Active Normal Faults Research Articles

The Segmented Campo Felice Normal Faults: Seismic Potential Appraisal by Application of Empirical Relationships Between Rupture Length and Earthquake Magnitude in the Central Apennines, Italy

AbstractDuring earthquakes, fault rupture can involve multiple segments in synchronous or cascade mechanisms, leading to an increasing magnitude of the mainshock or rate of aftershocks. Since the seismogenic portions of faults are inaccessible, studying the geometrical and mechanical interaction between exhumed fault segments can contribute to the understanding of multisegment and cascade earthquake scenarios at depth. We investigated a segmented active normal fault system in the Campo Felice area (central Italian Apennines), where fault scarps are well exposed. In this area, there are no instrumental‐historical records of intermediate‐strong earthquakes, although paleoseismology provided evidence for ancientMw > 5 earthquakes. Geometry and kinematics of the studied faults as well as their physical linkage and mechanical interaction were assessed. Results of field surveys and geological‐structural mapping, serial cross‐sections, and throw versus distance diagrams highlight different stages of mechanical interaction between the Campo Felice faults. The suitability of three empirical equations relating earthquake rupture length and magnitude was tested in comparison to a new equation that we developed considering the last sevenMw > 5.5 earthquakes (1997–2016) from the central Apennines. Results show that the Campo Felice faults can produce earthquakes with maximumMwof ∼5.8 and 6.2 with single or synchronous ruptures, respectively. In turn, Coulomb stress change modeling shows that the seismic hazard can increase considering a quasi‐synchronous or cascade activation of the Campo Felice faults together with nearby faults.

Structural and paleostress analysis within a fossil slow-spreading ridge: Tectonic processes involved during ocean expansion

This study aims to decipher the spatio-temporal chronology of tectonic processes leading to ocean widening at a slow-spreading oceanic ridge axis, involving mantle and gabbro exhumation and volcanism. Structural and petrographic studies of deformed lithologies were performed on peridotites, gabbros and basalts from the Chenaillet ophiolite (Alps, France). Inversion of fault-slip data reveals N030° and N060° σ3 paleostress trends. The dominant N030° extension, is consistent with the NNW-SSE direction of volcano feeder-dykes and ENE dipping low-angle normal faults crosscutting the mantle. The N060° extension accords with the mantle dome structure formation to the east. Low-angle faults intersect roots of volcanoes that thus belong to their hanging walls. Hydrothermalism is contemporaneous with or postdates low-angle faulting. A feeder-dyke major virgation northwards, synchronous with eruptions, suggests a dextral transform fault consistent with a N120° σ2. Oceanic expansion mechanisms are clarified. At the surface, magma eruption occurs along on-axis active high-angle normal faults, their footwalls enabling mantle exhumation. At depth, off-axis high-angle faults become low-angle faults as they spread at shallow level. With westward drift of the lithosphere, the uppermost levels of the ridge shift westward faster, such that volcanoes move to an off-axis position while their roots are cut by low-angle faults.

Multiple Lines of Evidence for a Potentially Seismogenic Fault Along the Central-Apennine (Italy) Active Extensional Belt–An Unexpected Outcome of the MW6.5 Norcia 2016 Earthquake

The Apenninic chain, in central Italy, has been recently struck by the Norcia 2016 seismic sequence. Three mainshocks, in 2016, occurred on August 24 (MW6.0), October 26 (MW5.9) and October 30 (MW6.5) 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 (MW4.6) 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 MW≥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.

Detecting active faults in intramountain basins using electrical resistivity tomography: A focus on Kashmir Basin, NW Himalaya

Kashmir basin in the NW Himalaya is surrounded by the main Himalayan boundary faults, has very well documented historical earthquakes and a good instrumental earthquake record. However, the causative faults of these earthquakes except the 8 October 2005 Kashmir earthquake (M7.6) are not known. One of many historical earthquakes that have struck and caused damage and destruction in the Kashmir basin is the 30 May 1885 Kashmir earthquake (~M6.3). The extensive damage due to this earthquake was reported in the NW part of the basin and as usual the causative fault is not known and mapped. As the earthquake related geomorphic features are not preserved due to the high erosion rates in the Kashmir Himalaya, we mapped certain active fault strands using high resolution digital elevation models (DEM) and the Google Earth imagery, later complemented by the field investigation in the NW Kashmir. The Electrical Resistivity Tomography (ERT) was carried out at certain identified sites in the macroseismic epicentral area of the 1885 Kashmir earthquake. The results show a local active normal fault which was named as the NW Kashmir fault. The ERT results were confirmed by excavating a trench and an already existing road cut at the ERT sites. The results show that ERT is a very useful shallow geophysical method to detect faults in the Karewas. Karewas are the Plio-Pleistocene and Holocene (reworked by rivers), fluvio-lacustrine, soft and unconsolidated, sand-clay-conglomerate sediments, deposited as distinct table-land geomorphic features in the Kashmir basin and are significantly water saturated.

Tectono-climatic controls of the early rift alluvial succession: Plio-Pleistocene Corinth Rift (Greece)

Proximal alluvial sediments represent a useful sedimentary archive to reconstruct the tectono-climatic history of continental rift basins. However, poor dating of coarse fluvial successions usually prevents high-resolution distinction of tectonic and climatic processes, and thus good determination of process rates. This paper presents a dating study of Plio-Pleistocene Kalavryta river system during the early history of the Corinth Rift (northern Peloponnese, Greece) based on magnetostratigraphy and palynology. This river system developed across several active normal fault blocks that are now uplifted along the southern rift margin. The detailed sedimentary record constrains alluvial architectures from the proximal basin to the river outlet where small deltas built into a shallow lake. In four magnetostratigraphy sections the correlation to the reference scale relies on the identification of the Gauss/Matuyama magnetic reversal and biostratigraphic elements. The river system developed between about 3.6 to 1.8 Ma, with sediment accumulation rates (SARs) ranging from 0.40 to 0.75 mm yr−1. SAR is lower in the alluvial fans than in the deltaic system, and higher at the centre of the normal fault depocentres than at the fault tip. By comparison with worldwide Cenozoic SARs, our values are higher but lie in the same range as those determined in coarse alluvial foreland basins. Moreover, in the context of overfilled intra-mountainous rift basins, these rates are minimum values and can be used as a proxy for accommodation rate. Therefore, early rift stratal wedges and growth synclines attest high sedimentation rates and also high rates of tectonic processes. Finally, in the distal river system, floral compositions and changes of vegetation deduced from palynological data are coherent with alternating fluvio-deltaic and shallow lacustrine deposits, which are linked to relative base level variations. Dry/cool climate is preferentially recorded during periods of low lake level, while the warm/moist climate is mainly recorded in prodelta deposits during periods of high lake level. This correlation suggests that, despite the dominant control of active faulting, climate is a key control of syn-rift stratigraphic architectures.

The paleoearthquakes of the Langshan Piedmont fault, North China since late Pleistocene

The Langshan Piedmont fault (LPF) is an active Holocene normal fault that borders Langshan Mountain and the Hetao Graben in the northwest of Ordos Block of China. In this study, paleoseismic trenching was undertaken at three sites and 11 fault outcrops are well exposed. The results show that eight paleoearthquake events occurred on the LPF since 43 ka BP, and six paleoearthquake events are complete since 14 ka BP, the latest event is 2300–2400 a BP; the LPF has the characteristic of quasi-periodic recurrence and the average recurrence interval is 2350 years. Therefore, there is a high probability that the LPF will have another earthquake. The vertical activity rate of the LPF is ~1.12 ​mm/yr since Holocene, and ~0.77 ​mm/yr since 14 ka BP. In this study, it is considered that the LPF is mainly characterized by simultaneous rupture of the whole segment. The vertical displacement of the paleoearthquake events is 0.8–2.5 ​m and the corresponding maximum paleoearthquake magnitude is M 7.4. The seismic hazard of Langshan area should not be ignored. The buildings in Langshan area, especially Wulatehouqi and Qingshan town, should be able to withstand a magnitude 8 earthquake.

Volcanotectonic interactions between inclined sheets, dykes, and faults at the Santorini Volcano, Greece

Dykes and inclined sheets are known occasionally to exploit faults as parts of their paths, but the conditions that allow this to happen are still not fully understood. In this paper, we report field observations from a swarm composed of 91 segments of dykes and inclined sheets, the swarm being particularly well-exposed in the mechanically layered caldera walls of the Santorini volcano, Greece. Here the focus is on dykes and sheets in the swarm that are seen deflected into faults and the mechanical conditions that encourage such deflections. In particular, we present new analytical and numerical models to explain the mechanical principles of dyke/sheet deflections into faults. The numerical models are applied to a normal-fault dipping 65° with a damage zone composed of parallel layers or zones of progressively stiffer rocks with increasing distance from the fault rupture plane. We model a sheet-intrusion, dipping from 0° to 90° and with an overpressure of alternatively 1 MPa and 5 MPa, approaching the fault. We further tested the effects of changing (1) the thickness of the sheet-intrusion, (2) the fault-zone thickness, (3) the fault-zone dip-dimension (height), and (4) the loading by, alternatively, regional tension and compression. We find that the stiffness of the fault core, where a compliant core characterises recently active fault zones, has pronounced effects on the orientation and magnitudes of the local stresses and, thereby, on the likelihood of dyke/sheet deflection into the fault zone. Similarly, the analytical models, focusing on the fault-zone tensile strength and energy conditions for dyke/sheet deflection, indicate that dykes/sheets are most likely to be deflected into and use steeply dipping recently active (zero tensile-strength) normal faults as parts of their paths.

High resolution morphometric analysis of the Cordone del Vettore normal fault scarp (2016 central Italy seismic sequence): Insights into age, earthquake recurrence and throw rates

We investigated the late Quaternary throw distribution of the main normal fault that ruptured during the Mw 6.5 2016 earthquake in central Italy by means of a high-resolution structure-from-motion (SfM)-derived Digital Surface Model (DSM). We focused on a key area along the Cordone del Vettore fault (CDV), which is part of the Vettore-Bove fault system (VBFS). The CDV displays a prominent compound post-glacial scarp that allowed the reconstruction of the along-strike cumulative throw distribution. We propose a geometric approach to calculate the CDV fault throw distribution from the reconstruction of a displaced glaciation-related erosional surface, used as a geomorphic marker, and a series of closely spaced cross profiles. The proposed calculation accounts for both the slip vector direction and the degraded scarp top, including field data on fault dip angles. Following this approach, we recognized two scarps with a minimum average fault throw of ~21 m and ~35 m for this section of the investigated fault strand.The correlation with the possible post-LGM (Last Glacial Maximum) deglaciation phases of the erosional surface suggests a minimum scarp age of 25–27 ka cal BP. Such an age provides a reasonable CDV fault throw rate of ~0.8 mm/a, comparable with known long-term throw rates of the VBFS and active Apennines normal faults. By comparing the reconstructed long-term Cordone del Vettore throw distribution with the 2016 coseismic one, ~24 2016-like surface faulting events are required to generate the main cumulative scarp, under the assumption of constant slip per event. This, along with the age of the scarp, yields an average earthquake recurrence time interval of ~1100 a. These results suggest the presence of multiple regional markers that correlates with different LGM (if not pre-LGM) major glacial phases, whose erosional processes allow the preservation of pre-existing bedrock fault scarp remnants.

Potential geothermal structure inferred from the electrical resistivity and seismic reflection models in the western Ilan Plain, NE Taiwan

The Ilan Plain is identified as the western extension of the Okinawa Trough in the northeastern Taiwan subduction system and is considered one of the most active geothermal areas in Taiwan. An east-west extending magma-like body caused by the westward of the Okinawa Trough had been revealed from seismic and geomagnetic studies. Two geological models have been suggested as an extensional strike-slip fault and normal fault models for the deep geothermal field in NE Taiwan. The difference of the main fault in the two geology models is the active normal strike-slip fault or inactive thrust fault and its dip directions. We investigated the electrical resistivity structure beneath the Ilan Plain using audio-magnetotelluric data to delineate the location of its geothermal reservoirs. The 3D electrical resistivity model is highly correlated with the normal fault model. The electrical resistivity model shows that the high conductivity anomaly distributes in the depths of 500-1,100 m south of the drilled geothermal observation wells. We correlate the anomalous high conductor with the reservoir and it could be controlled by the Chuoshui Fault and the Chukeng Fault. The meteoric water may propagate down through the high-permeability fault system that creates the geothermal system.

Reassessing Eastern Mediterranean Tectonics and Earthquake Hazard From the 365 CE Earthquake

AbstractThe hallmark of great earthquakes in the Mediterranean is the 21 July 365 CE earthquake and tsunami that destroyed cities and killed thousands of people throughout the Eastern Mediterranean. This event is intriguing because most Mediterranean subduction forearcs exhibit pervasive crustal extension and minimal definitive evidence exists for great subduction megathrust earthquakes, consistent with weak seismic coupling. This conundrum has led many to favor rupture of a previously unrecognized upper plate splay fault south of Crete in an M w 8.3–8.5 earthquake, uplifting a Cretan Holocene paleoshoreline by up to 9 m. Similar source mechanisms have been adapted for the region, which are commonly used for seismic and tsunami hazard estimation. We present an alternative model for Holocene paleoshoreline uplift and the 365 CE tsunami that centers on known active normal fault systems offshore of western and southwestern Crete. We use new and published radiocarbon dates and historical records to show that uplift of the Cretan paleoshoreline likely occurred during two or more earthquakes within 2–3 centuries. Visco‐elastic dislocation modeling demonstrates that the rupture of these normal faults fits observed data as well as reverse fault models but requires reduced slip and lower cumulative earthquake energy release (∼M w 7.9). Tsunami modeling shows that normal‐fault ruptures produce strong tsunamis that better match historical reports than a hypothetical reverse fault. Our findings collectively favor the interpretation that damaging earthquakes and tsunamis in the Eastern Mediterranean can originate on normal faults, highlighting the potential hazard from tsunamigenic upper plate normal fault earthquakes.

Polyphase extensional basins: interplay between tectonics and sedimentation in the Neogene Siena-Radicofani Basin (Northern Apennines, Italy)

Rift-basins are the shallow effects of lithosphere-scale extensional processes often producing polyphase faulting. Their sedimentary evolution depends on the mutual interplay between tectonics, climate, and eustasy. Estimating the role of each factor is generally a challenging issue. This paper is focused on the tectono-sedimentary evolution of the Neogene Siena-Radicofani Basin, a polyphase structural depression located in the inner Northern Apennines. Since Miocene, this basin developed after prolonged extensional tectonics, first as a bowl-shaped structural depression, later reorganized into a half-graben structure due to the activation of high-angle normal faults in the Zanclean. At that time the basin contained coeval continental and marine settings controlled by the normal faulting that caused the development of local coarse-grained depositional systems. These were investigated to: (i) discriminate between the influences of tectonics and climate on sedimentation patterns, and (ii) provide detailed time constraints on fault activity. The analysed successions were deposited in an interval between 5.08 and 4.52 Ma, when a climate-induced highstand phase occurred throughout the Mediterranean. However, evidence of local relative sea-level drops is registered in the sedimentary record, often associated with increased accommodation space and sediment supply. Such base-level fluctuations are not connected to climate changes, suggesting that the faults generally control sedimentation along the basin margins.

Joint Interpretation of Geophysical Results and Geological Observations for Detecting Buried Active Faults: The Case of the “Il Lago” Plain (Pettoranello del Molise, Italy)

We report a geophysical study across an active normal fault in the Southern Apennines. The surveyed area is the “Il Lago” Plain (Pettoranello del Molise), at the foot of Mt. Patalecchia (Molise Apennines, Southern Italy), a small tectonic basin filled by Holocene deposits located at the NW termination of the major Quaternary Bojano basin structure. This basin, on the NE flank of the Matese Massif, was the epicentral area of the very strong 26 July, 1805, Sant’Anna earthquake (I0 = X MCS, Mw = 6.7). The “Il Lago” Plain is bordered by a portion of the right-stepping normal fault system bounding the whole Bojano Quaternary basin (28 km long). The seismic source responsible for the 1805 earthquake is regarded as one of the most hazardous structures of the Apennines; however, the position of its NW boundary of this seismic source is debated. Geological, geomorphological and macroseismic data show that some coseismic surface faulting also occurred in correspondence with the border fault of the “Il Lago” Plain. The study of the “Il Lago” Plain subsurface might help to constrain the NW segment boundary of the 1805 seismogenic source, suggesting that it is possibly a capable fault, source for moderate (Mw < 5.5) to strong earthquakes (Mw ≥ 5.5). Therefore, we constrained the geometry of the fault beneath the plain using low-frequency Ground Penetrating Radar (GPR) data supported by seismic tomography. Seismic tomography yielded preliminary information on the subsurface structures and the dielectric permittivity of the subsoil. A set of GPR parallel profiles allowed a quick and high-resolution characterization of the lateral extension of the fault, and of its geometry at depth. The result of our study demonstrates the optimal potential of combined seismic and deep GPR surveys for investigating the geometry of buried active normal faults. Moreover, our study could be used for identifying suitable sites for paleoseismic analyses, where record of earthquake surface faulting might be preserved in Holocene lacustrine sedimentary deposits. The present case demonstrates the possibility to detect with high accuracy the complexity of a fault-zone within a basin, inferred by GPR data, not only in its shallower part, but also down to about 100 m depth.

Multitechnology characterization of an unusual surface rupturing intraplate earthquake: the ML 5.4 2019 Le Teil event in France

SUMMARY Metropolitan France is a region of slow tectonic deformation with sparse seismicity. On 11 November 2019, the ML 5.4 Le Teil earthquake became the largest seismic event recorded in the last 16 yr. This event was recorded by the national seismic networks and also by a wide variety of other geophysical techniques including infrasound and InSAR measurements. These complementary technologies offer the opportunity to investigate in detail the earthquake source characteristics and the associated ground motion attenuation. Both seismic waveform inversions and InSAR interferogram reveal a shallow rupture on a reverse fault with an associated moment magnitude of 4.8–4.9. Infrasound signals also provide fast evidences pointing towards the area of ground surface displacements, which coincides with La Rouvière fault, in the Cévennes fault system, known as a formerly active normal fault during the Oligocene. The very significant amount of seismic records also helps towards validating the GMPE laws available for the region. This multitechnology characterization documents the kinematics of this rare example of shallow intraplate fault reactivation.

Alluvial fan of Glazne river, Bansko town, SW Bulgaria

At the place where Banderitsa and Demyanitsa rivers and their tributaries ceased to be confined to their narrow valleys one of the most impressive alluvial fans in South Bulgaria is formed – the one of Glazne river. The river valley morphology, as well as the evolution and the position of the Glazne fan, are controlled by the active normal faulting in the NE slopes and foot of Pirin Mountain. Тhe Quaternary glaciations produced large volumes of debris in the river valleys. There is an agreement that the processes of sediment transfer from the mountain to the Razlog graben have been highly active at the time and immediately after the Pleistocene glaciations. As a result, in the Bulgarian geological and geomorphological reports and scientific papers, the age of the alluvial fans at the NE foot of Pirin Mountain is assumed to be Late Pleistocene–Early Holocene. The results of our studies require a re-evaluation of these ideas. Using widely accepted methods for natural hazard assessment, our field and historical research and analysis allow us to claim that the Glazne fan is active. Parts of Bansko, that are situated in the upper-middle parts of the alluvial fan, have been affected by at least two significant debris floods during the XX century. The conducted measures to control river behavior have an important effect on risk reduction, yet they lead to significant modification of the zones of active aggradation and this means that new actions against future events must be taken.

The thermo-tectonic evolution of the actively exhuming Mai'iu Fault footwall – Suckling-Dayman metamorphic core complex – in the Woodlark Rift of Papua New Guinea

The Mai'iu Fault in the Woodlark Rift of southeastern Papua New Guinea is an active north-dipping low-angle normal fault (LANF) that has exhumed the spectacular Suckling-Dayman metamorphic core complex (SDMCC) in its footwall. While its youthful domal geomorphology suggests recent tectonic exhumation of the SDMCC, the cooling and exhumation history of this active metamorphic core complex have not been studied in detail before. Here we provide the first zircon and apatite fission-track (FT) and (U-Th)/He thermochronometric data on the SDMCC based on a suite of samples from slip-parallel footwall transects and syn-extensional alluvial deposits shed from the emerging dome. In addition, we double dated zircon using U–Pb LA-ICP-MS. These chronometric techniques are complemented by temperature and pressure estimates from Raman spectroscopy of carbonaceous material (RSCM) and Al-in-amphibole and Al-in-biotite barometry on footwall phyllites/schists and granitoids, respectively. The data indicate that slip on the Mai'iu Fault had initiated by ~4 Ma. We show that slip on the Mai'iu Fault has persisted at cm/year rates since the onset of extension, making it one of Earth's most rapidly slipping continental LANF. Integrating temperature estimates from FT and (U-Th)/He thermochronometry and RSCM, we calculated a down-dip, fault-parallel paleo-field temperature gradient along the now-exhumed part of the Mai'iu Fault of ~11 °C/km. For a likely range of pre-extensional geothermal gradients in the Woodlark Rift (10–20 °C/km), this paleo-field temperature gradient implies an average initial dip of the Mai'iu Fault of ~46°. Given the present dip of ~21° at the surface, the thermal data reinforce other evidence that the footwall of the Mai'iu Fault has been back-rotated to the south by ≥20° during progressive unroofing since fault inception, consistent with a rolling hinge style evolution of the SDMCC.

Lithological and Topographic Impact on Soil Nutrient Distributions in Tectonic Landscapes: Implications for Pleistocene Human-Landscape Interactions in the Southern Kenya Rift

Tectonically active regions are characterized by complex landscapes comprising soils with heterogeneous physicochemical properties. Spatial variability of nutrient sources enhances landscape biodiversity and creates heterogeneous habitats potentially attractive for animals and humans. In this study, we analyze the role of geological processes in the distributions of soil nutrients in the southern Kenya Rift, a key region in the interpretation of early human-landscape interactions. Our aim is to determine how spatial variations in rock chemistry, as well as topographic gradients and localized zones of rock fracturing from tectonic faulting determine the distributions of plant-available soil nutrients in soils. We hypothesize that present-day soil nutrient levels reflect the long-term chemical and geomorphological characteristics of the landscape and underlying parent material, and that regions with high nutrient availability occur along pathways correlating with locations of hominin fossil sites. Analyses of 91 topsoil samples from the main geological units show that Calcium (Ca) deficiencies predominately occur in shallow soils developed on trachytic volcanic rocks and granitic gneisses, while high Ca levels are associated with basaltic parent material and sedimentary deposits of mixed sources. XRF analysis of rock samples confirms that CaO levels in trachyte rocks are significantly lower than those in basalts, and Ca mobilization in basalt is more effective than in trachyte. Along two toposequences in densely faulted basaltic and trachytic rocks, we observed slope dependent soil nutritional gradients and a systematic increase of the concentrations of Ca, Mg and SOC in topsoils of colluvial sediments downslope of active normal faults. Known hominin sites in the region are located either along corridors of long-term Ca availability or at short-term nutrient hotspots potentially related to active CO2 degassing along active fault zones. This implies a strategic advantage of Ca-rich regions for hominin subsistence strategies, such as provision of predictable constraints on the distribution and mobility of grazing animals in complex tectonic landscapes. Our study implies that geological processes impact nutrient distributions in the southern Kenya Rift. Results of this study have further implications for understanding the role of soils in the interpretation of hominin-landscape interactions in the early stages of human evolution.

Determining Histories of Slip on Normal Faults With Bedrock Scarps Using Cosmogenic Nuclide Exposure Data

AbstractCosmogenic exposure data can be used to calculate time‐varying fault slip rates on normal faults with exposed bedrock scarps. The method relies on assumptions related to how the scarp is preserved, which should be consistent at multiple locations along the same fault. Previous work commonly relied on cosmogenic data from a single sample locality to determine the slip rate of a fault. Here we show that by applying strict sampling criteria and using geologically informed modeling parameters in a Bayesian‐inference Markov chain Monte Carlo method, similar patterns of slip rate changes can be modeled at multiple sites on the same fault. Consequently, cosmogenic data can be used to resolve along‐strike fault activity. We present cosmogenic 36Cl concentrations from seven sites on two faults in the Italian Apennines. The average slip rate varies between sites on the Campo Felice Fault (0.84 ± 0.23 to 1.61 ± 0.27 mm yr−1), and all sites experienced a period of higher than average slip rate between 0.5 and 2 ka and a period of lower than average slip rate before 3 ka. On the Roccapreturo fault, slip rate in the center of the fault is 0.55 ± 0.11 and 0.35 ± 0.05 mm yr−1 at the fault tip near a relay zone. The estimated time since the last earthquake is the same at each site along the same fault (631 ± 620 years at Campo Felice and 2,603 ± 1,355 years at Roccapreturo). These results highlight the potential for cosmogenic exposure data to reveal the detailed millennial history of earthquake slip on active normal faults.

Assessment of Neotectonic Landscape Deformation in Evia Island, Greece, Using GIS-Based Multi-Criteria Analysis

This study deals with the assessment and mapping of neotectonic landscape deformation in the northern part of the Evia Island (Central Greece). Multi-Criteria Decision Analysis (MCDA) utilizing Analytic Hierarchy Process (AHP) and Weighted Linear Combination (WLC) procedures were conducted for the calculation of the Neotectonic Landscape Deformation Index (NLDI). The study is based on the combination of morphotectonic, geomorphological and geological parameters. The GIS-based spatial MCDA led to the classification of the study area into five classes of neotectonic deformation (from very low to very high) and to a neotectonic deformation map. The results were compared with the outputs of a relative tectonic activity classification approach based on quantitative geomorphic analysis at a regional scale, including site-specific field observations. Areas of high and very high deformation are related to the major active faults of Dirfis, Kandili and Gregolimano–Telethrio. Other minor active normal faults of medium to high seismic risk level, affecting the northern and northeastern parts of the island, are also associated with areas of intense landscape neotectonic deformation.

Seismic hazard of the western Makran subduction zone: Insight from mechanical modelling and inferred frictional properties

Western Makran is one of the few subduction zones left with a largely unconstrained seismogenic potential. According to the sparse GPS stations, the subduction is accumulating some strain to be released during future earthquakes. To enhance the seismic hazard assessment, we here propose to study the finite deformation of the western Makran accretionary wedge. Mechanical modelling is used to retrieve the spatial variations of the frictional properties of the megathrust, and discuss its seismogenic potential. To do so, we first build a structural map along the Iranian part of the Oman Sea and investigate three N-S seismic profiles. The profiles are characterized by a long imbricated thrust zone that takes place at the front of the wedge. A diapiric zone of shallow origin lies in between the imbricated zone and the shore. Along the eastern and western shores, active listric normal faults seem to root down to the megathrust. Eastern and western domains have developed similar deformation, with three zones of active faulting: the normal faults on shore, thrusts ahead of the mud diapirs, and the frontal thrusts. On the contrary, no normal faults are identified along the central domain, where a seamount is entering into subduction. Two mechanical analyses are performed to retrieve the frictional properties of the megathrust. We first apply the critical taper theory to constrain the pore fluid pressure of the wedge. We then apply the limit analysis on two selected profiles. Along the eastern profile, a transition from very low to extremely low friction is required to activate the large coastal normal fault (μdeepeff = 0.01-0.06, μmiddleeff = 0.003-0.012). To propagate the deformation to the front, an increase of friction along the imbricated zone is necessary (μfronteff = 0.017-0.031). The method could not be applied on the incomplete western profile. However, since the deformation is similar to the eastern profile, the same transitions of friction are expected. The Central domain is also characterized by very low effective friction; but, the absence of normal fault does not allow to evidence any frictional transition.Since dynamic effective friction coefficients are significantly lower than frictions at slow slip rate, the region of extremely low friction between the normal fault and the imbricated zone might reveal the location of a seismic asperity. The difference in deformation along strike would thus reveal the existence of two different asperities, one along the eastern domain and a second along the western domain. Since no earthquake have occurred in the region for, at least, the last 1000 years, an event of large magnitude may strike the Iranian Makran, in particular the Eastern domain.

The tectono-stratigraphic evolution of the Fucino Basin (central Apennines, Italy): new insights from the geological mapping of its north-eastern margin.

ABSTRACT We present the geological map of the north-eastern margin of the Fucino Basin, which is mainly characterized by Plio-Quaternary continental deposits that show transition from deeper-water lacustrine environment, marginal lacustrine system, and fluvial facies. These deposits unconformably overlie upper Messinian Lago-Mare sediments and pre-orogenic carbonate succession. The occurrence of Caspiocypris tiberina in the Plio-Quaternary lacustrine sediments, coupled with the normal magnetic polarity of Casa Colombaia section, led to suggest the onset of the sedimentation of these continental deposits to the late Piacenzian (2.58–3.04 Ma). The upper Messinian deposits are characterized by ostracod assemblages related to the Loxocorniculina djafarovi zone, pointing to the last Lago-Mare event of the Messinian Salinity Crisis (5.40–5.33 Ma). This new stratigraphic framework may be useful to refine the long-term slip rates of the still active normal faults that affect the north-eastern margin of the Fucino Basin.