Seismic damage in Quaternary fluvial gravels in low-seismicity thrust-and-fold-belts: Case study of the Outer Western Carpathians (Poland and Slovakia)

Abstract

In this contribution, we propose a model of Quaternary seismicity in the Outer Western Carpathians. The model presents results of analysis of fractured clasts performed in 268 exposures of Quaternary fluvial gravels within the ca. 5,000 km2 large segment of the Outer Western Carpathians comprising: Outer Carpathian nappes, the innermost part of the Carpathian Foredeep, and two intramontane basins – the Orava-Nowy Targ Basin and the Nowy Sącz Basin. Moreover, to precise stratigraphic position of the host gravels we performed OSL dating in 16 exposures and 14C dating in 4 exposures. Outside the intramontane basins, seismic damage in Quaternary strata is largely focused along all major overthrusts and some of the large-scale strike-slip and normal faults, whereas, within the intramontane basins, the damage is dispersed within the whole basins. Our results show that seismic damage within Quaternary strata in the Outer Western Carpathians results both from co-seismic fault rupture and from seismic shaking. During Quaternary times, the Outer Western Carpathians have been affected by earthquakes since the Pleistocene until Present. Seismic damage in Quaternary strata results from light (Mw5-) earthquakes with the exception of hanging limbs of the normal faults bordering the Orava-Nowy Targ Intramontane Basin which have been affected also by moderate (Mw5+) earthquakes. Our model can be significant for understanding seismic hazards in low-seismicity thrust-and-fold belts. In the studied case, this is important as the densely populated intramontane basins show the largest seismic damage.