Monitoring Ground Elevation Changes in the Larderello Geothermal Region, Tuscany, Italy

Abstract

In 1921-23 a precise leveling network, with more than 200 km of lines, was set up and measured in the Tuscan geothermal region comprising the Larderello area. In 1985-86 this topographic network was rearranged and leveling measurements were repeated. Negative elevation changes reaching a maximum of about 170 cm were observed across the areas of maximum fluid withdrawal and maximum fluid pressure decline. Leveling measurements carried out in 1989 show that elevation changes are no longer evident in the central Larderello area, but subsidence of less than 3 cm can still be ob served in some nearby areas exploited recently. The measured subsidence values cannot be ascribed solely to the compaction of reservoir rocks, as this would entail a pressure decline down to about 10 km depth. Since this figure seems excessive we hypothesize that compaction of the cover terrains is also involved.