Revealing Hidden Seismic Histories: Prehistoric Landslides as Indicators of Paleo-Earthquakes in the Outer Western Carpathians

Eastern Part of the Czech Republic in the Outer Western Carpathians (OWC), particularly the Javorníky Mts. range along the Czech-Slovakian border, has been traditionally considered a geologically stable region with documented low contemporary seismic activity. However, recent geomorphological analyses and field investigations reveal compelling evidence of prehistoric large-scale and highly mobile mass movements, potentially triggered by paleo-earthquakes. This study integrates high-resolution LiDAR mapping, field investigations and trenching, geophysical surveys, radiometric dating, and numerical modeling to reconstruct the paleo-seismic characteristic of the region. 
We identified those paleo-landslide features using high-resolution LiDAR data and assumed their relationship to past seismic activity by their close vicinity to a Holocene polyphase surface rupture of the Lidečko Fault. LiDAR mapping combined with the Electrical Resistivity Tomography (ERT) analyses provide valuable insights into the structural geology, lithology, failure mechanisms of paleo-landslides. Trenching and dating techniques, including radiocarbon and optically stimulated luminescence (OSL), help establish the timing of these events and their possible seismic triggers. Structural analysis of the Lidečko revealed the active strike-slip and oblique reverse kinematics with surface ruptures and liquefaction features, supporting the hypothesis of the landslides´ earthquake-induced origin.
Distinct three generations of landslides were identified as half-ellipsoidal depleted source zones about 400 m long, 200 wide and about 25 m deep with remnants of their accumulations at the toe and in the valley floor and different state of subsequent reworking by shallow slope processes. The fluidized mass was displaced for up to 1 km, of which up to 600 meters comprised totally flat riverbed. Radiometric dating of associated landslide-dam deposits revealed the landslides´ ages about 91 ka, 45 ka and 1.8 ka ago.
To accurately assess their potential coseismic origin, synthetic seismic acceleration data derived from waveform records in the OWC region is integrated into both Newmark Displacement Analysis (NDA) with the Velocity-Dependent Friction Law (VDFL) and the distinct element numerical modeling. This combined approach improves the simulation of rock mass and landslide dynamics under seismic loading conditions and ensures a more precise analysis of earthquake-induced slope processes. Specifically, PFC3D numerical modeling is employed to reconstruct the paleo-topography and simulate the long run-out behavior of paleo-landslides under various earthquake scenarios. These simulations provide deeper insights into the triggering mechanisms and movement patterns of such landslides.
The estimated magnitudes of past earthquakes challenge assumptions about the OWC's seismic stability and suggest significant unrecorded events. This study improves understanding of earthquake-induced landslides in stable regions and offers a framework for assessing long-term seismic hazards. The methods used can be applied to other areas with uncertain seismic histories, helping to better understand the connection between tectonics and landscape evolution.
The research was funded by the Grant Agency of the Czech Republic (GC22-24206J) and Taiwanese National Technological and Science Council (MOST/NTSC 111-2923-M-008-006-MY3).