Dipartimento di Scienze della Terra, Università degli Studi di Siena

A GPS-based geodetic study at a regional scale requires the availability of a dense network that is characterized by 10 km to 30 km spacing, typically followed in a few continuous GPS stations (CGPSs) and several nonpermanent GPS stations (NPSs). As short observation times do not allow adequate noise modeling, NPS data need specific processing where the main differences between NPSs and CGPSs are taken into account: primarily time-series length and antenna repositioning error. The GPS data collected in the 1999-2007 time-span from non-permanent measurement campaigns in the central Apennine area (Italy) that was recently hit by the Mw 6.3 L'Aquila earthquake (April 6, 2009) are here further analyzed to compute a reliable strain-rate field at a regional scale. Moreover, areas characterized by different kinematics are recognized, and a complete characterization of the regional-scale kinematics is attempted. These new data can be interpreted as indicators from the viewpoint of seismic risk assessment.

It is argued that the Plio-Quaternary deformation pattern in the Mediterranean region is compatible with a SSW-NNE convergence between Africa (Nubia) and Eurasia and that the significant difference between this kinematics and the one provided by global models (SSE-NNW convergence, e.g., the NUVEL-1) may be due to the fact that those models interpret North Atlantic data by adopting an oversimplified two-plate configuration, which cannot account for the occurrence of significant seismotectonic activity inside the presumed Nubia and Eurasia blocks. It is shown that the adoption of a new plate configuration involving the Iberia and Morocco microplates, strongly suggested by geological and seismotectonic evidence, makes it possible to identify a kinematic model compatible within errors with the constraints recognized in the Mediterranean region and with the NUVEL-1 North Atlantic data set. Some considerations are made about the reason why the present-day Nubia-Eurasia kinematic models inferred from geodetic observations are significantly different from long-term models, such as model NUVEL-1 and the one proposed in this work.