Microseismic assessment and fault characterization at the Sulcis (South-Western Sardinia) field laboratory

The general acceptance of the CO 2 geological storage by stakeholders passes through the assessment and mi-
tigation of risks, potentially induced or increased by the disposal activity. Injection of moderate to large
quantities of CO 2 in the sub-surface may unbalance local stress and trigger earthquakes if faults are critically
stressed, condition that is not easily verifiable. Pilot sites are therefore the best way to proceed further in order to
address such challenging issues. In such cases, the reconnaissance of faults and seismicity in the sub-surface,
before the onset of activity, is mandatory. In this paper, we present studies carried out in the site where the
Sotacarbo Fault Lab is going to be installed. This facility will be located in a very low seismic hazard region of
central Mediterranean, where reports on historical large earthquakes are poor. We show results from a series of
experiments aimed to monitor the background seismicity around the pilot site. As expected, seismicity is almost
absent down to small magnitude close to the future injection-test well. Further seismic imaging of the sub-
surface layers obtained by ambient noise tomography offers the ability to resolve the presence of a seismicity-
free fault located in the first 200 m below the surface, of which the last episode of activity is difficult to assess.
Our results encourage the use of this site to follow the response of the system to injection of small quantity of
CO2.