On the seismic potential of the Corsica–Sardinia block

The Corsica–Sardinia lithospheric block is traditionally viewed as a region of notoriously low seismicity. Earthquake catalogs report only three moderate earthquakes in the range of magnitudes 5.0–5.1. The scarcity of documented seismicity in the region does not allow for the reliable assessment of the seismic hazard. In this paper, we make an attempt to evaluate the seismic potential of the Corsica–Sardinia region employing the morphostructural zoning (MSZ) that allows for the identification of locations of potential earthquakes. The MSZ delineates the hierarchical system of morphostructural blocks, the network of lineaments bounding the blocks, and the loci of nodes formed around intersections of lineaments. Nodes are treated as earthquake controlling structures. We have used the existing criteria of seismicity defined earlier for seismogenic (M5+) nodes in Iberia and the Western Alps with the goal to identify seismogenic nodes capable of generating earthquakes M5+ in the Corsica–Sardinia block. We test the criteria of seismicity for these regions relying on modern models of the Mediterranean geodynamics that view the eastern margin of Iberia and Provence adjacent to the Western Alps as locations of the Corsica–Sardinia block before drifting. Due to a common tectonic evolution the structure of the Corsica–Sardinia block is roughly similar in the basic features to the structural setting of Iberia and southern France. Out of the 81 nodes delineated by MSZ (deliberately ignoring the available earthquake catalogue) we identify 24 nodes capable of earthquakes M5+ using the criteria of seismicity defined for Iberia. Nodes hosting three documented M5+ earthquakes are assigned to seismogenic ones and most of the nodes accommodating smaller events with magnitudes 4.0–4.9 are also classified as seismogenic by pattern recognition. Applying the criteria of seismicity defined for the Western Alps, we have properly identified only two nodes hosting the documented M5+ earthquakes and missed practically all the nodes with smaller events. The performed analysis reveals that the criteria of seismicity defined for Iberia are more pertinent for the identification of seismogenic nodes in Corsica–Sardinia, because they recognize as seismogenic the nodes marked by documented earthquakes. Our study suggests that the seismic potential of the Corsica–Sardinia block can be specified as low-to-moderate. The defined locations of seismogenic nodes provide key information for knowledgeable long-term seismic hazard assessment of the region.