Intraplate deformation in western Europe deduced from an analysis of the International Terrestrial Reference Frame 1997 (ITRF97) velocity field

Abstract

Although tectonic deformation in western Europe is essentially concentrated in the Appenines and Alpine (Alps, Pyrenees) mountain ranges, several large historical and instrumentally recorded earthquakes (M>6) are known in the supposedly “stable” part of Europe. Because of its accuracy and internal consistency at a global scale, the International Terrestrial Reference Frame 1997 (ITRF97) velocity field allows testing of intraplate rigidity in western Europe at a millimeter per year level. Using the full statistical information available on the ITRF97 velocities, we identify a subset of sites located in central Europe that satisfies a rigid cap rotation with residual velocities <1 mm/yr and therefore provide a stable Europe reference frame (SERF). In this reference frame we find residual velocities at European ITRF sites that are consistent with known active tectonic features. We identify a northward motion at sites located in Italy, with internal deformation of the Adriatic block rather than rigid plate motion and a westward motion of the westernmost part of Europe of the order of 1–2 mm/yr relative to central Europe. The relative motion of the Adriatic block and western Europe agrees with the current extension known in the Tyrrhenian sea and the Apennines. In central Europe, we find active deformation <1 mm/yr in the eastern Alps and western Carpathians. In the Alpine range our results indicate E‐W extension across the western Alps and N‐S compression across the central and eastern Alps, in agreement with the strain regime deduced from seismotectonic observations. In Belgium and the Netherlands we find residual velocities of 1–1.5 mm/yr to the northwest at all the sites, most likely accommodated along the Upper and Lower Rhine Graben structures. An important outcome of this study is the identification of internal deformation of the order of 1–2 mm/yr in an area usually interpreted as “stable” Europe. This result should be further checked as new, denser, and more accurate space geodetic data sets with longer observation time spans, become available for Europe.