Database of Active Faults in Slovenia: Compiling a New Active Fault Database at the Junction Between the Alps, the Dinarides and the Pannonian Basin Tectonic Domains

Abstract

We present the compilation of a new database of active faults in Slovenia, aiming at introducing geological data for the first time as input for a new national seismic hazard model. The area at the junction of the Alps, the Dinarides, and the Pannonian Basin is moderately seismically active. About a dozen Mw > 5.5 earthquakes have occurred across the national territory in the last millennium, four of which in the instrumental era. The relative paucity of major earthquakes and low to moderate fault slip rates necessitate the use of geologic input for a more representative assessment of seismic hazard. Active fault identification is complicated by complex regional structural setting due to overprinting of different tectonic phases. Additionally, overall high rates of erosion, denudation and slope mass movement processes with rates up to several orders of magnitude larger than fault slip rates obscure the surface definition of faults and traces of activity, making fault parametrization difficult. The presented database includes active, probably active and potentially active faults with trace lengths >5 km, systematically compiled and cataloged from a vast and highly heterogeneous dataset. Input data was mined from published papers, reports, studies, maps, unpublished reports and data from the Geological Survey of Slovenia archives and dedicated studies. All faults in the database are fully parametrized with spatial, geometric, kinematic and activity data with parameter descriptors including data origin and data quality for full traceability of input data. The input dataset was compiled through an extended questionnaire and a set of criteria into a homogenous database. The final database includes 96 faults with 240 segments and is optimized for maximum compatibility with other current maps of active faults at national and EU levels. It is by far the most detailed and advanced map of active faults in Slovenia.

Holocene surface-rupturing earthquakes on the Dinaric Fault System, western Slovenia

“…Since the Pliocene, N-S shortening is taken up by right-lateral motion on a NW-SE-trending strike-slip fault system known as the Dinaric Fault System (e.g. Poljak et al, 2000;Vrabec and Fodor, 2006;Placer et al, 2010;Moulin et al, 2016;Atanackov et al, 2021;Figs. 1-3).…”

“…The first geological evidence for the late Quaternary activity of the Idrija Fault came from faulted fluvial deposits in Kanomlja (Cunningham et al, 2006;Bavec et al, 2012) and in the Učja River valley (Vrabec, 2012). Geomorphological work showed that the fault offsets the regional drainage system and late Qua- Atanackov et al (2021). Historical and instrumental seismicity are from the SHEEC database (Stucchi et al, 2013;Grünthal et al, 2013); the 1511 Idrija earthquake is marked (note that the location is uncertain; the earthquake probably occurred either on the Idrija Fault or on the SW side of the mountain front in Italy).…”

“…Based on the mean slip rates and the total offset, Moulin et al (2016) concluded that the strike-slip movement on the fault probably originated in the early Pliocene. In a metaanalysis, Atanackov et al (2021) report a best estimate fault slip rate of 1 mm/a. Gosar (2020) used an extensometer to measure ongoing slip on a fault plane in the Učja River valley, but it remains unclear how this motion relates to the over-all fault kinematics.…”

“…Moulin et al (2016) estimated a slip rate of 1.45 ± 0.25 mm/a in the last 255 kyr for the Predjama Fault based on offset morphological markers and 36 Cl dating. Atanackov et al (2021) assigned an average slip rate of 0.7 mm/a in their meta-analysis. In our study area, the Predjama Fault offsets Mesozoic carbonates by several hun- dred metres right-laterally (Fig.…”

“…However, they must not be confused with the now inactive, SW-vergent Dinaric thrusts. It is well understood that the Dinaric rightlateral faults are active and that they accommodate a share of the relative motion between Adria and Europe (Poljak et al, 2000;Vrabec and Fodor, 2006;Placer et al, 2010;Moulin et al, 2016;Atanackov et al, 2021). However, so far very little is known about their earthquake record.…”