Role of the Crustal deformation processes on the seismicity: An approach, using combined dense GNSS velocity field in Europe

The impact of the crust deformation on the processes that control the seismic activity is still controversial. The seismic activity is usually thought to be associated with the active tectonic deformation as estimated from the horizontal displacements field: seismic active regions are usually dominated by important horizontal deformation controlled by tectonic activity. But this is not so clear on regions of low to moderate seismicity, where small horizontal deformation rates are commonly observed, similar to the rates detected for regions of no seismicity. In those regions, the non-tectonic processes such as the Glacial Isostatic Adjustment (GIA), may have a significant impact on the seismicity.

Since the deformation of low tectonic activity in Europe is usually piecewise, we combined 10 different GNSS velocity field solution to generate a dense GNSS solution to derive the 3D strain rate at continental scale: using the velocity solutions of common stations, the different datasets were converted to a common reference frame. Their uncertainties were homogenized, and a combined velocity field was computed considering the homogenized uncertainty of each independent solution. Finally, an automatized criterion of identification and outliers removal was applied, as well an adaptive smoothing scheme that depends on the station density, the noise, and the local tectonic deformation rate

The resulting 3D combined GNSS velocity field was interpolated and the horizontal strain rate was derived. Then, assuming the Hooke law for the earth crust, we decompose the vertical velocity field into a component due to tectonic deformation and a component due to isostatic rebound. To better understand the effects of horizontal tectonic deformation versus the flexure generated by GIA on the seismicity, the spatial distribution of the seismicity is compared to the strain rate map and the vertical velocity fields.