Crustal deformation from GNSS measurement and earthquake mechanism along Pieniny Klippen Belt, Southern Poland

Abstract

The dynamic geological features of the Pieniny Klippen Belt (PKB) in southern Poland are nowadays a focal point of researchers as it is recognised as an active zone of crustal discontinuity. In the present study, we employed long-term analysis of ground-based global navigation satellite system (GNSS) measurements (from 2004 to 2020) to probe the crustal deformation, strain rates, and rotational rates in the PKB unit and the surrounding region, i.e., Magura Nappe (MN) and Podhale Flysch (PF) units. Measured velocities from GNSS observables are modelled by the auto-regressive integrated moving average (ARIMA) method to comprehend the long-term tectonic deformation. Our results showed that the ARIMA-modelled velocity varied from ~ 0.15 to ~ 8.86 mm/yr, indicating about 8.71 mm/yr difference along all units. Such differences suggest that crustal slip along the active thrusts and folds is the major factor causing regional deformation. The strain rates in PKB are also varying from the western to the eastern part. The rotational rates in PKB show a counterclockwise (CCW) pattern similar to the strain rates. These patterns suggesting that the PKB was rotated in the CCW direction with a large angle during the Miocene period. Finally, we analysed the seismicity for a period from 2004 to 2020 by using Bayesian moment tensor inversion and multivariate Bayesian inversion. The Bayesian inversion was applied based on bootstrapping chain analysis to figure out the earthquake mechanism using moment tensor inversion for the mainshock that occurred in Poland on 20 July 2018. The inversion results for the 2018 earthquake resolved a thrusting mechanism with nodal plane-1 having a strike of 346°, dip of 32°, and rake of 92° and a nodal plane-2 with a strike of 163°, dip of 58°, and rake of 89°. Since the seismicity in the Poland region has experienced less significant earthquakes in the last century, it is reasonable to attribute this lower seismic activity to the correspondingly low slip rates discerned through geodetic monitoring efforts.