Active Tectonics in Tuscany (Central Italy): Ten Years of Seismicity (2009-2019)

Strong earthquakes (moment magnitude MW ≥ 5.5) are uncommon in Tuscany and surroundings (central Italy). The last strong seismic event occurred a century ago (September 7, 1920 Garfagnana, MW = 6.53). The paucity of seismic instrumental recordings hinders the identification of the tectonic regime active in Tuscany. On the other hand, the geological and geomorphological pieces of evidence collected so far, concerning potential active and capable faults, are scarce, fragmentary and ambiguous. In this work I shed light on the active deformation of Tuscany by using two independent approaches: earthquake source mechanisms and GNSS (GPS) geodetic measurements. I have considered 41 small seismic events (MW ≤ 5.1) that occurred in the study area during the last decade. The related source mechanisms (retrieved by the Time Domain Moment Tensor method) define a relatively clear picture of the active deformation: extension along the northern Apennine watershed and strike-slip regime within inner Tuscany, up to the Tyrrhenian coast. This pattern broadly agrees with the horizontal strain field reconstructed by the geodetic velocity field. The latter has been constrained by a network of 840 GPS stations located in Italy and neighboring countries, operating in the last 20 years.