The difficulty to distinguish natural and human related seismicity in a complex tectonically active area

Abstract

Human operations, such as mining, fluid production and the construction of a barrier lake in a tectonically active area can play an important role of triggering seismic events. An interesting area to study those phenomena is the northern part of the Upper Tiber Valley, which is characterized by the presence of a Low Angle Normal Fault, the so called Alto Tiberina Fault (ATF). The recent seismic activity of this fault line reflects the geodynamic behaviour in the regional stress field. Close to this fault zone, a 4.8 km deep borehole PSS1 is located which will be reopened at the end of 2010 to extract CO2. This will possibly lead to a change in the hydraulic equilibrium in this region with potential consequences for the overall local geodynamics. Crustal deformation and microseismicity could be induced by the extraction. Fluid pressure changes and their influence to the hydraulic conduits up to the natural fluid emissions sites (mofettes) will be investigated as part of an actively controlled forcing experiment on this fault. Further human activities like mining industry and the filling of water reservoirs influence the local stress field. The derivation of natural and human induced seismicity can be improved by a comprehensive analysis.