Seismic hazard analysis depends in part on understanding fault segmentation and slip distribution, which are partially recorded in the landscape during surface-rupturing earthquakes. Over time, surface processes degrade these features, challenging fault mapping. We use landscape evolution models to quantify this information loss in desert environments. Using post-earthquake lidar from the 2019 Ridgecrest (California) and 2010 El Mayor-Cucapah (Baja California) ruptures, we simulate landscape degradation using 2D linear diffusion in Landlab over 100, 1k, 5k, and 10k years, with a transport rate of 1 m²/kyr. We assess change in mappable fault trace length, fault zone width, and a “degradation coefficient” based on topographic slope change. Field validation in 2024 (Ridgecrest) supports the modeled degradation. Results show that 20–80% of original fault trace length remains after 10k years and fault zone width decreases from a mean of 30 m to ~2 m, causing older rupture zones to appear narrower and less complex than initially. Degradation is fastest in the first 100 years, then slows. Fault zones with simple, single-strand morphology retain more mappable length and degrade more slowly. Fault zone structure primarily controls degradation rate and fault trace visibility. These findings provide quantitative constraints on landform degradation, informing probabilistic displacement hazard models and fault mapping in tectonically active regions.

The July 2019 Ridgecrest sequence ruptured two nearly orthogonal faults, the left-lateral, NE-striking Salt Wells Valley fault (Mw 6.4) and the right-lateral, NW-striking Paxton Ranch fault (Mw 7.1), highlighting the hazard of multi-fault earthquakes in the Walker Lane. To test whether similar conjugate ruptures occurred previously, we excavated five paleoseismic trenches and constrained paleo-earthquake timing using luminescence ages. Salt Wells Valley exposures record the 2019 rupture and only one earlier surface-faulting earthquake (17-27 ka), indicating infrequent activity. In contrast, Paxton Ranch strata preserve two Holocene events (4.4-8.7 ka and 10.6-14.6 ka) and up to three late Pleistocene events (17 ka and older) in addition to 2019. These records indicate that rupture along the Paxton Ranch fault commonly occurs independently of the Salt Wells Valley fault. Slip rates based on 2019 displacements and these event intervals are 0.2-1.3 mm yr⁻¹ for Paxton Ranch and 0.01-0.09 mm yr⁻¹ for Salt Wells Valley. The 2019 sequence therefore represents an unusual pairing of an often-active dextral fault with a much less active sinistral fault. The contrasting recurrence and lack of overlap, together with regional paleoseismic patterns, indicate that synchronous rupture is not systematic but instead varies among faults within an evolving network. This suggests that seismic hazard reflects a fault system in which rupture is governed by time-dependent fault network interactions rather than independent, repeatable behavior of individual faults.

While secondary explosions are well documented in basaltic and pyroclastic deposits, they have rarely been studied on silicic lava flows. The Banco Bonito rhyolite flow (BBF), the youngest eruptive product of New Mexico's Valles Caldera, is dotted with numerous large explosion craters. We document the characteristics of these features and evaluate mechanisms of formation to advance the conceptual model for secondary explosion on silicic flows. Fifty-six explosion craters range from 62 to 243 m in diameter and 3 to 29 m in depth, with volumes on the order of 10(3)-10(5) m(3). They are circular to mildly elliptical (median ellipticity = 1.3) with pronounced ejecta rims and are spatially correlated with arcuate, discontinuous pressure ridges that span much of the lava surface. Textural zonation within the lava flow indicates potential locations for steam accumulation. A coarsely vesicular pumice (CVP) horizon capped by an impermeable rigid crust may have enabled the buildup and pressurization of steam, thus driving the explosions. Field-based textural mapping reveals that the CVP layer varies in thickness and depth across the flow, potentially accounting for observed crater variability. Notable disparities in volume between craters and their ejecta rims suggest a significant fraction of material was expelled distally, beyond the rim or into a transient ash cloud. Modeling ash clouds as instantaneous thermal plumes yields a median height of similar to 5 km, potentially occurring many years after flow emplacement, highlighting the scale of these events and their associated volcanic hazards.

The safety assessment of radioactive waste repositories requires scenarios and forecasts of the erosional, climatic, and tectonic future evolution. One of the major challenges in the assessment of long-term landscape evolution for safety is that the relevant processes, models and model parameters are subject to a range of significant uncertainties. Assessments should provide the full range of conceivable developments using the best available scientific knowledge. Here, we present an assessment framework for future erosion with a rigorous uncertainty management. The approach anticipates erosion from fluvial, hillslope, and glacial processes over a timescale of 105-106 years. Uncertainties are addressed in a hybrid way, using probabilistic methods in combination with a scenario approach, whereby the chosen scenarios cover a wide range of possibilities. A protocol was followed to derive model parameter uncertainties that respect individual estimates of experts. The entire process is accompanied by a sensitivity analysis. We used the workflow to assess erosion in Northern Switzerland over the next million years. The results serve as input to site a deep geological repository for nuclear waste in Switzerland and to demonstrate its long-term safety.

Mapping tectonic faults is challenging because mapping approaches are not standardized and some evidence for faulting is ambiguous due to surface processes that obscure the geomorphology. We developed and evaluated a new systematized approach for mapping faults and documenting geomorphic evidence based on desktop mapping using remote sensing data. Our approach works as a teaching tool to introduce fault mapping and in industry settings to establish consistent documentation. Using our approach, a mapper maps the landscape morphology, geomorphology, and surficial geology. The mapper uses the geomorphic indicator ranking approach to document the geomorphic indicators that support faulting such as scarps, triangular facets, and deflected streams. The resulting fault maps facilitate straightforward dissemination of information and build toward more accurate depictions of fault traces, which support understanding fault processes and predicting coseismic rupture location in a future earthquake. We evaluated our mapping approach as follows. (1) We qualified the geomorphology that best predicts future rupture location as having the lowest geomorphic indicator- to- rupture separation distance. Of the features tested, cut or offset alluvial fans, fault scarps, and lineaments performed the best. (2) We found similarities in the fault confidence rankings chosen by the mappers and those calculated from the mapped geomorphology. (3) To explore best practices in fault mapping, we conducted listening sessions with 18 participants and found that terminology and mapping process vary by experience level. More- experienced mappers tend to use more technical terms to describe the geomorphology while less- experienced mappers use vague descriptions and generalize nearby features.

The time interval between about three and two million years ago is a critical period in human evolution-this is when the genera Homo and Paranthropus first appear in the fossil record and a possible ancestor of these genera, Australopithecus afarensis, disappears. In eastern Africa, attempts to test hypotheses about the adaptive contexts that led to these events are limited by a paucity of fossiliferous exposures that capture this interval. Here we describe the age, geologic context and dental morphology of new hominin fossils recovered from the Ledi-Geraru Research Project area, Ethiopia, which includes sediments from this critically underrepresented period. We report the presence of Homo at 2.78 and 2.59 million years ago and Australopithecus at 2.63 million years ago. Although the Australopithecus specimens cannot yet be identified to species level, their morphology differs from A. afarensis and Australopithecus garhi. These specimens suggest that Australopithecus and early Homo co-existed as two non-robust lineages in the Afar Region before 2.5 million years ago, and that the hominin fossil record is more diverse than previously known. Accordingly, there were as many as four hominin lineages living in eastern Africa between 3.0 and 2.5 million years ago: early Homo1, Paranthropus2, A. garhi3, and the newly discovered Ledi-Geraru Australopithecus.

Mapping tectonic faults is challenging because mapping approaches are not standardized and some evidence for faulting is ambiguous due to surface processes that obscure the geomorphology. We developed and evaluated a new systematized approach for mapping faults and documenting geomorphic evidence based on desktop mapping using remote sensing data. Our approach works as a teaching tool to introduce fault mapping and in industry settings to establish consistent documentation. Using our approach, a mapper maps the landscape morphology, geomorphology, and surficial geology. The mapper uses the geomorphic indicator ranking approach to document the geomorphic indicators that support faulting such as scarps, triangular facets, and deflected streams. The resulting fault maps facilitate straightforward dissemination of information and build toward more accurate depictions of fault traces, which support understanding fault processes and predicting coseismic rupture location in a future earthquake. We evaluated our mapping approach as follows. (1) We qualified the geomorphology that best predicts future rupture location as having the lowest geomorphic indicator-to-rupture separation distance. Of the features tested, cut or offset alluvial fans, fault scarps, and lineaments performed the best. (2) We found similarities in the fault confidence rankings chosen by the mappers and those calculated from the mapped geomorphology. (3) To explore best practices in fault mapping, we conducted listening sessions with 18 participants and found that terminology and mapping process vary by experience level. More-experienced mappers tend to use more technical terms to describe the geomorphology while less-experienced mappers use vague descriptions and generalize nearby features.

Tectonic landforms and surficial lithologic age are essential data for producing quality late Quaternary fault maps and predicting coseismic fault rupture location before an earthquake. However, we lack a clear understanding of the relationship between tectonic landforms and shallow earthquake processes and how lithologic age relates to landform preservation. We assess how fault location error (rupture-to-fault separation distance) and coseismic displacement residual (difference between observed and predicted coseismic displacement) vary with tectonic landform and lithologic age for four historical earthquakes. Certain tectonic landforms identified before these earthquakes correlate with lower fault location errors and median displacements below model predictions. Faults cutting Holocene units exhibit the largest location errors, reflecting surface processes that erode or bury fault evidence. This study shows that tectonic landforms and lithologic age have a significant impact on fault location uncertainty and coseismic displacement, which should be considered in fault mapping and fault displacement assessment. Accurate maps of tectonic faults are essential for a variety of purposes including assessing seismic hazard, studying faults, and planning land-use. These fault maps typically rely on identifying features in the landscape formed by past earthquakes. Remote sensing data sets like imagery and elevation support this process. However, a major challenge in fault mapping is figuring out how to best interpret what the landforms indicate about faulting. In this study, we analyzed how confident we are about the location of faults mapped before four historical earthquakes. We found that faults indicated by prominent landforms better indicate where subsequent earthquake ruptures will occur relative to faults indicated by less noticeable landforms. We also show that fault mapping in Holocene units (representing the most recent geologic time-period) with meter-scale remote sensing data is particularly challenging. Our findings support making better informed fault maps based on a deeper understating of how clues in the landscape connect to faulting processes. Fault trace mapping is informed by tectonic landforms and surficial geology Uncertainty in fault location and predicted coseismic displacements correlate with tectonic landform type and lithologic age Faults indicated by prominent tectonic landforms have relatively low fault location error and accommodate high displacement

As continents break apart, the dominant mechanism of extension transitions from faulting and lithospheric stretching to magma intrusion and oceanic crust formation in a new ocean basin. A common feature of this evolution preserved at magmatic rifted margins worldwide are voluminous lava flows that erupted close to sea level during the final stages of development of the continent-ocean transition (COT). The mechanisms responsible for the generation of the melts that contribute to these voluminous flows, the so-called seaward dipping reflectors (SDR), and their significance in the context of COT development, are relatively poorly understood; they lie deep below post-rift strata along submarine rifted margins where they cannot be studied directly. Extensive coring of the Afar Stratoid Series - an areally-extensive sequence of Pliocene-aged basalts and intercalated sediments that lie atop the developing COT in the sub-aerial Afar Depression, northern Ethiopia - offers fresh scope to address this issue. We present a numerical model simulating the formation of enriched metasomes within the continental lithospheric mantle by the passage of magmas resembling modern axial basalts. Thermal destabilization of the metasome, caused by plate stretching, initiates melt formation within the metasome. These melts, when mixed with a depleted lithospheric mantle component, closely match the range of compositions of the Afar Stratoid Series lavas in this study. Metasomatic re-enrichment and subsequent melting of the lithospheric mantle during the COT may contribute to further plate thinning. These results demonstrate a novel mechanism by which large-volume flows may be erupted during the COT.

ABSTRACT A primary step toward assessing the time and size of future earthquakes is identifying earthquake recurrence patterns in the seismic record. The San Andreas fault (SAF) is one of the most studied active faults in the world. However, there is no unequivocal interpretation of paleoseismic data to determine the timing and rupture extent of the earthquakes that occurred prior to the historical 1857 and 1906 ruptures. The penultimate earthquake is the least well-dated earthquake along the Cholame, Carrizo, and Big Bend sections of the SAF. The main reason for this poor determination is because the past few hundred years have seen large natural fluctuations in atmospheric C14 concentration. These fluctuations mean that a single radiocarbon date may yield a calibrated age consisting of several possible age ranges. At sites along frequently rupturing faults with historical ruptures, such as the SAF and the North Anatolian fault in Turkey, determining the incision age of channels displaced only by the most recent earthquake can place a tighter minimum limit on the possible age range of the penultimate earthquake. In our study, we dated five sandy fill units with the post-infrared infrared-stimulated luminescence method on single feldspar grains of channel Sieh 31 in the Carrizo Plain. The data indicate the channel Sieh 31, offset ∼6 m during the 1857 earthquake, incised before ∼1740 ± 30 C.E. (1σ). This new result trims the age constraint of the penultimate earthquake that ruptured the Carrizo section of the SAF determined at the nearby Bidart Fan site from 1640–1857 to 1631–1745 C.E., tightening the age constraint by nearly 80 yr. The revised mean recurrence interval for surface rupturing earthquakes along the Carrizo section of the south-central SAF is 117 yr (95% confidence interval 62–255 yr). This approach can improve paleoearthquake age and slip-per-earthquake constraints.

AbstractFollowing observations made in a survey campaign along the Lost River Fault (Idaho, USA) in 2019, we integrate both original and previously published data to obtain a detailed segmentation of the fault sections that failed in the 1983 Borah Peak earthquake (Mw 6.9). The earthquake ruptured the topographic surface with an oblique-normal faulting mechanism, activating two SW-dipping fault segments (Thousand Springs and Warm Springs) and a branching SSW-dipping fault (Arentson Gulch Fault) and producing coseismic surface ruptures with up to 3 m of vertical separation. We augment the 1983 earthquake description by interpreting high-resolution topography and fault mapping. We use quality vertical separation data, rupture zone width measurements, and fault slip data to analyze major and minor structural-geometric complexities, highlighting a partition of the deformation and a fault segmentation into four detail levels (i.e., segments, sections, subsections, and sectors). Our work provides new details of the 1983 Borah Peak earthquake, constraints for paleoseismic and seismotectonic studies, and a methodological approach applicable in other areas of the world. Our fault-slip data show variations along fault-strike that we interpret as kinematic partitioning. In 1983, the main southern segment had a large rupture zone width, while the northern segment localized the deformation. The distributed ruptures accommodate a large portion of the rupture length (~19.5 km versus 31 km for the main rupture) and displacement (~66%). 83% of the surface faulting and 80% of the displacement are located at the hanging wall of the main rupture. There is a strong correlation between vertical separation, rupture zone width, rupture position (footwall or hanging wall), and fault geometry. We highlight the control of the obliquity and kinematic partitioning in the surface expression of the earthquake propagation. We interpret the coseismic (i.e., 1983) and long-term (i.e., Quaternary) behavior, showing that the two activated segments had similar cumulated behaviors in distributing the deformation between synthetic and antithetic ruptures, despite the different geometries. Our results have implications for fault rupture behavior with application to rupture hazard.

Detrital zircons from two major rift basins within the East African Rift System (EARS) provide a means to evaluate not only sediment provenance and landscape dynamics in sedimentary basins, but also the timing of the silicic volcano-tectonic evolution of the rift system. We sampled from drill cores collected by the Hominin Sites and Paleolakes Drilling Project (HSPDP) in Ethiopia and Kenya to study the detrital mineral records of the Northern Awash (NA; 3.3–2.9 Ma) and West Turkana (WTK; 1.9–1.4 Ma) drill cores. We performed (U-Th)/He and U/Pb analyses on detrital zircons using single crystal laser ablation double dating (LADD) techniques. Analyses of four NA samples yielded zircon 206Pb/238U dates younger than ∼45 Ma, consistent with derivation from silicic volcanic rocks associated with EARS activity. Most of these samples lack zircon 206Pb/238U dates from ∼22–13 Ma, due to a decrease in silicic volcanism and a watershed configuration limiting delivery of silicic source materials to the sample site. NA zircon 206Pb/238U dates imply a sedimentary source from the western Afar margin, with a transition to more localized sediment reworking within the Afar Depression after a major regional tectonic reorganization and formation of a disconformity at ∼2.9 Ma. The WTK sample yielded many zircons with Cenozoic 206Pb/238U dates similar to those from the NA core, but the WTK sample also sources a small population of Neoproterozoic zircons associated with rocks from the Mozambique Belt and reworked sedimentary deposits. Despite being recorders of predominantly silicic activity, the detrital zircon U/Pb dates from both drill sites track the established timing of major volcanic phases in the EARS. A subset of zircons from both sites has concordant 206Pb/238U and (U-Th)/He dates, indicating a short duration between zircon crystallization and eruption of the host volcanic rock, but the majority of zircon (U-Th)/He dates are significantly younger than the 206Pb/238U dates for the same zircon. Some (U-Th)/He dates are even younger than the depositional age of the sedimentary sample from which it was collected. The observed spread in zircon (U-Th)/He dates likely reflects partial resetting associated with late mafic volcanism and/or hydrothermal activity within this dynamic rift environment.

Paleoanthropologists have long speculated about the role of environmental change in shaping human evolution in Africa. In recent years, drill cores of late Neogene lacustrine sedimentary rocks have yielded valuable high-resolution records of climatic and ecosystem change. Eastern African Rift sediments (primarily lake beds) provide an extraordinary range of data in close proximity to important fossil hominin and archaeological sites, allowing critical study of hypotheses that connect environmental history and hominin evolution. We review recent drill-core studies spanning the Plio–Pleistocene boundary (an interval of hominin diversification, including the earliest members of our genus Homo and the oldest stone tools), and the Mid–Upper Pleistocene (spanning the origin of Homo sapiens in Africa and our early technological and dispersal history). Proposed drilling of Africa's oldest lakes promises to extend such records back to the late Miocene. ▪ High-resolution paleoenvironmental records are critical for understanding external drivers of human evolution. ▪ African lake basin drill cores play a critical role in enhancing hominin paleoenvironmental records given their continuity and proximity to key paleoanthropological sites. ▪ The oldest African lakes have the potential to reveal a comprehensive paleoenvironmental context for the entire late Neogene history of hominin evolution.

The Apennine mountain belt is a seismically active region showing coupled extensional- and compressional tectonic regimes. The bulk of the seismic energy is released along the normal-fault systems paralleling the topographic divide where earthquakes with 6.0W<7.0 have occurred both in historical- and recent times. Moderately-energetic compressive/transpressive earthquakes (4.0W<6.0), which occurred in the last 50 years, are associated instead with recent activity along the outer front of the fold-and-thrust belt. The relatively-low slip rates (1-3 mm/y), peculiar geological settings, fault systems’ immaturity hamper the assessment of Quaternary fault activity, challenging estimation of the seismic hazard. We present the results of multiscale-multidisciplinary approaches carried out in the Sibillini Mts and peri-Adriatic piedmont of Abruzzo and Molise regions, located in the Apennine extensional- and compressional domain, respectively. In detail: * we investigated the area beyond the northern tip of the Mt Vettore-Mt Bove Fault (VBF), where a remarkable seismicity rate was observed after the 2016 (Mw 6.5) Norcia earthquake. We interpreted primary topographic attributes to direct geological field surveys. We compared (on-surface) evidence of distributed deformation with results coming from 3D assessment of fault slip tendency with computation of Coulomb failure function across the potential fault surfaces. We pointed out the seismogenic character of the ∼13 km-long Pievebovigliana master normal Fault (PBF), which strikes N155°E, dips SW and is in right-lateral en echelon setting with respect to the VBF. The reconstructed geometry of the immature PBF is compatible with the occurrence of Mw≥6.0 earthquakes; * we addressed the hypothesis of late Quaternary activity along the Apennines Outer Front (SAOF), in central-southern Italy, where compressional tectonics is well documented until the Lower-Middle Pleistocene and the front is buried under Plio-Pleistocene foredeep deposits. By integrating topographic- and fluvial network analyses along with morphotectonic investigation of fluvial terraces we found, in the Abruzzo region, variable evidence of rock uplift along segments of the SAOF and inward structures, on its hanging wall. The observed pattern of anomalies is difficult to explain with long-wavelength regional uplift alone and agrees with the regional seismotectonic framework. Despite the low deformation-rate context challenging the interpretation of the topographic and geomorphic signals, the study suggests a reconsideration of late Quaternary active thrusting in central-southern Italy. Despite the different tectonic contexts, the study areas belong to, and the diversity in scale and resolution of the input data, the integration of different methods of investigation turned out successful while dealing with active tectonics in low-deforming-rate regions. Our results along the Apennines confirm how multidisciplinarity boosts the chance to decipher clues of active tectonics and unveil potentially seismogenic sources. This work has received funding from DiSPuTer - University ‘G. d’Annunzio’ of Chieti-Pescara and from the European Union’s Horizon 2020 research and innovation programme, under Grant Agreement #795396.

We present high-resolution mapping and surface faulting measurements along the Lost River fault (Idaho-USA), a normal fault activated in the 1983 (Mw 6.9) earthquake. The earthquake ruptured ~35 km of the fault with a maximum throw of ~3 m. From new 5 to 30 cm-pixel resolution topography collected by an Unmanned Aerial Vehicle, we produce the most comprehensive dataset of systematically measured vertical separations from ~37 km of fault length activated by the 1983 and prehistoric earthquakes. We provide Digital Elevation Models, orthophotographs, and three tables of: (i) 757 surface rupture traces, (ii) 1295 serial topographic profiles spaced 25 m apart that indicate rupture zone width and (iii) 2053 vertical separation measurements, each with additional textual and numerical fields. Our novel dataset supports advancing scientific knowledge about this fault system, refining scaling laws of intra-continental faults, comparing to other earthquakes to better understand faulting processes, and contributing to global probabilistic hazard approaches. Our methodology can be applied to other fault zones with high-resolution topographic data.

Modern Homo sapiens engage in substantial ecosystem modification, but it is difficult to detect the origins or early consequences of these behaviors. Archaeological, geochronological, geomorphological, and paleoenvironmental data from northern Malawi document a changing relationship between forager presence, ecosystem organization, and alluvial fan formation in the Late Pleistocene. Dense concentrations of Middle Stone Age artifacts and alluvial fan systems formed after ca. 92 thousand years ago, within a paleoecological context with no analog in the preceding half-million-year record. Archaeological data and principal coordinates analysis indicate that early anthropogenic fire relaxed seasonal constraints on ignitions, influencing vegetation composition and erosion. This operated in tandem with climate-driven changes in precipitation to culminate in an ecological transition to an early, pre-agricultural anthropogenic landscape.

The Carrizo Plain, the only closed basin in California’s Southern Coast Ranges, preserves landforms and deposits that record both climate change and tectonic activity. An extensive system of clay dunes documents the elevations of late Pleistocene and Holocene pans. Clay dune elevations, drowned shorelines, eroded anticlinal ridges, and zones of perturbed soil chemistry provide evidence of two lake levels higher than today’s (currently 581 m above sea level [masl]), one at ~591 masl at ca. 20 ka and another at ~585 masl that existed at ca. 10 ka, based on optically stimulated luminescence (OSL) dates on clay dune sediment. Two cores from the abandoned floor of the lake provide additional evidence of a long-lived lake in the Carrizo Plain during the late Pleistocene. The longer of the two cores (~42 m) was sampled for palynology, environmental magnetism, and scanning electron microscope–petrography. The magnetic susceptibility signal contains two notable features corresponding to sedimentary materials consistent with reducing conditions. The higher of these features occurs near the surface, and the lower occurs at ~18 m depth. A 14C date on charcoal from the upper reduced zone places the top of this zone at no older than 22.6–20.9 cal ka. This date is consistent with the OSL date on geomorphic features associated with a highstand above ~591 masl. Assuming that reducing conditions correspond to at least a few meters’ depth of relatively fresh water, the new 14C date suggests that the upper reduced zone represents a marine isotope stage (MIS) 2 pluvial maximum lake in the Carrizo Plain. Pollen and ostracodes from the reduced sediments indicate a wetter and cooler climate than today. These conditions would have been capable of sustaining a lake with water much less saline than that of the modern lake. The timing of the oldest documented highstand (no later than 20 ka) is consistent with a modified jet stream migration model and is not consistent with a tropical incursion model. Northeast-to-southwest asymmetry across the lake floor may be consistent with southwestward tilting driven by Coast Range shortening normal to the San Andreas fault, as is seen throughout the region.

The Apenninic chain, in central Italy, has been recently struck by the Norcia 2016 seismic sequence. Three mainshocks, in 2016, occurred on August 24 (M W 6.0), October 26 (M W 5.9) and October 30 (M W 6.5) along well-known late Quaternary active WSW-dipping normal faults. Coseismic fractures and hypocentral seismicity distribution are mostly associated with failure along the Mt Vettore-Mt Bove (VBF) fault. Nevertheless, following the October 26 shock, the aftershock spatial distribution suggests the activation of a source not previously mapped beyond the northern tip of the VBF system. In this area, a remarkable seismicity rate was observed also during 2017 and 2018, the most energetic event being the April 10, 2018 (M W 4.6) normal fault earthquake. In this paper, we advance the hypothesis that the Norcia seismic sequence activated a previously unknown seismogenic source. We constrain its geometry and seismogenic behavior by exploiting: 1) morphometric analysis of high-resolution topographic data; 2) field geologic- and morphotectonic evidence within the context of long-term deformation constraints; 3) 3D seismological validation of fault activity, and 4) Coulomb stress transfer modeling. Our results support the existence of distributed and subtle deformation along normal fault segments related to an immature structure, the Pievebovigliana fault (PBF). The fault strikes in NNW-SSE direction, dips to SW and is in right-lateral en echelon setting with the VBF system. Its activation has been highlighted by most of the seismicity observed in the sector. The geometry and location are compatible with volumes of enhanced stress identified by Coulomb stress-transfer computations. Its reconstructed length (at least 13 km) is compatible with the occurrence of M W ≥6.0 earthquakes in a sector heretofore characterized by low seismic activity. The evidence for PBF is a new observation associated with the Norcia 2016 seismic sequence and is consistent with the overall tectonic setting of the area. Its existence implies a northward extent of the intra-Apennine extensional domain and should be considered to address seismic hazard assessments in central Italy.