GNGTS 2013 - Atti del 32° Convegno Nazionale

As it may be seen, the transient causes positive displacement up-wards and along the directions indicated in the legend between 2007 and 2008, and opposite trend in 2009. In order to state, whether the transient is due to tectonic phenomena or, vice versa, has an hydrologic origin, as found by Zerbini et al. (2010) in a neighboring area, we calculated the seismic energy released in the region in the same periods (e.g. Franceschina et al. , 2006), as well as the hydrological balance. The first is defined as: where E is the seismic energy and MD is the earthquake duration magnitude. For the calculus of the hydrological balance, we started from the meteorological stations of the regional council networks nearest to each of the GPS stations and corrected the de- trended cumulative curves for the estimated evapo-transpiration, using the Thornthwaite (1948) formula: where and with PET = estimated potential evapotranspiration (mm/month), Ta is the average daily temperature, N is the number of days in the month, L is the average length of the day, and l is the heat index. We compared GPS displacements, seismic energy, and hydrological balance in time, at time interval of about two months, starting from 2005 to 2010. There is a certain correlation between the time variations of the seismic energy distribution in the region and the ones of the deformation field induced by the transient. On the contrary, the variations in time of the hydrological balance distribution appear less in agreement, varying more slowly. Fig. 3 – Solid lines: horizontal displacements along the directions shown in the legend box, along which the displacement is maximum for each station; dashed lines: vertical components. Constant values are applied to the curves to enable the comparison between the various sites. Grey dashed, vertical lines indicate the years. 200 GNGTS 2013 S essione 1.2