Spyridoula Vassilopoulou

Long term and seasonal ground deformation monitoring of Larissa Plain (Central Greece) by persistent scattering interferometry

The land subsidence which occurs at the Larissa Basin (Thessaly Plain, Central Greece) is due to various causes including aquifer system compaction. Deformation maps of high spatial resolution deduced by the Persistent Scattering Interferometry (PSI) technique (using radar scenes from ERS and ENVISAT satellites) for the period 1992–2006 were produced to study the spatial and temporal ground deformation.A developed GIS database (including geological, tectonic, morphological, hydrological, meteorological and watertable variation from wells in the area) offered the possibility of studying in detail the intense subsidence. The PSI based average deformation image clearly shows that subsidence generally takes place inside the Larissa Plain ranging from 5–250 mm. The largest amplitude rates (−25 mm/yr) are observed around the urban area of Larissa City (especially at Gianouli and Nikea villages), while the Larissa City center appears to be relatively stable with a tendency to subside. The rest of the plain regions seem to subside at moderate rates (about 5–10 mm/yr). The surrounding mountainous area is stable, or has slightly been uplifted with respect to the NE located reference point. It was found that there is a correlation between the seasonal water-table variation (deduced from wells data), the seasonal water demand for irrigation associated with specific types of cultivation (cotton fields), the monthly rainfall, and the observed subsidence rate in the rural regions of the Thessaly Plain.

GROUND DEFORMATION OF ZAKYNTHOS ISLAND (WESTERN GREECE) OBSERVED BY PSI AND DGPS

Ground deformation studies based on Differential GPS (DGPS) measurements and Permanent Scatterers InSAR (PSI)* analysis using ERS (1992-2000) and ENVISAT (2003-2010) radar data have been conducted on Zakynthos Island (Western Greece) covering the period 1992 to 2012. These results were compared, validated and integrated with geological, geotectonic and seismological data to evaluate possible pre-earthquake deformation process, and the present tectonic regime. The PSI results indicate that a slight subsidence had occurred during the period 1992-2000, while uplift has mainly observed in 2003-2010. DGPS results for 2005-2006 indicated strong opening of the southern part of the island, while in the period 2006-2012 the amplitude of deformation is relatively smaller. The occurrence of the seismic outbreak that took place offshore to the south of Zakynthos during 2005-2006 may have contributed to the different deformational pattern as revealed by the ERS and ENVISAT PSI products, and also elucidate the DGPS results.

Ground deformation study of KOS island (SE Greece) based on Squee-SAR™ interferometric technique

The SE part of the Hellenic Volcanic Arc (HVA), including Kos, Yali and Nisyros islands, is geodynamically very active and of high tectonic unrest, where the largest volumes of volcanic products were emitted during the past 160,000 years. The SqueeSAR™ Interferometric technique based on ENVISAT radar data has been applied in Kos to spatially and temporally study the ground deformation for the period 2003-2010. The observed LOS velocity field, with values ranging between -4 to +4 mm/yr, combined with small standard deviation velocity (<;1.4 mm/yr) and acceleration (-0.5 to 1.5 mm/yr2) values reveal an almost linear type of ground deformation. These small velocity values in conjunction with intermediate seismicity occurring only off-shore, indicate ground deformation of aseismic local character. The strongest subsidence is associated with local geothermal areas, as well as rural areas due to intense water pumping. Motions along the main faulting zones have also been clearly identified.

Crustal stress and seismic activity in the Ionian archipelago as inferred by satellite- and ground-based observations, Kefallinia, Greece

Abstract Different observational techniques are compared in order to investigate possible correlations in seismic activity. The study site is the island of Kefallinà (Greece), where measurements available included (1) DInSAR, DGPS, and DEM data, (2) soil exhalation measured by monitoring Radon (Rn) well content, and (3) acoustic emissions (AE) at high and low frequency (point-like records with high temporal resolution). AE records provide: (1) relative time variation of the applied stress intensity and (2) the state of fatigue of stressed rock volumes, the AE source. Our results indicate that the large spatial scale (poor time resolution) may be considered quite satisfactory, whereas fractal analysis of the AE time series displayed some discrepancies when compared to analogous investigations in the Italian Peninsula. Therefore, some refinement is needed in order to reach more precise interpretations of the relevant information available with this kind of data. However, both sets of observations appear in agreement with each other, although more exhaustive investigations would require a suitable array of point-like AE and Rn (or other) measuring sites, as well as longer data series. The latter are particularly helpful for detailed interpretations of the different occurrences within tectonically complex settings where crustal stress crises are marked by various types of geological phenomena.

Combined Squee-SAR TM and GPS ground deformation study of Nisyros-Yali volcanic field (Greece) for period 2002–2012

This study presents the spatial and temporal ground-deformation pattern of the Nisyros-Yali volcanic field after the period of the seismic crisis (1996-1998) based on the local GPS network remeasurement and the analysis of Interferometric data (2003-2010) applying the SqueeSARTM technique. The GPS results indicated intense subsidence in the northern and central parts of Nisyros that caused the western and eastern flanks of the island to “collapse” towards its center. The observed LOS velocity field of the SqueeSARTM analysis revealed a nearly linear type of ground deformation, exhibiting values ranging between -3 to +3mm/yr with small standard deviations. The interferometric results have also shown subsidence along the northern and central parts of the island, and an inherent eastward horizontal component at its southeastern part. The overall pattern of the observed subsidence in the area after 2000 is consistent with decrease of pressure in the associated magma chambers and hydrothermal system.

Ground deformation in the broader area of the Atalanti fault zone (Central Greece) based on GPS & PSI-WAP

The Persistent Scatterer Interferometry Wide Area Product (PSI-WAP) based on ERS1 & ERS2 radar data has been used in the seismic active area of Atalanti Faulting Zone (Central Greece) to spatially and temporally study the ground deformation for the period 1992-2003. The observed LOS velocity field, with values ranging between -0.5 to -5.0 mm/yr, combined with small standard deviation velocity values reveals an almost linear type of ground deformation. The most intense subsidence was associated to alluvia deposits and man made activities (intense water pumping). Differential motions along the main faulting zones have also been clearly identified. GPS results reflected a similar pattern of motions (subsidence) with the identified interferometric image. The recorded seismicity in the area is not significant for the PSI-WAP period. The micro-seismic activity (M<;3) is mainly confined peripherally and does not seem to confidently affect the observed ground deformation.