1st Croatian Conference on Earthquake Engineering 1CroCEE 2021

Paleoseismological techniques have been developed to investigate past seismic activity on faults and provide valuable data for estimating the seismic hazard of an area, especially when the historical earthquake record is much shorter than the average earthquake cycle. Paleoseismic evidence can include joints, discrete faults, folds, soft-sediment deformation and liquefaction, depending on the magnitude of the paleoseismic event, the type of source fault, and the material disturbed (McCalpin, 2009). In Slovenia, the first attempts of modern paleoseismological studies were made in the Krško Basin in the early 2000s and later successfully carried out to study the reverse Vodice fault in Ljubljana Basin and the major regional strike-slip Idrija fault in western Slovenia. This contribution presents the paleoseismological evidence for large past earthquakes on the Vodice and Idrija faults, obtained during several exploratory trenching campaigns in the last decade. Two exploratory trenches were made on the Vodice fault, which additionally confirmed the tectonic origin of the 10 km long fault scarp and provided evidence of the last major earthquake that disrupted the sediments within the trench about 9 thousand years ago (Jamšek Rupnik et al., 2015). The first paleoseismological trench on the Idrija fault was conducted at the Kanomlja site, which showed that the last major earthquake on this fault corresponds to the historical Idrija earthquake of 1511 Mw6.8 (Bavec et al., 2013). A recent study of the paleoseismic history of the Idrija fault near Most na Soči suggests that frequent large earthquakes occurred during the penultimate glaciation and revealed local fault complexities due to geometric and kinematic changes of the fault at this location (Jamšek Rupnik et al., 2019). In addition to the scientific results, this contribution highlights the practical lessons and pitfalls to be considered in paleoseismic trenching under specific environmental conditions in the transition zone between the Alps, the Dinarides and the Pannonian Basin tectonic domains.

References:
- Bavec, M., Atanackov, J., Celarc, B., Hajdas, I., Jamšek Rupnik, P., Jež, J., Kastelic, V., Milanič, B., Novak, M., Skaberne, D., Žibret, G. (2013). Evidence of Idrija fault seismogenic activity during the Late Holocene including the 1511 Mm 6.8 earthquake. In: Grützner, C. (ed.), et al. Seismic hazard, critical facilities and slow active faults : proceedings of the 4th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA Days), 9-15 October 2013. Aachen: Grützner & Reicherter Geosolutions, p. 23-26.
- Jamšek Rupnik, P., Atanackov, J., Skaberne, D., Jež, J., Milanič, B., Novak, M., Lowick, S., Bavec, M. (2015). Paleoseismic evidence of the Vodice fault capability (Ljubljana Basin, Slovenia). In: Blumetti, A. M. (ed.), et al. 6th International INQUA Meeting on Paleoseismology, Active Tectonics and Archaeoseismology, 19-24 April 2015, Pescina, Fucino Basin, Italy, (Miscellanea INGV, 27). Roma: Istituto nazionale di geofisica e vulcanologia, p. 423-426.
- Jamšek Rupnik, P., Žebre, M., Jež, J., Preusser, F., Zajc, M., Monegato, G. (2019). Deformed Pleistocene deposits in Most na Soči, W Slovenia. In: Rožič, B. (ed.). Treatises, reports, 24th Meeting of Slovenian Geologists, Ljubljana, november 2019, (Geološki zbornik, 25). Ljubljana: Univerza v Ljubljani, Naravoslovnotehniška fakulteta, Oddelek za geologijo, p. 41-44.
- McCalpin, J.P. ed. (2009). Paleoseismology (Vol. 95). Academic press.