Fault Damage Zone

Characterization of fractures in an arkosic sandstone from the western damage zone of the San Andreas Fault (SAF) at San Andreas Fault Observatory at Depth (SAFOD) was used to better understand the origin of damage and to determine the scale dependence of fracture fabric and fracture density. Samples for this study were acquired from core taken at approximately 2.6 km depth during Phase 1 drilling at SAFOD. Petrographic sections of samples were studied using an optical petrographic microscope equipped with a universal stage and digital imaging system, and a scanning electron microscope with cathodoluminescence (SEM-CL) imaging capability. Use of combined optical imaging and SEM-CL imaging was found to more successfully acquire true fracture density at the grain scale. Linear fracture density and fracture orientation were determined for transgranular fractures at the whole thin section scale, and intragranular fractures at the grain scale. The microscopic scale measurements were compared to measurements of mesoscopic scale fractures in the same core, as well as to published data from an ancient, exhumed trace of the SAF in southern California. Fracturing in the damage zone of the SAF fault follows simple scaling laws from the grain scale to the km scale. Fracture density distributions in the core from SAFOD are similar to distributions in damaged arkosic sandstone of the SAF along other traces. Transgranular fractures, which are dominantly shear fractures, indicate preferred orientation approximately parallel to the dominant sets of the mesoscale faults. Although additional work is necessary to confirm general applicability, the results of this work demonstrate that fracture density and orientation distribution over a broad range of scales can be iii determined from measurements at the mesoscopic scale using empirical scaling relations.

Fault stepovers are features where the main trace of a fault steps from one segment to the next in either an underlapping or overlapping manner. Stepovers exert a critical influence on crustal permeability and are known to control phenomena such as the migration of hydrocarbons and the location of geothermal fields. In the Kalgoorlie‐Ora Banda greenstone district, Western Australia, we demonstrate a spatial association between stepovers and gold deposits. It is shown that although underlapping stepover geometries are typically rare in fault systems, they are anomalously associated with gold deposits. Further, the along‐strike and across‐strike dimensions of both underlapping and overlapping fault stepovers fit, to a first‐order approximation, the same self‐similar trend. Boundary element modelling of Coulomb failure stress changes is used to explain these observations in terms of damage generated by rupture events on the bounding fault segments and associated aftershock sequences. O...

Double-difference (DD) tomography is a generalization of DD location; it simultaneously solves for the three-dimensional velocity structure and seismic event locations. DD tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale. This method is able to produce more accurate event locations and velocity structure near the source region than standard tomography, which uses only absolute arrival times. We conduct a stability and uncertainty analysis of DD tomography based on a synthetic data set. Currently three versions of the DD tomography algorithms exist: tomoDD, tomoFDD and tomoADD. TomoDD assumes a flat earth model and uses a pseudo-bending ray-tracing algorithm to find rays between events and stations while tomoFDD uses a finite-difference travel-time algorithm and the curvature of the Earth is considered. Both codes are based on a regularly distributed inversion grid, with the former for a local scale and the latter for a regional scale. In contrast, tomoADD adapts the inversion mesh to match with the data distribution based on tetrahedral and Voronoi diagrams. We discuss examples of applying DD tomography to characterize fault zone structure, image high-resolution structure of subduction zones, and determine the velocity structure of volcanoes.

Supposed or potential Devonian igneous rocks in the accretionary complex of southern Chile were investigated using sensitive high-resolution ion microprobe U-Pb dating of zircon, with Hf-and O-isotope analyses of selected grains. Ages of 384 ± 3 and 382 ± 2 Ma are confirmed for two igneous bodies (another having been previously dated at 397 ± 1 Ma). Detrital zircon ages in the host rocks, some associated with Devonian marine fossils, indicate maximum possible sedimentation ages of c. 330 -385 Ma. Devonian ages of 391 ± 10 and 374 ± 3 Ma for plutonic rocks at the western edge of the North Patagonian Massif are somewhat older than those of orthogneisses in the western flank of the Andes near Chaitén (361 ± 7 and 364 ± 2 Ma). O and Hf isotopes indicate that the Devonian intrusions in the accretionary complex crystallized from mantle-derived magmas, whereas those in the North Patagonian Massif show a strong crustal influence, corresponding to oceanic and continental margin subduction environments of magma genesis, respectively. Devonian zircon provenance in the accretionary complex was from the North Patagonian Massif and not from the mantle-derived intrusions, suggesting that the accretionary complex formed an integral part of the Gondwana margin during Devonian-Carboniferous times.

During the preparation of this work were performed numerical modeling based on an adequate conceptual framework, contemplating interpret and predict the response of this hydro geological material, to effects of alterations in the environment can have on the evolution over time of the water pressure in the pores, the total stress and displacement. The modeling of hydrological and mechanical aspects were used for this work, taking as reference the conditions under which they were made the extension work of the laboratory. iv iv INDICE AGRADECIMIENTOS .

The Sea of Marmara is traversed by the North Anatolian Fault system and also presents abundant emission sites of methane gas into the water column. In order to assess the spatial relationship between gas emissions and active faults, the distribution of distances between gas emission sites and the nearest fault is calculated and compared with the distribution of distances between a uniform random distribution of points (Poisson process representing the null hypothesis of an absence of relationship between gas emissions and faults) and the nearest fault. Interestingly, the distance distribution for the Poisson process is nearly exponential, indicating that the fault map does not have a characteristic scale other than that representing the intensity of the fault network. The distance distribution for the observed gas emissions is significantly narrower than that arising from the Poisson process, with a Kolmogorov distance of 0.25±0.02. The crossing point between the two distributions defines the characteristic half-width of the swath of gas emission sites around the mapped active faults. For the whole Sea of Marmara data set a characteristic half-width of 900-1000 m is found which matches the half-width of the seafloor deformation zone observed around the main active fault. When the same analysis is applied to zones covering the Western High and the Central High it is found that the swath of gas emissions is wider on the Central High (2 km half-width), and not clearly related to the seafloor deformation zone there. This difference is put in perspective with recent work showing that creep is occurring on the western segment of the Main Marmara Fault (this also causing microseismicity) while the central Istanbul-Silivri segment may have remained locked since the 1766 magnitude 7+ earthquake. This suggests that aseismic slip (and not only earthquake occurrence) effectively maintains high permeability conduits in fault zones in sediments.

Petrographic and XRF analyses of the magmatic rock from JabukaShoal, 2300 m west of Jabuka Islet (central Adriatic Sea) revealedthat the rock is gabbro. This new location of magmatic rocks in theAdriatic confirms their linear arrangement, and indicates the presenceof an important fault line which predisposed the occurrences of magmaticrocks.

Observations of coseismic pulverization in porous sedimentary rocks in fault damage zones are scarce, in contrast to coseismic pulverization of crystalline rocks. Also, juxtaposition of stiff crystalline rocks and compliant porous rocks across a fault often yields an asymmetric damage zone geometry, with less damage in the more compliant side. In this study, we argue that such asymmetry near the sub-surface occurs because of a different response of lithology to similar transient loading conditions. Uniaxial unconfined high strain rate loadings with a split Hopkinson pressure bar were performed on dry and water saturated Rothbach sandstone core samples. Bedding anisotropy was taken into account by coring the samples parallel and perpendicular to the bedding. The results show that pervasive pulverization below the grain scale, such as observed in crystalline rock, does not occur in the sandstone samples for the explored strain rate range (60-150 s -1 ). Damage is mainly restricted to the scale of the grains, with intragranular deformation occurring only in weaker regions where compaction bands are formed. The presence of water and the bedding anisotropy mitigate the formation of compaction bands and motivates intergranular dilatation. The competition between inter-and intragranular damage during dynamic loading is explained with the geometric parameters of the rock in combination

Chalk is exposed in the Heidestrasse quarry at Lägerdorf, at the top of the NE-SW trending Krempe salt ridge. Structural data indicate the presence of two joint sets, striking almost parallel and perpendicular to the salt ridge, respectively, and of a set of conjugate extensional faults and fault zones striking NW-SE, i.e. almost perpendicular to the salt ridge. Within the overall NW-SE trend of joints and faults, strike variations occur from the massive chalk exposed in the lower half of the quarry, to the overlying layered chalk. A large variability characterizes the normalized spacing of both joint sets, which does not show any clear trend with layer dip. In situ measurements indicate that the cross-sectional permeability of tight joints increases 1e2 orders of magnitude with respect to the undeformed chalk. We propose that joint and fault azimuthal variability resulted from changes through time of the stress ellipsoid at the top of the salt ridge, while joint spacing variability is associated with the weak mechanical influence of bedding in chalk. Azimuthal variability improves fracture connectivity and, hence, permeability and fluid flow.

The Neogene Siwalik sequence of western Arunachal Pradesh comprises northward dipping thrust sheets structurally below the Main Boundary Fault (MBT) and above the Main Frontal Thrust (MFT). The Sub-Himalayan fold and thrust belt comprises four lithotectonic units between MBT and MFT. From oldest to the youngest these units are Kimi, Dafla, Subansiri and Kimin Formations. The Kimi Formation is equivalent to Lower Siwalik; Dafla and Subansiri formations are equivalent to the Middle Siwalik, while the Kimin Formations represent Upper Siwalik respectively. In the Kameng sector, Tipi Thrust is interpreted to be an intraformational thrust within Subansiri Formation; the Dafla Formations are trusted over the Subansiri Formation relatively at a higher structural level. Compaction and subsequent strong horizontal north to south compression led to the development of numerous zones of cataclasis in the Dafla and Subansiri sandstones. Earlier diagenetic fabrics in the sandstones have been modified considerably due to subsequent development of deformational grain scale microstructures under compression. The Pure Compaction Bands were formed in the initial stage under raised porosity and permeability. These are transformed to Shear Enhanced Compaction Bands and subsequently to Compactional Shear Bands when deformation assumes a simple shear mode under low porosity and permeability value. Higher degree of compaction is evident in the Dafla sandstone compared to that of the Subansiri sandstone which inferred on the basis of the type of the grain contacts, grain packing, frequency of pressure solution seams and segregated micaceous bands.

Space heating and cooling using geothermal heat exchangers is a promising environmentally friendly green energy solution. Modeling these energy storage systems is crucial for optimizing their design and operation. In this context, the present study consists of numerically investigating the effects of various physical properties, including thermal conductivity, density, and specific heat capacity of each material, as well as flow velocity, on the process of heat transfer in vertical geothermal heat exchangers using coaxial pipes to optimize their energy performance. Numerical simulations were carried out using Gambit-Fluent software. Different materials that make up the coaxial heat exchanger structure studied were tested to highlight their effects on the progress of heat flux and temperature. Thermal and fluid mechanics aspects were also studied. At the end of this study, a comparative analysis was carried out using the U-tube geothermal heat exchanger. The results indicate that the heat exchanger using a coaxial tube demonstrates superior thermal efficiency compared to the U-tube configuration. It has been found that using a low velocity with an appropriate selection of tube, grout, and soil materials results in enhanced dynamic exchanges, thereby enhancing the thermal efficiency of the geothermal exchanger.

Simulation of mechanized tunneling and on-site excavation require very good knowledge of the geomechanical material properties. Identification of the material must be fast and continuously perfomed during tunnel excavation for the best possible strategies for advancing the tunnel boring machine. We present in this work the use of the extended Kalman filter (EKF) for identification of the inclined fault zone ahead of the face. The EKF showed fast and stable convergence of the model parameters under study. In comparison with the particle swarm optimization technique applied to the same back analysis problem, faster convergence of the identified parameters as well as high robustness with respect to the choice of the initial parameter values have been observed.

Se caracterizaron 2 sistemas hidrotermales, ubicados respectivamente en Ciénaga (Magdalena) y Becerril (Cesar), detallando componentes geológicos como fallas locales y zona de mezcla de fluido. Por medio de la proporción de carbonatos, sulfatos y cloruros, se establecieron dos condiciones distintas de aporte calórico, en Becerril a 3 metros de profundidad referente a la base de emanación, las temperaturas oscilan entre (30-34)°C, siendo enriquecidas por fases carbonatadas (CaCO3) condicionando la procedencia del fluido a un calentamiento por enterramiento, calificándolo como un Manantial Hidrotermal de Entalpia Baja (Potencial bajo), los datos en Ciénaga  a 4 metros de profundidad referente a la base de emanación, poseen temperaturas entre (41-45) °C, con predominancia de (SO4) en la solución, además de material triturado de formaciones circundantes, sugiere condiciones geológicas de zona de falla, calentadas por una fase de vapor en mescla con aguas superficiales, siendo establecid...

Faults play an intricate role in hydrocarbon migration and accumulation since they can serve either as a conduit or a seal. Quantitative evaluation of fault opening/sealing properties requires the selection of valid and optimal parameters among numerous geological factors to characterize the hydraulic behaviors of faults. The present study focuses on the Chengbei Step-Fault Area in the Qikou Depression, Bohai Bay Basin, NE China, because hydrocarbon migration and accumulation in this area occurred in a relatively short period so that accumulated hydrocarbons can be used as an indicator to deduce hydraulic connectivity of a fault zone between two sites. Various geological parameters pertinent to a fault, such as burial depth, dip angle, throw, strike, percentage of sandstone of faulted intervals, fluid pressure in faulted mudstone, stress normal to the fault plane, and shale gouge ratio, are analyzed to assess their effectiveness in characterizing fault connectivity. An index, the fault-connectivity probability (N p), is proposed to evaluate the possibility that a fault has been once serving as a migration pathway. The statistical relationship between N p and any a geological parameter may be used to indicate the effectiveness of this parameter in characterizing the connectivity of a fault during hydrocarbon migration. The correlation coefficient of a relationship is a good indicator of the effectiveness; and the results are generally in agreement with qualitative assessments. Parameters representing a single geological factor are generally ineffective, whereas those representing implicitly or explicitly two or more factors, such as shale gouge ratio, stress normal to the fault plane, and fault opening index, are more effective.

Structurally controlled, syn-rift, clastic depocentres are of economic interest as hydrocarbon reservoirs; understanding the structure of their bounding faults is of great relevance, e.g. in the assessment of faultcontrolled hydrocarbon retention potential. Here we investigate the structure of the Dombjerg Fault Zone (Wollaston Forland, NE Greenland), a syn-rift border fault that juxtaposes syn-rift deep-water hangingwall clastics against a footwall of crystalline basement. A series of discrete fault strands characterize the central fault zone, where discrete slip surfaces, fault rock assemblages and extreme fracturing are common. A chemical alteration zone (CAZ) of fault-related calcite cementation envelops the fault and places strong controls on the style of deformation, particularly in the hanging-wall. The hanging-wall damage zone includes faults, joints, veins and, outside the CAZ, disaggregation deformation bands. Footwall deformation includes faults, joints and veins. Our observations suggest that the CAZ formed during early-stage fault slip and imparted a mechanical control on later fault-related deformation. This study thus gives new insights to the structure of an exposed basin-bounding fault and highlights a spatiotemporal interplay between fault damage and chemical alteration, the latter of which is often underreported in fault studies. To better elucidate the structure, evolution and flow properties of faults (outcrop or subsurface), both fault damage and fault-related chemical alteration must be considered.

Introduction. It is well known that fault zones are generally characterized by a highly fractured low-velocity belt (damage zone), hundreds of meter wide, bounded by higher-velocity area (host rock) that can broaden for some kilometres (Ben-Zion et al,. 2003; Ben-Zion and Sammis, 2003, 2009 and references therein). Such geometrical setting and impedance contrast is in principle proficient to produce local amplification of ground motion (Peng and Ben-Zion, 2006; Calderoni et al., 2010; Cultrera et al., 2003; Seeber et al., 2000), as well as to support the development of fault zone trapped waves. There is a large number of papers that describe propagation properties of fault-guided waves (e.g., Li et al., 1994; Mizuno, Nishigami, 2006) in terms of ground motion amplification having a propensity to be maximum along the fault-parallel direction. These observations, both in theoretical and experimental approaches deal with almost pure strike slip faults such as the S. Andreas and the Anatolian faults (see Li et al., 2000; Ben Zion et al., 2003). Studies about local seismic response nearby fault zones have been performed in Italy and in California by Cultrera et al. (2003), Calderoni et al. (2010), Pischiutta et al. (2012) who observed evidences of ground motion amplification in the fault zone environments and strong directional effects with high angle to the fault strike. Similar studies, performed by Rigano et al. (2008) and Di Giulio et al. (2009) documented the presence of a systematic polarization of horizontal ground motion, near faults located on the eastern part of the Etnean area, that was never coincident with the strike of the tectonic structures. These directional effects were observed both during local and regional earthquakes, as well as using ambient noise measurements, therefore suggesting the use of microtremors for investigating ground motion polarization properties along and across the main tectonic structures of all the volcanic area. All the observations showed evidence of directional amplifications not parallel to the fault strike, as would have been expected for trapped waves. In the present study, the results of new measurements are shown and discussed. The data were recorded in newly investigated tectonic structures of the volcano located both on the western flank of Mt. Etna (Ragalna fault system) and on the eastern flank of the volcano (Piedimonte fault) as well as in a non-volcanic area (Malta Island), located in the Hyblean foreland. Moreover, several measurements were performed in areas significantly distant from the studied tectonic structures (Piano dei Grilli and Malta area), in order to observe how directional effects can change at increasing distance from the fault lines. Tectonic of the study area. Southeastern Sicily is located in a complex tectonic region being at the boundary between African and European plates (see inset map in Fig. 1a). Along this border, Mt. Etna, a basaltic volcano more than 3300 m high and with a diameter of about 40 km, resulting from the interaction of regional tectonics and local scale volcano-related processes (McGuire and Pullen, 1989), is sited. The island of Malta is placed in the Hyblean foreland, belonging to the African plate. Although the sedimentary platform on which the Maltese islands are situated was formed during the Triassic, there are no surface outcrops of this age. Most of the formations here outcropping were deposited during the Oligocene and Miocene when the whole area was part of the Malta-Ragusa platform and, as such, attached to the African margin (Pedley et al., 1978). The whole study area is delineated by the crossing of lithosphere structures that give rise to the origin of Mt. Etna and by the presence of the Malta Hyblean fault system that runs down the Sicilian coast towards the Ionian sea. A series of horst and graben structures, NW-SE and NNW-SSE oriented, that are linked to the Malta-Hyblean escarpment, characterize indeed the tectonic setting of this area. On Malta, the geo-structural pattern is dominated by two intersecting fault systems which alternate in tectonic activity. An older ENE-WSW trending fault, the Victoria Lines Fault (or Great Fault), traverses the islands and is crossed by a younger NW-SE trending fault, the Maghlaq Fault 214 GNGTS 2012 SESSIONE 2.2 GNGTS 2012 SESSIONE 2.2 GNGTS 2012 SESSIONE 2.2 GNGTS 2012 SESSIONE 2.2 GNGTS 2012

Mass transport by aqueous fluids is a dynamic process in shallow crustal systems, redistributing nutrients as well as contaminants. Rock matrix diffusion into fractures (void space) within crystalline rock has been postulated to play an important role in the transient storage of solutes. The reacted volume of host rock involved, however, will be controlled by fluid-rock reactions. Here we present the results of a study which focusses on defining the length scale over which rock matrix diffusion operates within crystalline rock over timescales that are relevant to safety assessment of radioactive and other long-lived wastes. Through detailed chemical and structural analysis of natural specimens sampled at depth from an active system (Toki Granite, Japan), we show that, contrary to commonly proposed models, the length scale of rock matrix diffusion may be extremely small, on the order of centimetres, even over timescales of millions of years. This implies that in many cases the import...

Étude comparée de la fracturation observable sur carottes de forage et obtenue par diagraphie. Application au marbre de Saint-Béat (31) Résumé L'analyse structurale d'un massif rocheux dans le cadre d'un projet de tunnel passe dans la majorité des cas par une analyse des discontinuités présentes grâce à l'imagerie de paroi. Cette méthode de reconnaissance est combinée à d'autres techniques pour reconnaître l'ensemble des caractéristiques du massif. Cette technique, très utile, présente néanmoins des limites d'application qu'il convient de prendre en compte. Pour illustrer notre propos, nous nous sommes appuyés sur le cas des reconnaissances menées pour le tunnel de Saint-Béat, en comparant les discontinuités relevées sur imagerie numérique de paroi et manuellement sur carottes. Nous avons mis en avant les biais induits par ces méthodes, biais qu'il convient de prendre en compte pour mieux caractériser la géométrie du réseau de fractures considéré. Mots-clés : imagerie de paroi, carottes, densité de fracturation, marbre.

Étude comparée de la fracturation observable sur carottes de forage et obtenue par diagraphie. Application au marbre de Saint-Béat (31) Résumé L'analyse structurale d'un massif rocheux dans le cadre d'un projet de tunnel passe dans la majorité des cas par une analyse des discontinuités présentes grâce à l'imagerie de paroi. Cette méthode de reconnaissance est combinée à d'autres techniques pour reconnaître l'ensemble des caractéristiques du massif. Cette technique, très utile, présente néanmoins des limites d'application qu'il convient de prendre en compte. Pour illustrer notre propos, nous nous sommes appuyés sur le cas des reconnaissances menées pour le tunnel de Saint-Béat, en comparant les discontinuités relevées sur imagerie numérique de paroi et manuellement sur carottes. Nous avons mis en avant les biais induits par ces méthodes, biais qu'il convient de prendre en compte pour mieux caractériser la géométrie du réseau de fractures considéré. Mots-clés : imagerie de paroi, carottes, densité de fracturation, marbre.

The present study investigates mode I interlaminar fracture toughness of aramid/epoxy, carbon/epoxy and intra-ply hybrid composites, obtained from carbon and aramid fibres as the reinforcement of an epoxy matrix, maintaining the total fibre content equal to 50 wt.%. The bidirectional, woven fabric specimens were fabricated using vacuum moulding technique. Double Cantilever Beam (DCB) test configuration was used to study the Mode I interlaminar fracture toughness. Two not very different pre-crack lengths were considered for the present study, namely 40 and 42 mm, to show the influence of small variations on crack development during fracture. The obtained results are compared according to their energy release rate GIC: this indicates that the intra-ply composition shows enhanced delamination resistance with respect to the other two materials. The results also show that the intra-ply hybrid composite has the highest fracture toughness. The maximum critical load and corresponding deflection are closely related in experimental results and theoretical prediction.

The secondary (metachronous) magnetization components identified in the Precambrian complexes of the Karelian Craton have been analyzed. The average directions of high-temperature components (deviations from the true direction) have been calculated based on the contribution of secondary magnetization components resulting from tectonomagmatic events of uneven ages. The Precambrian key poles often coincide with the vector sum of the Phanerozoic magnetization components of uneven ages. The conclusion on the primary/secondary origin of the Precambrian paleomagnetic poles should be made on the basis of the integrated petro-and paleomagnetic and isotope data and geological correlations, rather than based on only the paleomagnetic reliability tests.

In the basement fractured reservoirs, geometric parameters of fractures constitute the main properties for modeling and prediction of reservoir behavior and then fluid flow. This study aims to propose geometric description and quantify the multiscale network organization and its effect on connectivity using a wide-ranging scale analysis and orders scale classification. This work takes place in the Noble Hills (NH) range, located in the Death Valley (DV, USA). The statistical analyses were performed from regional maps to thin sections. The combination of the length datasets has led to compute a power law exponent around −2, meaning that the connectivity is ruled by the small and the large fractures. Three domains have been highlighted in the NH: (1) domain A is characterized by a dominance of the NW/SE direction at the fourth order scale; (2) domain B is characterized by a dominance of the E/W and the NW/SE directions at respectively the fourth and third order scales; (3) domain C is...

Investigation of the Surco pluton, a granodioritic body approximately 12 km in diameter and age 20 Ma, located near Lima, Peru, was initiated in order to obtain a geomagnetic reversal record. More than 300 samples provide a complete section through the intrusion. Preliminary results obtained using conventional paleomagnetic techniques indicate that the western part of the pluton records the ambient field behavior well; a consistent reversed direction is followed by a partial reversed to normal transition as one progresses into the core of the intrusion. Plots of NRM vs. IRM(S) demagnetization indicate a steady decrease in the geomagnetic field intensity prior to the reversal. The intrusion does not appear to have recorded the recovery of the normal intensity after the reversal. The existence of a complete section through the intrusion permitted, in principle, the observation of a symmetrical record of the reversal from each side of the pluton. However, the results from the eastern Surco section present a confusing picture and reveal significant variations in rock magnetic and remanence properties along section. Magnetic properties of mineral separates were studied in an attempt to understand variability in the rock as a paleomagnetic recorder. In general, the feldspars contain an unstable magnetization, while the mafic minerals hold a more stable magentization. In the eastern Surco, there are considerable variations in their magnetic properties.

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Siendo el objetivo del presente estudio determinar la capacidad de sostenimiento de las placas para pernos de roca de mayor aplicación en el Perú, ha sido necesario realizar pruebas de compresión y tracción sobre cuatro tipos de placas: Python, Expanbol y dos tipos para los pernos Hydrabolt. Las pruebas se llevaron a cabo en el Laboratorio de Materiales de la PUCP, a partir de las cuales se concluye que las placas que sufren menor deformación global a la compresión son las Python, que se deforma 3,5 mm para una carga máxima de 109,68 KN, y las placas refiladas Hydrabolt son las que más se deforman, 25,10 mm para la carga máxima de 40,56 KN. Es de destacar que las placas Python tienen 0,7 mm mayor espesor que las Hydrabolt y son muy rígidas. Las placas que más se deforman por compresión y tracción son las Expanbol (586,44 %), seguido por las placas refiladas Hydrabolt. Las que menos se deforman son las Python, 16,30 % (compresión) y 15,43 % (tracción central). Asimismo, las placas su...

We delineate shallow structures of the Mozumi-Sukenobu fault, central Japan, using fault zone waves generated by nearsurface explosions and detected by a seismometer array. Two explosive sources, S1 and S2, were placed at a distance of about 2 km from the array, and the other two, S3 and S4, were at a distance of about 4 km. Fault zone head waves and fault zone trapped waves following direct P wave arrivals were clearly identified in the seismograms recorded by a linear seismometer array deployed across the fault in a research tunnel at a depth of 300 m. Synthetic waveforms generated by a 3-D finite-difference (3-D FD) method were compared with observed fault zone waves up to 25 Hz. The best fitting model indicates a 200-m-wide lowvelocity zone extending at least to shot site S1 located 2 km east of the seismic array with a 20% decrease in the P wave velocity relative to the wall rock. The width of the low-velocity zone is consistent with the fault zone defined by direct geological observation in the research tunnel. However, the low-velocity zone should disappear just to the east of the site S1 to explain the observed fault zone waves for shot S3 and S4 located 4 km east of the seismometer array. Yet the observation and the simulation show notable trapped wave excitation even though shots S3 and S4 are outside the fault zone. These results indicate that (1) the effective waveguide for seismic waves along the fault does not exist east of source site S1 although the surface traces of the fault are observed in this region, and (2) considerable trapped waves can be excited by sources well outside the fault zone. These results highlight the along-strike variability in fault zone structure.

Crystalline-rock aquifers generally yield limited groundwater resources. However, some highly productive aquifers may be encountered, typically near tectonic discontinuities. In this study, we used a multidisciplinary experimental field approach to investigate the hydrogeological behavior of a sub-vertical permeable fault zone identified by lineament mapping. We particularly focused our investigations on the hydrogeological interactions with neighboring reservoirs. The geometry of the permeable domains was identified from geological information and hydraulic test interpretations. The system was characterized under natural conditions and during a 9-week large-scale pumping test. We used a combination of piezometric analysis, flow logs, groundwater dating and tracer tests to describe the interactions between permeable domains and the general hydrodynamical behaviors. A clear vertical compartmentalization and a strong spatial heterogeneity of permeability are highlighted. Under ambient conditions, the vertical permeable fault zone allows discharge of deep groundwater flows within the superficial permeable domain. The estimated flow across the total length of the fault zone ranged from 170 to 200 m 3 /day. Under pumping conditions, hydrological data and groundwater dating clearly indicated a flow inversion. The fault zone appears to be highly dependent on the surrounding reservoirs which mainly ensure its recharge. Groundwater fluxes were estimated from tracer tests interpretation. This study demonstrates the hydrogeological capacities of a sub-vertical fault aquifer in a crystalline context. By describing the hydrological behavior of a fault zone, this study provides important constrain about groundwater management and protection of such resources.

Studying seismic response at complex geological settings is a challenge due the occurrence of site effects related to widespread faulting/ fracturing characteristics of the rock masses. Fault-related site effect is always a crucial aspect of an assessment of seismic hazard, but especially in assessments of areas where urban settlements are located in the proximity of regional fault zones. In order to detail the correlation between fault properties and seismic noise response (in terms of directional amplification), we have used a multidisciplinary approach to study a pervasively faulted limestone sequence cropping out in the central Apennines (Italy). We integrated results from (1) geological and structural surveys, (2) in situ geomechanical analyses and (3) geophysical measurements (ambient noise measurements processed with the H/V technique) performed along and across a 50 m-thick, NW-SE-striking fault zone cutting through a limestone sequence. We then reconstructed the architecture of the fault zone by individualising different structural domains (a fault core and two damage zones) and, eventually, we evaluated the fracture intensity across the fault zone by correlating structural (discontinuity spacing, discontinuity pervasivity, size of lithons) and geomechanical (rebound hardness index provided by the Schmidt hammer) parameters. Ambient noise measurements documented a variability of directional amplification across the fault zone and in the surrounding undeformed rock mass, making it possible to recognise possible site effects. The results show the occurrence of a main NE-SWtrending directional amplification oriented perpendicular to the strike of dominant slip structures within the fault core, whereas minor polarisation trends are transversal-to-perpendicular to the strike of subsidiary structures within the damage zones. The results support evidence of structurally-controlled directional amplification due to the stiffness anisotropy produced by the orientation of fault-related structures. When compared with results from published studies, our dataset can be used for understanding factors (i.e. the meso-scale fault properties) leading to directional amplification within a fault zone. Accordingly, we discuss our results in terms of the seismic response of the fault zones and the mitigation of seismic hazard in areas associated to tectonic activity.

We present new observations of the geometry and pattern of fault growth from the Thyolo fault, an 85 km long border fault in the southern Malawi Rift, from high-resolution topography and field observations. The rift has a polyphase tectonic history and the Thyolo fault is located towards the edge of the Proterozoic Unango Terrane. Recent activity is demonstrated by an 18.6 ± 7.7 m high fault scarp. Different patterns of segmentation are indicated by fault geometry and fault displacement profiles: two substantial reductions in scarp height do not coincide with surface geometry changes. The surface scarp is divided into two geometrically defined overlapping sections, which are joined by a ~5 km long, fault perpendicular scarp. The scarp height in this linking section is similar to the bounding sections, yet the river drainage network and sediment depocenter distribution is not typical of relay zones. Microstructural and compositional analyses show a 15-180 m thick damage zone with an ...

To evaluate the relationship between the enrichment of REEs and U mineralization, we carried out Principal Component Analysis (PCA) of sandstones above the Phoenix U deposits and in the REE-rich Maw Zone in the eastern Athabasca Basin. The Phoenix deposits, with indicated resources of 70.2 M lbs U 3 O 8 , occur along the unconformity and a steeply dipping fault in the basement at ca. 400 m depth. The Maw Zone, a breccia pipe with surface exposure of 300 by 200 m, consists of highly silicified, hematitized, dravitic tourmaline-rich rocks with high REE (<8.1 wt. % as total REE oxides). The Maw Zone is ca. 4 km southwest from the south end of Phoenix deposits and does not contain high U (< 7.8 ppm U) contents. PCA of sandstones above the Phoenix deposits shows that U is associated with Heavy REEs (HREE)+Y, Light REEs (LREE) and Pb, and inversely correlated with Ti, Zr, Al, and Th. The Maw Zone displays different element groupings as revealed by PCA: U is strongly correlated with V, Cr, Fe, Ni, Cu, Cd, Na, Li and Ba, but very weakly correlated with HREEs+Y, and inversely with LREEs and P. Relative enrichment of HREEs, Y, and P suggests xenotime is the predominant host of the HREEs. The grouping of LREEs+Sr+Th+P suggests the occurrence of monazite and/or aluminum phosphate-sulphate (APS) minerals. A mineralogical study confirmed xenotime and APS minerals as the major host of HREEs and LREEs, respectively. These REE-bearing minerals precipitated from hydrothermal fluids during the brecciation of hematitized sandstones. The positive association between U

This paper presents the results of a study about the main aspects that affect the behavior of soil nailing structures, the interaction between the main elements of the system, its behavioral variables, and its contribution to the overall stability of the system. Four types of Bogota city soil, hard clays, soft clays, dense sands, and loose sands, were analyzed (this classification applies for the soils studied in the present investigation). For characterizing the materials, the results of the field and laboratory tests of the soil studies for phases I and II of the elevated railway were used. We performed models in the equilibrium programs SNAP-2 and Slide, and in the finite element program RS2.

Mass transport by aqueous fluids is a dynamic process in shallow crustal systems, redistributing nutrients as well as contaminants. Rock matrix diffusion into fractures (void space) within crystalline rock has been postulated to play an important role in the transient storage of solutes. The reacted volume of host rock involved, however, will be controlled by fluid-rock reactions. Here we present the results of a study which focusses on defining the length scale over which rock matrix diffusion operates within crystalline rock over timescales that are relevant to safety assessment of radioactive and other long-lived wastes. Through detailed chemical and structural analysis of natural specimens sampled at depth from an active system (Toki Granite, Japan), we show that, contrary to commonly proposed models, the length scale of rock matrix diffusion may be extremely small, on the order of centimetres, even over timescales of millions of years. This implies that in many cases the import...

Understanding faults is challenging but not impossible. Looking at the Punchbowl fault, an ancient trace of the San Andreas Fault in the Transverse Ranges of southern California, is one way to understand a fault that has been studied for years and still hasn't been fully understood. I am interested in grasping the formation and structures of the damage zone of large displacement continental transform faults, in particular the San Andreas Fault. To do this, I characterized the fractures in the damage zone of the Punchbowl Fault. The fractures associated with the Punchbowl Fault include open mode fractures, transgranular cracks, transgranular filled cracks, calcite filled veins, hematite filled veins, shear fractures, and the list continues. The Punchbowl formation rock samples had already been gathered by other students and I went back and looked at new traits of the fracture system, specifically on the microscale. I separated the fractures into three categories; open fractures (OF), shear fractures (SF), and shear fractures with fill (SOF). Each of these rock samples were put on thin sections to observe on a microscale. Eventually I was able to count the number of fractures on a coarse grid and determine the fracture density. The fracture density data showed a decrease in fracture density the further away the samples

<Key points> Both landforms and tectonic stress conditions influence three-dimensional topographic stress and predicted bedrock fracture patterns Spatial variations in the thickness of a fracture-rich zone can be approximated from topographic curvature and tectonic stress conditions Interaction between tectonic stress and topography may influence landforms by creating spatial variations in groundwater flow and weathering

Here, we present an experimental study of the fracturing of anisotropic migmatite with plane-parallel structure (foliation). Four specimens, with different dips of foliation, including subhorizontal (13°), subvertical (86°), and oblique (47°, 67°), were uniaxially loaded up to failure. Acoustic emission monitoring and ultrasonic sounding were applied for fracturing characterization. In case of subhorizontal and subvertical foliation, the tensile source type played an important role before reaching nucleation stress when shearing became dominant. The dominance of non-tension microcracking was characteristic for oblique foliation. The uniaxial loading of migmatite resulted in triaxial stress state regardless of the foliation dip. The minimum stress axis was in the subhorizontal direction of the foliation dip. The triaxial stress state caused the preferential orientation of induced shear and tension microcracks that had the same azimuthal orientation as the foliation. Preferential microcracking resulted in preferential orientation of the failure plane. Based on the anisotropic behavior of migmatite's characteristic mechanical properties, as well as its mechanism of failure that is typical for anisotropic rocks, the obtained conclusions may be generalized for other types of metamorphic anisotropic rocks with a plane-parallel structure.

Here, we present an experimental study of the fracturing of anisotropic migmatite with plane-parallel structure (foliation). Four specimens, with different dips of foliation, including subhorizontal (13°), subvertical (86°), and oblique (47°, 67°), were uniaxially loaded up to failure. Acoustic emission monitoring and ultrasonic sounding were applied for fracturing characterization. In case of subhorizontal and subvertical foliation, the tensile source type played an important role before reaching nucleation stress when shearing became dominant. The dominance of non-tension microcracking was characteristic for oblique foliation. The uniaxial loading of migmatite resulted in triaxial stress state regardless of the foliation dip. The minimum stress axis was in the subhorizontal direction of the foliation dip. The triaxial stress state caused the preferential orientation of induced shear and tension microcracks that had the same azimuthal orientation as the foliation. Preferential microcracking resulted in preferential orientation of the failure plane. Based on the anisotropic behavior of migmatite's characteristic mechanical properties, as well as its mechanism of failure that is typical for anisotropic rocks, the obtained conclusions may be generalized for other types of metamorphic anisotropic rocks with a plane-parallel structure.

Although the North Anatolian Shear Zone is one of the main lithospheric‐scale strike‐slip deformation zone in the world, playing a prominent role in the complex geodynamic interaction among the Eurasian, Anatolian and Arabian plates, the onset time of its activity remains highly controversial. Here, we tackle this issue by utilizing nannofossil biostratigraphy on deposits from the Taşcilar basin, a pull‐apart basin that we have identified inside the North Anatolian Shear Zone overprinting the Intra‐Pontide suture zone. The syn‐tectonic sedimentary succession of the Taşcilar basin developed completely during the early Eocene (Ypresian; CNE4–CNE5 Zones). The strike‐slip faulting related to the initial onset of the North Anatolian Shear Zone can likely be constrained within the Ypresian, suggesting that the westward escape of the Anatolian plate along the North Anatolian Shear Zone started in the early Eocene.

Structures within very large displacement, mature fault zones, such as the North Branch San Gabriel Fault (NBSGF), are the product of a complex combination of processes. Off-fault damage within a damage zone and first-order geometric asperities, such as bends and steps, are thought to affect earthquake rupture propagation and energy radiation, but the effects are not completely understood. We hypothesize that the rate of vii

In congested urban area it is common to do excavation several meters lower than ground surface to have sufficient space for car parking and electromechanical facilities. Excavation is one of hazardous tasks in the context of civil engineering activities. Geotechnical assessments coupled with engineering geology explorations play important role in reducing hazards associated with excavation. In these excavation works, especially in megacities, concentration on engineering geology aspects of the sites is usually at least or ignored. That is, geological features of the site in addition to the geotechnical properties have to be studied. On the basis of observations, between different case studies, and in one of excavations, this paper presents documented problems encountered governing by presence of a large fault zone. Of these problems are uncontrolled deformation in some parts of the retaining wall and its consequent to damage neighboring buildings, local uprising water table and its effect on the internal and external slope stability. This case study has been done on hard soils that faulting has generated a wide crushed zone with tight fault planes. In this case, it is advised to consider these weak planes in modeling when engineers want to evaluate slope stability safety factor by limit equilibrium analysis and/or calculation of deformation due to excavation by finite element method. These collaborations have to be continued along the excavation implementation because, in these cases, supports with sufficient capacity with the slot excavation (sequential excavation dictated by soil conditions) are needed. That is, two disciplines of geotechnical engineering and engineering geology should support together properly. Therefore, I selected one of problematic project in that there was not such reconciliation between geotechnical and geological data thereby it experienced damage from these defects.