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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.

Abstract: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.