High-resolution deformation maps from the Southern-Eastern Alps compiled from 5-yr-long radar interferometric time-series

Entering the terminal phase of continental collision, the European Alps exhibit surface deformation rates at the mm-level. Uplift peaks in the Central Alps at 2-3 mm/yr as a result of the post-glacial isostatic rebound, slab tearing, and erosion. Horizontal rate changes of <2 mm/yr are observed in the Southern-Eastern Alps due to the anticlockwise rotation of the Adriatic lithosphere. Here, N–S shortening is primarily accommodated at the densely-populated foothills of the Southern Alps, where seismicity is abundant and includes M6+ earthquakes like the devastating M_w6.5 Friuli earthquake in 1975. Further north and beyond the ESE-trending, dextral Periadriatic fault, the Eastern Alps extrude into the Pannonian basin. Today’s fault slip rates are constrained by Global Navigation Satellite System (GNSS) data with an inter-station distance too sparse to provide a detailed insight into plate locking—a vital component of estimating the fault’s seismic potential.

We present 4D-deformation data of the SE-Alps in unprecedented resolution (~400 m, 6 days). The rate maps were derived from radar-interferometric time-series collected since 2017 by the European Sentinel-1 satellites. Each of the assembled 240-km-wide radar tiles consists of 300+ images. The interferograms were automatically generated, phase-unwrapped, and corrected for atmospheric and topographic signal contributions. We estimated the deformation rates using the LiCSBAS time-series analysis software that involves a small-baseline approach and accounts for spatio-temporal coherence and seasonality. By tying the individual, relative InSAR rates—observed in two look directions—into a Eurasian reference frame based on by published GNSS rates we decompose them into east and vertical rates.

Our results illuminate the extreme, to which we can push the InSAR signal-detection threshold if the signal-backscatter properties are as challenging as in the vegetated SE-Alps: The predominant, vertical rates result from a mixture of isostatic, tectonic and anthropogenic processes, overlaid by a soil-moisture bias; the horizontal shortening rates align northwards, to which the radar satellites is least sensitive. Nevertheless, our rates provide new, dense deformation data and highlight processes yet undetected by the GNSS monitoring network.