Volcanic spreading forcing and feedback in geothermal reservoir development, Amiata Volcano, Italia

Faults strengthening and seismicity induced by geothermal exploitation on a spreading volcano, Mt. Amiata, Italia

“…Detailed descriptions of the regional geology of the Amiata volcano area may be found in Brogi (2008), in the 1:10,000 Geologic Map of Amiata volcano by Regione Toscana, RT (2006RT ( -2009 and in Ferrari et al (1996), Cadoux and Pinti (2009) and Borgia et al (2014).…”

“…Post-collisional extensional tectonics in the area, from Middle Miocene to Present, produced the collapse and thinning of the lithosphere and of the overthickened crust, with associated renewed sedimentation, emplacement of plutons, uplift, and finally volcanic activity. Borgia et al (2014) show that, due to gravity and intrusive doming, the volcanic edifice becomes normally faulted while sinking and spreading on its ductile clayey (Ligurian) and evaporitic (Tuscan) substratums ( Fig. 1 and 2b).…”

“…All these faults, being the result of the spreading of Amiata' edifice, tend to remain through time in a nearly 'permanent' critically-stressed condition. That is, after a slip event the stress is recharged relatively fast onto fault planes due to the continuous outward spreading of the edifice (Borgia et al, 2014).…”

“…We observe that at this distance we include both the extensional structures that dissect the volcanic edifice and the compressive structures at the base of the volcano (Fig. 1), all of which are related to the volcanic spreading process (Borgia et al, 2014).…”

“…1). We anticipate from the conclusions that geothermal exploitation at Amiata may have augmented faults' segments strength within and around the geothermal fields, while, due to volcanic spreading and regional tectonics, stresses are continuously accumulated on faults and are eventually released through coseismic strain (Borgia et al, 2014). We describe 'tectonic-fracturing' events occurring mainly from within the volcanic edifice to below the exploited geothermal field; in addition we identify several 'hydro-fracturing' events that correlate with geothermal fluids production/injection from the reservoir.…”