Comparative Analysis of Methods to Estimate Geodetic Strain Rates from GNSS Data in Italy

Our ability to estimate surface deformation rates in the Central Mediterranean has considerably
enhanced in the last decade thanks to the growth of continuous Global Navigation Satellite
System (GNSS) networks. Focusing on the Apennine/Alpine seismogenic belt, this area offers the
opportunity to test the use of geodetic strain rates for constraining active tectonic processes and
for seismic hazard assessments. Given the importance of geodetic strain rate models in modern
hazard estimation approaches, however, one has to consider that different approaches can provide
significantly different strain rate maps. Despite the increasing availability of GNSS velocity data,
in fact, strain rate models can significantly differ, because of the spatial heterogeneity of GNSS
station locations and inherent strategies in computing strain rates. Using a dense GNSS velocity
dataset, this study examines three methods for estimating horizontal strain rates, described in the
recent literature, and selected to represent approaches of increasing mathematical complexity. The
advantages, drawbacks, and optimal settings of each method are discussed. The main result is an
ensemble of strain rate models that enable the evaluation of epistemic uncertainties in seismicity
rate models constrained by geodetic velocities.