Morphotectonics of LANF-controlled Plio-Quaternary grabens (Lunigiana-Garfagnana, Italy)

We report first results of structural and morphotectonic analyses aimed to characterize active and potentially seismogenic faults in the Lunigiana and Garfagnana basins. These basins are Pliocene-Holocene asymmetric grabens that lie in the hanging wall of a regional, east-dipping, low angle detachment that is imaged in seismic profiles deepening beneath the Apennines down to a depth of ~13 km. Seismic lines highlight E-dipping synthetic faults dipping between 30° and 60° down to depths of ~5km before soling onto the low-angle detachment. In contrast, W-dipping antithetic faults show on average higher dip angles of 50° to 70° and root on the detachment at depths of less than 5km. Topographic metrics including drainage patterns, river long profiles, indices of channel concavity, stream-length gradient of modelled long profiles, steepness and swath profiles are used to better constrain the effects of active slip on these faults as they rupture and help shape the current topography. We quantify the relationships between these faults and watershed-scale geomorphology using a 10 m digital topography to extract channel and basin metrics. The E-dipping faults with strongest geomorphic signature of Late Quaternary activity are the Mulazzo and Olivola-Soliera faults in the Lunigiana and the Casciana-Sillicano and Bolognana-Gioviana faults in the Garfagnana. The most important W-dipping splays in terms of late Quaternary activity are the Groppodalosio and Compione-Comano faults in the Lunigiana and the M.Prato-Colle Uccelliera-M.Mosca alignment in the Garfagnana. The Tendola-Equi Terme-Gramolazzo alignment is a high angle E-W right- lateral transfer zone. This alignment, quite evident in aerial photographs and in seismic lines, is interpreted as a transfer zone of active extension between the Lunigiana and Garfagnana grabens. Computation of geomorphic indices is in good agreement with the seismological data, suggesting that historic earthquakes in the area can be associated with these mapped faults that are further capable of generating surface ruptures and contributing to the production of local relief.