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Neotectonic activity of the Skawa River Fault Zone (Outer Carpathians, Poland)

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Author(s): Witold ZUCHIEWICZ | Antoni K. TOKARSKI | Anna ŚWIERCZEWSKA | Nguyen Quoc CUONG

Journal: Annales Societatis Geologorum Poloniae
ISSN 0208-9068

Volume: 79;
Issue: 1;
Start page: 67;
Date: 2009;
Original page

Keywords: neotectonics | morphotectonics | fractured clasts | seismic hazard | Skawa River valley | Outer Carpathians | Poland

ABSTRACT
The Skawa River catchment basin in the Outer Western Carpathians of Poland is situated upon morphostructures showing differentiated mobility in the Quaternary. Long profile of river channel reveals the lowest values of concavity index among the Polish Outer Carpathian rivers, pointing to low degree of river profile maturity, particularly in its middle reach coinciding with a zone of abnormally high river bed gradients.The Skawa River valley utilizes in its middle and northern reaches the Skawa River Fault Zone (SRFZ) composed of differently oriented oblique-slip faults, visible on DEM images as well-marked, rectilinear topolinea- ments. The NNW–SSE to N–S faults in the Silesian Nappe were probably reactivated in Late Pleistocene times as normal faults downthrowing their eastern sides, as shown by abnormally high position of the Weichselian Early Glacial straths on the western valley side. Such an episode of neotectonic activity (late Early Glacial times of the Last Glacial stage) has not been recognized so far in the other river valleys of the Polish segments of the Western Outer Carpathians. We conclude that some of the NNW–SSE to N–S trending faults were reactivated as strike-slip faults. This would conform to the present day stress arrangement within the Polish segment of Carpathians. Moreover, deformations of the Pleistocene straths between Osielec in the south and Wadowice–Zator areas in the north appear to indicate both pre-Weichselian and Weichselian reactivation of the Silesian and – to a lesser extent – Magura frontal thrusts. These movements continued also in the Holocene, although to a smaller extent, most probably due to moderately strong and/or strong earthquakes of magnitudes exceeding 5.5–5.7, resulting in clast fracturing within Holocene alluvium, particularly strong on the Silesian frontal thrust, and less intensive on the Carpathian marginal and Magura frontal thrusts, as well as on some faults that belong to the SRFZ.We are convinced that the record of seismically-induced clast fracturing on one of major fault zones in the Outer Carpathians should lead to revision of the hitherto-existing seismic risk assessment of this region, and particularly of the city of Kraków and other urbanized areas, as well as the planned artificial water reservoir at Świnna Poręba.

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