UWAGI O NEOTEKTONICE POLSKI: WYBRANE PRZYKŁADY

Abstract

NEOTECTONICS OF POLAND: SELECTED EXAMPLES

Abstract. Neotectonic studies in Poland concern mainly manifestations of those tectonic movements that have been active in Late Neogene and Quaternary times, as well as geodetically measured recent vertical and horizontal crustal motions. Among problems of particular interest, the following should be listed: periodicity of neotectonic (mostly Quaternary) activity, estimation of the parametres of the neotectonic stress field, amplitudes and rates of Quatemary and recent movements, development of neotectonic troughs and young faults, mutual rełationships among photolineaments, geological structures and recent seismicity, as welI as the role of tectonic reactivation of fault zones due to human activity. Neotectonic faults in Poland have developed in Neogene and Quaternary times due to reactivation of Laramide or older structures, or in the Quaternary due to reactivation of Neogene faults. The size of throw of Quaternary faults changes
from 40-50 m and >100 m in the Sudetes and the Lublin Upland, to several - several tens of metres in the Carpathians. The average rate of faulting during Quaternary times has been 0.02 to 0.05 mm/yr, what enables one to include these structures into the domains of inactive or low-activity faults. A similar conclusion can be drawn from the results of repeated precise levellings and GPS campaigns. Strike-slip
displacements have been postulated for some of these faults. Isolated faults in Central Poland have shown middle Quaternary thrusting of the order of 40-50 m, and same of the Outer Carpathian overthrusts tend to reveal young Quaternary activity, as indicated, among others, by concentrations of fracturcd pebbles within the thrust zones. Episodes of increased intensity of faulting took place in the earły Quaternary, in the Mazovian (Holsteinian) Interglacial, and during or shortly after the Odranian (Drenthe) glacial stage. Same of the faults have also been active in Holocene times. Recent seismic activity is often rełated to strike-slip faults, which in the Carpathians trend ENE-WSW and NE-SW, whereas outside the Carpathians they are oriented parallel to the margin of the East-European Platform and the Sudclic Marginal Fault. Recent stress measurements indicate that the Carpathians are being exposed to tectonic push from the hinterland, which generates NNE-oriented compression in the eastern part of the Outer Carpathian fold-and-thrust belt. This push is transmitted farther to the north along the marginal part of the East-European Platform. Successive accommodation of this push is evidenced by systematic distortion of tectonie compression from NNE-SSW in the southern segment to NNW- SSE in the Baltic portion of the East-European Platform, where the Carpathian push is balanced with the North Atlantic ridge push. Within the Trans-European Suture Zone, frequent stress rotations between N-S and NW-SE in vertical borehole sections and among boreholes suggest a discrete strike-slip accommodation of the Carpathian push. Dominance of strike-slip fault stress regime was constrained by hydraulic fracturing tests in boreholes located in SE Poland, while in western Poland extensional stress regime with some amount of strike-slip component prevails.