Gravity and magnetic modeling of Central Italy: insights into the depth extent of the seismogenic layer

In this work, the crustal volume struck by the 2016-2017 seismic sequence in Central and Northern Apennines is investigated using unconstrained and constrained 3D inversion of the observed Bouguer anomaly. In order to focus on the area encompassing the two mainshocks of the sequence, we perform a regional signal removal on the data as a pre-processing step. This residual dataset is then inverted in 3D to model density contrasts at depth. We perform a series of inversion to test different geological scenarios. We first invert with the conventional method for the recovery of a smooth density distribution. We then introduced geological knowledge with basement and turbidites geometries retrieved from the most recent geological and geophysical models in the area. Best-fitting residual density values are inverted for the basement and upper region and used as constraints in a sub-sequent inversion. We found that, regardless of the constraints adopted, the density distribution with depth is compatible with previous models and supports the hypothesis of a low-density upper basement, possibly phyllitic in composition. We compare our modeling results to the spatial distribution at depth of major seismic events during the 2016-2017 period. The location of these events appears to be concentrated within the upper denser units, while the deeper events often occur in a region of major density change that we interpret as the top of the basement.