Abstract
Abstract. The Dinaric Fault System in western Slovenia, consisting of NW–SE-trending, right-lateral strike-slip faults, accommodates the northward motion of Adria with respect to Eurasia. These active faults show a clear imprint in the morphology, and some of them hosted moderate instrumental earthquakes. However, it is largely unknown if the faults also had strong earthquakes in the late Quaternary. This hampers our understanding of the regional tectonics and the seismic hazard. Geological evidence of co-seismic surface ruptures only exists for one historical event, the 1511 Idrija earthquake with a magnitude of ∼ M 6.8, but the causative fault is still disputed. Here we use geomorphological data, near-surface geophysical surveys, and paleoseismological trenching to study two of these faults: the Predjama Fault and the Idrija Fault. In a paleoseismological trench across the Predjama Fault we found deformation features that may have been caused by an earthquake between 13–0.7 ka, very likely not earlier than 8.4 ka. At the Idrija Fault, a surface-rupturing earthquake happened around 2.5 ka. We show that instrumental and historical seismicity data do not capture the strongest events in this area.
Highlights
This paper is concerned with Holocene surface-rupturing earthquakes on strike-slip faults belonging to the Dinaric Fault System (DFS) in western Slovenia (Fig. 1)
With a combination of geomorphological investigations, near-surface geophysical surveys, and paleoseismological trenching we show that surface-rupturing earthquakes happened on the Predjama and Idrija faults in western Slovenia in the Holocene
At least one earthquake on the Predjama Fault resulted in a vertical displacement of ∼ 0.5 m and an unknown amount of horizontal offset
Summary
This paper is concerned with Holocene surface-rupturing earthquakes on strike-slip faults belonging to the Dinaric Fault System (DFS) in western Slovenia (Fig. 1). Slejko et al, 1989), the faults are named Dinaric faults because they strike parallel to the trend of the Dinarides. They must not be confused with the inactive, SW-vergent Dinaric thrusts. Very little is known about their earthquake record. In this rather slowly deforming region, strong but rare earthquakes may dominate the overall seismic moment release. Identifying the strongest earthquake events in the late Quaternary will, help to better understand the regional active tectonics, shed light on the role of individual faults in the deformation of the crust, and better inform seismic hazard assessments
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