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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. [ABSTRACT FROM AUTHOR]

The Mountain Front Flexure marks a dominant topographic step in the frontal part of the Zagros Fold–Thrust Belt. It is characterized by numerous active anticlines atop of a basement fault. So far, little is known about the relative activity of the anticlines, about their evolution, or about how crustal deformation migrates over time. We assessed the relative landscape maturity of three along-strike anticlines (from SE to NW: Harir, Perat, and Akre) located on the hanging wall of the Mountain Front Flexure in the Kurdistan Region of Iraq to identify the most active structures and to gain insights into the evolution of the fold–thrust belt. Landscape maturity was evaluated using geomorphic indices such as hypsometric curves, hypsometric integral, surface roughness, and surface index. Subsequently, numerical landscape evolution models were run to estimate the relative time difference between the onset of growth of the anticlines, using the present-day topography of the Harir Anticline as a base model. A stream power equation was used to introduce fluvial erosion, and a hillslope diffusion equation was applied to account for colluvial sediment transport. For different time steps of model evolution, we calculated the geomorphic indices generated from the base model. While Akre Anticline shows deeply incised valleys and advanced erosion, Harir and Perat anticlines have relatively smoother surfaces and are supposedly younger than the Akre Anticline. The landscape maturity level decreases from NW to SE. A comparison of the geomorphic indices of the model output to those of the present-day topography of Perat and Akre anticlines revealed that it would take the Harir Anticline about 80–100 and 160–200 kyr to reach the maturity level of the Perat and Akre anticlines, respectively, assuming erosion under constant conditions and constant rock uplift rates along the three anticlines. Since the factors controlling geomorphology (lithology, structural setting, and climate) are similar for all three anticlines, and under the assumption of constant growth and erosion conditions, we infer that uplift of the Akre Anticline started 160–200 kyr before that of the Harir Anticline, with the Perat Anticline showing an intermediate age. A NW-ward propagation of the Harir Anticline itself implies that the uplift has been independent within different segments. Our method of estimating the relative age difference can be applied to many other anticlines in the Mountain Front Flexure region to construct a model of temporal evolution of this belt. [ABSTRACT FROM AUTHOR]

The Mountain Front Flexure marks a dominant topographic step in the frontal part of the Zagros Fold-Thrust Belt. It is characterized by numerous active anticlines atop of an underlying basement fault. So far, little is known about the relative activity of the anticlines, about their evolution, and about how crustal deformation migrates over time. We assessed the relative landscape maturity of three along-strike anticlines (from SE to NW: Harir, Perat, and Akre) located on the hanging wall of the Mountain Front Flexure in the Kurdistan Region of Iraq to identify the most active structures and to get insights into the evolution of the fault and thrust belt. Landscape maturity was evaluated using geomorphic indices such as hypsometric curves, hypsometric integral, surface roughness, and surface index. Subsequently, numerical landscape evolution models were run to estimate the relative time difference between the onset of growth of the three anticlines, using the present-day topography of the Harir Anticline as a base model. A stream power equation was used to introduce fluvial erosion, and a hillslope diffusion equation was applied to account for colluvial sediment transport. For different time steps of model evolution, we calculated the geomorphic indices generated from the base model. While Akre Anticline shows deeply incised valleys and advanced erosion, Harir and Perat anticlines have relatively smoother surfaces and are supposedly younger than the Akre Anticline. The landscape maturity level decreases from NW to SE. A comparison of the geomorphic indices of the model output to those of the present-day Akre Anticline topography revealed that it would take the Harir Anticline 70±10kyr and 200±20kyr to reach the maturity level of the Perat and Akre anticlines, respectively, assuming constant erosion and rock uplift rates along the three anticlines. Since the factors controlling geomorphology (lithology, structural setting and climate) are similar for all three anticlines, and under the assumption of constant growth and erosion rates, we infer that uplift of the Akre Anticline started 200±20kyr before that of the Harir Anticline, with the Perat Anticline showing an intermediate age. A NW-ward propagation of the Harir Anticline itself implies that the uplift has been independent within different segments rather than being continuous from NW to SE. Our method of estimating the relative age difference can be applied to many other anticlines in the Mountain Front Flexure region to construct a model of temporal evolution of this belt. [ABSTRACT FROM AUTHOR]

Dilatant faults often form in rocks containing preexisting joints, but the effects of joints on fault segment linkage and fracture connectivity are not well understood. We present an analogue modeling study using cohesive powder with pre-formed joint sets in the upper layer, varying the angle between joints and a rigid basement fault. We analyze interpreted map-view photographs at maximum displacement for damage zone width, number of connected joints, number of secondary fractures, degree of segmentation and area fraction of massively dilatant fractures. Particle imaging velocimetry provides insight into the deformation history of the experiments and illustrates the localization pattern of fault segments. Results show that with increasing angle between joint-set and basement-fault strike the number of secondary fractures and the number of connected joints increase, while the area fraction of massively dilatant fractures shows only a minor increase. Models without pre-existing joints show far lower area fractions of massively dilatant fractures while forming distinctly more secondary fractures. [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]