Academic literature on the topic 'Fault zones – Maine'
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Journal articles on the topic "Fault zones – Maine"
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Keen, C. E., W. A. Kay, D. Keppie, F. Marillier, G. Pe-Piper, and J. W. F. Waldron. "Deep seismic reflection data from the Bay of Fundy and Gulf of Maine: tectonic implications for the northern Appalachians." Canadian Journal of Earth Sciences 28, no. 7 (July 1, 1991): 1096–111. http://dx.doi.org/10.1139/e91-099.
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Three deep-penetration seismic reflection profiles were collected off southwest Nova Scotia to determine the crustal structure and geometry beneath the Avalon and Meguma zones of the Appalachian Orogen in Canada. Onshore geological features have been traced seawards using new gravity and magnetic anomaly maps. The seismic data can also be correlated with the previous United States Geological Survey profile in the central Gulf of Maine.Two seismically distinct lower crustal blocks are identified: the Avalon and Sable lower crustal blocks, separated by a major north-dipping reflection zone that cuts the entire crust. The recognition of the Sable block adds a fourth block to the three already identified in the Canadian Appalachians. The Sable block is overlain by the Meguma Zone. The Avalon Zone overlies at least the northern part of the Avalon lower crustal block. Although offshore extension of geological features is not unequivocal, it appears that a north-dipping reflection zone southwest of Nova Scotia marks the site of Devonian thrusting of Avalon Zone over Meguma Zone. In the Bay of Fundy to the north, two south-dipping reflection zones are interpreted as major thrusts, possibly placing Avalon lower crust over a unit with different tectonic affinities. The Fundy Fault is a Carboniferous thrust within the Avalon block along the coast of New Brunswick; this was reactivated during Mesozoic extension as a transtensional fault. Extensional displacement farther southwest was probably accommodated along east-west-trending faults and small rift basins associated with them.
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Sullivan, Walter A., and Emma J. O’Hara. "A natural example of brittle-to-viscous strain localization under constant-stress conditions: a case study of the Kellyland fault zone, Maine, USA." Geological Magazine 159, no. 3 (November 15, 2021): 421–40. http://dx.doi.org/10.1017/s0016756821001035.
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AbstractThis article integrates field, powder X-ray diffraction and microstructural data to constrain deformation mechanisms in and the rheology of granite-derived fault rocks exposed along the SE side of the crustal-scale, strike-slip Kellyland fault zone. Deformation in this area of the Kellyland fault zone localized during cooling and is marked by (1) foliated granite, (2) a ∼50 m wide band of pulverized foliated granite, (3) a ∼2.8 m wide breccia zone hosting coeval shear zones, and (4) a >100 m wide ultramylonite zone. The earliest fabric in the foliated granite is defined by elongated quartz grains, and quartz dislocation creep was the rate-controlling deformation mechanism. Seismogenic deformation initiated when recorded flow stresses reached 96–104 MPa at temperatures of 400–450 °C and is marked by coeval pulverization and formation of breccia. Interseismic viscous creep at similar flow stresses is recorded by mutual cross-cutting relationships between breccia-hosted shear zones, brittle fractures and pseudotachylyte. Field and microstructural observations indicate that breccia-hosted shear zones are low-strain equivalents of the >100 m wide ultramylonite zone, and seismogenic deformation abated as the ultramylonite formed. The rheology of ultramylonites was governed by grain-size-sensitive creep at 112–124 MPa flow stresses. Hence, from the onset of seismogenesis, the Kellyland fault zone was likely a constant-stress system wherein the rate-controlling mechanism shifted from episodic seismogenic slip and interseismic viscous creep to steady state grain-size-sensitive creep in ultramylonites derived from brittle fault rocks. Flow stresses recorded by these rocks also imply that the whole zone was relatively weak if the brittle–viscous transition and uppermost viscous zone are the strongest part of the crust.
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Marple, Ronald T., and James D. Hurd. "LiDAR and other evidence for the southwest continuation and Late Quaternary reactivation of the Norumbega Fault System and a cross-cutting structure near Biddeford, Maine, USA." Atlantic Geology 55 (October 28, 2019): 323–59. http://dx.doi.org/10.4138/atlgeol.2019.011.
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High-resolution LiDAR (light detection and ranging) images reveal numerous NE-SW-trending geomorphic lineaments that may represent the southwest continuation of the Norumbega fault system (NFS) along a broad, 30- to 50-km-wide zone of brittle faults that continues at least 100 km across southern Maine and southeastern New Hampshire. These lineaments are characterized by linear depressions and valleys, linear drainage patterns, abrupt bends in rivers, and linear scarps. The Nonesuch River, South Portland, and Mackworth faults of the NFS appear to continue up to 100 km southwest of the Saco River along prominent but discontinuous LiDAR lineaments. Southeast-facing scarps that cross drumlins along some of the lineaments in southern Maine suggest that late Quaternary displacements have occurred along these lineaments. Several NW-SE-trending geomorphic features and geophysical lineaments near Biddeford, Maine, may represent a 30-km-long, NW-SE-trending structure that crosses part of the NFS. Brittle NWSE-trending, pre-Triassic faults in the Kittery Formation at Biddeford Pool, Maine, support this hypothesis.
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Doll, William E., Carol D. Rea, John E. Ebel, Sandra J. Craven, and John J. Cipar. "Analysis of Shallow Microearthquakes in the South Sebec Seismic Zone, Maine, 1989–1990." Seismological Research Letters 63, no. 4 (October 1, 1992): 557–66. http://dx.doi.org/10.1785/gssrl.63.4.557.
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Abstract Fifteen years of regional monitoring by the New England Seismic Network indicated a locally high level of seismicity near South Sebec, between the towns of Milo and Dover-Foxcroft in central Maine. Most of the events were located in a diffuse zone south of the distinctive, ENE trending Harriman Pond Fault (HPF) which is indicated by brittle deformation in outcrop and is represented as a depression in topographic maps and satellite images. A portable network consisting of both digital and analog instruments was deployed during the summers of 1989 and 1990 in order to characterize the pattern of the microearthquakes and to determine high-resolution epicenters, depths, and fault plane solutions. Seventy-three events were detected during the experiment, of which 28 could be located. Many of the events south of the fault lie along a NNW trending line which has no major expression in the surface geology. Only, a few of the events are subparallel to the HPF. The first motion data were insufficient for the determination of any fault plane solutions.
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Doll, William E., William J. Domoracki, John K. Costain, Cahit Çoruh, Allan Ludman, and John T. Hopeck. "Seismic reflection evidence for the evolution of a transcurrent fault system: The Norumbega fault zone, Maine." Geology 24, no. 3 (1996): 251. http://dx.doi.org/10.1130/0091-7613(1996)024<0251:srefte>2.3.co;2.
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West Jr, David P., Charles V. Guidotti, and Daniel R. Lux. "Silurian orogenesis in the western Penobscot Bay region, Maine." Canadian Journal of Earth Sciences 32, no. 11 (November 1, 1995): 1845–58. http://dx.doi.org/10.1139/e95-142.
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New 40Ar/39Ar mineral ages from rocks collected west of Penobscot Bay, Maine, indicate this region was regionally deformed, metamorphosed to amphibolite facies conditions, and intruded by plutons in Silurian times rather than in the Devonian as previously assumed. Disturbed hornblende age spectra, along with the presence of some Devonian felsic plutons and extensive retrograde metamorphic textures do suggest, however, that these rocks were subsequently affected by low-grade Devonian thermal events. In sharp contrast, rocks west of the Sennebec Pond thrust fault, a major tectono-stratigraphic boundary in this region, lack a significant Silurian tectono-thermal signature, and instead record the effects of intense Devonian deformation and high-grade regional metamorphism. The data suggest the two regions experienced very different pre-Devonian histories and were most likely juxtaposed by the Sennebec Pond thrust fault in latest Silurian to Early Devonian time. Rocks now exposed east of the Sennebec Pond fault probably occupied much higher structural levels during Devonian orogenesis and were not subjected to the same intense Devonian deformation and metamorphism as those rocks now found to the west of this structure. The Silurian tectonism now recognized in this region bears striking resemblance to events of similar age recorded along the northwest margin of the Avalon composite terrane throughout much of Atlantic Canada. This greatly extends the zone of Silurian orogenesis in the northern Appalachians and requires that previous models of New England middle Paleozoic tectonism be significantly revised.
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Ludman, Allan. "Evolution of a transcurrent fault system in shallow crustal metasedimentary rocks: the Norumbega fault zone, eastern Maine." Journal of Structural Geology 20, no. 1 (January 1998): 93–107. http://dx.doi.org/10.1016/s0191-8141(97)00094-1.
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Wiebe, Robert A., Stephan Kolzenburg, Shane M. Rooyakkers, and John Stix. "Plutonic record of a caldera-forming silicic eruption: The shatter zone of the Cadillac Mountain granite, coastal Maine." Geosphere 17, no. 1 (January 6, 2021): 1–22. http://dx.doi.org/10.1130/ges02252.1.
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Abstract Although it is widely accepted that large silicic calderas are associated with voluminous synvolcanic intrusive complexes at depth, geological evidence for caldera-forming eruptions preserved in plutonic rocks has largely been elusive. Here, we document a rare example of such evidence in the Cadillac Mountain intrusive complex, Maine (USA), where erosion has revealed a remarkable marginal “shatter zone” that records evidence for a major caldera-forming eruption. This shatter zone, up to >1 km wide, is bounded by a steep ring fault at its outer margin, which grades inward into Cadillac Mountain granite. Its outer margins are characterized by intensely brecciated and deformed country rock injected by felsite veins, reflecting explosive fragmentation associated with eruptive decompression. This marginal facies grades inward to a chaotic mélange of variably rounded and remelted country rock blocks in granitic matrix, reflecting debris eroded from ring fault conduit walls and milled in an eruptive jet before collapsing onto crystal mush. Further inward, blocks up to 80 m in size were stoped from the collapsing chamber roof and settled onto strong mush. Textural and chemical variations in the shatter zone matrix reveal syneruptive ascent of distinct silicic and more mafic magma from depth, which was likely drawn through the highly permeable shatter zone toward areas of low pressure beneath active vents. The Cadillac Mountain shatter zone provides clear evidence for a major eruption preserved in the plutonic record and supports the origin of some granites as the cumulate roots of large silicic volcanic systems.
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West, David P., and Mary K. Roden-Tice. "Late Cretaceous reactivation of the Norumbega fault zone, Maine: Evidence from apatite fission-track ages." Geology 31, no. 7 (2003): 649. http://dx.doi.org/10.1130/0091-7613(2003)031<0649:lcrotn>2.0.co;2.
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West, David P., and Daniel R. Lux. "Dating mylonitic deformation by the 40Ar-39Ar method: An example from the Norumbega Fault Zone, Maine." Earth and Planetary Science Letters 120, no. 3-4 (December 1993): 221–37. http://dx.doi.org/10.1016/0012-821x(93)90241-z.
Full textDissertations / Theses on the topic "Fault zones – Maine"
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Authemayou, Christine. "Partitionnement de la convergence oblique en zone de collision : Exemple de la chaîne du Zagros (Iran)." Phd thesis, Aix-Marseille 3, 2006. http://tel.archives-ouvertes.fr/tel-00071020.
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Ce travail présente les résultats de l'analyse tectonique des deux décrochements dextres majeurs de la chaîne du Zagros formée lors de la collision des plaques Arabie/Eurasie au Néogène. La Main Recent Fault (MRF), marquant la limite nord-occidentale du Zagros, accommode une partie de l'obliquité de la convergence Arabie/Eurasie. Dans le Zagros central, la faille de Kazerun (KF), faille de socle de direction NS, recoupe entièrement la largeur de la chaîne. Elle est associée à des failles décrochantes, dont la faille de Karehbas, qui définissent un éventail ouvert vers le SE et pointant vers la terminaison SE de la MRF.L'étude structurale et cinématique de ces failles permet de documenter une ré-organisation des structures et de la déformation dans le Zagros au cours du Néogène. Entre 9 et 5 Ma, la déformation transpressive distribuée à l'arrière de la chaîne a cessé au moment de la mise en place de la MRF impliquant le partitionnement de la convergence. Vers 3 Ma, la terminaison SE de la MRF s'est connectée à la terminaison nord de la KF. Par l'intermédiaire des failles du Zagros central formant le système en éventail, le déplacement de la MRF se voit dès lors distribué vers l'est sur les plis et les chevauchements du Zagros oriental. A l'échelle du Zagros, ces failles peuvent donc être perçues comme formant la terminaison en queue de cheval de la MRF.
L'analyse de marqueurs géomorphologiques datés (datation 36Cl, datation U/Th) et décalés par ces failles permet de déterminer le taux de déplacement horizontal le long des décrochements sur les derniers 140 ka. Il est de 6 ± 1 mm/an pour la MRF. Il varie du nord au sud de la KF de 4 mm/an à presque 0 mm/an. Il est de 6 ± 1.5 mm/an pour la faille de Karebhas. Ces vitesses, au regard des données GPS disponibles, permettent de conclure à un partitionnement total de l'obliquité de la convergence le long de la MRF, et à un transfert progressif du mouvement de la MRF du NW vers le SE sur les terminaisons courbées et chevauchantes des trois zones de failles de la KF et des failles associées.
L'activation de ce système de failles dextres est liée à la ré-organisation de la collision Arabie-Eurasie, à 5 ± 2 Ma. L'hypothèse d'un détachement du panneau lithosphérique Arabique subduit sous le Zagros et l'Iran central est considéré comme une cause de la mise en place du partitionnement.
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Agudelo, William. "Imagerie sismique quantitative de la marge convergente d'Equateur-Colombie : Application des mèthodes tomographiques aux données de sismique réflexion multitrace et réfraction-réflexion grand-angle des campagnes SISTEUR et SALIERI." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2005. http://tel.archives-ouvertes.fr/tel-00010415.
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Mon travail de thèse se propose d'étudier la structure, les propriétés physiques et les processus géodynamiques de la zone de subduction d'Equateur-Colombie grâce à l'adaptation et le développement d'outils d'imagerie sismique (inversion de formes d'ondes 'alias' tomographie en diffraction) et à leur application aux données de sismique marine multitrace (MCS) et grand-angle OBS (WA) acquises en Equateur-Colombie pendant les campagnes SISTEUR et SALIERI. Ces outils m'ont permis de réaliser une imagerie fine et quantitative à trois niveaux : l'imagerie superficielle (~ 0-3 km), l'imagerie à profondeur intermédiaire (~ 3-10 km) et l'imagerie profonde (~ 10-30 km). Dans le domaine superficiel, j'ai effectué une cartographie fine et quantitative des propriétés physiques des sédiments au voisinage du BSR (Bottom Simulating Reflector), interpreté comme la base de stabilité des hydrates de gaz. Sur le profil SIS-40 situé sur la marge sud de la Colombie, j'ai pu identifier la présence de failles qui perturbent localement le BSR. Les résultats présentés sous la forme d' une série de logs adjacents de l'image migrée en profondeur, montrent que certaines régions du BSR sont caractérisées par une augmentation de la vitesse (1470-1650 m/s), indiquant la présence d'une faible quantité d'hydrates de gaz au dessus du BSR; d'autres zones situées immédiatement sous le BSR sont caractérisées par une diminution de la vitesse (~1200 m/s), liée à la présence de gaz libres piégés sous la couche d'hydrate de gaz. A des profondeurs moyennes j'ai étudié la structure du chenal de subduction (profil SIS-72). Le chenal constitue la limite mécanique entre la plaque chevauchante et la plaque plongeante. Il est délimité à son toit par un fort réflecteur interprété comme le décollement interplaque et à sa base par le toit très réflectif de la croûte océanique en subduction. L'imagerie fine et quantitative des propriétés physiques du décollement interplaque permet de mieux comprendre le rôle de la circulation des fluides et des variations lithologiques et physiques, sur le couplage mécanique inter-plaque. En raison de la sensibilité de la méthode de tomographie en diffraction au macro-modèle de vitesse, un code de correction de ce modèle a été implémenté, afin d'obtenir des images tomographiques fiables (i.e. géométrie et amplitudes correctes). Du fait de la bande passante limitée de la source et de la longueur du dispositif d'acquisition limitée à 4.5 km, les images tomographiques ont une résolution spatiale limitée : l'image tomographique présente un déficit des petits et grands nombre d'onde (fréquences spatiales) limitant ainsi l' interprétation géologique des paramètres physiques cartographiés. Un traitement spécifique basé sur la modélisation des traces sismiques a été implémenté. L'image tomographique, traitée comme une série de traces verticales, constitue la donnée observée. L'espace des modèles est constitué par un ensemble de modèles impulsionnels et unidimensionnels de Terre construits aléatoirement. Ces modèles sont dégradés par convolution avec une estimation de l'ondelette source afin de fournir une représentation synthétique de l'image tomographique « observée ». La minimisation de la fonction coût entre les traces migrées et les traces synthétiques est effectuée dans le cadre d'une inversion globale par recuit simulé (VFSA= « Very Fast Simulated Annealing »). Le modèle moyen issu de cette procédure fournit un modèle 2D fin de vitesse, fonction de la profondeur et comparable à la limite de la résolution théorique de la source. A l'issue de ce traitement, des perturbations de vitesse positives sont mises en évidence au toit de la croûte, et d'autres négatives accompagnent certains segments du niveau du décollement. Ces dernières sont probablement associées à la présence de fluides. Le domaine plus profond a été étudié à partir des données MCS et WA dans le double but (1) d'améliorer la résolution spatiale des images sismiques du Moho et du contact interplaque en relation avec la zone sismogène, et (2) de détecter la présence d'anomalies crustales de vitesse et d'analyser leur relation avec les zones d'aspérité sismologiques. L'utilisation conjointe des données de sismique MCS et WA a été mise en oeuvre pour prolonger vers le bas les images de sismique verticale et tenter ainsi d'établir une relation entre les processus profonds et les manifestations en surface. L'application de la chaîne de traitement au profil SIS-44 a permis d'obtenir un modèle de vitesse bien contraint jusqu'à 25 km de profondeur. Ce modèle met en évidence des réflecteurs profonds (Moho et contact interplaque ) et des réflecteurs plus superficiels (splay fault), dont l'interprétation était initialement incertaine sur les images migrées en temps.
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Agudelo, Zambrano William Mauricio. "Imagerie sismique quantitative de la marge convergente d'Equateur-Colombie : application des méthodes tomographiques aux données de sismique réflexion multitrace et réfraction-réflexion grand-angle des campagnes SISTEUR et SALIERI." Paris 6, 2005. https://tel.archives-ouvertes.fr/tel-00010415.
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Sithole, Nompumelelo. "A study into the main structural features of the Namaqua region and their relation to the intrusion of the Keimoes Suite." 2013. http://hdl.handle.net/11394/3877.
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>Magister Scientiae - MScThe thesis provides a study into the main structural features of the Namaqua Region and their relation to the intrusion of the Keimoes Suite. This was achieved by producing a digitized map of the Namaqua Region structural framework using a LandSAT image and MOVE software for remote sensing. The structural framework showed an array of shear zones and fault systems which trend in a NW-SE direction. The validation of the sense of movement, location and orientation of the shear zones was done by field mapping. The general orientation of all shear zones was NW-SE. The sense of movement along the Neusspruit, Boven Rugzeer and Trooilapspan shear zones was found to be dextral strike slip movement and the Cnydas shear zone had a sinistral strike slip movement. The location of the shear zones were determined by analyzing the deviation in general foliation trend which was visualized using Rose Diagrams. The field data and the remote sensing were found to agree with the transpressive environment of the Namaqua Region. The oblique collision of the Namaqua-Natal crustal block with the Kaapvaal Craton during the orogenic event at ~1.2 Ga created a compressionalgeotectonic setting which allowed for the intrusion of the early to late syn-tectonic Keimoes Suite granites. The lateral escape of the Namaqua-Natal crustal block took place along the western margin of the Kaapvaal Craton. This was brought on by prolonged compression which resulted in the formation of a releasing bend in the Namaqua Region. This releasing bend produced the negative flower structure with dextral shear zones which facilitated the intrusion of the post-tectonic Keimoes Suite granites.
Book chapters on the topic "Fault zones – Maine"
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Zhang, G. Y., Y. X. Xiao, J. H. Zhang, and J. Y. Luo. "Study on Optimization of Row Spacing Between Steel Arches in Deep Buried Fault Cave Sections." In Lecture Notes in Civil Engineering, 412–29. Singapore: Springer Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-1260-3_38.
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AbstractAs a widely used support form in tunnel support, the support effect of steel arch is influenced by the row distance between steel arches. In F8 fault fracture zone of the North Main Canal of Letan Reservoir in Guangxi, the support system of “steel arch + shotcrete” in this faulted cavern section was equalized with elastic modulus and yield stress by using theoretical analysis and numerical simulation, and the characteristic curves of rock support of deeply buried circular cavern under modified axisymmetric loading were obtained. The sensitivity analysis and optimization study of the spacing between steel arches were conducted by using FLAC3D. The results show that with the increase of steel arch spacing, the cavity wall displacement increases, the support reaction force decreases nonlinearly, and the radial displacement and plastic zone around the cavity continue to increase. When the distance between steel arches >600 mm, the deformation of cavern perimeter changes abruptly and the plastic zone increases significantly. Based on comprehensive analysis, the optimization suggestions of steel arch are proposed.
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Swanson, Mark T. "Pseudotachylyte-bearing strike-slip faults in mylonitic host rocks, Fort Foster Brittle Zone, Kittery, Maine." In Earthquakes: Radiated Energy and the Physics of Faulting, 167–79. Washington, D. C.: American Geophysical Union, 2006. http://dx.doi.org/10.1029/170gm17.
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Zolnikov, Konstantin P., Dmitrij S. Kryzhevich, and Aleksandr V. Korchuganov. "Regularities of Structural Rearrangements in Single- and Bicrystals Near the Contact Zone." In Springer Tracts in Mechanical Engineering, 301–22. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-60124-9_14.
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AbstractThe chapter is devoted to the analysis of the features of local structural rearrangementsin nanostructured materialsunder shear loadingand nanoindentation. The study was carried out using molecular dynamics-based computer simulation. In particular, we investigated the features of symmetric tilt grain boundary migration in bcc and fcc metals under shear loading. The main emphasis was on identifying atomic mechanisms responsible for the migration of symmetric tilt grain boundaries. We revealed that grain boundaries of this type can move with abnormally high velocities up to several hundred meters per second. The grain boundary velocity depends on the shear rate and grain boundary structure. It is important to note that the migration of grain boundary does not lead to the formation of structural defects. We showed that grain boundary moves in a pronounced jump-like manner as a result of a certain sequence of self-consistent displacements of grain boundary atomic planes and adjacent planes. The number of atomic planes involved in the migration process depends on the structure of the grain boundary. In the case of bcc vanadium, five planes participate in the migration of the Σ5(210)[001] grain boundary, and three planes determine the Σ5(310)[001] grain boundary motion. The Σ5(310)[001] grain boundary in fcc nickel moves as a result of rearrangements of six atomic planes. The stacking order of atomic planes participating in the grain boundary migration can change. A jump-like manner of grain boundary motion may be divided into two stages. The first stage is a long time interval of stress increase during shear loading. The grain boundary is motionless during this period and accumulates elastic strain energy. This is followed by the stage of jump-like grain boundary motion, which results in rapid stress drop. The related study was focused on understanding the atomic rearrangements responsible for the nucleation of plasticity near different crystallographic surfaces of fcc and bcc metals under nanoindentation. We showed that a wedge-shaped region, which consists of atoms with a changed symmetry of the nearest environment, is formed under the indentation of the (001) surface of the copper crystallite. Stacking faults arise in the (111) atomic planes of the contact zone under the indentation of the (011) surface. Their escape on the side free surface leads to a step formation. Indentation of the (111) surface is accompanied by nucleation of partial dislocations in the contact zone subsequent formation of nanotwins. The results of the nanoindentation of bcc iron bicrystal show that the grain boundary prevents the propagation of structural defects nucleated in the contact zone into the neighboring grain.
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Souza De, Stéphane, Stéphane Perrouty, Benoît Dubé, Patrick Mercier-Langevin, Robert L. Linnen, and Gema R. Olivo. "Chapter 2: Metallogeny of the Neoarchean Malartic Gold Camp, Québec, Canada." In Geology of the World’s Major Gold Deposits and Provinces, 29–52. Society of Economic Geologists, 2020. http://dx.doi.org/10.5382/sp.23.02.
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Abstract The Malartic gold camp is located in the southern part of the Archean Superior Province and straddles the Larder Lake-Cadillac fault zone that is between the Abitibi and Pontiac subprovinces. It comprises the world-class Canadian Malartic deposit (25.91 Moz, including past production, reserves, and resources), and smaller gold deposits located along faults and shear zones in volcanic and metasedimentary rocks of the Abitibi subprovince. North of the Larder Lake-Cadillac fault zone, the Malartic camp includes 2714 to 2697 Ma volcanic rocks and ≤2687 Ma turbiditic sedimentary rocks overlain by ≤2679 to 2669 Ma polymictic conglomerate and sandstone of the Timiskaming Group. South of the fault, the Pontiac subprovince comprises ≤2685 Ma turbiditic graywacke and mudstone, and minor ultramafic to mafic volcanic rocks and iron formations of the Pontiac Group. These supracrustal rocks were metamorphosed at peak greenschist to lower amphibolite facies conditions at ~2660 to 2658 Ma, during D2 compressive deformation, and are cut by a variety of postvolcanic intrusions ranging from ~2695 to 2640 Ma. The Canadian Malartic deposit encompasses several past underground operations and is currently mined as a low-grade, open-pit operation that accounts for about 80% of the past production and reserves in the camp. It dominantly consists of disseminated-stockwork replacement-style mineralization in greenschist facies sedimentary rocks of the Pontiac Group. The mineralized zones are spatially associated with the Sladen fault and ~2678 Ma subalkaline to alkaline porphyritic quartz monzodiorite and granodiorite. Field relationships and isotopic age data for ore-related vein minerals indicate that gold mineralization in the Canadian Malartic deposit occurred at ~2665 to 2660 Ma and was contemporaneous with syn- to late-D2 peak metamorphism. The smaller deposits in the camp include auriferous disseminated-stockwork zones of the Camflo deposit (1.9 Moz) and quartz ± carbonate-pyrite veins and breccias (0.6 Moz) along faults in chemically and mechanically favorable rocks. The age of these deposits is poorly constrained, but ~2692 Ma postmineral dikes, and ~2625 Ma hydrothermal titanite and rutile from the Camflo deposit highlight a long and complex hydrothermal history. Crosscutting relationships and regional geochronological constraints suggest that an early episode of pre-Timiskaming mineralization occurred at >2692 Ma, shortly after the end of volcanism in the Malartic camp, and postmetamorphic fluid circulation may have contributed to concentration or remobilization of gold until ~2625 Ma. However, the bulk of the gold was concentrated in the Canadian Malartic deposit during the main phase of compressive deformation and peak regional metamorphism.
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Zakeri, Negar Sadat Soleimani, and Saeid Pashazadeh. "Data Mining Techniques on Earthquake Data." In Improving Knowledge Discovery through the Integration of Data Mining Techniques, 183–99. IGI Global, 2015. http://dx.doi.org/10.4018/978-1-4666-8513-0.ch010.
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Active faults are sources of earthquakes and one of them is north fault of Tabriz in the northwest of Iran. The activation of faults can harm humans' life and constructions. The analysis of the seismic data in active regions can be helpful in dealing with earthquake hazards and devising prevention strategies. In this chapter, structure of earthquake events along with application of various intelligent data mining algorithms for earthquake prediction are studied. Main focus is on categorizing the seismic data of local regions according to the events' location using clustering algorithms for classification and then using intelligent artificial neural network for cluster prediction. As a result, the target data were clustered to six groups and proposed model with 10 fold cross validation yielded accuracy of 98.3%. Also, as a case study, the tectonic stress on concentration zones of Tabriz fault has been identified and five features of the events were used. Finally, the most important points have been proposed for evaluation of the nonlinear model predictions as future directions.
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Ludman, Allan, and Susan Gibbons. "Multistage shearing of the Deblois granite in the Kellyland fault zone, eastern Maine." In Norumbega Fault System of the Northern Appalachians. Geological Society of America, 1999. http://dx.doi.org/10.1130/0-8137-2331-0.41.
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Swanson, Mark T. "Dextral transpression at the Casco Bay restraining bend, Norumbega fault zone, coastal Maine." In Norumbega Fault System of the Northern Appalachians. Geological Society of America, 1999. http://dx.doi.org/10.1130/0-8137-2331-0.85.
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Unruh, Jeffrey. "Upper plate deformation during blueschist exhumation, ancestral western California forearc basin, from stratigraphic and structural relationships at Mount Diablo and in the Rio Vista Basin." In Regional Geology of Mount Diablo, California: Its Tectonic Evolution on the North America Plate Boundary. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.1217(10).
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ABSTRACT Late Cenozoic growth of the Mount Diablo anticline in the eastern San Francisco Bay area, California, USA, has produced unique 3D exposures of stratigraphic relationships and normal faults that record Late Cretaceous uplift and early Tertiary extension in the ancestral California forearc basin. Several early Tertiary normal faults on the northeast flank of Mount Diablo have been correlated with structures that accommodated Paleogene subsidence of the now-buried Rio Vista basin north of Mount Diablo. Stepwise restoration of deformation at Mount Diablo reveals that the normal faults probably root into the “Mount Diablo fault,” a structure that juxtaposes blueschist-facies rocks of the Franciscan accretionary complex with attenuated remnants of the ophiolitic forearc basement and relatively unmetamorphosed marine forearc sediments. This structure is the local equivalent of the Coast Range fault, which is the regional contact between high-pressure Franciscan rocks and structurally overlying forearc basement in the northern Coast Ranges and Diablo Range, and it is folded about the axis of the Mount Diablo anticline. Apatite fission-track analyses indicate that the Franciscan rocks at Mount Diablo were exhumed and cooled from depths of 20+ km in the subduction zone between ca. 70−50 Ma. Angular unconformities and growth relations in the Cretaceous and Paleogene stratigraphic sections on the northeast side of Mount Diablo, and in the Rio Vista basin to the north, indicate that wholesale uplift, eastward tilting, and extension of the western forearc basin were coeval with blueschist exhumation. Previous workers have interpreted the structural relief associated with this uplift and tilting, as well as the appearance of Franciscan blueschist detritus in Late Cretaceous and early Tertiary forearc strata, as evidence for an “ancestral Mount Diablo high,” an emergent Franciscan highland bordering the forearc basin to the west. This outer-arc high is here interpreted to be the uplifted footwall of Coast Range fault. The stratigraphic and structural relations exposed at Mount Diablo support models for exposure of Franciscan blueschists primarily through syn-subduction extension and attenuation of the overlying forearc crust in the hanging wall of the Coast Range fault, accompanied by (local?) uplift and erosion of the exhumed accretionary prism in the footwall.
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Tomascak, Paul B., Eirik J. Krogstad, and Richard J. Walker. "Significance of the Norumbega fault zone in southwestern Maine: Clues from the geochemistry of granitic rocks." In Norumbega Fault System of the Northern Appalachians. Geological Society of America, 1999. http://dx.doi.org/10.1130/0-8137-2331-0.105.
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Hubbard, Mary S., and Hui Wang. "Temperature variability during shear deformation: An interpretation of microstructures along the central Norumbega fault zone, Maine." In Norumbega Fault System of the Northern Appalachians. Geological Society of America, 1999. http://dx.doi.org/10.1130/0-8137-2331-0.25.
Full textConference papers on the topic "Fault zones – Maine"
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Noufal, Abdelwahab. "Fault Planes Materials Fill Characteristics, UAE." In Abu Dhabi International Petroleum Exhibition & Conference. SPE, 2021. http://dx.doi.org/10.2118/207217-ms.
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Abstract Abu Dhabi subsurface fault populations triggered basin system in diverse directions, because of their significant role as fluid pathways. Studying fault infill materials, fault geometries, zone architecture and sealing properties from outcrops as analogues to the subsurface of Abu Dhabi, and combining these with well data and cores are the main objectives of this paper. The fault core around the fault plane and in areas of overlap between fault segments and around the fault tip include slip surfaces and deformed rocks such as fault gouge, breccia, and lenses of host rock, shale smear, salt flux and diagenetic features. Structural geometry of the fault zone architecture and fault plane infill is mainly based on the competency contrast of the materials, that are behaving in ductile or in a brittle manner, which are distributed in the subsurface of Abu Dhabi sedimentary sequences with variable thicknesses. Brittleness is producing lenses, breccia and gouge, while, ductile intervals (principally shales and salt), evolved in smear and flux. The fault and fractures are behaving in a sealy or leaky ways is mainly dependent on the percentage of these materials in the fault deformation zone. The reservoir sections distancing from shale and salt layers are affected by diagenetic impact of the carbonates filling fault zones by recrystallized calcite and dolomite. Musandam area, Ras Al Khaima (RAK), and Jabal Hafit (JH) on the northeast- and eastern-side of the UAE represents good surface analogues for studying fault materials infill characteristics. To approach this, several samples, picked from fault planes, were analysed. NW-trending faults system show more dominant calcite, dolomite, anhydrites and those closer to salt and shale intervals are showing smearing of the ductile infill. The other linked segments and transfer faults of other directions are represented by a lesser percentage of infill. In areas of gravitational tectonics, the decollement ductile interval is intruded in differently oriented open fractures. The studied outcrops of the offshore salt islands and onshore Jabal Al Dhanna (JD) showing salt flux in the surrounding layers that intruded by the salt. The fractures and faults of the surrounding layers and the embedment insoluble layers are highly deformed and showing nearly total seal. As the salt behaving in an isotropic manner, the deformation can be measured clearly by its impact on the surrounding and embedment's insoluble rocks. The faults/fractures behaviour is vicious in migrating hydrocarbons, production enhancement and hydraulic fracturing propagation.
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Kelson, Keith I., Christopher S. Hitchcock, John N. Baldwin, James D. Hart, James C. Gamble, Chih-Hung Lee, and Frank Dauby. "Fault Rupture Assessments for High-Pressure Pipelines in the Southern San Francisco Bay Area, California." In 2004 International Pipeline Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ipc2004-0212.
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The San Andreas, Hayward, and Calaveras faults are major active faults that traverse the San Francisco Bay area in northern California, and may produce surface rupture during large earthquakes. We assessed the entire Pacific Gas & Electric Company natural gas transmission system in northern California, and identified several locations where primary pipelines cross these faults. The goal of this effort was to develop reasonable measures for mitigating fault-rupture hazards during the occurrence of various earthquake scenarios. Because fault creep (e.g., slow, progressive movement in the absence of large earthquakes) occurs at the pipeline fault crossings, we developed an innovative approach that accounts for the reduction in expected surface displacement, as a result of fault creep, during a large earthquake. In addition, we used recently developed data on the distribution of displacement across fault zones to provide likely scenarios of the seismic demand on each pipeline. Our overall approach involves (1) identifying primary, high-hazard fault crossings throughout the pipeline system, (2) delineating the location, width, and orientation of the active fault zone at specific fault-crossing sites, (3) characterizing the likely amount, direction, and distribution of expected surface fault displacement at these sites, (4) evaluating geotechnical soil conditions at the fault crossings, (5) modeling pipeline response, and (6) developing mitigation measures. At specific fault crossings, we documented fault locations, widths, and orientations on the basis of detailed field mapping and exploratory trenching. We estimated fault displacements based on expected earthquake magnitude, and then adjusted these values to account for the effects of fault creep at the ground surface. Fault creep decreases the amount of expected surface fault rupture, such that sites having high creep rates are expected to experience proportionally less surface displacement during a large earthquake. Lastly, we modeled the expected amount of surface offset to reflect the distribution of offset across the fault zone, based on data from historical surface ruptures throughout the world. Where specific fault crossings contain a single primary fault strand, we estimated that 85% of the total surface offset occurs on the main fault and the remainder occurs as secondary deformation. At sites where the pipeline crosses multiple active fault strands in a broad zone, we consider complex rupture distributions. Using this approach yields realistic, appropriately conservative estimates of surface displacement for assessing seismic demands on the pipelines.
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Karasaki, Kenzi, Celia Tiemi Onishi, Erika Gasperikova, Junichi Goto, Hiroyuki Tsuchi, Tadashi Miwa, Keiichi Ueta, Kenzo Kiho, and Kimio Miyakawa. "Development of Characterization Technology for Fault Zone Hydrology." In ASME 2010 13th International Conference on Environmental Remediation and Radioactive Waste Management. ASMEDC, 2010. http://dx.doi.org/10.1115/icem2010-40121.
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Several deep trenches were cut, and a number of geophysical surveys were conducted across the Wildcat Fault in the hills east of Berkeley, California. The Wildcat Fault is believed to be a strike-slip fault and a member of the Hayward Fault System, with over 10 km of displacement. So far, three boreholes of ∼ 150m deep have been core-drilled and borehole geophysical logs were conducted. The rocks are extensively sheared and fractured; gouges were observed at several depths and a thick cataclasitic zone was also observed. While confirming some earlier, published conclusions from shallow observations about Wildcat, some unexpected findings were encountered. Preliminary analysis indicates that Wildcat near the field site consists of multiple faults. The hydraulic test data suggest the dual properties of the hydrologic structure of the fault zone. A fourth borehole is planned to penetrate the main fault believed to lie in-between the holes. The main philosophy behind our approach for the hydrologic characterization of such a complex fractured system is to let the system take its own average and monitor a long term behavior instead of collecting a multitude of data at small length and time scales, or at a discrete fracture scale and to “up-scale,” which is extremely tenuous.
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Markou, N., and P. Papanastasiou. "3D Geomechanical Reservoir Modelling in Faulted Reservoirs." In International Geomechanics Symposium. ARMA, 2022. http://dx.doi.org/10.56952/igs-2022-167.
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Abstract In this study, we present a three-dimensional (3D) geomechanical reservoir model for a faulted and compartmentalized reservoir in the Eastern Mediterranean. A series of alternative production scenarios performed using a simulation model that accounts for consolidation and plasticity deformation of the rocks. Plastic yielding is mainly developed in fault slip zones of narrow extent whereas it appears that there is low risk of plastic behavior in the main reservoir. The slip conditions become complex in the fault contact surfaces where local areas close to fault connections are more pronounced to slip creating localized areas of smaller faulted zones. Displacement magnitudes, are controlled by the structural boundary conditions and the geometrical shape of each fault block. Overall, the higher displacements develop in the near fault region while in the remote from the fault area the vertical displacement is nearly constant as it is clearly governed by the reservoir depletion. Furthermore, changes of normalized permeability can be drawn in the 3D space providing additional insights of heterogeneous distribution. Introduction Petroleum geomechanics become important in reservoirs highly impacted by faults mechanics and overpressure zones. An operator has to well define the fault structural geometry of the field and assess early in the producing life of a reservoir whether production will be affected by the presence of naturally occurring fractures though some faults and fractures cannot be identified even at the early stages of a field production. Reservoir depletion increases the stress carried by the load-bearing grain frame of the reservoir rock. Stress analysis can be extended to identify rock failure conditions that can lead to the creation of new faulted systems in the subsurface formations. Geomechanics play an important role in identifying the stress conditions in a faulted reservoir system and the potential of slip activation of an existing fault. Extensive accounts on the importance of reservoir geomechanics can be found in the classical books of Fjaer et al., (2008) and Zoback, (2010). Finite element analysis can be used to simulate the tectonic movement to match borehole observations (Plumb et al., 1998).
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Khan, Imran, Shakeel Ahmad, Rana Faisal Shahzad, Muhammad Akram Qureshi, Zahoor Khan, Shabeer Ahmad, and Uzair Hamid Awan. "Geomechanical Modelling to Identify Sub-Seismic Faults and Fractures Characteristics Using Elastic Dislocation (ED) Theory: A Case Study from Potwar Foldbelt, Upper Indus Basin (UIB) of Pakistan." In ADIPEC. SPE, 2022. http://dx.doi.org/10.2118/211645-ms.
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Abstract The study will address the failure reasons of wells and point out the high-density fracture zones, to drain out the remaining hydrocarbons in the field. A robust 3D geological model was developed based on 3D seismic interpretation. The rock mechanical properties of carbonates were incorporated. The total strain i.e., the background or remote strain (Bulk deformation) and the strain from displacement along the fault surfaces are mapped to each segment/element of the generated fault surfaces. This total strain calculates stresses and the failure for deformation surface. The geomechanical model based on Elastic Dislocation (ED) theory identified strain fields on horizon surface / observation grids and then finally fractures corridor and their characteristics i.e. distribution, orientation. Fault planes generated from interpretation play a major role in the ED method for fracture analysis. The fault surface consists of an array of panels, each contributing to the ED equation calculation. The main outcome is the sub-seismic faults and fractures identification around larger faults on the horizontal observation medium. The identified fractures corridors characteristics, distribution and orientation changes along the strike of the major fault system. In the developed ED model the predicated fractures system are parallel to the major reverse fault direction, but oblique fractures corridor is also observed along the middle segments, aligning with observed variations in structure dip. The crestal portion of the anticline has a higher density of fractures than the rim. The ED modelling fractures results were verified against FMI data of the targeted horizon, which demonstrated that the wells which were drilled in high-density fracture zones (modelled) have produced hydrocarbons and vice versa. There is a correlation between modelled results with image logs and well-testing results (DST's), which increases the reliance on the ED theory's ability to correctly identify small-scale (sub-seismic) fractures, joints and faults system. The Eocene carbonate reservoirs have low primary porosity and permeability. The productivity of these reservoirs is dependent on permeable natural fractures and sub-seismic faults. The identification of these features is a major problem before drilling while, conventional techniques do not provide optimum solutions to their understanding. A case study of compressional tectonic regime in Himalayan fold & thrust belts is presented here, where an integrated approach is applied in the form of geomechanical modelling, which is built on the ED theory provide a reliable base for well planning.
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Levin, Vadim, William Menke, Yiran Li, and Andrea Servali. "LITHOSPHERIC EXPRESSION OF THE NORUMBEGA FAULT ZONE IN NORTH COASTAL MAINE." In 54th Annual GSA Northeastern Section Meeting - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019ne-328048.
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Sullivan, Walter A. "RHEOLOGIC EVOLUTION OF A CRUSTAL-SCALE STRIKE-SLIP FAULT ZONE: A CASE STUDY OF THE KELLYLAND FAULT ZONE IN EASTERN MAINE." In 54th Annual GSA Northeastern Section Meeting - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019ne-328268.
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Zervando, Y. V., and O. V. Elisheva. "PREREQUISITES FOR FILLING THE RESERVOIRS OF THE NEOCOMIAN INTERVAL OF THE SECTION OF THE AI-YAUN AREA WITH HYDROCARBONS." In All-Russian Youth Scientific Conference with the Participation of Foreign Scientists Trofimuk Readings - 2021. Novosibirsk State University, 2021. http://dx.doi.org/10.25205/978-5-4437-1251-2-133-137.
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The report considers structural-tectonic, geochemical and hydrodynamic condi-tions of preservation of the potential oil reservoir BC8 at the Ai-Yaunskoye field. Formation BS8 has a good reservoir in the area. The reservoir deposits are represented by a reservoir of marine genesis with high filtration-volume properties.Because of the faults, the formation has a block structure.The BS8 formation in the Ai-Yaun area is in the zone of potential oil-bearing strata. As of today, one of the blocks has opened an aquifer. The rest of the blocks have not yet been drilled. Therefore, the potential of these sediments is considered unexplored to the end. According to the analysis of the fault model, some of the faults are considered to be through. Hydrocarbons could have migrated along these faults up the section to the PK 1–2 reservoirs. Some of the faults are considered screens, which increases the chances of the BS8 formation discovering oil deposits in it in other tectonic blocks of the reservoir.
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Audivet, Cinthia, Horacio Pinzón, Jesus García, Marlon Consuegra, Javier Alexander, and Marco Sanjuán. "Data Segmentation Criteria Assessment for Fault Detection Techniques Based on Principal Component Analysis for Natural Gas Transmission System." In ASME 2018 Power Conference collocated with the ASME 2018 12th International Conference on Energy Sustainability and the ASME 2018 Nuclear Forum. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/power2018-7479.
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Statistical analytics, as a data extraction and fault detection strategy, may incorporate segmentation techniques to overcome its underlying limitations and drawbacks. Merging both techniques shall provide a more robust monitoring structure to address the proper identification of normal and abnormal conditions, to improve the extraction of fundamental correlation among variables, and to improve the separation of both main variation and natural variation (noise) subspaces. This additional feature is key to limit the false alarm rate and to optimize the fault detection time when it is implemented on industrial applications. This paper presents an analysis to determine whether a segmentation approach, as a previous step of detection, enhances the fault detection strategies, specifically the principal component analysis performance. The data segmentation criteria assessed in this study includes two approaches: a) Sources (well) of the transmitted natural gas and b) Promigas’ natural gas pipeline division defined by the Energy and Gas Regulation Commission (CREG in Spanish). The performance assessment of segmentation criteria was carried out evaluating the false alarm rate and detection time when the natural gas transmission network presents faults of different magnitude. The results show that the implementation of a segmentation criteria provides an advantage in terms of the detection time, but it depends of the fault magnitude and the number of clusters. The detection time is improved by 25% in the case scenario I, when transition zones are considered. On the other hand, the detection time is slightly better with less than 10% in the case scenario II, where the segmentation is geographical.
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Djezzar, Sofiane, Aldjia Boualam, Habib Ouadi, Aimen Laalam, Nadia Mouedden, Ahmed Merzoug, and Abderraouf Chemmakh. "Geological Characterization of Lower Devonian Reservoirs in Reggane Basin, Algeria." In SPE Annual Technical Conference and Exhibition. SPE, 2022. http://dx.doi.org/10.2118/210162-ms.
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Abstract In the Reggane basin, the most promising petroleum system is represented by the Lower Devonian, Cambro-Ordovician, and Carboniferous reservoirs. Most of the traps are linked to structures with very complex geometry, generally leaning on reverse faults, under superficial detachment levels. The generation of hydrocarbons took place, in the Paleozoic during the burial period (Upper Devonian-Carboniferous) and probably during the overheating of the Jurassic. The basin architecture is the outcome of a superposition of several tectonic phases from the Caledonian to the Hercynian tectonic events. The main reservoirs are in the North-East part of the basin, namely the Lower Devonian, Ordovician, and Carboniferous. The Gedinnian and the Siegenian are the main reservoirs of the Lower Devonian sequence, with the Emsian as a secondary reservoir. The Carboniferous and Ordovician reservoirs became targets after the discovery of dry gas in the Kahlouche and Anzeglouf areas. The main gas fields in the Reggane basin are Hassi-M’dakane, Feidjet-El-Had, Kahal-Tabalbala, Djebel-Hirane, Kahlouche, Tiouliline, Reggane, Azrafil, and Anzeglouf. The current geometry of the Reggane basin is marked by two major structural axes, resulting from a complex tectonic history. Reggane basin is elongated NW – SE, relatively asymmetric. The southern flank of the basin is characterized by a hallow dip plunging towards the North and affected by rare reverse faults. On the other hand, the northern flank is affected by many faults and folds. These faults arrangement of the various faults that have affected this basin can be broken down into two main sets: NW - SE set: this direction is very important; it all appears along the northern edge of the basin and presents a comparable direction to the Ougarta ridge. A set of submeridian directions: concentrated in the SE part of the basin (eastern periclinal closure constituting the transition zone between the Reggane basin and the Azzel Matti slab). This fault sets form an extension of the major submeridian accidents in the Hoggar shield. Two other directions of less represented the E-W faults forming an accident relay along the edge of the basin with the Ougarta ridge and the NE - SW faults. This study will help to define the quality and extension of the Lower Devonian sandstone reservoirs in the northern part of the Reggane basin, the construction of favorable zone maps for exploration with risk-weighted reservoir spaces, identification, and evaluation of "Tight Gas Reservoir", and trap analysis and petroleum potential the Reggane basin.
Reports on the topic "Fault zones – Maine"
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Doll, W. E., J. K. Costain, W. J. Domoracki, C. Coruh, A. Ludman, and J. Hopeck. Geophysical and Geological Characterization of Tectonic Features in the Bottle Lake Plutonic Complex and Norumbega Fault Zone, eastern Maine. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1990. http://dx.doi.org/10.4095/130879.
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Arcone, Steven, James Lever, Laura Ray, Benjamin Walker, Gordon Hamilton, and Lynn Kaluzienski. Ground-penetrating radar profiles of the McMurdo shear zone, Antarctica, acquired with an unmanned rover : interpretation of crevasses, fractures, and folds within firn and marine ice. Engineer Research and Development Center (U.S.), December 2021. http://dx.doi.org/10.21079/11681/42620.
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The crevassed firn of the McMurdo shear zone (SZ) within the Ross Ice Shelf may also contain crevasses deep within its meteoric and marine ice, but the surface crevassing prevents ordinary vehicle access to investigate its structure geophysically. We used a lightweight robotic vehicle to tow 200- and 40 MHz ground-penetrating radar antennas simultaneously along 10 parallel transects over a 28 km² grid spanning the SZ width. Transects were generally orthogonal to the ice flow. Total firn and meteoric ice thickness was approximately 160 m. Firn crevasses profiled at 400 MHz were up to 16 m wide, under snow bridges up to 10 m thick, and with strikes near 35°–40° to the transect direction. From the top down, 200- MHz profiles revealed firn diffractions originating to a depth of approximately 40 m, no discernible structure within the meteoric ice, a discontinuous transitional horizon, and at least 20 m of stratified marine ice; 28–31 m of freeboard found more marine ice exists. Based on 10 consecutive transects covering approximately 2.5 km², we preliminarily interpreted the transitional horizon to be a thin saline layer, and marine ice hyperbolic diffractions and reflections to be responses to localized fractures, and crevasses filled with unstratified marine ice, all at strikes from 27° to 50°. We preliminarily interpreted off nadir, marine ice horizons to be responses to linear and folded faults, similar to some in firn. The coinciding and synchronously folded areas of fractured firn and marine ice suggested that the visibly unstructured meteoric ice beneath our grid was also fractured, but either never crevassed, crevassed and sutured without marine ice inclusions, or that any ice containing crevasses might have eroded before marine ice accretion. We will test these interpretations with analysis of all transects and by extending our grid and increasing our depth ranges.
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Jackson, G. D. Bedrock geology, northwest part of Nuluujaak Mountain, Baffin Island, Nunavut, part of NTS 37-G/5. Natural Resources Canada/CMSS/Information Management, 2021. http://dx.doi.org/10.4095/314670.
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The map area lies about 40 km northwest of Baffinland's iron mine. Dykes of unit mAnA3 within unit mAnA2 suggest that unit mAnA2 predates unit mAnA3. Unit nAMqf, basal Mary River Group unit, includes regolith material from units mAnA2 and mAnA3. Unit mAnAm may include some dykes of unit nAMb. The Mary River Group was deposited in a volcanic-arc environment, yielding zircon U-Pb ages mostly in the range of 2.88 to 2.72 Ga. Iron-formation (unit nAMi) is approximately 276 m thick locally, with oxide facies (unit nAMio) being most abundant. The quartzite triangle west of 'Iron lake' (unofficial name) may be a small horst. The main east-west-trending synclinal fold, including the area around 'Iron lake' and the no. 4 ore deposit, is upright, nearly isoclinal, and plunges mostly easterly at both ends with small scale anticlines and synclines in the middle. Magnetite constitutes about 75% of high-grade iron deposits in the north limb, whereas hematite predominates in south-limb deposits. K-Ar and Rb-Sr ages indicate middle Paleoproterozoic overprinting. Central Borden Fault Zone was active at ca. 1.27 Ga and during or after Ordovician time. Note: please be aware that the information contained in CGM 408 is based on legacy data from the 1960-1990s and that it has been superseded by regional-scale information contained in CGM 403.