Search

The Periadriatic Fault system (PAF) ranks among the largest post-collisional structures of the European Alps. Recent geodetic data suggest that a fraction of the Adria–Europe convergence is still being accommodated in the Eastern Alps. However, the historical seismicity records along the easternmost segment of the PAF are ambiguous, and instrumental records indicate that seismotectonic deformation is mostly concentrated in the adjacent Southern Alps and Dinarides. Both electron spin resonance (ESR) and optically stimulated luminescence (OSL) dating methods can be used to date coseismic slip (with a combined range covering a few decades to a couple of million years) in slowly deforming fault zones, such as the PAF. Since the saturation doses of the quartz ESR signals are larger than quartz and feldspar OSL, ESR enables establishing a maximum age of the last resetting event of the system, while OSL allows constraining their minimum age when the signal is in saturation. We collected fault gouge samples from three localities along the easternmost segment of the PAF. For ESR, we measured the signals from the Al center in quartz comparing the results from the single aliquot additive dose (SAAD) and single aliquot regenerative (SAR) dose protocols. For OSL, we recorded the infrared stimulated luminescence signal at 50°C (IR50) and post-infrared infrared-stimulated luminescence signal at 225 °C (pIRIR225). Our dating results indicate that the studied segment of the PAF system accommodated seismotectonic deformation during the Quaternary, with a maximum age for the last resetting event of the system ranging from 1075 ± 48 to 552 ± 26 ka (ESR SAR) and minimum ages in the range from 196 ± 12 to 281 ± 16 ka (saturation of pIRIR225). The obtained ages suggest that the studied segment of the PAF could be considered at least as a potentially active fault. [ABSTRACT FROM AUTHOR]

The northward motion of the Adriatic plate with respect to the Alps leads to thrusting on E-W striking fault in NE Italy and to right-lateral strike-slip faulting on NW-SE trending Dinaric structures in W Slovenia. GPS data allow to understand the collision on a regional scale, but the networks are either not dense enough to draw conclusions on the activity of individual faults, or displacement rates across these faults are below GPS resolution. Instrumental seismicity in the Alpine-Dinarides transition zone is higher than elsewhere in the Alps. However, only few reliable moment tensor solutions of moderate to strong earthquakes depict the slip vectors and the geometry of single faults, and the background seismicity >M3 is rather diffuse. Strong historical earthquakes with magnitudes exceeding M6 are documented in our study area, but in most cases they cannot be tied to the fault that ruptured. Published paleoseismic evidence for surface-rupturing earthquakes is very limited, but geomorphological studies have shown that a number of thrust faults in NE Italy and strike-slip faults W Slovenia have been active in the Quaternary. So far there is little data on slip rates of individual faults, on their earthquake history and recurrence intervals, and on their seismic potential. It is not clear if crustal deformation is distributed across many active structures or if few main faults take up most of the deformation. The transition between head-on thrusting in N Italy and right-lateral motion on NW-trending faults in Slovenia needs further research.In this study we used remote sensing, field studies, near-surface geophysics, and palaeoseismology to better understand crustal deformation as a response to the Adria-Alpine convergence. We focussed on the right-lateral strike-slip faults in W Slovenia. High-resolution digital elevation models from LiDAR and drones allowed us to image geomorphological evidence of active tectonics and potentially surface-rupturing earthquakes in the Late Quaternary. The widespread karst made it difficult to apply classical techniques of tectonic geomorphology, which mainly use landscape features shaped by surface drainage and the associated sedimentation and erosion. However, the high-resolution data proved to be useful in identifying offset and deformed marker surfaces. Field mapping and structural data helped to trace the active faults and to determine their sense of motion. Near-surface geophysics were applied to image the shallowest parts of several faults and to identify deformation in young geological units. Based on these data we excavated paleoseismological trenches to date paleo-earthquakes.Our results show that a number of roughly parallel, NW-SE trending strike-slip faults in Slovenia have been active in the Late Quaternary. Crustal deformation appears to be not taken up by one or two main structures only, but rather distributed in a wide shear zone and across many faults. This is in contrast to the Alpine front further west in NE Italy, where deformation is rather localised on S-vergent thrusts along the front of the Southern Alps. Given the low rate of overall deformation, the distributed faulting results in low fault slip-rates and large recurrence intervals of strong and even surface-rupturing earthquakes. [ABSTRACT FROM AUTHOR]