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The coexistence of shortening and extensional tectonic regimes is a common feature in orogenic belts. The westernmost end of the Western Mediterranean is an area undergoing shortening related to the 5 mm/yr NNW‒SSE convergence of the Nubia and Eurasia Plates. In this region, the Central Betic Cordillera shows a regional ENE‒WSW extension. Here, we present GNSS‐derived geodetic data along a 170 km‐long transect orthogonal to the main active normal faults of the Central Betic Cordillera. Our data indicate that the total extension rate along the Central Betic Cordillera is 2.0 ± 0.3 mm/yr. Extension is accommodated in the eastern (0.8 ± 0.3 mm/yr in the Guadix‐Baza Basin) and western (1.3 ± 0.3 mm/yr in the Granada Basin) parts of the Central Betic Cordillera, while no extension is recorded in the central part of the study area. Moreover, our data permit us to quantify, for the first time, short‐term fault slip rates of the Granada Fault System, which is one of the main seismogenic sources of the Iberian Peninsula. We deduce a fault slip rate of ∼1.3 ± 0.3 mm/yr for the whole Granada Basin, with 0.9 ± 0.3 mm/yr being accommodated in the Granada Fault System and 0.4 ± 0.3 mm/yr being accommodated in the southwestern sector of the Granada Basin, where no active faults have been previously described at the surface. The heterogeneous extension in the Central Betic Cordillera could be accommodated by shallow high‐angle normal faults that merge with a detachment at depth. Part of the active extension could be derived from gravitational instability because of underlying over‐thickened crust. Plain Language Summary: We present here high‐precision GPS data obtained in S Spain. In this area tectonic deformation of the Earth crust is related to the convergence between Nubia (Africa) and Eurasia Plates. Under this general convergence setting, our study area is undergoing extensional deformation. GPS data permit us to quantify and characterize this extension. The total extension in our study area is 2.0 ± 0.3 mm/yr. But this extension is heterogeneous, as it concentrates in two areas to the east and to the west, separated by a zone with no extension. Moreover, our data permit to quantify, for the first time, short‐term fault slip rates of the Granada Fault System (0.9 ± 0.3 mm/yr). This parameter is essential to characterize the seismic hazard of this structure, which is one of the main seismogenic sources of the Iberian Peninsula. We also discuss the subsurface geometry of the faults accommodating this heterogeneous extension and the crustal mechanism responsible for that. Key Points: We quantify active extension within a collisional orogen (Betic Cordillera, SE Spain)Extension in the Central Betic Cordillera is heterogeneousWe quantify, for the first time, short‐term slip rate of the Granada Fault System, one of the main seismogenic sources of Spain [ABSTRACT FROM AUTHOR]

The relationships between kinematics and fault geometry for the coseismic ruptures from the 24th and February 25, 1981 earthquake sequence in the eastern Gulf of Corinth (Ms 6.7 and 6.4) are analysed. The two earthquakes ruptured faults located across strike rather than along strike as typifies other earthquake sequences. In detail, surface ruptures formed on the sub-parallel Pisia and Skinos Faults, with an 8 km along-strike overlap zone, separated across strike by < 2 km. The largest coseismic offsets occurred in the overlap zone. The 41-year-old ruptures are still well preserved as bedrock fault plane lichen-free stripes and colluvial ruptures, allowing detailed structural mapping at 213 rupture localities. A comparison between our measurements and Jackson et al. (1982) showed no overall consistent signal of post-seismic slip as some of our measurements were greater and some smaller than those recorded in 1981. The ruptures produced a single maximum asymmetric profile (Pisia: maximum throw of 223 cm) and a double maxima profile (Skinos: maximum throw of 109 cm and 130 cm). The shapes of the profiles differed in previous earthquakes on these faults, as evidenced by an older lichen-free stripe, implying non-characteristic earthquakes. Summing the two overlapping throw profiles across-strike reveals a single maximum symmetric bell-like profile. Using the above observations on coseismic offsets, kinematic information, and the geometry of faults, a rupture scenario has been proposed in terms of fault bends and corrugation orientations which suggests that parts of each fault may have ruptured in each earthquake. • Fault geometry and slip kinematic observations help understand the rupture style formed during Greece's 1981 earthquakes. • The across-strike Pisia and Skinos Faults appear to interact based on their combined surface slip distributions. • The Pisia and Skinos Faults exhibit no resolvable post-seismic slip in 41 years since the earthquakes. • The Pisia and Skinos Faults produce non-characteristic earthquakes. • Slip vector convergence and divergence toward the hangingwall may reveal the presence of major fault bends. [ABSTRACT FROM AUTHOR]

Uncertainty concerning the processes responsible for slip-rate fluctuations associated with temporal clustering of surface faulting earthquakes is a fundamental, unresolved issue in tectonics, because strain-rates accommodated by fault/shear-zone structures are the key to understanding the viscosity structure of the crust and seismic hazard. We constrain the timing and amplitude of slip-rate fluctuations that occurred on three active normal faults in central Italy over a time period of 20–30 kyrs, using in situ 36Cl cosmogenic dating of fault planes. We identify five periods of rapid slip on individual faults lasting a few millennia, separated time periods of up to 10 millennia with low or zero slip-rate. The rapid slip pulses migrated across the strike between the faults in two waves from SW to NE. We replicate this migration with a model where rapid slip induces changes in differential stress that drive changes in strain-rate on viscous shear zones that drive slip-rate variability on overlying brittle faults. Earthquakes increase the differential stress and strain-rate on underlying shear zones, which in turn accumulate strain, re-loading stress onto the overlying brittle fault. This positive feedback produces high strain-rate episodes containing several large magnitude surface faulting earthquakes (earthquake clusters), but also reduce the differential stress on the viscous portions of neighbouring fault/shear-zones slowing the occurrence of large-magnitude surface faulting earthquakes (earthquake anticlusters). Shear-zones on faults experiencing anticlusters continue to accumulate viscous strain at a lowered rate, and eventually this loads the overlying brittle fault to failure, initiating a period of rapid slip through the positive feedback process described above, and inducing lowered strain-rates onto neighbouring fault/shear-zones. We show that these patterns of differential stress change can replicate the measured earthquake clustering implied by the 36Cl data. The stress changes are related to the fault geometry in terms of distance and azimuth from the slipping structure, implying that (a) strain-rate and viscosity fluctuations for studies of continental rheology, and (b) slip-rates for seismic hazard purposes are to an extent predictable given knowledge of the fault system geometry. [ABSTRACT FROM AUTHOR]

Abstract: The causative source of the first damaging earthquake instrumentally recorded in the Island of Ischia, occurred on 21 August 2017, has been studied through a multiparametric geophysical approach. In order to investigate the source geometry and kinematics we exploit seismological, Global Positioning System, and Sentinel‐1 and COSMO‐SkyMed differential interferometric synthetic aperture radar coseismic measurements. Our results indicate that the retrieved solutions from the geodetic data modeling and the seismological data are plausible; in particular, the best fit solution consists of an E‐W striking, south dipping normal fault, with its center located at a depth of 800 m. Moreover, the retrieved causative fault is consistent with the rheological stratification of the crust in this zone. This study allows us to improve the knowledge of the volcano‐tectonic processes occurring on the Island, which is crucial for a better assessment of the seismic risk in the area. [ABSTRACT FROM AUTHOR]

New bathymetric and seismic reflection data from the Santorini–Amorgos Tectonic Zone in the southern Cyclades have been analysed and a description of the morphology and tectonic structure of the area has been presented. The basins of Anhydros, Amorgos and Santorini–Anafi have been distinguished together with the intermediate Anhydros Horst within the NE-SW oriented Santorini–Amorgos Tectonic Zone which has a length of 60–70 km and a width of 20–25 km. The basins represent tectonic grabens or semi-grabens bordered by the active marginal normal faults of Santorini–Anafi, Amorgos, Ios, Anhydros and Astypalaea. The Santorini–Anafi, Amorgos and Ios marginal faults have their footwall towards the NW where Alpine basement occurs in the submarine scarps and their hangingwall towards the southeast, where the Quaternary sediments have been deposited with maximum thickness of 700 m. Six sedimentary Units 1–6 have been distinguished in the stratigraphic successions of the Santorini–Anafi and the western Anhydros Basin whereas in the rest area only the upper four Units 3–6 have been deposited. This shows the expansion of the basin with subsidence during the Quaternary due to ongoing extension in a northwest-southeast direction. Growth structures are characterized by different periods of maximum deformation as this is indicated by the different sedimentary units with maximum thickness next to each fault. Transverse structures of northwest-southeast direction have been identified along the Santorini–Amorgos Tectonic Zone with distinction of the blocks/segments of Santorini, Anhydros/Kolumbo, Anhydros islet and Amorgos. Recent escarpments with 7–9 m offset observed along the Amorgos Fault indicate that this was activated during the first earthquake of the 7.5 magnitude 1956 events whereas no recent landslide was found in the area that could be related to the 1956 tsunami. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the characteristics of the landslides developed in the epicentral area of AD 1556 M~8.5 Huaxian Earthquake, and discuss their relations to the active normal faults in the SE Weihe Graben, Central China. The results from analyzing high-resolution remote-sensing imagery and digital elevation models (DEMs), in combination with field survey, demonstrate that: (i) the landslides observed in the study area range from small-scale debris/rock falls to large-scale rock avalanches; (ii) the landslides are mostly developed upon steep slopes of ≥30°; and (iii) the step-like normalfault scarps along the range-fronts of the Huashan Mountains as well as the thick loess sediments in the Weinan area may facilitate the occurrence of large landslides. The results presented in this study would be helpful to assess the potential landslide hazards in densely-populated areas affected by active normal faulting. [ABSTRACT FROM AUTHOR]

Abstract: The easternmost sector of the Gulf of Corinth, the Beotia area in Central Greece, is an area with active normal faults located between the two major rift structures of Central Greece, the Gulf of Corinth and the North Gulf of Evia. These active normal faults include WNW to E–W and NE to ENE-trending faults affect the landscape and generate basin and range topography within the Beotia. We study four normal fault zones and drainage basin geometry in the easternmost sector of the Gulf of Corinth to document the impact of active tectonics on the landscape evolution. Fault and drainage geometry are investigated based on detailed field mapping and high-resolution digital elevation models. Tectonic geomorphic analysis using several parameters of active tectonics provides information concerning the relative tectonic activity and fault growth. In order to detect areas of lateral stream migration that could indicate recent tectonic activity, the Transverse Topographic Symmetry Factor and the Asymmetry Factor are used to analyse drainage basin geometry in six large drainage basins and a drainage domain covering the study area. Our results show that vertical motions and tilting associated with normal faulting influence the drainage geometry and its development. Values of stream-gradient indices (S L) are relatively high close to the fault traces of the studied fault zones suggesting high activity. Mountain-front sinuosity (S mf) mean values along the fault zones ranges from 1.08 to 1.26. Valley floor width to valley height ratios (V f) mean values along the studied fault zones range between 0.5 and 1.6. Drainage basin shape (B S) mean values along the fault zones range from 1.08 to 3.54. All these geomorphic parameters and geomorphological data suggest that the analyzed normal faults are highly active. Lateral fault growth was likely produced by primarily eastward propagation, with the WNW to E–W trending faults being the relatively more active structures. [Copyright &y& Elsevier]

Abstract: Vertical offsets of Late Pleistocene–Holocene deposits and landforms are combined with slip-direction indicators on dipping active normal faults in central Italy to produce velocity and strain-rate fields averaged since 12–18 ka for a 5 by 5 km grid. Maximum strain-rates of 0.078±0.0156 ppm/yr, or 0.052±0.01 ppm/yr across a distance of 63,639 m imply maximum NE–SW extension rates of 5.0±1.0 mm/yr or 3.3±0.66 mm/yr depending on whether rates are averaged over 12 ka or 18 ka. The high spatial resolution reveals that strain-rates vary by up to 0.04±0.008 or 0.06±0.012 ppm/yr over a distance of only c. 7 km along the strike of the fault system, again depending on the timescale chosen. For the first time, these data allow a comparison of rates derived over time periods that would contain numerous seismic cycles with those measured with GPS that represent either interseismic strain, or displacements due to a single large earthquake with some interseismic strain. Overall, the rates compare reasonably well with those measured geodetically or derived from seismic moment summations (<0.12 ppm/yr and generally in the range of 0.10–0.06 ppm/yr; 6.36–3.82 mm/yr). However, the present wide spacing of geodetic sites (30–40 km) means that the small-scale spatial variations in strain-rate since 12–18 ka have not yet been resolved using GPS. This makes it difficult to compare strain measured geodetically with that released during historical earthquakes to assess whether excess strain will be released in an impending earthquake. [Copyright &y& Elsevier]

High-resolution topographic datasets are being increasingly applied in studies of active tectonics for precise quantification of lateral and vertical offsets of landforms. Digital elevation models (DEM) acquired by airborne light detection and ranging (LiDAR) have also been used for morphological analysis of tectonic scarps to infer the seismic-slip history of active faults. However, the high cost of conducting LiDAR studies limits its widespread application. In contrast, the potential applicability of the low-cost and portable small unmanned aerial vehicles (sUAV) combined with structure-from-motion (SfM) techniques to investigate morphological features of fault-generated scarps and their paleoseismic implications has not been fully explored. Here, based on sUAV-acquired DEMs and field observations, we present a case study of the morphological features of fault scarps along the Seertengshan Piedmont Fault (SPF), a major boundary fault of the Hetao Graben, North China, and discuss their paleoseismic implications. The results demonstrate that low-angle (<25°) scarp slopes along the SPF suggestive of a long period of erosion are consistent with the results of paleoseismological studies (i.e., the most recent surface-faulting event occurred >2000 years ago). The observed 1.8–2.5-m-high fault scarps with single slope sections probably represent the most recent incremental displacements associated with surface-rupturing earthquake(s). Topographic data acquired by sUAV are suitable for quantitative morphological analyses of fault-generated scarps in actively deforming regions and can contribute to assessments of seismic hazard. • Erosion for c.a. >2000 yr has resulted in low-angle scarp slopes of <25°. • Scarps of 1.8–2.5 m with single slope sections represent most recent displacements. • Seismic hazards posed by the Wujiahe segment need further investigations. [ABSTRACT FROM AUTHOR]

The tectonic activity and potential for linkage of adjacent active faults are crucial for seismic assessment. As the two largest faults that bound the Weihe Graben (central China), the Qinling Northern Piedmont Fault (QNF, ~200 km) and the Huashan Piedmont Fault (HPF, ~150 km) are mainly responsible for seismic risk in this densely-populated area, where the 1556 M 8.5 Huaxian earthquake occurred with 830,000 fatalities. However, their tectonic activity and the degree of interaction remain poorly constrained, hampering an adequate seismic risk assessment of the Weihe Graben. Here, we integrate 23 new 10Be-derived catchment-averaged denudation rates of ~0.06–0.32 mm/yr with topographic metrics to evaluate the seismic risk. The results demonstrate that the landscape of the Qinling and Huashan Mountains is in transient state in response to the tectonic perturbations of the QNF and the HPF, with tectonic knickpoints formed along main streams and tributaries, and widespread unstable drainage divides. These two faults have comparable tectonic activity, and are potentially capable of generating earthquakes with the maximum magnitude of M w ~7.7–7.9. Moreover, they have likely started linking, posing a greater seismic risk than previously estimated. • We use 10Be-derived denudation rates and topographic indices to evaluate seismic risk. • The landscape of the Huashan and Qinling Mountains are in transient state. • Two major boundary faults have comparable tectonic activity. • These faults can generate earthquakes of M w ~7.7–7.9, and have likely started linking. [ABSTRACT FROM AUTHOR]

• Field observations demonstrate the geometry and kinematics of Seertengshan Piedmont Fault. • Both planar and curved normal faults characterize the outcropping fault zones. • Sequential development of normal faults resulted in rotation of fault blocks. • Similarity of geometry and kinematic behaviors exists at multiple spatial scales. Although rotation of fault blocks during seismic and long-term periods has long been recognized in extensional tectonic regimes, the geometry and kinematic behaviors of normal faults at outcrop scale have scarcely been investigated in sufficient detail. In this study, combining with the analysis of high-resolution topography acquired by small unmanned aerial vehicle (sUAV) using the structure-from-motion (SfM) technique, we present the results of our field observations on the structural characteristics of the Seertengshan Piedmont Fault (SPF), a major active normal fault bounding the northern margin of the Hetao Graben, North China. Although previous studies have reported the recent tectonic activity of this fault including timing of most recent earthquake, average slip rate and repeat time of paleo-earthquakes, few of them have focused on geometric patterns of the outcropping fault zones, which provide excellent outcrop-scale examples to investigating geometry and kinematics of active normal faults. Besides the observed prominent fault scarps indicative of recent tectonic activity along the SPF, outcrop observations indicate that in some cases both planar and curved normal faults are developed, forming complex fault zones. Sequential development of normal faults may have rotated the early-formed fault blocks, resulting in shallowly dipping faults and highly tilted strata. Collectively, structural similarities probably exit among normal faults at multiple spatial scales. We suggest that the results of this study are also helpful for a better understanding of structural development and evolution in other actively extending areas. [ABSTRACT FROM AUTHOR]