Microseismicity related to gravity-induced slope deformations for risk management

Abstract

An accelerometric array installed on 4 September 2008, has been used to manage the geological risk in the Peschiera Springs drainage plant of Rome’s aqueduct, located in the Central Apennines approximately 80 km from Rome, Italy. The plant occupies a carbonatic slope that is extensively involved in gravitational deformations, which are responsible for underground failures such as cracks and collapses of karst caves. To distinguish among different types of recorded events, an automated procedure was implemented taking into account duration, peak of ground acceleration (PGA) and its variation within the accelerometric array. The main sequence of underground failures so far recorded was related to the L’Aquila seismic sequence occurred in April 2009. Moreover, a very intense sequence of underground failures occurred in September 2011 that was not related to seismic events, i.e. only due to the gravitational processes affecting the slope. These evidences prove that the ongoing gravitational slope deformations have a key role in predisposing and/or causing the underground failures within the karst rock mass of the Peschiera Spring slope. A control index (CI) is daily computed as a function of sub-indexes which are derived from the rate of cumulative Arias intensity of underground failures, the frequency of underground failures and the frequency of earthquakes. The CI index identifies “ordinary”, “alert” or “emergency” levels of attention and represents a fundamental tool for managing the geological risk associated with the deformational process affecting the drainage plant.