Seismic crustal deformation in the Southern Apennines (Italy)

With the aim of estimating the rates of seismic moment and deformation in seismic zones of southern Italy, constraints on tectonic style and kinematics data from geophysical and geologic data were integrated with the traditional constraints from seismicity catalogues. Seismotectonic considerations indicate that the region can be divided into four broad crustal seismogenic volumes, of relatively homogeneous deformation: an extensional crustal volume in the western part of the Southern Apennines and three crustal volumes characterized by a transcurrent regime in the eastern area. For each crustal volume, the annual seismic moment release showing the rate of the deformation was estimated by integrating magnitude-frequency relations of historical earthquakes. The application of a Monte Carlo simulation systematically incorporated the uncertainties of the input parameters. The results show that the westernmost crustal volume is undergoing extension, with velocity of similar to 1.2 mm/a (along a nearly NE-SW direction), whereas the easternmost volumes are undergoing transcurrent deformation, with an along-strike deformation axis oriented along a nearly E-W direction, with velocities of similar to 1 mm/a, similar to 1.2 mm/a and similar to 0.1 mm/a, respectively for the northern, central and southern volumes. The errors affecting the estimate of the crustal deformation using the seismicity catalogues may be significant. The parameters with the largest contribution are the coefficients of the magnitude-moment relationship; the second and third contributors are the coefficients of the magnitude-frequency distribution and the maximum magnitude. Uncertainties in the geometrics and kinematics parameters have slight, minor effects. Furthermore, the effects of the crustal model (and the consequent earthquake association) are of the same order as the uncertainties of the parameters involved in the computation. These results agree with recent GPS data and geological slip rates in terms of direction and rate of deformation.