The 1984 Abruzzo earthquake (Italy): an example of seismogenic process controlled by interaction between differently oriented synkinematic faults

The evolution of the seismogenic process associated with the M_s 5.8 Sangro Valley earthquake of May 1984 (Abruzzo, central Italy) is closely controlled by the Quaternary extensional tectonic pattern of the area. This pattern is characterised by normal faults mainly NNW striking, whose length is controlled by pre-existing Mio–Pliocene N100±10° left-lateral strike-slip fault zones. These are partly re-activated as right-lateral normal-oblique faults under the Quaternary extensional regime and behave as transfer faults.Integration of re-located aftershocks, focal mechanisms and structural features are used to explain the divergence between the alignment of aftershocks (WSW–ENE) and the direction of seismogenic fault planes defined by the focal mechanisms (NNW–SSE) of the main shock and of the largest aftershock (M_s=5.3).The faults that appear to be involved in the seismogenic process are the NNW–SSE Barrea fault and the E–W M. Greco fault. There is field evidence of finite Quaternary deformation indicating that the normal Barrea fault re-activates the M. Greco fault as right-lateral transfer fault. No surface faulting was observed during the seismic sequence. The apparently incongruent divergence between aftershocks and nodal planes may be explained by interpreting the M. Greco fault as a barrier to the propagation of earthquake rupturing. The rupture would have nucleated on the Barrea fault, migrating along-strike towards NNW. The sharp variation in direction from the Barrea to the M. Greco fault segments would have represented a structural complexity sufficient to halt the rupture and subsequent concentration of post-seismic deformation as aftershocks around the line of intersection between the two fault planes.Fault complexities, similar to those observed in the Sangro Valley, are common features of the seismic zone of the Apennines. We suggest that the zones of interaction between NW–SE and NNW–SSE Plio-Quaternary faults and nearly E–W transfer faults, extending for several kilometres in the same way as M. Greco does, might act as barriers to the along-strike propagation of rupture processes during normal faulting earthquakes. This might have strong implications on seismic hazard, especially for the extent of the maximum magnitude expected on active faults during single rupture episodes.     

Detection of detached forced-regressive nearshore wedges: a case study from the central-southern Siena Basin (Northern Apennines, Italy)

The detection of detached nearshore wedges formed in response to relative sea-level drops is considered one of the hottest topics in sequence stratigraphic analysis due to their importance as reservoir analogues. In fact, they usually constitute sandy and porous bodies generally encased in impermeable clay, thus presenting a good potential as traps for fluids. This paper focuses on the sequence stratigraphic analysis of the Pliocene deposits cropping out in the central-southern sector of the Siena Basin (Tuscany, Italy), a post-collisional basin of the Northern Apennines. The exposed sedimentary succession was investigated through a detailed sedimentological and stratigraphic approach, integrated by biostratigraphic analyses, aimed at a better characterization of the infilling history of this sector of the basin. Specifically, this study revealed the occurrence of repeated facies shifts that allowed the identification of two depositional sequences. In detail, a thick sand-rich body far from the basin margins, and previously considered as a turbiditic lobe, has been reinterpreted as formed in a nearshore setting during a fall in relative sea level. This body is totally encased in offshore clay, and due to the lack of physical connection with the related HST deposits, it has to be considered as a detached forced-regressive wedge. The present work led to the recognition of some sedimentological and stratigraphic features typical of falling stage systems tract deposits (e.g. presence of intrabasinal recycled materials, sedimentological evidence of a pre-existing fluvial network subsequently eroded) that can provide useful clues for the identification of detached forced-regressive nearshore wedges in core studies and poorly exposed settings.     

Exhumation patterns along shallow low‐angle normal faults: an example from the Altotiberina active fault system (Northern Apennines,Italy)

A multi‐method approach (palaeothermal and thermochronological analyses; thermal modelling) is applied to reconstruct the exhumation history of the Altotiberina Fault (ATF), a representative example of crustal‐scale active low‐angle normal faulting in the Northern Apennines (Italy). Thermal maturity and thermochronological data yield similar burial histories but different exhumation patterns for the sedimentary successions in the hangingwall and the footwall of the ATF. Since 3.8 Ma, the ATF footwall has exhumed at rates of 0.90 mm a^?1. Exhumation led to bending and deactivation of the ATF uppermost portion as a result of tectonic unloading and isostatic adjustment, followed by migration of extension and the development of a set of domino‐like, east‐dipping normal faults, rooting on the buried portion of the ATF. ATF activity and isostatic rebound exhumed Triassic rock units from depths of about 4 km. We suggest that isostatic instability is accommodated at shallow crustal levels, in a similar way to what is observed on larger structures at mid‐low crustal levels.     

Growth of vertically segmented normal faults

The geometry and evolution of vertically segmented normal faults, with dip separations of < ca 11.5 m have been studied in a coastal outcrop of finely bedded Cretaceous chalk at Flamborough Head, U.K. Fault trace segments are separated by both contractional and extensional offsets which have step, overlap or bend geometries. The location of fault trace offsets is strongly controlled by lithology occurring at either thin (ca 1 mm-8 cm) and mechanically weak marl layers or partings between chalk units. Fault segmentation occurred during either fault nucleation within, or propagation through, the strongly anisotropic lithological sequence. An inverse relationship between fault displacement and number of offsets per length of fault trace reflects the progressive destruction of offsets during fault growth. The preservation of fault offsets is therefore dependent on offset width and fault displacement. Fault rock, comprising gouge and chalk breccia, may vary in thickness by 1.5–2.0 orders of magnitude on individual fault traces. Strongly heterogeneous fault rock distributions are most common on small faults (< 10 cm displacement) and are produced mainly by destruction of fault offsets. Shearing of fault rock with increasing displacement gives rise to a more homogeneous fault rock distribution on large faults at the outcrop scale.     

Integrated near surface geophysics across the active Mount Marzano Fault System (southern Italy): seismogenic hints

Here, we describe an original geophysical multi-method approach applied to the Mount Marzano Fault System. This is one of the most hazardous seismogenic faults of the Apennines (Irpinia, southern Italy), and it was responsible for the 1980, Mw 6.9, earthquake, along with many others before. We carried out electrical resistivity tomography (ERT), ground penetrating radar (GPR) measurements, and horizontal-to-vertical spectral ratio (HVSR) microtremor analysis along several common transects designed across the potential and/or certain fault traces. The data obtained from these non-invasive, inexpensive, expeditious methods mutually integrate with and complement each other, providing a valuable subsurface image of the near surface fault architecture. ERT depicts the general shallow image of the fault zone and of the fault-controlled sedimentary basin, with the depth of the buried bedrock cross-correlated through ambient-noise HVSR results. GPR delineates the very shallow geometry of the fault and of the associated deformation. Coupled with previous paleoseismological studies, these data allow the evaluation of some fault parameters and the precise locating of the fault trace, to aid future paleoseismological investigations aimed at seismic risk reduction programs.     

Evidence for coupled reverse and normal active faulting in W Iberia: The Vidigueira–Moura and Alqueva faults (SE Portugal)

The Vidigueira–Moura fault (VMF) is a 65 km long, E–W trending, N dipping reverse left-lateral late Variscan structure located in SE Portugal (W Iberia), which has been reactivated during the Cenozoic with reverse right-lateral slip. It is intersected by, and interferes with the NE–SW trending Alentejo–Plasencia fault. East of this intersection, for a length of 40 km the VMF borders an intracratonic tectonic basin on its northern side, thrusting Paleozoic schists, meta-volcanics and granites, on the north, over Cenozoic continental sediments preserved in the basin, on the south. West of the faults intersection, evidence of Cenozoic reactivation is scarce. In the eastern sector, Plio-Quaternary VMF reactivation is indicated by geomorphologic, stratigraphic, and structural data, showing reverse movement with a right-lateral strike-slip component, in response to a NW–SE trending compressive stress. An average vertical displacement rate of 0.06 to 0.08 mm/yr since late Pliocene (roughly the last 2.5 Ma) is estimated. The Alqueva fault (AF) is a subparallel, northward dipping, 7.5 km long anastomosing fault zone that affects Palaeozoic basement rocks, and is located 2.5 km north and on the hanging block of the VMF. The AF is also a reverse left-lateral late Variscan structure, which has been reactivated during the Tertiary with reverse right-lateral slip; however, Plio-Quaternary reactivation was normal left-lateral, as shown by abundant kinematical criteria (slickensides) and geomorphic evidence. It shows an average displacement rate of 0.02 mm/yr for the vertical component of movement in the approximately last 2.5 Ma. It is proposed that the normal displacements on the AF result from tangential longitudinal strain on the upthrown block of the VMF above a convex ramp of this main reverse structure. According to this model of faults interaction, the AF is interpreted to work as a bending-moment fault sited above the VMF thrust ramp. Consequently, it is expected that the displacements on the AF increase towards the topographic surface with the increase in the imposed extension, declining downwards until they vanish above or at the VMF ramp. In order to constrain the proposed scheme, numerical modeling was performed, aiming at the reproduction of the present topography across the faults using different geodynamic models and fault geometries and displacements.     

Structure of a normal seismogenic fault zone in carbonates: The Vado di Corno Fault,Campo Imperatore,Central Apennines (Italy)

The Vado di Corno Fault Zone (VCFZ) is an active extensional fault cutting through carbonates in the Italian Central Apennines. The fault zone was exhumed from ∼2 km depth and accommodated a normal throw of ∼2 km since Early-Pleistocene. In the studied area, the master fault of the VCFZ dips N210/54° and juxtaposes Quaternary colluvial deposits in the hangingwall with cataclastic dolostones in the footwall. Detailed mapping of the fault zone rocks within the ∼300 m thick footwall-block evidenced the presence of five main structural units (Low Strain Damage Zone, High Strain Damage Zone, Breccia Unit, Cataclastic Unit 1 and Cataclastic Unit 2). The Breccia Unit results from the Pleistocene extensional reactivation of a pre-existing Pliocene thrust. The Cataclastic Unit 1 forms a ∼40 m thick band lining the master fault and recording in-situ shattering due to the propagation of multiple seismic ruptures. Seismic faulting is suggested also by the occurrence of mirror-like slip surfaces, highly localized sheared calcite-bearing veins and fluidized cataclasites. The VCFZ architecture compares well with seismological studies of the L'Aquila 2009 seismic sequence (mainshock M_W 6.1), which imaged the reactivation of shallow-seated low-angle normal faults (Breccia Unit) cut by major high-angle normal faults (Cataclastic Units).     

The seismogenic thickness in Italy: constraints on potential magnitude and seismic hazard

The thickness of the seismogenic layer is a key parameter for seismic hazard, since it can be used to constrain the maximum depth of faulting and the potential magnitude. In this study, we compute the seismogenic thickness in the Italian region by defining the lower seismicity cut‐off, using high‐quality hypocentral locations of earthquakes that occurred in the past decade. Along the eastern Alps, the seismogenic thickness is about 12–14 km, laterally homogeneous along the entire south‐verging thrust front. In the Apennines extensional belt, lateral changes in seismogenic thickness are evident, and correlate with changes in the seismic energy released by past earthquakes. The potential magnitude is larger in the southern Apennines where the seismogenic thickness is greater (16–18 km) than in the northern Apennines where it is less (6–10 km) and seismic energy is partially released by the creeping of faults.     

Magnetic fabric of Pleistocene continental clays from the hanging-wall of an active low-angle normal fault (Altotiberina Fault,Italy)

Anisotropy of magnetic susceptibility (AMS) represents a valuable proxy able to detect subtle strain effects in very weakly deformed sediments. In compressive tectonic settings, the magnetic lineation is commonly parallel to fold axes, thrust faults, and local bedding strike, while in extensional regimes, it is perpendicular to normal faults and parallel to bedding dip directions. The Altotiberina Fault (ATF) in the northern Apennines (Italy) is a Plio-Quaternary NNW–SSE low-angle normal fault; the sedimentary basin (Tiber basin) at its hanging-wall is infilled with a syn-tectonic, sandy-clayey continental succession. We measured the AMS of apparently undeformed sandy clays sampled at 12 sites within the Tiber basin. The anisotropy parameters suggest that a primary sedimentary fabric has been overprinted by an incipient tectonic fabric. The magnetic lineation is well developed at all sites, and at the sites from the western sector of the basin it is oriented sub-perpendicular to the trend of the ATF, suggesting that it may be related to extensional strain. Conversely, the magnetic lineation of the sites from the eastern sector has a prevailing N–S direction. The occurrence of triaxial to prolate AMS ellipsoids and sub-horizontal magnetic lineations suggests that a maximum horizontal shortening along an E–W direction occurred at these sites. The presence of compressive AMS features at the hanging-wall of the ATF can be explained by the presence of gently N–S-trending local folds (hardly visible in the field) formed by either passive accommodation above an undulated fault plane, or rollover mechanism along antithetic faults. The long-lasting debate on the extensional versus compressive Plio-Quaternary tectonics of the Apennines orogenic belt should now be revised taking into account the importance of compressive structures related to local effects.     

Growth of normal faults in multilayer sequences: A 3D seismic case study from the Egersund Basin,Norwegian North Sea

We investigate the structural style and evolution of a salt-influenced, extensional fault array in the Egersund Basin (Norwegian North Sea) through analysis of 3D reflection seismic and well data. Analysis of fault geometry/morphology, throw distribution and syn-kinematic strata reveal an intricate but systematic style of displacement and growth, suggesting an evolution of (1) initial syn-sedimentary fault growth contemporaneous with salt mobilization initiated during the Late Triassic, (2) cessation of fault activity and burial of the stagnant fault tips, and (3) subsequent nucleation of new faults in the cover above contemporaneous salt re-mobilization initiated during the Late Cretaceous, with downward propagation and linkage with faults. Stage 3 was apparently largely controlled by salt mobilization in response to basin inversion, as reactivated faults are located where the underlying salt is thick, while the non-reactivated faults are found where salt is depleted. Based on the 3D-throw analyses, we conclude that a combination of basement faulting and salt (re-) mobilization is the driving mechanisms behind fault activation and reactivation. Even though the sub- and supra-salt faults are mainly geometrically decoupled through the salt, a kinematic coupling must have existed as sub-salt faults still affected nucleation and localization of the cover faults.     

Inner structure and deformation mechanisms of normal faults in conglomerates and carbonate grainstones (Granada Basin,Betic Cordillera,Spain): Inferences on fault permeability

In the southeastern area of the Neogene-Quaternary Granada Basin, ∼E–W trending normal faults crosscut ∼80 m-thick clay-bearing conglomerates and ∼30–40 m-thick carbonate grainstones containing centimeter-thick microconglomerate and sand interbeds. Three fundamental failure modes took place during fault nucleation: (1) phyllosilicate shear banding in the conglomerates, (2) jointing, mainly in the carbonate grainstones and (3) pressure solution in the carbonate matrix and grains of the microconglomerate and sand interbeds. Within the conglomerates, normal faults developed by pronounced clay smearing and, ultimately, cataclasis. Jointing also occurred within some of the pebbles surrounding the cataclastic rocks. In contrast, in the carbonate grainstones fault growth was characterized by predominant jointing and rock fragmentation, which localized in the extensional quadrants and/or releasing jogs of the evolving slip surfaces. Brecciation and cataclasis occurred only around the well-developed slip surfaces. Based upon their inner structure, we qualitatively assign a combined barrier-conduit fluid behavior to the tens of meters-throw normal faults juxtaposing the conglomerates against the carbonate grainstones. The inner fault cores inhibit fault-orthogonal fluid flow along their entire length. Instead, fault damage zones act as fluid barriers in the conglomerates, and as composite fluid conduits in the carbonate grainstones.     

Fluid migration and origin of a mud volcano in the Northern Apennines (Italy): the role of deeply rooted normal faults

ABSTRACT In the foothills of the Northern Apennines mud volcanoes are locally aligned along active normal faults, which allow surface leakage of fluids derived from deep sources (>3–6 km). The chemical and isotopic analysis of the fluids of a mud volcano, coupled with the reconstruction of its geological setting, allowed an investigation of the processes of migration and fluid flow. The fault system associated with the Regnano mud volcano drains a deep Miocene reservoir (foredeep marine deposits), which supplies formation water and thermogenic methane that has migrated from underlying Mesozoic carbonates. The muds from the volcano contain late Eocene microfossils and are extruded only during paroxysmal events. They have a shallower origin (about 1 km) from the base of Tertiary marine deposits deposited upon the upper tectonic nappe of the chain (Ligurian unit). This case study suggests that normal faults are very effective in controlling surface emissions.     

Relationships between thrusts and normal faults in curved belts: New insight in the inversion tectonics of the Central-Northern Apennines (Italy)

The relationships between thrusts and normal faults represent primary constraints in the reconstruction of the modes and timing of pre-, syn- and post-orogenic deformation events in fold-and-thrust belts. Such relationships are well exposed in curved orogenic belts where the thrusts are oblique to the trend of normal faults.We study the NNE–SSW-trending Olevano-Antrodoco-Sibillini oblique thrust and its crosscutting relationships with NW–SE-trending normal faults in order to constrain the Neogene–Quaternary deformation history of the Central-Northern Apennine (Italy). The analysis of structural and geological data allowed us to reconstruct the geometric and kinematic constraints of two inversion events: 1 – During the Pliocene, positive inversion reactivated the NNE–SSW-trending pre-existing Ancona-Anzio normal fault as the Olevano-Antrodoco-Sibillini oblique thrust ramp and caused the shortcut of NW–SE-oriented normal faults; 2 – During the Quaternary, negative inversion reactivated NW–SE-trending pre-thrusting normal faults.The growth of the NW–SE Quaternary normal faults causes seismicity and is responsible of the development of wide Quaternary intramontane basins. Their distribution and the related seismicity have been controlled and compartmentalized by NNE–SSW-trending oblique thrusts. Thus, the crosscutting relationships between thrusts and normal faults are crucial in seismic hazard assessment.     

Normal fault corrugation: implications for growth and seismicity of active normal faults

Large normal faults are corrugated. Corrugations appear to form from overlapping or en échelon fault arrays by two breakthrough mechanisms: lateral propagation of curved fault-tips and linkage by connecting faults. Both mechanisms include localized fault-parallel extension and eventual abandonment of relay ramps. These breakthrough mechanisms produce distinctive hanging wall and footwall geometries indicative of fault system evolution. From such geometries, we can estimate the positions of tilted relay ramps or ramp segments and ramp internal deformation in incompletely exposed or poorly imaged fault systems. We examine the evolution of normal fault corrugations at Fish Slough (California), Yucca Mountain (Nevada), and Pleasant Valley (Nevada), in the Basin and Range province. We discuss how evolution of the Pleasant Valley and Yucca Mountain systems relates to seismicity. For example, the 1915 Pleasant Valley earthquake produced four en échelon ruptures that appeared as overlapping segments of a single immature fault at depth. At Yucca Mountain, we argue that an en échelon array, which includes the Solitario Canyon and Iron Ridge faults, should be considered a single source, such that western Yucca Mountain could experience up to a M_w 6.9 earthquake compared to M_w 6.6 estimates for the largest individual segment.     

Deformation features within an active normal fault zone in carbonate rocks: The Gubbio fault (Central Apennines, Italy)

The Gubbio fault is an active normal fault defined by an important morphological scarp and normal fault focal mechanism solutions. This fault truncates the inherited Miocene Gubbio anticline and juxtaposes Mesozoic limestones in the footwall against Quaternary lacustrine deposits in the hanging wall. The offset is more than 2000 m of geological throw accumulated during a poly-phased history, as suggested by previous works, and has generated a complex zone of carbonate-rich fault-related structures. We report the results of a multidisciplinary study that integrates detailed outcrop and petrographic analysis of two well-exposed areas along the Gubbio fault zone, geochemical analysis (fluid inclusions, stable isotopes, and trace elements) of calcite-sealed fault-related structures and fault rocks, and biostratigraphic controls. Our aims are: (i) the characterization of the deformation features and their spatial–temporal relationships, and (ii) the determination of the P/T conditions and the fluid behaviour during deformation to achieve a better understanding of fluid–rock interaction in fault zones.We show that few of the observed structures can be attributed to an inherited shortening phase while the most abundant structures and fault rocks are related to extensional tectonics. The outcropping extensional patterns formed at depths less than 2.5–3 km, in a confined fluid system isolated from meteoric water, and the fault structures are the response to a small amount of cumulated displacement, 12–19% of the total geological throw.     

Statistical approach for the geochemical signature of two active normal faults in the western Corinth Gulf Rift (Greece)

Soil–gas measurements of different gas species were performed in two distinct areas of the Corinth Gulf Rift (Greece): the Aigion-Neos Erineos-Lambiri (ANEL) fault zone and the Rion-Patras fault zone. Both zones lie in one of the most seismically active areas of the Euro-Mediterranean region, where a fast-opening continental rift is located. In particular, the geochemical investigations were focused on fault segments and fracture systems previously inferred by geomorphological, lithological and structural studies.In this work the applicability of soil–gas geochemistry surveys for the exploration of buried/hidden faults was tested by using various statistical methods. Moreover, a comprehensive geostatistical treatment of the collected data provided new insights into the control exerted by active structures on deep-seated gas migration towards the surface. In both investigated areas, the highest ²²²Rn and CO₂ concentration peaks correspond with zones where the interaction among fracture and fault segments was inferred by structural and morphological methods. This indicates a clear correlation between the shape and orientation of the anomalies and the different attitude and kinematic behavior of the faults recognized in the two areas. Furthermore, obtained results show that gases migrate preferentially through zones of brittle deformation by advective processes, as suggested by the relatively high rate of migration needed to obtain anomalies of short-lived ²²²Rn in the soil pores.     

Fractures and faults in volcanic rocks (Campi Flegrei,southern Italy): insight into volcano-tectonic processes

The present study was focused to analyze fractures and faults in the Campi Flegrei calderas presently hosting several volcanic edifices, such as lava domes, scoria, and tuff cones. A complex network of fractures and faults affects the volcanic rocks, mostly as planar with highly variable density. Frequently faults appearing as conjugate structures showing normal kinematics often associated with ductile deformation such as drag folds and deflexed layers, suggesting a syn-eruption deformation. However, the most of faults, mainly hosted along the caldera/crater rims, are very steep with dominant normal and secondary reverse movements. The fracture pattern indicates a slight prevalence of NE–SW and NW–SE directions, but N–S and E–W trends also occur. Fractures and faults found in rocks older than 15 ka (Neapolitan Yellow Tuff included), measured in western and eastern sectors of the study area, indicate a rotation of ca. 30° of the main directions among these two sectors. For the faults occurring along the caldera/crater rims, we suggest a kinematic evolution characterized by the reactivation of tensile fractures previously formed in response to both regional extension and locale resurgent dome. Finally, normal faults located in the central sector of caldera, between La Starza and Accademia localities, cutting the youngest volcanic deposits, indicate a constant NNE–SSW extension probably related to the caldera resurgence.     

Deformation patterns of upper Quaternary strata and their relation to active tectonics,Po Basin,Italy

Despite increased application of subsurface datasets below the limits of seismic resolution, reconstructing near‐surface deformation of shallow key stratigraphic markers beneath modern alluvial and coastal plains through sediment core analysis has received little attention. Highly resolved stratigraphy of Upper Pleistocene to Holocene (Marine Isotope Stage 5e to Marine Isotope Stage 1) alluvial, deltaic and coastal depositional systems across the southern Po Plain, down to 150 m depth, provides an unambiguous documentation on the deformation of previously flat‐lying strata that goes back in time beyond the limits of morphological, historical and palaeoseismic records. Five prominent key horizons, accurately selected on the basis of their sedimentological characteristics and typified for their fossil content, were used as highly effective stratigraphic markers (M1 to M5) that can be tracked for tens of kilometres across the basin. A facies‐controlled approach tied to a robust chronology (102 radiocarbon dates) reveals considerable deformation of laterally extensive nearshore (M1), continental (M2 and M3) and lagoon (M4 and M5) marker beds originally deposited in a horizontal position (M1, M4 and M5). The areas where antiformal geometries are best observed are remarkably coincident with the axes of buried ramp anticlines, across which new seismic images reveal substantially warped stratal geometries of Lower Pleistocene strata. The striking spatial coincidence of fold crests with the epicentres of historic and instrumental seismicity suggests that deformation of marker beds M1 to M5 might reflect, in part at least, syntectonically generated relief and, thus, active tectonism. Precise identification and lateral tracing of chronologically constrained stratigraphic markers in the ¹⁴C time window through combined sedimentological and palaeoecological data may delineate late Quaternary subsurface stratigraphic architecture at an unprecedented level of detail, outlining cryptic stratal geometries at the sub‐seismic scale. This approach is highly reproducible in tectonically active Quaternary depositional systems and can help to assess patterns of active deformation in the subsurface of modern alluvial and coastal plains worldwide.     

Geomorphological signatures of the evolution of active normal faults along the Langshan Mountains,North China

Segmentation, propagation, and linkage of normal faults often occur in regions of active extension, and observations of the distribution and structural properties of segment boundaries can provide important insights for seismic hazard assessment. In this study, we carry out quantitative geomorphological analysis to evaluate the relative tectonic activity along the Langshan Piedmont Fault (LPF), which bounds the NW margin of the Hetao Graben, North China. On the basis of obtained morphometric indices (HI, BS, Smf, VF, SLK, and χ), tectonic knickpoint heights, footwall topography, and small unmanned aerial vehicles (sUAV)-based field observations, we demonstrate that: (i) The Langshan landscape is in a state of disequilibrium in response to active rock uplift and channel incision; (ii) The LPF consists of two major fault segments with lengths of 65 and 95 km, respectively, which likely have been linked with each other; (iii) Rupturing of the whole of one segment can generate an earthquake of M_w ~7.3–7.5, and earthquake magnitude may reach M_w ~7.8 if the entire fault trace of ~160 km is ruptured, posing a significant seismic risk in the western Hetao Graben. These findings would further our understanding of normal fault evolution through space and time in actively extending regions.