Quaternary slip rates along the frontal thrust system of the Pede-Apennine margin, between the Enza and Panaro valleys, Emilia Romagna, Italy

The study area is located on the Emilia Pede-Apennine Margin, between the Reno and the Enza valleys. This area is marked by the Pede-Apennine Thrust Front (PTF) (Boccaletti et al., 1985), which separates the internal sectors of the Northern Apennines from the external thrust fronts (ETF), buried underneath the Quaternary deposits of the Po Plain. Growth strata layouts, related to PTF activity, can be observed in discontinuous outcrops along the Pede-Apennine Margin. In this study, the reconstruction of Quaternary deformation rates was addressed by means of the analysis of growth strata and structural field data. Therefore, we carried out a structural and geological survey of the stratigraphic units that present a growth strata layout. We collected a dataset made up of mesoscopic joints and faults to which the application of a stress inversion procedure yielded a sub-horizontal N-NE-oriented s1. Two sets of numerical models (for a total of 104) were built considering two transects across the PTF, referred herein to as Quattro Castella and Scandiano, where the SSW-dipping Pede-Apennine thrust (PAT, which is the main PTF structure), is nearly surfacing along the margin. The Trishear Fault-propagation Folding mechanism (Erslev, 1991) was applied to the considered transects by using the software Fault Fold (Allmendinger, 1998). For both transects a best fit model was chosen, by comparing the geological data with the obtained outputs. With the data provided by the best fit models, we then obtained the PAT deformation rates in the study area. At Quattro Castella, averaged minimum values over the last 1,07 Myr, are: slip rate 0,79 mm/yr, propagation rate 1,96 mm/yr, shortening rate 0,50 mm/yr, and uplift rate 0,62 mm/yr. At Scandiano averaged minimum values over the last 800 kyr are: slip rate 0,70 mm/yr, propagation rate 2,10 mm/yr, shortening rate 0,44 mm/yr, and uplift rate 0,59 mm/yr. The obtained values are compatible with others determined in adjoining areas, and thus can be considered representative of the PAT in the analysed sector. Finally, our models suggest that, along the considered transects, the PAT is best depicted as a high-angle thrust fault (> 50°). Allmendinger R.W. 1998. Inverse and forward numerical modelling of trishear fault propagation-folds. Tectonics, 17, 640-656. Boccaletti M., Coli M., Eva C., Ferrari G., Giglia G., Lazzarotto A., Merlanti F., Nicolich R., Papani G. & Postpichl D. 1985. Consideration on the seismotectonics of the Northern Apennines. Tectonophysics, 117, 7-38. Erslev E.A. 1991. Trishear fault-propagation folding. Geology, 19, 617-620.