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monitoring of the “Sant’Alberto” gas reservoir (Po Plain, Northern
Italy). The project was commissioned to INGV in the framework
of the activities planned by the oil & gas E&P company PoValley
Energy (PVE), aiming to exploit the underground deposit.
After estimating the ambient seismic noise of the area, we
hypothesized a microseismic network composed of five stations
installed in a 8.0x8.0 km2 area centered on the surface projection
of the reservoir. Moreover, due to the high noise levels observed,
we also considered the possible installation of a borehole station
at 200 m depth. Detection and localization thresholds were
estimated by comparing the power spectral density of
hypothetical seismic sources located in the crustal volume
surrounding the reservoir, with the mean power spectra of the
ambient seismic noise observed (or hypothesized) at each
station-site. Two crustal volumes for the earthquakes
detection were considered: the inner domain of detection,
DI (8.6x8.6x4.0 km3), within which we should ensure the
highest network performance, and the extended domain of
detection, DE (18.6x18.6x9.0 km3). Simulations show that: 1)
five surface stations installed within the surface projection of
DI ensure localization thresholds ranging between 0.7 and 0.8
within DI; 2) the installation of the borehole station allows to
improve the detection threshold everywhere within DI, and
up to ML =-0.4 nearby the reservoir; and 3) localization
thresholds obtained in the crustal volume included in DE,
but not in DI, show values around ML = 1.0.
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