scholarly journals The Altotiberina Low-Angle Normal Fault (Italy) Can Fail in Moderate-Magnitude Earthquakes as a Result of Stress Transfer from Stable Creeping Fault Area

Geosciences ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 144
Author(s):  
Luigi Vadacca
Keyword(s):  
Stress Transfer ◽  
Normal Fault ◽  
Normal Faults ◽  
Seismic Potential ◽  
Interseismic Coupling ◽  
Rate And State Friction ◽  
Seismic Cycles ◽  
Dip Angle ◽  
Locked Fault ◽  
Moderate Magnitude

Geological and geophysical evidence suggests that the Altotiberina low-angle (dip angle of 15–20 ° ) normal fault is active in the Umbria–Marche sector of the Northern Apennine thrust belt (Italy). The fault plane is 70 km long and 40 km wide, larger and hence potentially more destructive than the faults that generated the last major earthquakes in Italy. However, the seismic potential associated with the Altotiberina fault is strongly debated. In fact, the mechanical behavior of this fault is complex, characterized by locked fault patches with a potentially seismic behavior surrounded by aseismic creeping areas. No historical moderate (5 ≤ Mw ≤ 5.9) nor strong (6 ≤ Mw ≤ 6.9)-magnitude earthquakes are unambiguously associated with the Altotiberina fault; however, microseismicity is scattered below 5 km within the fault zone. Here we provide mechanical evidence for the potential activation of the Altotiberina fault in moderate-magnitude earthquakes due to stress transfer from creeping fault areas to locked fault patches. The tectonic extension in the Umbria–Marche crustal sector of the Northern Apennines is simulated by a geomechanical numerical model that includes slip events along the Altotiberina and its main seismic antithetic fault, the Gubbio fault. The seismic cycles on the fault planes are simulated by assuming rate-and-state friction. The spatial variation of the frictional parameters is obtained by combining the interseismic coupling degree of the Altotiberina fault with friction laboratory measurements on samples from the Zuccale low- angle normal fault located in the Elba island (Italy), considered an older exhumed analogue of Altotiberina fault. This work contributes a better estimate of the seismic potential associated with the Altotiberina fault and, more generally, to low-angle normal faults with mixed-mode slip behavior.

scholarly journals 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

2021 ◽  
Vol 9 ◽  
Author(s):  
Federica Ferrarini ◽  
Rita de Nardis ◽  
Francesco Brozzetti ◽  
Daniele Cirillo ◽  
J Ramón Arrowsmith ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Tectonic Setting ◽  
Central Italy ◽  
Stress Transfer ◽  
Normal Fault ◽  
Normal Faults ◽  
Coulomb Stress ◽  
Seismic Sequence ◽  
Seismogenic Fault ◽  
Seismogenic Source

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 (MW 5.9) 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.

Strain Analysis of Transfer Faults in Extending Regions: Inferences from Micropolar Theory

2021 ◽  
Author(s):  
Bülent Tokay ◽  
Erdin Bozkurt
Keyword(s):  
Strain Analysis ◽  
Normal Fault ◽  
Normal Faults ◽  
Block Rotation ◽  
Micropolar Theory ◽  
Orthogonal Direction ◽  
Extensional Tectonic ◽  
Series Of Experiments ◽  
Dip Angle ◽  
Transfer Faults

<p>Transfer faults are generally identified as transversely oriented discrete faults linking normal fault segments in extensional tectonic settings.  The presence of the transfer faults in fault networks provides displacement transfer between the normal faults. The role and tectonic significance of transfer faults in overall extensional deformation of the upper crust is however not known very well. Micropolar theory extended by J-2 plasticity facilitates evaluation of a deforming medium in which cataclastic flow takes place with respect to each component of deformation. In this study, a series of experiments based on the Micropolar theory are performed, using fault-slip patterns, to better understand interplay among dip angle of normal and transfer faults connecting to each other, angle of linkage, and extensional direction. Synthetic linkage cases are created systematically considering various orientation of both faults sharing common stretching direction.<br>Our findings reveal that in orthogonal and oblique linkage cases, 3D strain field is mostly observed; a few cases exhibit plane strain. All cases are subjected to simple shearing. In cases of orthogonal linkage, extensional direction is predominantly oblique to the strike of the normal faults. Many of these cases have no block rotation (microrotation) independent from macrorotation. No particular relationship between changing dip amount of faults and direction of extension is observed. In cases of oblique linkage, (sub)orthogonal direction of extension appear in nearly half of experiments, especially those including normal faults dipping less than 60˚. The frequency of non-zero microrotation is seen apparently more than that in orthogonal linkage cases.<br>The study represents that structural togetherness of the transfer and normal faults essentially can accommodate complete micropolar strain in a region. This further suggests that not only the normal faults but the transfer faults should also be considered as major primary structural elements in extending domains.</p>

The 4 December 2015 Mw 7.1 Normal-Faulting Antarctic Plate Earthquake and Its Seismotectonic Implications

2020 ◽  
Vol 110 (3) ◽  
pp. 1090-1100
Author(s):  
Ronia Andrews ◽  
Kusala Rajendran ◽  
N. Purnachandra Rao
Keyword(s):  
Body Wave ◽  
Focal Depth ◽  
Normal Fault ◽  
Normal Faults ◽  
Oceanic Plate ◽  
Normal Faulting ◽  
Transform Faults ◽  
Wave Inversion ◽  
Spreading Ridges ◽  
Southeast Indian Ridge

ABSTRACT Oceanic plate seismicity is generally dominated by normal and strike-slip faulting associated with active spreading ridges and transform faults. Fossil structural fabrics inherited from spreading ridges also host earthquakes. The Indian Oceanic plate, considered quite active seismically, has hosted earthquakes both on its active and fossil fault systems. The 4 December 2015 Mw 7.1 normal-faulting earthquake, located ∼700  km south of the southeast Indian ridge in the southern Indian Ocean, is a rarity due to its location away from the ridge, lack of association with any mapped faults and its focal depth close to the 800°C isotherm. We present results of teleseismic body-wave inversion that suggest that the earthquake occurred on a north-northwest–south-southeast-striking normal fault at a depth of 34 km. The rupture propagated at 2.7  km/s with compact slip over an area of 48×48  km2 around the hypocenter. Our analysis of the background tectonics suggests that our chosen fault plane is in the same direction as the mapped normal faults on the eastern flanks of the Kerguelen plateau. We propose that these buried normal faults, possibly the relics of the ancient rifting might have been reactivated, leading to the 2015 midplate earthquake.

Earthquake ruptures tied to long-lived plate interface deformation 

2021 ◽  
Author(s):  
Nadaya Cubas ◽  
Philippe Agard ◽  
Roxane Tissandier
Keyword(s):  
Subduction Zones ◽  
Earthquake Hazard ◽  
Mechanical Analysis ◽  
Physical Parameters ◽  
Plate Interface ◽  
Interface Deformation ◽  
Earthquake Hazard Assessment ◽  
Interseismic Coupling ◽  
Rate And State Friction

<p>Predicting the spatial extent of mega-earthquakes is an essential ingredient of earthquake hazard assessment. In subduction zones, this prediction mostly relies on geodetic observations of interseismic coupling. However, such models face spatial resolution issues and are of little help to predict full or partial ruptures of highly locked patches. Coupling models are interpreted in the framework of the rate-and-state friction laws. However, these models are too idealized to take into account the effects of a geometrically or rheologically complex plate interface. In this study, we show, from the critical taper theory and a mechanical analysis of the topography, that all recent mega-earthquakes of the Chilean subduction zone are surrounded by distributed interplate deformation emanating from either underplating or basal erosion. This long-lived plate interface deformation builds up stresses ultimately leading to earthquake nucleation. Earthquakes then propagate along a relatively smooth surface and are stopped by segments of heterogeneously distributed deformation. Our results are consistent with long-term features of the subduction margin, with observed short-term deformation as well as physical parameters of recovered subducted fragments. They also provide an explanation for the apparent mechanical segmentation of the megathrust, reconciling many seemingly contradictory observations on the short- and long-term deformation. Consequently, we propose that earthquake segmentation relates to the distribution of deformation along the plate interface and that slip deficit patterns reflect the along-dip and along-strike distribution of the plate interface deformation. Topography would therefore mirror plate interface deformation and could serve to improve earthquake rupture prediction.</p>

scholarly journals Coulomb stress transfer and fault interaction over millennia on non-planar active normal faults: the Mw 6.5–5.0 seismic sequence of 2016–2017, central Italy

2017 ◽  
Vol 210 (2) ◽  
pp. 1206-1218 ◽  
Author(s):  
Zoe K. Mildon ◽  
Gerald P. Roberts ◽  
Joanna P. Faure Walker ◽  
Francesco Iezzi
Keyword(s):  
Main Shock ◽  
Central Italy ◽  
Stress Transfer ◽  
Historical Record ◽  
Normal Faults ◽  
Coulomb Stress ◽  
Seismic Sequence ◽  
Fault Interaction ◽  
Slip Rates ◽  
Stress Changes

Abstract In order to investigate the importance of including strike-variable geometry and the knowledge of historical and palaeoseismic earthquakes when modelling static Coulomb stress transfer and rupture propagation, we have examined the August–October 2016 A.D. and January 2017 A.D. central Apennines seismic sequence (Mw 6.0, 5.9, 6.5 in 2016 A.D. (INGV) and Mw 5.1, 5.5, 5.4, 5.0 in 2017 A.D. (INGV)). We model both the coseismic loading (from historical and palaeoseismic earthquakes) and interseismic loading (derived from Holocene fault slip-rates) using strike-variable fault geometries constrained by fieldwork. The inclusion of the elapsed times from available historical and palaeoseismological earthquakes and on faults enables us to calculate the stress on the faults prior to the beginning of the seismic sequence. We take account the 1316–4155 yr elapsed time on the Mt. Vettore fault (that ruptured during the 2016 A.D. seismic sequence) implied by palaeoseismology, and the 377 and 313 yr elapsed times on the neighbouring Laga and Norcia faults respectively, indicated by the historical record. The stress changes through time are summed to show the state of stress on the Mt. Vettore, Laga and surrounding faults prior to and during the 2016–2017 A.D. sequence. We show that the build up of stress prior to 2016 A.D. on strike-variable fault geometries generated stress heterogeneities that correlate with the limits of the main-shock ruptures. Hence, we suggest that stress barriers appear to have control on the propagation and therefore the magnitudes of the main-shock ruptures.

Normal fault growth and segment linkage in a gravitationally detached delta system: evidence from 3D seismic reflection data from the Ceduna Sub-basin, Great Australian Bight

2015 ◽  
Vol 55 (2) ◽  
pp. 467
Author(s):  
Alexander Robson ◽  
Rosalind King ◽  
Simon Holford
Keyword(s):  
Seismic Reflection ◽  
Fault Plane ◽  
Structural Evolution ◽  
Normal Fault ◽  
Fault System ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Listric Fault ◽  
Dip Angle ◽  
Fault Growth

The authors used three-dimensional (3D) seismic reflection data from the central Ceduna Sub-Basin, Australia, to establish the structural evolution of a linked normal fault assemblage at the extensional top of a gravitationally driven delta system. The fault assemblage presented is decoupled at the base of a marine mud from the late Albian age. Strike-linkage has created a northwest–southeast oriented assemblage of normal fault segments and dip-linkage through Santonian strata, which connects a post-Santonian normal fault system to a Cenomanian-Santonian listric fault system. Cenomanian-Santonian fault growth is on the kilometre scale and builds an underlying structural grain, defining the geometry of the post-Santonian fault system. A fault plane dip-angle model has been created and established through simplistic depth conversion. This converts throw into fault plane dip-slip displacement, incorporating increasing heave of a listric fault and decreasing in dip-angle with depth. The analysis constrains fault growth into six evolutionary stages: early Cenomanian nucleation and radial growth of isolated fault segments; linkage of fault segments by the latest Cenomanian; latest Santonian Cessation of fault growth; erosion and heavy incision during the continental break-up of Australia and Antarctica (c. 83 Ma); vertically independent nucleation of the post-Santonian fault segments with rapid length establishment before significant displacement accumulation; and, continued displacement into the Cenozoic. The structural evolution of this fault system is compatible with the isolated fault model and segmented coherent fault model, indicating that these fault growth models do not need to be mutually exclusive to the growth of normal fault assemblages.

Basement-involved inversion at the Appalachian structural front, western Newfoundland: an interpretation of seismic reflection data with implications for petroleum prospectivity

2004 ◽  
Vol 52 (3) ◽  
pp. 215-233 ◽  
Author(s):  
Glen S. Stockmal ◽  
Art Slingsby ◽  
John W.F. Waldron
Keyword(s):  
Seismic Reflection ◽  
Hanging Wall ◽  
Normal Fault ◽  
Hydrocarbon Exploration ◽  
Normal Faults ◽  
Apparent Magnitude ◽  
Seismic Reflection Data ◽  
The Public ◽  
Reflection Data ◽  
New Interpretation

Abstract Recent hydrocarbon exploration in western Newfoundland has resulted in six new wells in the Port au Port Peninsula area. Port au Port No.1, drilled in 1994/95, penetrated the Cambro-Ordovician platform and underlying Grenville basement in the hanging wall of the southeast-dipping Round Head Thrust, terminated in the platform succession in the footwall of this basement-involved inversion structure, and discovered the Garden Hill petroleum pool. The most recent well, Shoal Point K-39, was drilled in 1999 to test a model in which the Round Head Thrust loses reverse displacement to the northeast, eventually becoming a normal fault. This model hinged on an interpretation of a seismic reflection survey acquired in 1996 in Port au Port Bay. This survey is now in the public domain. In our interpretation of these data, the Round Head Thrust is associated with another basement-involved feature, the northwest-dipping Piccadilly Bay Fault, which is mapped on Port au Port Peninsula. Active as normal faults in the Taconian foreland, both these faults were later inverted during Acadian orogenesis. The present reverse offset on the Piccadilly Bay Fault was previously interpreted as normal offset on the southeast-dipping Round Head Thrust. Our new interpretation is consistent with mapping on Port au Port Peninsula and north of Stephenville, where all basement-involved faults are inverted and display reverse senses of motion. It also explains spatially restricted, enigmatic reflections adjacent to the faults as carbonate conglomerates of the Cape Cormorant Formation or Daniel’s Harbour Member, units associated with inverted thick-skinned faults. The K-39 well, which targeted the footwall of the Round Head Thrust, actually penetrated the hanging wall of the Piccadilly Bay Fault. This distinction is important because the reservoir model invoked for this play involved preferential karstification and subsequent dolomitization in the footwalls of inverted thick-skinned faults. The apparent magnitude of structural inversion across the Piccadilly Bay Fault suggests other possible structural plays to the northeast of K-39.

Interseismic coupling, seismic potential, and earthquake recurrence on the southern front of the Eastern Alps (NE Italy)

2014 ◽  
Vol 119 (5) ◽  
pp. 4448-4468 ◽  
Author(s):  
D. Cheloni ◽  
N. D'Agostino ◽  
G. Selvaggi
Keyword(s):  
Eastern Alps ◽  
Earthquake Recurrence ◽  
Seismic Potential ◽  
Ne Italy ◽  
Interseismic Coupling

Tectonic evolution of the Gediz Graben: field evidence for an episodic, two-stage extension in western Turkey

2004 ◽  
Vol 141 (1) ◽  
pp. 63-79 ◽  
Author(s):  
ERDİN BOZKURT ◽  
HASAN SÖZBİLİR
Keyword(s):  
Normal Fault ◽  
Geological Mapping ◽  
Normal Faults ◽  
High Angle ◽  
Western Turkey ◽  
Menderes Massif ◽  
Total Displacement ◽  
Field Evidence ◽  
Back Arc ◽  
Short Time

Western Turkey is one of the most spectacular regions of widespread active continental extension in the world. The most prominent structures of this region are E–W-trending grabens (e.g. Gediz and Büyük Menderes grabens) and intervening horsts, exposing the Menderes Massif. This paper documents the result of a recent field campaign (field geological mapping and structural analysis) along the southern margin of the modern Gediz Graben of Pliocene (∼ 5 Ma) age. This work provides field evidence that the presently low-angle ductile-brittle detachment fault is cut and displaced by the high-angle graben-bounding normal faults with total displacement exceeding 2.0 km. The evolution of the N–S extension along the Gediz Graben occurred during two episodes, each characterized by a distinct structural styles: (1) rapid exhumation of Menderes Massif in the footwall of low-angle normal fault (core-complex mode) during the Miocene; (2) late stretching of crust producing E–W grabens along high-angle normal faults (rift mode) during Pliocene–Quaternary times, separated by a short-time gap. The later phase is characterized by the deposition of now nearly horizontal sediments of Pliocene age in the hanging walls of the high-angle normal faults and present-day graben floor sediments. The evolution of extension is at variance with orogenic collapse and/or back-arc extension followed by the combined effect of tectonic escape and subduction rollback processes along the Aegean-Cyprean subduction zone. Consequently, it is misleading to describe the Miocene sediments exhumed on shoulders of the Gediz Graben as simple graben fill.

scholarly journals The Stratigraphy and Structure of the Madamar-Salakh-Qusaybah Range and Natif-Fahud Area in the Oman Mountains

1996 ◽  
Vol 1 (1) ◽  
pp. 1 ◽  
Author(s):  
S.S. Hanna ◽  
J.D. Smewing
Keyword(s):  
Late Cretaceous ◽  
Debris Flows ◽  
Normal Fault ◽  
Normal Faults ◽  
Void Space ◽  
The South ◽  
Oman Mountains ◽  
Oil Flow ◽  
Structural Growth ◽  
Positive Feature

Melanges and debris flows with clasts derived from the top of the Natih Formation found in shales in the base of the Aruma Group indicate that a period of Structural growth on the platform took place during Aruma deposition in the Late Cretaceous. In this respect the platform in the Jebel Salakh area may have undergone a similar period of structural growth in the Late Cretaceous to the Fahud area where a syn-Aruma normal fault down throwing to the South accounts for a difference in the stratigraphic thickness of the Aruma of 1 km. A younger series of debris flows in the Aruma of the Sufrat al Khays area to the South of Jehel Salakh is dated as Campanian/Maastrichtian. The clasts in these flows were derived exclusively from the Simsima limestones. Natih-derived elasts are conspicuously absent. This is taken to indicate that the Madamar-Salakh Qusaybah range was covered by Aruma sediments at this time and did not form the distinctive positive feature seen at present - i.e. Madamar-Salakh-Qusaybah range folding though partly Late Cretaceous is mainly Post-Manslrichtian in age. This Post Maastrichtian event in the Madamar-Salakh-Qusaybah range produced a series of doubly-plunging anticlines in the Cretaceous strata- These folds show a high degree of brittle extension in the form of normal faults and extensional fractures, The faults are delineated by fault gouge with visibly interconnected void space. In the subsurface, if such fractures were developed in a fold closure similar to those seen at the surface in the Madamar-Salakh-Qusaybah range. then they could provide preferred conduits for oil flow and the harrier to fluid flow provided by the Aruma shale seal could lead to a hydrocarbon accumulation.

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