Contemporary crustal extension in the Umbria-Marche Apennines from regional CGPS networks and comparison between geodetic and seismic deformation

We present the results of the analysis of a GPS velocity field in the Umbria-Marche Apennines (Central Italy). To obtain the largest station density we collected raw GPS data from GNSS networks of different types and purposes. Despite the limited time span of some GPS stations the resulting velocity field shows a high degree of consistency both spatially and in terms of comparison with other independent informations. We derived a continuos strain rate field applying a spline interpolation technique which provide a smooth estimate of the deformation field. The main feature of the obtained strain rate field is a continuous band of high strain rates coincident with the area of largest historical and instrumental seismic release and whose directions of the principal axes agree with geological and seismological informations. We translate the strain rate field into geodetic moment rate using the Kostrov formula to evaluate the potential seismic activity of the region and compare it with actual seismic release in the last 720 year from Mw > 5.5 earthquakes. This comparison highlights a large deficit in the seismic release with respect to the overall potential seismic activity from the geodetic moment rate. This discrepancy can be resolved with a large amount of seismicity to be released in the next future or allowing significant aseismic slip and deformation.