Deformed Pleistocene deposits in Most na So?i,

We studied a profile of deformed Pleistocene deposits exposed in a cliff in Most na So?i, Western Slovenia (Figures 1 and 2). The deformations are located within the Idrija Fault Zone, an active dextral strike slip fault zone. Despite being one of the most prominent faults with greatest seismogenic potential in Slovenia, studies documenting the Idrija Fault past seismic activity are scarce. Outcrops thus present a great opportunity to investigate its seismic activity. To document the profile of interest we ran a photogrammetry survey and terrestrial laser scanning (Figure 3). Using these data, we logged the profile in detail and described sedimentological characteristics of each layer. Sediments were dated by luminescence. Ground penetrating radar (GPR) was employed to study the extension of deformations on both sides of the visible profile. The studied profile is composed of well-stratified, but mostly poorly-sorted and clast-supported gravel and conglomerate, with exchanging roundness from subangular to rounded and with intercalated layers of silt, sand and breccia (Figure 4). Sediments are tilted and dissected with a series of NE-SW striking faults (A to P) exhibiting normal and transtensional offsets within graben, half-grabens and horsts (Figures 4 and 5). Apparent normal offsets are several tens of centimeters large with two largest ones reaching 1.4 m. The largest individual apparent normal offset reaches 85 cm and possibly 1.4 m. The continuity of deformation is indicated on the radargrams both laterally and towards deeper parts. The succession is interpreted as glaciofluvial deposits with exchanging slope material. Luminescence analysis places the deposition of the studied section into MIS 6 to MIS 5d, with the MIS 6 being more likely considering regional correlations. At least three deforming events can be interpreted, occurring during and after deposition of the logged succession. Faults D and F accumulated the offset during at least two deforming events, while the others recorded one event. The offset along faults D and F increases with depth. Different deforming mechanisms are considered and discussed including tectonic, glaciotectonic and slope processes. Considering geometrical and kinematical data the deformations are interpreted as being tectonic. The sediments in the investigated location were thus repeatedly deformed within the transtensional fault zone since MIS 6. Since the faults are approximately perpendicular to the general strike of the Idrija Fault, they are interpreted as secondary associated faults within the major fault zone. The transtensional style of deformation can be explained with the change of the Idrija Fault strike from 305° northwestward to 315° southeastward of Most na So?i. At this point the Idrija Fault also changes its character of deformation constrained along a narrow fault zone southeastward to deformation distributed along several branches northwestward. Acknowledgement: this study was undertaken as part of the program P1-0011, Regional Geology, financed by the Slovenian Research Agency (ARRS). The terrestrial laser scanning and photogrammetry survey was performed by Gregor Novakovi? from Vitrum laser in?eniring d.o.o. We used the GPR equipment from the same company. We thank the landowners, the Miklav?i? family, for their permission to work on the profile and kind assistance during our filed work. Members of GeoZS Regional geology department and geology students are acknowledged for their help in cleaning the profile.