Investigating Of causes Short and Long Term Ground Deformation by Implementing Sar Interferometric Techniques in Larissa
Fakhri, Falah
HAROKOPEIO UNIVERSITY OF ATHENS, GREECE

The town of Larissa is the capital of Thessaly and is located in the eastern part of Central Greece. According to the historical seismicity, this settlement is characterized as having medium to high seismicity due to the fact that the last earthquake with high magnitude (Ms = 6.1) occurred in 1941. Furthermore three normal active faults cross the settlement. However, according to the Institute of Geodynamics of the National Observatory of Athens, no earthquake with a magnitude greater than Mw = 4 has been observed since 1941. Based on this scientific question that no earthquake with a magnitude greater than Mw = 4 has been observed since 1941, this research has been implemented. Consequently the objectives of this study are to verify the possibility of implementing Synthetic Aperture Radar (SAR) interferometric techniques to detect short- and long-term deformation in addition to investigating the factors that affect ground deformation within the settlement. Three interferometric SAR techniques have been implemented using GAMMA Software (S/W): conventional, stacking interferometric and interferometric point target analysis. Two datasets ERS1/2 and ASAR ENVISAT of ascending and descending tracks have been used during the periods 19952008 and 19922010, respectively. Results of three techniques ascending and descending tracks indicate to subsidence and uplift deformation are distributed over all the settlement. The results of conventional and stacking interferometric techniques for two tracks indicate the possibility that fault movement has an effect on ground deformation and moreover is affected by the type of lithology. The results of the persistent scatterer technique for two tracks reveal and/or indicate the possibility of impacting fault movement and type of lithology on ground deformation through the application of spatial correlation between the location of point candidates and fault traces. In spite of the controversy regarding the gap since the last large magnitude earthquake in 1941, which so far remains the major issue, fault movements causing small magnitude earthquakes varying between M = 3 and M = 4 may be attributed to the impact of mutual processes between swelling and shrinkage of clay minerals. These processes are activated through the successive operations of water withdrawal and compensation. With regard to their types, these clay minerals consist of two layers of aluminium to one layer of silicon or two layers to two layers of aluminium to one layer of silicon. One of these clay minerals, which constitutes 16% of the study area, is montmorillonite. As a consequence, the low magnitude earthquake may be attributed to it. However, there is still a need to implement a tectonic study within the settlement of Larissa and in the eastern part of northern Thessaly. The other main reason for subsidence is the compaction of materials, which can be deduced from the type of lithology, which is alluvial. Since it consists of mostly loose fluvial material which has low coherence of materials, it shows more vulnerability. Consequently this compression of materials may also contribute to causing microearthquakes of magnitude 34, gradually leading to high subsidence. Á