Crustal structure and Moho depth profile crossing the central Apennines (Italy) along the N42 degree parallel.

We present results from a teleseismic receiver-function study of the crustal structure in the
central Apennines (Italy). Data from fifteen stations deployed in a linear transect running
along the N42 degree parallel were used for the analysis. A total number of 364 receiver
functions were analyzed. The crustal structure has been investigated using the neighborhood
algorithm inversion scheme proposed by Sambridge [1999a], obtaining crustal thicknesses,
bulk crustal VP/VS ratio and velocity-depth models. In each inversion, the degree of constraint
of the different parameters has been appraised by the Bayesian inference algorithm by
Sambridge [1999b]. The study region is characterized by crustal complexities and intense
tectonic activity (recent volcanism, orogenesis, active extensional processes), and these
complexities are reflected in the receiver functions. However, the relatively close spacing
among the seismometers (about 20 km) helped us in the reconstruction of the crustal structure
and Moho geometry along the transect. Crossing the Apennines from west to east, the Moho
depth varies by more than 20 km, going from a relatively shallow depth (around 20 km) on
the Tyrrhenian side, deepening down to about 45 km depth beneath the external front of the
Apenninic orogen, and rising up again to about 30 km depth in correspondence of the
Adriatic foreland. Despite the strong variability of the crustal thickness, the average crustal VS values show little variation along the transect, fluctuating around 3 km/s. The average VP
values obtained from the VS and VP /VS are generally lower than 6 km/s.