Present-day surface deformation of the Alpine region inferred from geodetic techniques

摘要

We provide a present-day surface-kinematics model for the Alpine region and surroundings based on a high-level data analysis of about 300 geodetic stations continuously operating over more than 12?years. This model includes a deformation model, a continuous surface-kinematic (velocity) field, and a strain field consistently assessed for the entire Alpine mountain belt. Special care is given to the use of the newest Global Navigation Satellite Systems (GNSS) processing standards to determine high-precision 3-D station coordinates. The coordinate solution refers to the reference frame IGb08, epoch 2010.0. The mean precision of the station positions at the reference epoch is ±1.1 mm in N and E and ±2.3 mm in height. The mean precision of the station velocities is ±0.2 mm?a sup?1/sup in N and E and ±0.4 mm?a sup?1/sup in height. The deformation model is derived from the point-wise station velocities using a geodetic least-squares collocation (LSC) approach with empirically determined covariance functions. According to our results, no significant horizontal deformation is detected in the Western Alps, while across the Southern and Eastern Alps the deformation vectors describe a progressive eastward rotation towards Pannonia. This kinematic pattern also makes evident an increasing magnitude of the deformation from 0.1?mm?a sup?1/sup in the western part of Switzerland up to about 1.3?mm?a sup?1/sup in the Austrian Alps. The largest shortening is observed along the southern front of the Eastern Alps (in the northern area of the Venetian-Friuli Basin) and in the northern part of the Apennine Peninsula, where rates reach 2 and 3?mm?a sup?1/sup , respectively. The average accuracy of the horizontal deformation model is ±0.2 mm?a sup?1/sup . Regarding the vertical kinematics, our results clearly show an ongoing average uplift rate of 1.8?mm?a sup?1/sup of the entire mountain chain, with the exception of the southern part of the Western Alps, where no significant uplift (less than 0.5?mm?a sup?1/sup ) is detected. The fastest uplift rates (more than 2?mm?a sup?1/sup ) occur in the central area of the Western Alps, in the Swiss Alps, and in the Southern Alps in the boundary region between Switzerland, Austria, and Italy. The general uplift observed across the Alpine mountain chain decreases towards the outer regions to stable values between 0.0 and 0.5?mm?a sup?1/sup and, in some cases, to subsidence like in the Liguro-Proven?al and Vienna basins, where vertical rates of ?0.8 and ?0.3 mm?a sup?1/sup are observed, respectively. In the surrounding region, three regional subsidence regimes are identified: the Rh?ne-Bresse Graben with ?0.8 mm?a sup?1/sup , the Rhine Graben with ?1.3 mm?a sup?1/sup , and the Venetian-Friuli Basin with ?1.5 mm?a sup?1/sup . The estimated uncertainty of our vertical motion model across the Alpine mountain belt is about ±0.3 mm?a sup?1/sup . The strain field inferred from the deformation model shows two main contrasting strain regimes: (i)?shortening across the south-eastern front of the Alps and the northern part of the Dinarides and (ii)?extension in the Apennines. The pattern of the principal strain axes indicates that the compression directions are more or less perpendicular to the thrust belt fronts, reaching maximum values of 20 × 10 - 9 a sup?1/sup in the Venetian-Friuli and Po basins. Across the Alpine mountain belt, we observe a slight dilatation regime in the Western Alps, which smoothly changes to a contraction regime in western Austria and southern Germany, reaching maximum shortening values of 6 × 10 - 9 a sup?1/sup in north-eastern Austria.