GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Inferences on the seismotectonics of the Lunigiana-Garfagnana area by focal plane solutions of historical earthquakes E. Eva 1 , F. Pettenati 2 , S. Solarino 1 1 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Nazionale Terremoti 2 Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, OGS Introduction The Lunigiana and Garfagnana area (Tuscany, northern Italy) is a region of active tectonics, seismicity, and suspected seismogenic reactivation of preexisting normal faults (Brozzetti et al., 2009; Eva et al., 2014). Its basins are part of a series of early Pliocene to Quaternary, NW–SE oriented extensional grabens (Argnani et al., 2003). The whole area is seismically active and has been shaken by several strong earthquakes in the last millenium until the most recent 2013 earthquakes, confirming that it is one of the most active areas of the northern Apennines. The most important historical earthquakes occurred on 7 May 1481 (Imax VIII MCS; Mw ~ 5.6); 14 February 1834 (Imax IX MCS; Mw ~ 5.8); 11 April 1837 (Imax X MCS; Mw ~ 5.8); and 7 September 1920 (Imax X MCS; Mw ~ 6.5) (CPTI 11 catalogue, Rovida et al., 2011). These events are located through macroseismic data with the exception of the September 1920 earthquake that has also been investigated using instrumental data by Solarino (2005). The study provided an instrumental location, including depth, for many events occurred in the Lunigiana-Garfagnana area in the twentieth century and proved that macroseismic locations are sometimes not well constrained and may lead to wrong seismotectonic interpretations. In 2014, Eva et al., analysed the seismicity of the area applying the high precision location algorithm HypoDD (Waldhauser and Ellsworth, 2000) finding that most of the seismicity of the western zone is located in the Lunigiana graben, N-NW of the Apuane Alps; at depth, the Lunigiana seismicity deepens to the east parallel to the top of the basement, which in turn coincides with an extensional detachment (~30° E-dipping); finally, the Lunigiana seismicity terminates southwards with a dense cluster of epicentres oriented nearly E-W, parallel to the transfer fault zone that delimits the Apuane Alps to the north; south of this cluster, a strong reduction of seismicity is observed and the locations are shifted to the eastern sector. However, that analysis did not include the 2013 events. It has to be remarked that in the last 30 years the transfer zone area, e.g. the sector between the two grabens, north of the Apuane Alps, has experienced frequent and stronger earthquakes than the surrounding areas. In January and June 2013, this sector was hit by several earthquakes, the major of which were the Mw 5.1 located