearly the seasonal changes of crops in the lower delta area. Eventually, radar technology gave the opportunity to discriminate shallow areas, which does not appear in satellite optical data. Concurrently, the effect of wind direction was investigated

Subsidence monitoring within the Athens Basin (Greece) using space radar interferometric techniques

The application of conventional SAR Interferometry (InSAR) together with the two techniques of sub-centimeter accuracy, the Stacking and the Permanent Scatterers (PS) Interferometry, were used to study the ground deformation in the broader area of Athens for the period 1992 to 2002. Using the Stacking interferometric method, 55 ERS-1&2 SAR scenes, between 1992 and 2002, were acquired producing 264 differential interferograms. Among these only 60 were finally selected as fulfilling certain criteria. The co-seismic deformation associated with the Athens Earthquake (Mw = 5.9, September 7, 1999) was excluded from the analytical procedure in an attempt to present results of only aseismic character. In total ground subsidence results of about 12 mm in the southern suburbs of Athens, but higher value of about 40 mm in the northern ones for the period 1992-2002. Based on the PS technique, a precise average annual deformation rate-map was generated for the period 1992-1999, ending just before the Athens earthquake event. Both circular and elongated-shape areas of subsidence are recognizable especially in the northern part of the Athens Basin (3-4 mm/yr), as well as at its southern part (1-3 mm/yr). In addition, a rate of 2-3 mm/yr is also yielded for some part of the Athens city center. Subsidence rates of 1-2 mm/yr are measured at the western part of the basin over an area of old mining activities, and around the newly built Syntagma Metro Station. The correlation of the observed deformation patterns with respect to the spatial distribution of water pumping, older mining activities, metro line tunneling and other local geological parameters is examined and discussed. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB