Holocene surface rupturing earthquakes on the Dinaric Fault System, western Slovenia

Abstract. The Dinaric Fault System in western Slovenia, consisting of NW-SE trending, right-lateral strike-slip faults, accommodates the northward motion of Adria with respect to Eurasia. These active faults show a clear imprint in the morphology and some of them hosted moderate instrumental earthquakes. However, it is largely unknown if the faults also had strong earthquakes in the Late Quaternary. This hampers our understanding of the regional tectonics and the seismic hazard. Geological evidence of co-seismic surface ruptures only exists for one historical event, the 1511 Idrija Earthquake with a magnitude of ~M6.8, but the causative fault is still disputed. Here we use geomorphological data, near-surface geophysical surveys, and paleoseismological trenching to show that two of these faults, the Predjama Fault and the Idrija Fault ruptured in strong earthquakes in the Holocene. In a paleoseismological trench across the Predjama Fault we found at least one earthquake with a minimum magnitude of MW6.1 that occurred between 13–0.7 ka, very likely not earlier than 8.4 ka. At the Idrija Fault, a surface-rupturing earthquake with a magnitude of at least MW6.1 happened in the last ~2.1 ka. This event could correspond to the 1511 Idrija earthquake. Our results show that the faults rupture in rare, but strong earthquakes, which dominate the seismic moment release. We show that instrumental and historical seismicity data do not capture the strongest events in this area. The fact that many of the NW-SE trending, parallel faults are active implies that the deformation in western Slovenia is distributed, rather than focussed on one major structure.

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Holocene surface-rupturing earthquakes on the Dinaric Fault System, western Slovenia

Solid Earth ◽

10.5194/se-12-2211-2021 ◽

2021 ◽

Vol 12 (10) ◽

pp. 2211-2234

Author(s):

Christoph Grützner ◽

Simone Aschenbrenner ◽

Petra Jamšek Rupnik ◽

Klaus Reicherter ◽

Nour Saifelislam ◽

...

Keyword(s):

Late Quaternary ◽

Active Faults ◽

Historical Seismicity ◽

Fault System ◽

Historical Event ◽

Near Surface ◽

Geological Evidence ◽

Geophysical Surveys ◽

Deformation Features ◽

Surface Ruptures

Abstract. The Dinaric Fault System in western Slovenia, consisting of NW–SE-trending, right-lateral strike-slip faults, accommodates the northward motion of Adria with respect to Eurasia. These active faults show a clear imprint in the morphology, and some of them hosted moderate instrumental earthquakes. However, it is largely unknown if the faults also had strong earthquakes in the late Quaternary. This hampers our understanding of the regional tectonics and the seismic hazard. Geological evidence of co-seismic surface ruptures only exists for one historical event, the 1511 Idrija earthquake with a magnitude of ∼ M 6.8, but the causative fault is still disputed. Here we use geomorphological data, near-surface geophysical surveys, and paleoseismological trenching to study two of these faults: the Predjama Fault and the Idrija Fault. In a paleoseismological trench across the Predjama Fault we found deformation features that may have been caused by an earthquake between 13–0.7 ka, very likely not earlier than 8.4 ka. At the Idrija Fault, a surface-rupturing earthquake happened around 2.5 ka. We show that instrumental and historical seismicity data do not capture the strongest events in this area.

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Geodynamic and seismotectonic model of a long-lived transverse structure: The Schio-Vicenza Fault System (NE Italy)

Solid Earth ◽

10.5194/se-12-1967-2021 ◽

2021 ◽

Vol 12 (8) ◽

pp. 1967-1986

Author(s):

Dario Zampieri ◽

Paola Vannoli ◽

Pierfrancesco Burrato

Keyword(s):

Active Faults ◽

Strike Slip ◽

Southern Alps ◽

Fault System ◽

Thrust Belt ◽

Geological Evidence ◽

Slip Activity ◽

Seismological Data ◽

Moderate Seismicity ◽

Northern Segment

Abstract. We make a thorough review of geological and seismological data on the long-lived Schio-Vicenza Fault System (SVFS) in northern Italy and present for it a geodynamic and seismotectonic interpretation. The SVFS is a major and high-angle structure transverse to the mean trend of the eastern Southern Alps fold-and-thrust belt, and the knowledge of this structure is deeply rooted in the geological literature and spans more than a century and a half. The main fault of the SVFS is the Schio-Vicenza Fault (SVF), which has a significant imprint in the landscape across the eastern Southern Alps and the Veneto-Friuli foreland. The SVF can be divided into a northern segment, extending into the chain north of Schio and mapped up to the Adige Valley, and a southern one, coinciding with the SVF proper. The latter segment borders to the east the Lessini Mountains, Berici Mountains and Euganei Hills block, separating this foreland structural high from the Veneto-Friuli foreland, and continues southeastward beneath the recent sediments of the plain via the blind Conselve–Pomposa fault. The structures forming the SVFS have been active with different tectonic phases and different styles of faulting at least since the Mesozoic, with a long-term dip-slip component of faulting well defined and, on the contrary, the horizontal component of the movement not being well constrained. The SVFS interrupts the continuity of the eastern Southern Alps thrust fronts in the Veneto sector, suggesting that it played a passive role in controlling the geometry of the active thrust belt and possibly the current distribution of seismic release. As a whole, apart from moderate seismicity along the northern segment and few geological observations along the southern one, there is little evidence to constrain the recent activity of the SVFS. In this context, the SVFS, and specifically its SVF strand, has accommodated a different amount of shortening of adjacent domains of the Adriatic (Dolomites) indenter by internal deformation produced by lateral variation in strength, related to Permian–Mesozoic tectonic structures and paleogeographic domains. The review of the historical and instrumental seismicity along the SVFS shows that it does not appear to have generated large earthquakes during the last few hundred years. The moderate seismicity points to a dextral strike-slip activity, which is also corroborated by the field analysis of antithetic Riedel structures of the fault cropping out along the northern segment. Conversely, the southern segment shows geological evidence of sinistral strike-slip activity. The apparently conflicting geological and seismological data can be reconciled considering the faulting style of the southern segment as driven by the indentation of the Adriatic plate, while the opposite style along the northern segment can be explained in a sinistral opening “zipper” model, where intersecting pairs of simultaneously active faults with a different sense of shear merge into a single fault system.

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A photogrametric study on active faults in the Nepal Himalayas

Journal of Nepal Geological Society ◽

10.3126/jngs.v2i0.36175 ◽

1982 ◽

Vol 2 ◽

pp. 67-80

Author(s):

Takashi Nakata

Keyword(s):

Active Fault ◽

Late Quaternary ◽

Lateral Displacement ◽

Active Faults ◽

Aerial Photographs ◽

Fault System ◽

Lateral Movement ◽

Active Faulting ◽

Quaternary Period ◽

Late Quaternary Period

Active faults in the Nepal Himalayas are identified by means of interpretation of vertical aerial photographs. They are mainly distributed along the major tectonic lines as older geological faults and are classified into four groups, the Main Central Active Fault system, the active faults in the Lower Himalayas, the Main Boundary Active Fault system and active faults along the Himalayan Front Fault. The mode of active faulting is closely related to the strikes of the faults. Along the NW-SE and NE-SW trending faults, lateral displacement with northward drop is prevailing, and right-lateral movement along the former and left-lateral movement along the latter is a rule in the sense of displacements. On the other hand, dip-slip faulting is observed mainly along the E-W trending faults belonging to the Main Boundary Active Fault system. However, apparent displacement along the faults is mostly of northward drop. It is considered that active faulting along the major tectonic lines except the Himalayan Front Fault does not favor the upheaval of the Himalayan ranges during the late Quaternary period.

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GPR signature of Quaternary faulting: a study from the Mt. Pollino region, southern Apennines, Italy

10.5194/se-2021-75 ◽

2021 ◽

Author(s):

Maurizio Ercoli ◽

Daniele Cirillo ◽

Cristina Pauselli ◽

Harry M. Jol ◽

Francesco Brozzetti

Keyword(s):

Late Quaternary ◽

Active Faults ◽

Normal Fault ◽

Data Interpretation ◽

Seismic Gap ◽

Southern Apennines ◽

Near Surface ◽

Radar Images ◽

Sedimentary Fill ◽

Continental Basin

Abstract. With the aim of unveiling evidence of Late Quaternary faulting, a series of Ground Penetrating Radar (GPR) profiles were acquired across the Campotenese continental basin (Mt. Pollino region) in the southern Apennines active extensional belt (Italy). A set of forty-nine 300 MHz and 500 MHz GPR profiles, traced nearly perpendicular to a buried normal fault, were acquired and carefully processed through a customized workflow. The data interpretation allowed us to reconstruct a pseudo-3D model depicting the boundary between the Mesozoic bedrock and the sedimentary fill of the basin, which were in close proximity to the fault. Once reviewing and defining the GPR signature of faulting, we highlight in our data how near surface alluvial and colluvial sediments appear to be dislocated by a set of conjugate (west and east-dipping) discontinuities that penetrate inside the underlying Triassic dolostones. Close to the contact between the continental deposits and the bedrock, some buried scarps which offset wedge-shaped deposits are interpreted as coseismic ruptures, subsequently sealed by later deposits. Although the use of pseudo-3D GPR data implies more complexity linking the geophysical features among the radar images, we have reconstructed a reliable subsurface fault pattern, discriminating master faults and a series of secondary splays. We believe our contribution provides an improvement in the characterization of active faults in the study area which falls within the Pollino seismic gap and is considered potentially prone to severe surface faulting. Our aim is for our approach and workflow to be of inspiration for further studies in the region as well as for similar high seismic hazard areas characterized by scarcity of near-surface data.

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Active and recent deformation at the Southern Alps – Ligurian basin junction

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/s0016774600023878 ◽

2001 ◽

Vol 80 (3-4) ◽

pp. 255-272 ◽

Cited By ~ 23

Author(s):

C. Larroque ◽

N. Béthoux ◽

E. Calais ◽

F. Courboulex ◽

A. Deschamps ◽

...

Keyword(s):

Western Europe ◽

Active Faults ◽

Southern Alps ◽

Historical Seismicity ◽

Data Set ◽

Seismic Reflection Data ◽

Geological Evidence ◽

Reflection Data ◽

Rate Versus ◽

Ligurian Basin

AbstractThe Southern Alps – Ligurian basin junction is one of the most active seismic areas in Western Europe countries. The topographic and the structural setting of this region is complex because of (i) its position between the high topography of the Southern Alps and the deep, narrow Ligurian oceanic basin, and (ii) the large number of structures inherited from the Alpine orogeny. Historical seismicity reveals about twenty moderate-size earthquakes (up to M=6.0), mostly distributed along the Ligurian coast and the Vésubie valley. A recent geodetic experiment shows a significant strain rate during the last 50 years in the area between the Argentera massif and the Mediterranean coastline. Results of this experiment suggest a N-S shortening of about 2-4 mm/yr over the network, this shortening direction is consistent with the seismological (P-axes of earthquakes) and the microtectonic data. The Pennic front (E-NE of the Argentera massif) and the northern Ligurian margin are the most seismically active areas. In the Nice arc and in the Argentera massif, some seismic lineaments correspond to faults identified in the field (such as theTaggia-Saorge fault or the Monaco-Sospel fault). In the western part of the Alpes Maritimes, no seismic activity is recorded in the Castellane arc. In the field, geological evidence, such as offsets of recent alluvial sediments, recent fault breccia, speleothem deformations, radon anomalies and others indicates recent deformation along these faults. Nevertheless, to this date active fault scarps have not been identified: this probably results from a relatively high erosion rate versus deformation rate and from the lack of Quaternary markers. We also suspect the presence of two hidden active faults, one in the lower Var valley (Nice city area) and the other one at the base of the Argentera crustal thrust-sheet. Offshore, along the northern Ligurian margin, the seismic reflection data shows traces of Quaternary extensional deformation, but the accuracy of the data does not yet allow the construction of a structural map nor does it allow the determination of the continuity between the offshore and onshore structures. From these data set we propose a preliminary map of 11 active faults and we discuss the questions which remain unsolved in the perspective of seismic hazard evaluations.

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Geodynamic and seismotectonic model of a long-lived transverse structure: The Schio-Vicenza Fault System (NE Italy)

10.5194/se-2021-29 ◽

2021 ◽

Author(s):

Dario Zampieri ◽

Paola Vannoli ◽

Pierfrancesco Burrato

Keyword(s):

Active Faults ◽

Strike Slip ◽

Southern Alps ◽

Field Analysis ◽

Fault System ◽

Thrust Belt ◽

Geological Evidence ◽

Slip Activity ◽

Moderate Seismicity ◽

Northern Segment

Abstract. We make a thorough review of geological and seismological data on the long-lived Schio-Vicenza Fault System (SVFS) in northern Italy and present for it a geodynamic and seismotectonic interpretation. The SVFS is a major and high angle structure transverse to the mean trend of the Eastern Southern Alps fold-and-thrust belt, and the knowledge of this structure is deeply rooted in the geological literature and spans for more than a century and a half. The main fault of the SVFS is the Schio-Vicenza Fault (SVF), which has a significant imprint in the landscape across the Eastern Southern Alps and the Veneto-Friuli foreland. The SVF can be divided into a northern segment, extending into the chain north of Schio and mapped up to the Adige Valley, and a southern one, coinciding with the SVF proper. The latter segment borders to the east the Lessini, Berici Mts. and Euganei Hills block, separating this foreland structural high from the Veneto-Friuli foreland, and continues southeastward beneath the recent sediments of the plain via the blind Conselve-Pomposa fault. The structures forming the SVFS have been active with different tectonic phases and different style of faulting at least since the Mesozoic, with a long-term dip-slip component of faulting well defined and, on the contrary, the horizontal component of the movement not well constrained. The SVFS interrupts the continuity of the Eastern Southern Alps thrust fronts in the Veneto sector, suggesting that it played a passive role in controlling the geometry of the active thrust belt and possibly the current distribution of seismic release. As a whole, apart from moderate seismicity along the northern segment and few geological observations along the southern one, there is little evidence to constrain the recent activity of the SVFS. In this context, the SVFS, and specifically its SVF strand, has been referred to as a sinistral strike-slip boundary of the northeastern Adriatic indenter. The review of the historical and instrumental seismicity along the SVFS shows that it does not appear to have generated large earthquakes during the last few hundred years. The moderate seismicity point to a dextral strike-slip activity, which is also corroborated by the field analysis of antithetic Riedel structures of the fault cropping out along the northern segment. Conversely, the southern segment shows geological evidence of sinistral strike-slip activity. The geological and seismological apparently conflicting data can be reconciled considering the faulting style of the southern segment as driven by the indentation of the Adriatic plate, while the opposite style along the northern segment can be explained in a sinistral opening "zipper" model, where intersecting pairs of simultaneously active faults with different sense of shear merge into a single fault system via a zippered section.

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Analysing landforms, borehole logs, and geophysics, for localization and assessment of active faults in the central Vienna Basin (Austria)

10.5194/egusphere-egu2020-18834 ◽

2020 ◽

Author(s):

Michael Weissl ◽

Decker Kurt ◽

Adrian Flores-Orozco ◽

Matthias Steiner

Keyword(s):

Active Faults ◽

Fault System ◽

Tectonic Activity ◽

Fluvial Sediments ◽

River Channels ◽

Vienna Basin ◽

Geothermal Resources ◽

Near Surface ◽

Growth Strata ◽

Fault Scarps

The formation of pull apart basins and normal faulting at splays along the Vienna Basin strike-slip fault system resulted in the dissection of the Pleistocene river terraces of the Danube. Displacements of terrace segments are visible on the surface as fault scarps or dells what allows mapping the system of active faults. Furthermore displacement rates can be estimated from the elevation of the basis and the thickness of Quaternary fluvial sediments.With regard to the prospective utilization of geothermal resources in the area of Vienna a research group was built (Geotief Explore 3D, funded by Wien Energie and FFG) with the objective to identify, map, and assess, Quaternary faults, because such rupture zones are not suitable for the reinjection of thermal water in view of the hazard of triggered earthquakes.Normal splay faults define the eastern and western margins of Pleistocene Danube terraces north of Vienna. The bodies of these terraces are built up of coarse sandy gravel and sand whereas their surfaces are covered with aeolian and alluvial sediments of the last glacial. Tectonic displacements during the Pleistocene left distinct marks in the late glacial landform configuration of the terraces. Therefore many fault scarps and fault related valleys are clearly cognizable in high resolution LiDAR and satellite images.During the last decade three distinct fault scarps of the Vienna Basin Transform Fault situated at the terrace edges could be investigated by trenching and transect analysis. Actual research has the objective to model the 3D geometry of the base of the Quaternary strata (horizon Base Quaternary) from a compilation of shallow drillings and the construction of a regional isopach map showing the thickness of Quaternary (growth-) strata.In the course of research it becomes apparent that within the tectonically subsided areas evidence of neotectonics is overprinted by fluvial sediments and alluvium what hinders accurate localization of faults. However, the sinuosity of palaeochannels in the Danube floodplain seems to be related to tectonics and therefore the pattern of former river channels can be used as sign for tectonic activity during the Pleistocene. In places where signs for active faulting are completely overprinted by fluvial sedimentation and cryoturbation the approved methods for the localization and the assessment of active faults are electrical resistivity tomography and near-surface seismics.

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Signature of coseismic slip in unconsolidated Quaternary gravels, Campo Imperatore, Italy

10.5194/egusphere-egu2020-7192 ◽

2020 ◽

Cited By ~ 1

Author(s):

Matteo Demurtas ◽

Fabrizio Balsamo ◽

Mattia Pizzati

Keyword(s):

Grain Size ◽

Microstructural Analysis ◽

Early Pleistocene ◽

Fault System ◽

Grain Size Analysis ◽

Near Surface ◽

Geological Evidence ◽

Fault Surface ◽

Mechanics Of Faulting ◽

Late Pleistocene To Holocene

Faulting in seismically active regions commonly involves the deformation of unconsolidated to poorly lithified sediments. The seldom occurrence of seismic slip within these deposits appears to be counterintuitive if compared to classic crustal strength profiles that predict a velocity-strengthening behaviour for the first few km of depth. Therefore, the investigation of geological evidence for coseismic faulting within unconsolidated deposits is a key step towards a broader understanding of mechanisms of strain accommodation at shallow to near-surface depth.Here we document the occurrence of minor faults within an unconsolidated colluvial fan at the hanging wall of the Vado di Corno Fault Zone (VCFZ) in the Central Apennines, Italy. The VCFZ is part of the active Campo Imperatore Fault System and accommodated 1-2 km of displacement since Early-Pleistocene. The deposits lie in direct contact with the master fault surface, are Late-Pleistocene to Holocene in age, and consist of angular carbonatic clasts, up to tens of centimetres in size, derived from the dismantling of the VCFZ footwall.Studied faults are organised in two main sets: (i) subvertical, N-S trending dip-slip faults, parallel to the fan long axis, and (ii) WNW-ESE striking faults, synthetic and antithetic to the VCFZ master fault surface (N195/55&#176;). Both fault sets are striated and commonly have positive relief with respect to the host deposits. Some of these faults show a fault core up to 5-6 cm thick, bounded by discrete and well-developed polished surfaces. Locally, particularly in fine-grained gravel levels, the occurrence of extreme strain localisation (i.e. millimetric ultracataclastic layers with truncated clasts) along mirror-like fault surfaces is observed. Grain size analysis of undeformed and faulted gravels shows an increase of the power-law exponent (fractal dimension) from values of D = 1.65-2.2 in the undeformed host rocks up to D = 2.9 in the cataclastic slip zones. Microstructural analysis suggests cataclasis is the main deformation mechanism leading to grain size reduction along faults, whereas intergranular pressure solution becomes widespread moving away from the slip zone where fluid circulation was present.Collectively, our observations provide new insights into the mechanics of faulting and strain accommodation in the shallowest part of the crust (< 1 km) and new evidence to understand the propagation of seismic ruptures within shallow unconsolidated deposits.

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Mixed-Mode Seismic Slip and Aseismic Creep on a Highly Active Low-Angle Normal Fault System in Papua New Guinea

10.5194/egusphere-egu2020-230 ◽

2020 ◽

Author(s):

James Biemiller ◽

Laura Wallace ◽

Luc Lavier

Keyword(s):

Papua New Guinea ◽

Normal Fault ◽

New Guinea ◽

Fault System ◽

Normal Faults ◽

Fault Mechanics ◽

Fault Rocks ◽

Near Surface ◽

Geological Evidence ◽

Seismic Slip

Whether low-angle normal faults (LANFs; dip < 30&#176;) slip in large earthquakes or creep aseismically is a longstanding problem in fault mechanics. Although abundant in the geologic record, active examples of these enigmatic &#8216;misoriented&#8217; structures are rare and extension rates across them are typically less than a few mm/yr. As such, geodetic and seismological observations of LANFs are sparse and can be difficult to interpret in terms of earthquake cycles. With a long-term slip rate of ~1 cm/yr, the Mai&#8217;iu fault in Papua New Guinea may be the world&#8217;s most active LANF and thus offers an outstanding natural laboratory to evaluate seismic vs. aseismic behavior of LANFs. Here, we use new results from a campaign GPS network to determine the degree of locking vs. aseismic creep on the Mai&#8217;iu fault and evaluate these results in the context of geological evidence for mixed seismic and aseismic slip in exhumed Mai&#8217;iu fault rocks.We derive velocities from GPS measurements with 3-4 km station spacing above the shallowest portions of the fault, which dips 21-25&#176; at the surface. Dislocation modeling of these velocities is consistent with 6-8 mm/yr of horizontal extension, corresponding to ~1 cm/yr dip-slip rates on a 27-35&#176;-dipping fault. Strain rates and vertical derivatives of horizontal stress rates derived from these velocities confirm localized extension across the fault. We compare and evaluate two interseismic locking models that fit the data best: one in which the fault deforms by shallow near-surface creep updip of a deeper zone of increased interseismic coupling which soles into a steadily creeping shear zone at depth, and one in which the fault creeps steadily downdip of a shallowly locked patch. These results combined with field and microstructural evidence from the exhumed fault rocks suggest that the fault slips by a mixture of brittle frictional (seismic slip, fracturing, and cataclastic creep) and viscous (stress-driven dissolution-precipitation creep, or pressure solution) processes. Using depth-constrained mechanical properties and stress conditions inferred from exhumed fault rocks, we model the time-dependent competition between frictional slip and viscous creep to assess where and how elastic strain accumulates along the Mai&#8217;iu fault, and whether the fault is capable of hosting or nucleating earthquakes.

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Evidence of active tectonics in the Augusta Basin (eastern Sicily, Italy) by Chirp sub-bottom sonar investigation

Annals of Geophysics ◽

10.4401/ag-6371 ◽

2014 ◽

Vol 56 (5) ◽

Author(s):

Claudia Pirrotta ◽

Maria Serafina Barbano ◽

Daniela Pantosti ◽

Paolo Marco De Martini

Keyword(s):

Active Faults ◽

Active Tectonics ◽

Fault System ◽

Normal Faults ◽

Strong Earthquakes ◽

The Holocene ◽

Regional Seismicity ◽

Holocene Sediments ◽

Recent Activity ◽

Fault Scarps

A Chirp sub-bottom sonar investigation was performed in the 150 km2 wideAugustaBasin, located in the eastern Sicily Ionian coast, a region repeatedly hit by strong earthquakes in historical time, with the end of identifying possible evidence of active tectonics. Seismostratigraphy shows two main reflectors: R1, formed between 60 ka and 19 ka BP, and R2 that is the top of the Holocene deposits. Morphobathymetry reveals two marine abrasion surfaces, Ms1 and Ms2 that are related to the 35 ka and 25 ka BP marine high stills, respectively. This study highlights that R1 and the onlapping Holocene sediments are affected by normal and probably strike-slip faulting. A set of NE-SW striking normal faults represents the oldest system, because they dislocate R1 but not the Holocene deposit. NNW-SSE striking extensional faults show more recent activity since they displace Ms2, the Holocene sequence and cause seafloor up-warping. NE-SW normal faults produce asymmetric basins where the Holocene deposits form wedged bodies. ENE-WSW left-lateral faults dissect a paleo-island, Ms2 and the NNW-SSE fault system. Moreover, seismically induced slumps involving the Holocene sediments, are found at the foot of some fault scarps. The presence of slumped bodies and active faults indicates ongoing deformation in the basin. Identified active faults are consistent with the main regional Malta Escarpment fault system, of which they can be considered as the incipient westernmost extension. This study supports the hypothesis that the Malta Escarpment is active and can be responsible for the regional seismicity.

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