Geodetic slip-rates from block-modeling of a dense GPS velocity field in Italy: new clues on seismic potential from comparison with seismic moment release

Abstract

The growing number of GPS stations in Italy and surrounding regions allows to study, with increasingly spatial details, the velocity gradients across the major seismogenic faults belonging to the complex Central Mediterranean segment of the Nubia-Eurasia plate boundary. If the regional scale pattern of the strain-rate field has been already constrained by several authors, adopting different schemes of sparse velocities interpolation algorithms, showing consistency with seismotectonics data, an estimate of the geodetic slilp-rates at a regional scale is still missing. In this work we use data from > 1000 GPS stations to determine a uniformly defined velocity field, though the analysis of position time-series realized in the ITRF08 reference frame. We use an elastic block-modeling approach to model interseismic fault slip-rates while accounting for rotations of crustal blocks within the complex Central Mediterranean microplates mosaic. We use available catalogues of active faults and instrumental seismicity to define the model geometry, where faults are parameterized as uniformly slipping rectangular planes. The model provides a good fit to the horizontal velocities and fault kinematics that are largely consistent with other geological and seismotectonics information. The estimated geodetic slip-rates are generally faster than the geological ones, considering the large uncertainties associated to the available geologic rates. We use the best-fit block model to calculate a continuous horizontal velocity field and the resulting strain-rate field, which is converted into seismic-moment accumulation rate. We compare the geodetic moment rate with the seismic moment rate obtained from summation of historical and instrumental seismic catalogues, homogeneously pre-processed. The comparison shows areas characterized by moment deficits, opening new clues on the seismic potential of Italy.