Deciphering the Interplay between Reservoir Loading and Dynamic Stresses at the Pertusillo Reservoir

Abstract

Our ability to comprehend the underlying mechanisms of dynamic earthquake triggering (DET) is often hindered due to a lack of concurrent static stress and pore-pressure change observations. Here, we utilize the known reservoir-induced seismicity near the Pertusillo Reservoir in southern Italy as a natural experiment to track how changes in static stress and pore pressure from hydrological operations are related to DET around the reservoir. A ∼13-month (May 2005–June 2006) high-resolution seismicity catalog is utilized to compute the DET rate for potential triggering sources. The observed DET rate of ∼16% is comparable with other tectonic and volcanic regions. However, the enhanced DET rate (∼23%) around the Pertusillo Reservoir occurs when the reservoir contains its largest seasonal load as well as during the seasonal drawdown period. This suggests that periodic stress loading and pore-pressure changes are possibly the leading mechanisms controlling DET susceptibility at the Pertusillo Reservoir. Furthermore, varying triggering rates for different earthquake clusters illustrate the dependence of DET on the spatial variation of static stress, pore pressure, and the underlying crustal heterogeneities. That said, we conclude that the DET sensitivity of the Pertusillo Reservoir is possibly influenced by reservoir loading. However, longer-term monitoring is required to further elucidate this dependence.