Relationship between seismicity and water level of the Pertusillo reservoir (southern Italy)

The Pertusillo reservoir, located in the High Agri Valley (southern Italy), represents an example of a site affected by continued reservoir-induced seismicity. Although it has been shown that annual fluctuation can be considered the main forcing of the induced seismicity in this area, an investigation of the relationships between the seismicity and some water level parameters of the Pertusillo reservoir carried out in this paper. The aim is to understand, apart from the annual fluctuation, if one or more of these parameters play a dominant role in inducing seismicity year after year SW of the reservoir. The findings of this study suggest that the exceedance of water levels over the previous maxima did not trigger any historical earthquake. In addition, the daily water level rate and the duration for which the maximum water level is maintained do not play any significant role in inducing seismicity. The maximum amplitude of water level change in a hydrological cycle as low as 8 m appears to be large enough to trigger the seismicity SW of the Pertusillo reservoir, whereas higher maximum amplitudes of water level in a hydrological cycle seem not to increase the seismicity rate. Furthermore, it is shown that a long-lasting increase of the water level may lead to induced earthquakes with larger magnitude. Finally, it is demonstrated that the geology of the area SW of the reservoir may provide favourable conditions for the water level fluctuations to induce seismicity in that region, whereas a different geology to the NE of the reservoir is the cause of negligible pore pressure increase.