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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 region around the town Albstadt, SW Germany, was struck by four damaging earthquakes with magnitudes greater than 5 during the last century. These earthquakes occurred along the Albstadt Shear Zone (ASZ), which is characterized by more or less continuous microseismicity. As there are no visible surface ruptures that may be connected to the fault zone, we study its characteristics by its seismicity distribution and faulting pattern. We use the earthquake data of the state earthquake service of Baden-Württemberg from 2011 to 2018 and complement it with additional phase picks beginning in 2016 at the AlpArray and StressTransfer seismic networks in the vicinity of the ASZ. This extended data set is used to determine new minimum 1-D seismic vp and vs velocity models and corresponding station delay times for earthquake relocation. Fault plane solutions are determined for selected events, and the principal stress directions are derived. The minimum 1-D seismic velocity models have a simple and stable layering with increasing velocity with depth in the upper crust. The corresponding station delay times can be explained well by the lateral depth variation of the crystalline basement. The relocated events align about north–south with most of the seismic activity between the towns of Tübingen and Albstadt, east of the 9 ∘ E meridian. The events can be separated into several subclusters that indicate a segmentation of the ASZ. The majority of the 25 determined fault plane solutions feature an NNE–SSW strike but NNW–SSE-striking fault planes are also observed. The main fault plane associated with the ASZ dips steeply, and the rake indicates mainly sinistral strike-slip, but we also find minor components of normal and reverse faulting. The determined direction of the maximum horizontal stress of 140–149 ∘ is in good agreement with prior studies. Down to ca. 7–8 km depth SHmax is bigger than SV ; below this depth, SV is the main stress component. The direction of SHmax indicates that the stress field in the area of the ASZ is mainly generated by the regional plate driving forces and the Alpine topography. [ABSTRACT FROM AUTHOR]

We describe two previously unreported, 5-7 km long normal fault scarps (NFS) occurring atop fault-related anticlines in the coastal ranges of the Dinarides fold-and-thrust belt in southern Montenegro, a region under predominant contraction. Both NFS show well-exposed, 6-9 m high, striated and locally polished fault surfaces in limestones, documenting active faulting during the Holocene. Sharply delimited ribbons on free rock faces show different color, varying karstification and lichen growth and suggest stepwise footwall exhumation, typical of repeated normal faulting earthquake events. Displacements, surface rupture lengths and geometries of the outcropping fault planes imply paleoearthquakes with Mw ~ 6 ± 0.5 and slip rates of c. 0.3-0.5 mm/yr since the Last Glacial Maximum. Slip rates based on cosmogenic 36Cl data from the scarps are significantly higher: modeling suggests 1.5 ± 0.1 mm/yr and 6-15 cm slip every c. 35-100 yrs, commencing c. 6 kyr ago. The total throw on both NFS - although poorly constrained - is estimated to max. 200 m, and offsets the basal thrust of a regionally important tectonic unit. Both NFS are incipient extensional structures that postdate growth of the fault-related anticlines on top of which they occur. Interestingly, the position of the extensional features agrees with recent geodetic data, suggesting that our study area is located exactly at the transition from NE-SW-directed shortening in the northwest to NE-SW-directed extension to the southeast. While the contraction reflects ongoing Adria-Europe convergence taken up along the frontal portions of the Dinarides, the incipient extensional structures might be induced by rollback of the Hellenic slab in the SE, whose effects on the upper plate appear to be migrating along-strike the Hellenides towards the northwest. The newly found NFS provide evidence for a kinematic change of a thrust belt segment over time. Alternatively, the NFS might be regarded as second-order features accommodating changes in dip of the underlying first-order thrust faults to which they are tied genetically. [ABSTRACT FROM AUTHOR]

The region around the town Albstadt, SW Germany, was struck by four damaging earthquakes with magnitudes greater than five during the last century. Those earthquakes occurred along the Albstadt Shear Zone (ASZ) which is characterized by more or less continuous microseismicity. As there are no surface ruptures visible which may be connected to the fault zone, its characteristics can only be studied by its seismicity. We use the earthquake data of the state earthquake service of Baden-Württemberg from 2011 to 2018 and complement it with additional phase picks beginning 2016 at the AlpArray and StressTransfer seismic networks in the vicinity of the ASZ. This extended dataset is used to determine new minimum 1-D seismic vp and vs velocity models and corresponding station delay times for earthquake relocation. Fault plane solutions are determined for selected events and the direction of the maximum horizontal stress is derived. The minimum 1-D seismic velocity models have a simple and stable layering with increasing velocity with depth in the upper crust. The corresponding station delay times can be well explained by the lateral depth variation of the crystalline basement. The relocated events align north-south with most of the seismic activity between the towns of Tübingen and Albstadt east of the 9° E meridian. The events can be separated into several subclusters which indicate a segmentation of the ASZ. The majority of the 36 determined fault plane solutions features a NNE-SSW strike, but also NNW-SSE striking fault planes are observed. The main fault plane associated with the ASZ is dipping steeply and the rake indicates mainly sinistral strike-slip, but we also find minor components of normal and reverse faulting. The determined direction of the maximum horizontal stress of 147° is in good agreement with prior studies. This result indicates that the stress field in the area of the ASZ is mainly generated by the regional plate driving forces as well as the Alpine topography. [ABSTRACT FROM AUTHOR]

The Kalabagh Fault Zone in the western Sub-Himalayas is a dextral strike slip fault zone that exhibits a push-up block in the stepover zone of the two fault segments. The inception of the push-up block occurred along the restraining faults that form two morphotectonic bends along the mountain front at Zaluch and in the South of Thathi. The landform was further developed by en-echelon fold and thrust sequence up to Khairabad in the North and Ghundi village in the South. The aseismically moving fault zone has experienced earthquakes during late Quaternary forming surface expressions in the West of the push-up block at Khairabad, Larkakki and Ghundi. The Khairabad and Ghundi sections are the active tectonic fronts of the stepover zone. Displacements caused by these seismic activities has deformed Quaternary sediments creating stream deflections, surface ruptures, pressure ridges, uplifted sediments at the mountain front, foreland ridges and uplifted alluvial fan. Offsets in the late Quaternary sediments indicate the Kalabagh Fault is active and seismic events of M w ≥ 6 has formed these ground effects. Furthermore, stratigraphic correlations of fluvial sediments indicate the Indus River has been flowing in the NS direction along the northern segment of the Kalabagh Fault. Uplift of the push-up block in the Kalabagh Fault Zone and subsequent deposition of the alluvial fans has caused westward diversion of the Indus River. [ABSTRACT FROM AUTHOR]

The eastern Rhine Graben Boundary Fault (eastern RGBF) forms the eastern margin of the Upper Rhine Graben (URG), the most seismically active area in the plate interiors of Europe. Despite seismic activity posing a significant threat to the densely populated URG and critical facilities therein, only a few studies have documented the paleoearthquake history and associated seismic hazard, focusing mainly on the western margin. We present the results of the first paleoseismological trenching ever conducted on the central section of the eastern RGBF. Following high-resolution near-surface geophysical studies, we excavated six trenches near Ettlingen-Oberweier (south of Karlsruhe, Germany) on one of its secondary fault strands. The nearly-vertical fault is transtensional left-lateral and splits into several NNW-SSE en échelon branches, forming a negative flower structure. Stratigraphic and structural relationships along with radiocarbon and Optically Stimulated Luminescence dating reveal a minimum of three surface-rupturing paleoearthquakes with a Mw of potentially 6.5 ± 0.5, occurring from old to young, >56 ka (E X), between 54 and 19 ka (E Y), and between 15 and 1 ka (E Z). The events are poorly constrained in age due to erosional unconformities. Based on the cumulative vertical separation of 1.2 ± 0.3 m, we calculate an average vertical slip rate of 0.02 ± 0.005 mm/yr. From a horizontally offset alluvial channel, we infer a cumulative left-lateral slip of 5.9 ± 0.7 m and derive an average horizontal slip rate of 0.1 ± 0.01 mm/yr. The average net slip rate is 0.1 ± 0.02 mm/yr for the past 59.5 ± 3.8 ka. This value represents a minimum slip rate for the eastern RGBF, considering slip distribution within the different fault strands of the fault system. Our findings highlight the seismic potential of the eastern RGBF, providing new evidence of the Late Pleistocene and Holocene tectonic activity of its central section. • We present the first paleoseismic data ever collected on the central section of the eastern Rhine Graben Boundary Fault. • We provide evidence of a minimum of three Late Pleistocene to Holocene surface-rupturing paleoearthquakes. • An average net slip rate of 0.1 ± 0.02 mm/yr is estimated for the past 59.5 ± 3.8 ka. • Our data illustrates the transtensional regime in the Upper Rhine Graben. [ABSTRACT FROM AUTHOR]

Uplift of mountain ranges is induced by tectonic activity and often prompts erosion of elevated surfaces and subsequent sediment deposition in the foreland and on mountain slopes. Simultaneously, the fluvial systems that are often responsible for these erosive and sedimentary processes are strongly affected not only by sudden local impulses (e.g. earthquakes, landslides, debris flows), but also by regional and global climate dynamics. This case study aims to determine the interplay of these different processes in one of the most tectonically active intraplate regions of the world. In the Gobi Altai of SW Mongolia the India-Eurasia collision localises as E-W to NW-SE striking sinistrally transpressive mountain ridges which overprint and reactivate crustal fabrics related to older tectonic events. The northernmost expression of this mountain belt is the Gurvan Bogd range, which formed due to fault activity along the Bogd Fault Zone that last ruptured in 1957 in the M 8.3 Bogd- or Gobi Altai earthquake. Surface ruptures related to this earthquake were observed along 350 km, and (mostly fluvial) markers were offset 3-4 m horizontally (locally 5-7 m) and 2-3 m vertically. The recurrence of major earthquakes along this fault was determined to be 3-5 ka and is evident from high topography (up to 3957 m), as well as from scarps and drainages with cumulative offsets. In SW Mongolia, the study of paleo-earthquakes with such recurrence intervals is facilitated by arid climate conditions which enable the investigation of not only the recent tectonic history, but also of its effect on fluvial and lacustrine deposits in relation to that of large scale climate fluctuations. We analyse the morphology of fluvial pathways and deposits of the Gurvan Bogd system at different scales. The comparison of observations at the regional scale from 12 m resolution satellite data with local 10-15 cm resolution digital elevation models (DEMs) derived from drone flights shows that large scale alluvial fan morphology is generally related to regional climatic and mainly Pleistocene processes. At the small scale, high resolution DEMs show that local, recent events are more evident: terrace abandonment and channel deflections are a direct response to fault ruptures. Ground-penetrating radar (GPR) measurements across fault scarps as well as existing and new optically stimulated luminescence (OSL) and cosmogenic nuclide ages are analysed to confirm such interpretations and to characterise known and newly localised tectonic structures. We aim to extrapolate our evaluation of the influential factors on the Gurvan Bogd landscape system to construct a basin-scale landscape evolution model that may have implications for the regional Quaternary evolution of southwest Mongolia. [ABSTRACT FROM AUTHOR]