Active Straining of the Balkans Peninsula: insights from spatial geodesy (InSAR and GNSS)

The Balkans Peninsula is one of the most seismic areas in Europe, with destructive earthquakes causing significant damage and fatalities in recent decades. Recent seismic activity (Mw 6+), occurring in diverse tectonic settings, reflects the complexity of the regional geodynamic setting. Despite efforts, the Balkans remains poorly instrumented compared to other European regions.

The latest study of the regional kinematics [1], based on a combination of GNSS velocity fields, indicates that most of the peninsula is expected to move at very low velocities ranges, well below 1 cm/yr. Large areas remain devoted of GNSS stations, and the overall network is too sparse to identify deformation associated with each individual active structures. While InSAR has been used locally for coseismic or anthropogenic displacement studies, no regional-scale study has yet quantified long-term interseismic velocities.

 Our aim is to take advantage of a new InSAR dataset processed by the FLATSIM service [2] based on Sentinel-1 data over the western Balkans. FLATSIM interferograms, displacement time series and velocity maps are available over the region, covering 360 000 km². With a ground resolution of 240 m and 6-12 days temporal resolution, this dataset is used to better quantify the current deformation. From the FLATSIM displacement time series, we initially separate the linear, seasonal, and, where necessary, coseismic components for each track. We then reference the InSAR velocity maps (the extracted linear components) into an ITRF14 reference frame [3], adapting the approach of [4]. This allows us to produce the first large-scale InSAR velocity field for the Balkans Peninsula, referenced in ITRF14 , with very limited use of GNSS data.

We then analyze serial profiles of LOS velocities across major active structures in the region. This reveals, with unmatched resolution, tectonic deformation patterns related, for example, to the Dinaric thrusts , or to lithospheric processes across the eastern Balkans, where a 150 km-long wavelength North-South velocity gradient exceeding 1 cm/yr is observed north of the Gulf of Corinth, over Central Macedonia and Thessaly regions.

We then perform a standard 3D decomposition of the LOS velocity field. There, we use the 2D GNSS velocity field provided by [1], along with a newly refined velocity dataset interpolated from its original dataset, based on a Bayesian transdimensional estimation (Bstrain code, [5]). The horizontal component is estimated either as an eastern component, fixing the northern component at that given by the interpolated GNSS field, or using the azimuth of this GNSS field as the direction of the horizontal component. This 3D decomposition highlights the added value of InSAR in providing spatially continuous data and unveils new insights, in particular regarding horizontal velocity field, where the localization of transtension in the inner Albanides is clearly refined. Finally, the richness of the dataset leaves many more motions to explore, including landslides, basins or aquifers [6], or induced by anthropogenic activities [7].

References:

[1] Piña‐Valdés et al. (2022), 10.1029/2021JB023451

[2] Thollard et al. (2021), 10.3390/rs13183734

[3] Altimimi et al. (2016), 10.1002/2016JB013098

[4] Lemrabet et al. (2023), 10.1029/2022JB026251

[5] Pagani et al. (2021), 10.1029/2021JB021905

[6] Serpelloni et al. (2018), 10.1002/2017JB015252

[7] Métois et al. (2020), 10.5194/se-11-363-2020