Quaternary faulting in the Western Carpathians: Insights into paleoseismology from cave deformations and damaged speleothems (Demänová Cave System, Low Tatra Mts)

Abstract

Multiphase cave conduit offset and related speleothem damage in the Demänová Cave System (DCS; the Low Tatra Mts, Central Western Carpathians) were dated with U-series methods, revealing five events: (1) 570 (442)–417 ka, (2) 306–291 ka, (3) 184–130 ka, (4) ~19 ka, and (5) 2.56–2.3 ka. To decipher the cause of the damage, we combined geochronological data with structural, geomorphological, and seismological research. Gravity sliding as a probable source of damage is unlikely since the Demänová Valley has deepened only to a small extent for the past 550 ka and the steep fissure guiding the studied parts of the DCS extends below the recent valley. However, coseismic block sliding cannot be unambiguously excluded, as Newmark displacement analysis revealed that any >M7 earthquake in the 25 km range could have produced a 10-cm pseudostatic displacement. The studied offsets were accompanied by shaking, as inferred from fallen stalagmites and stalactites; hence, distant earthquakes are plausible damage sources. We applied ground-motion models and compared them with seismicity and scant prehistoric and historical data to identify and quantify the probable seismic source, which is most likely the Sub-Tatric Fault located 17.5 km from the cave. As inferred from the applied ground-motion models, a > M7 event on the Sub-Tatric Fault would generate a PGA >4 m/s2 in the cave despite the attenuation, which is above the threshold horizontal ground acceleration forcing the majority of speleothems to break.Although the mechanism that leads to cave passage offsets remains unclear we consider them as an off-fault damage caused by secondary faulting related to postseismic surface vertical movements, or less likely but not out of the realm of possibility distributed rupturing.