Separation of Poroelastic and Elastic Processes of an Aquifer From Tectonic Phenomena Using Geodetic, Seismic, and Meteorological Data in the Pollino Region, Italy

Abstract

Velocity variations obtained from ambient seismic noise are sensitive to many factors. We aimed to disentangle these processes in a 10-year-long recording of seismic noise from a single station in the Pollino region, in southern Italy. This region is characterized by aquifers and by a relatively short period of high seismic activity that included slow slip events and a urn:x-wiley:15252027:media:ggge22677:ggge22677-math-0001 earthquake that occurred on October 25, 2012. We apply two models that estimate the water level inside an aquifer, which show a good correlation with the measured urn:x-wiley:15252027:media:ggge22677:ggge22677-math-0002, showing that the velocity variations are inversely proportional to the pore pressure inside the aquifer. Our interpretation is further confirmed by geodetic measurements that show that in a direction parallel to the strike angle of the fault rupture, the expansion-contraction displacement of the zone follows the same patterns observed in the models and in the velocity variations, as a result of the pressure generated by the water on its interior. Going one step further, we analyze the nature of the small discrepancies between the measured and modeled velocity variations. These correlate well with the rainfall and with the vertical geodetic measures, which indicates an elastic response of the zone to the loading generated by the rainwater. Comparisons between these variables allow us to clearly identify the period of the seismic activity in the zone, which is represented by the characteristic drop in the seismic velocity in the period from the beginning of 2012 to mid-2013.