Fracture Sets Research Articles

Feasibility of characterizing an aligned fracture set from azimuthal amplitude variations of PP and converted waves

The amplitude variation with azimuth (AVAz) is commonly used to predict subsurface fracture properties. Published analyses demonstrate the ambiguous characterization from PP-wave AVAz for a vertical set of rotationally variant fractures. Thus, it is worth analyzing the extra information hidden in the converted wave AVAz. We have considered the linear-slip theory to model a vertical or tilted set of rotationally variant fractures in either of two welded half-spaces with polar anisotropy. We investigate the AVAz of PP and converted waves to determine their ability to create unambiguous fracture characterizations. Reflectivity approximations are derived for PP and converted waves to extract their AVAz attributes exclusively depending on fracture properties. We consider pseudo-PSV and pseudo-PSH waves with linear reflectivity approximations transformed from the nonlinear ones for typical converted waves in fractured media. The pseudoconverted waves degenerate into the typical PSV and PSH waves when the incident medium is azimuthally isotropic. For a vertical fracture set, the AVAz of PSV and PSH waves conveys no more deterministic fracture information than that of PP waves. It is demonstrated that the unambiguous characterization is feasible for a fluid-filled vertical fracture set, whereas it might be not for a gas-filled one. For a tilted fracture set, the fracture normal azimuth can be obtained uniquely from the AVAz of PSV or PSH waves but ambiguously from the PP-wave counterpart. Using multiwave AVAz attributes only gives rather vague estimates of the fracture tilt angle. For vertical and titled fracture sets, numerical model tests demonstrate overall better inversions from jointly using PP and PSV waves than solely using either of them.

Characteristics and Main Controls of Tectonic Fractures and Their Contribution to Deep Tight Reservoirs: A Case Study of the Huoshiling-Shahezi Formations in Gudian Half-Graben, Songliao Basin, China

AbstractThe deep volcanic and clastic rocks in the Songliao Basin are typical tight reservoirs with ultralow porosity and permeability. Natural fracture determines the effective reservoirs in the deep strata. Integrated core and thin section observations, image logging, physical property measurement, X-ray diffraction, and seismic attribute analysis were applied to ascertain the characteristics and genetic mechanisms of the tectonic fractures in the Huoshiling-Shahezi Formations of the Gudian half-graben. The contribution of the fractures to deep tight reservoirs was also discussed. Results showed that tectonic fractures are mainly tension, shear, and slip fractures. The density of the fractures in andesitic tuffs with high clay minerals content is significantly higher than that in the other rock types. The main controls of the developmental degree of fractures are tectonism. Three sets of fractures were identified based on the genetic connection between fracture formation and tectonic stress. The NNW-trending tension fractures were formed in the syn-rift stage and successively extended in the post-rift stage. The regional compressional stress drove the formation of the NEE-trending shear fractures and NNW-trending “X” plane-conjugated shear fractures in the postextrusion stage. The averaged porosity and permeability of the reservoirs are generally less than 6.0% and lower than 0.06 mD. The pores can hardly independently provide migration pathways and storage spaces, but the fractures significantly improved the reservoir properties. The fractures were well developed in the regions near the Gudian fault, fault transfer zones, and volcanoes, indicating the distribution of potential reservoirs. Moreover, unraveling the types and orientations of the fractures will provide an essential basis for the analysis of hydrocarbon migration and hydraulic fracture treatments.

Antibiotic cement-coated intramedullary nail is cost-effective for the initial treatment of GAⅢ open tibia fractures

ObjectiveTo evaluate the cost-effectiveness of antibiotic cement-coated intramedullary nails (IMN) in the initial management of Gustilo-Anderson type Ⅲ (GAIII) open tibia fractures. MethodsA break-even equation was used to analyze the costs associated with antibiotic cement-coated IMN and postoperative infection following GAⅢ open tibia fractures. This equation produced a new infection rate, which defines what percentage the antibiotic coated IMN needs to decrease the initial infection rate for its prophylactic use to be cost-effective. The postoperative infection rate used for calculations was 30%, a value established in current literature for these fracture types (6–33%). The institutional costs associated with a single operative debridement and resultant inpatient stay and treatment were determined. A sensitivity analysis was conducted to demonstrate how various total costs of infection and different infection rates affected the break-even rate, the absolute risk reduction (ARR), and the number needed to treat (NNT). ResultsFinancial review yielded an average institutional cost of treating a postoperative infection to be $13,282.85. This number was inclusive of all procedures during an inpatient stay. The added cost of the antibiotic coated implant to the hospital is $743.42. Utilizing the break-even formula with these costs and a 30% initial infection rate, antibiotic coated IMN was economically viable if it decreased infection rate by 0.056% (NNT = 1,785.714). ConclusionThis break-even analysis model suggests the initial use of an antibiotic coated IMN in the setting of GAⅢ open tibia fractures is cost-effective.

Risk Factors for Infection and Subsequent Adverse Clinical Results in the Setting of Operatively Treated Pilon Fractures.

To determine patient-specific and injury-specific factors that may predict infection and other adverse clinical results in the setting of tibial pilon fractures. Retrospective chart review. Level 1 academic trauma center. Two hundred forty-eight patients who underwent operative treatment for tibial pilon fractures between 2010 and 2020. External fixation and/or open reduction and internal fixation. Fracture-related infection rates and specific bacteriology, risk factors associated with development of a fracture-related infection, and predictors of adverse clinical results. Two hundred forty-eight patients were enrolled. There was an infection rate of 21%. The 3 most common pathogens cultured were methicillin-resistant Staphylococcus aureus (20.3%), Enterobacter cloacae (16.7%), and methicillin-resistant Staphylococcus aureus (15.5%). There was no significant difference in age, sex, race, body mass index, or smoking status between those who developed an infection and those who did not. Patients with diabetes mellitus ( P = 0.0001), open fractures ( P = 0.0043), and comminuted fractures (OTA/AO 43C2 and 43C3) ( P = 0.0065) were more likely to develop a fracture-related infection. The presence of a polymicrobial infection was positively associated with adverse clinical results ( P = 0.006). History of diabetes was also positively associated with adverse results ( P = 0.019). History of diabetes and severe fractures, such as those that were open or comminuted fractures, were positively associated with developing a fracture-related infection after the operative fixation of tibial pilon fractures. History of diabetes and presence of a polymicrobial infection were independently associated with adverse clinical results. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

A novel image-based approach for interactive characterization of rock fracture spacing in a tunnel face

This paper presents a novel integrated method for interactive characterization of fracture spacing in rock tunnel sections. The main procedure includes four steps: (1) Automatic extraction of fracture traces, (2) digitization of trace maps, (3) disconnection and grouping of traces, and (4) interactive measurement of fracture set spacing, total spacing, and surface rock quality designation (S-RQD) value. To evaluate the performance of the proposed method, sample images were obtained by employing a photogrammetry-based scheme in tunnel faces. Experiments were then conducted to determine the optimal parameter values (i.e. distance threshold, angle threshold, and number of fracture trace grouping) for characterizing rock fracture spacing. By applying the identified optimal parameters involved in the model, the proposed method could lead to excellent qualitative results to a new tunnel face. To perform a quantitative analysis, three methods (i.e. field, straightening, and the proposed method) were employed in the same study and comparisons were made. The proposed method agrees well with the field measurement in terms of the maximum and average values of measured spacing distribution. Overall, the proposed method has reasonably good accuracy and interactive advantage for estimating the ultimate fracture spacing and S-RQD. It can be a possible extension of existing methods for fracture spacing characterization for two-dimensional (2D) rock tunnel faces.

Formation evaluation of Deccan (basalt) trap basement of Kutch Offshore basin, Gulf of Kutch, India

Deccan basalt trap that serves as basement rock for a large sedimentary expanse in western India has long been expected to be a hydrocarbon prospect. In the last decade or so, the Kutch Offshore basin, located in western India and towards the outer extends of these traps, has reported gas indications in some of the drilled wells. These indications have sufficed the need to characterize these fractured basements for commercial hydrocarbon potential. Deccan basalt trap is a combination of multiple lava flows where the base of each flow is massive, and the top is weathered or vesicular or brecciated. The present study identifies these textural variations within basalt using conventional open hole logs and delineates the zones with good reservoir properties. Various methods such as the density-neutron cross plots, density-sonic travel time overlay, and weathering scale generated using deep resistivity values have proven to be useful in differentiating weathered and fresh basalt intervals. The ratio of deep and shallow resistivity was used to identify permeable zones within the basalt. The weathered and fresh basalt zones were integrated with permeable zones to identify four reservoir facies (Fractured basalt, Massive basalt, Weathered basalt having permeability, and Weathered Basalt with no permeability) in the studied wells. The micro resistivity image data proved to be of great help in identifying vesicular and brecciated basalt facies along with weathered/fractured basalt and the conventional log signatures of these basalt facies were standardized in this study. Two sets of natural fractures were also identified from resistivity image data in Deccan basalts. The main trend has strike orientation in NE-SW and the other set in NW-SE direction. Maximum and minimum stress directions estimated from drilling-induced fractures and borehole breakouts are 10–40° N and 100–130° N, respectively. This study has given key insights into the various facies present in the Deccan trap and standardizes a methodology to identify interesting reservoir zones within the basalt. The study helps to reduce the uncertainties in the formation evaluation of the Deccan trap extends of the Kutch Offshore.

Does tranexamic acid reliably reduce blood loss in proximal femur fracture surgery?

PurposeThe aim of our study was to investigate the use of tranexamic acid in patients with proximal femoral fractures and compare the total blood loss, transfusion rates, complications, and the application method.MethodsA retrospective single center cohort study (level I trauma center) with 1479 patients treated operatively for a proximal femoral fracture between January 2016 and June 2020 was performed. 1 g of tranexamic acid was applied (systemic, topic or combined application). Patient data, surgical procedure, complications, and mortality were assessed. Hemoglobin levels, blood loss and transfusion rates for patients with and without tranexamic acid and the application methods were compared.Results667 femoral neck fractures, 701 pertrochanteric and 109 subtrochanteric fractures were included. Mean age was 80.8 years. 274 patients received tranexamic acid. At admission average hemoglobin was 12.2 g/l. Hemoglobin drop postoperatively was less after tranexamic acid (9.72 vs. 9.35 g/dl). Transfusion rates were lowered significantly by 17.1% after tranexamic acid. Blood loss was reduced for all patients after tranexamic acid independent of fracture morphology. The combination of 1 g i.v. and 1 g topical-applied tranexamic acid seems to be more effective. Complication rates did not differ.ConclusionTranexamic acid is effective in reducing blood loss and transfusion rates, without increasing the risk of thromboembolic events after proximal femoral fractures. For open reduction and nailing and arthroplasty in fracture setting combined topical and single i.v. application seems most effective and closed reduction with nailing can be treated by single dose i.v. application of 1 g tranexamic acid.

Calibration of Complex Discrete Fracture Network Using Microseismic Events and Fracture Propagation Modelling with Seamless Reservoir Production Simulation

Abstract During the unconventional reservoir development, a proper modelling of the underground fracture networks and their effects on production is crucial for reservoir development potential and realistic economic analysis. Conventionally, the complex fracture system formed by hydraulic and natural fractures is extremely difficult to capture, let alone to numerically simulate it. Most importantly, the current best solution can only rely on the knowledge of the natural fractures from the geology and geophysics team and hydraulic fractures from the engineering team. Nevertheless, this solution fails to realize the dynamic stress regime variations when fracturing jobs are done within the horizontal wellbore. In this study, a variety of data source and modelling tools is harnessed to delineate a more realistic and representative discrete fracture network (DFN). The first step is to obtain the original natural fractures already depicted from geological and geophysical information and the statistical information regarding the spatial configurations of this DFN. Next, a new set of natural fractures is generated by an in-house natural fracture generator while preserving the spatial characteristics of the original natural fractures at the same time. Then, a combined DFN of the original natural fracture and newly generated natural fractures is accomplished. This combined DFN is then intensity-calibrated by the given microseismic cloud events, especially focusing on the near-wellbore region. Then, a displacement discontinuity method- (DDM-) based in-house hydraulic fracture propagation model is used to generate hydraulic fractures with complex boundaries, honoring the fracturing job logistics from the engineering team. After this step, an ultimate and highly representative DFN can be achieved. By applying this very novel workflow, DFN characterizations of both a single-well scenario and well-pad (3 wells) scenarios have been highly successful. Statistics such as the cluster-wise hydraulic fracture half-length, height, aperture, and numbers of activated/nonactivated natural fractures can be easily presented. Through the powerful numerical method called the embedded discrete fracture model (EDFM), production simulation and stimulated reservoir volume evaluation can be seamlessly studied. Extents of 3D drainage volumes can also be plotted with ease. Overall, a holistic picture regarding the unconventional reservoir’s underground DFN can be reliably depicted, using the proposed workflow.

Triassic multistage antimony-gold mineralization in the Precambrian sedimentary rocks of South China: Insights from structural analysis, paragenesis, 40Ar/39Ar age, in-situ S-Pb isotope and trace elements of the Longwangjiang-Jiangdongwan orefield, Xuefengshan Mountain

The Xiangzhong (XZ) Basin and its neighboring Xuefengshan (XFS) Mountain in South China, as one of the world-class antimony (Sb) producers, have provided appropriately 67% of globally exploited Sb metal (0.46 million tons) in human history. The associated gold (Au) with Sb in this region is also of significant economic values. In previous studies, these Sb-Au deposits were debated as a diversity of genetic types such as epithermal, magmatic-hydrothermal, sedimentary exhalative (SEDEX) and orogenic Sb-Au deposits. To evaluate these genesis hypotheses, we select the representative Longwangjiang-Jiangdongwan (LWJ-JDW) orefield to reveal the Sb-Au accumulation process and metal-fluid sources of these deposits. Our orefield-scale structural analysis shows that the localization of principal Sb-Au orebodies is controlled by a NE-striking sinistral shearing system composed by an integrated set of NE-striking and SE-dipping fractures in the pre-ore folded Neoproterozoic Wuqiangxi slate. Two chief ore periods were identified, including the marine sedimentation (SI, pyrite nodular) and tectonic-metamorphic hydrothermal period (SⅡ−SⅣ, Sb-Au veins). The second period is further subdivided into three stages of SⅡ (pre-tectonic deformed pyrite-milky quartz veins), Siii (syn-tectonic pyrite-arsenopyrite-stibnite-quartz veins) and SⅣ (post-tectonic stibnite-calcite veinlets). It is notable that gold precipitation is significantly prior to Sb ores at LWJ-JDW. Three sericite samples throughout SⅡ−SⅣ yield a group of well-defined 40Ar/39Ar plateau ages (253 ± 4, 234 ± 3 and 206 ± 2 Ma, respectively). This indicates the multistage Sb-Au mineralization initiated from Early Triassic and terminated at Late Triassic time. Further trace elements analyses show the earliest nodular PyI is enriched in a list of As, Ni, Sb, Cu, Se, Co, Pb, Zn and Ti that can be analogy to the diagenetic pyrite in the organic-rich marine sedimentary rocks. Extremely high Sb (median, 1107 ppm) and mediate Au (0.07 ppm) are monitored in PyI, indicative of the initial Sb and Au involvement from the Neoproterozoic sedimentation. Comparably, sulfides of the later SⅡ−SⅣ possess a similar spectrum of trace elements but with highly variable concentrations. All the sulfide generations host the wide range of in-situ δ34SV-CDT values (–23.9 to −3.7‰ for SⅠ, −7.6 to −2.9‰ for SⅡ−SⅣ, respectively), indicating sulfur originally sourced from bacterial sulfate reaction (BSR) of the Neoproterozoic seawater sulfates, and then gradually reduced by thermochemical sulfate reaction (TSR) during the subsequent Au-Sb-induced tectonic-metamorphic hydrothermal activity. The lead isotope compositions in accordance with the evolution lines of upper crust and orogen, implying that the Pb were chiefly sourced from host slate of the Wuqiangxi Formation and its underlying basement. Synthesis of these data, we proposed that the Sb-Au accumulation at LWJ-JDW was caused by the multistage mineralization from Neoproterozoic marine sedimentation to Triassic episodic deformation and metamorphic processes (253–206 Ma).

Fractures in the Niagara Escarpment in Ontario, Canada: distribution, connectivity, and geohazard implications

AbstractThe Niagara Escarpment is a geological feature located in southern Ontario, Canada, and the northeastern United States, comprising highly fractured sandstone, shale and carbonates deposited during the Ordovician and Silurian periods. Differential erosion of the strata has generated a steep cliff face which bisects the city of Hamilton, Ontario. Geological fractures are widespread in the escarpment and result in the formation of unstable blocks of rock subject to erosion through rockfall. This presents structural stability issues of concern due to the proximity of the escarpment to urban infrastructure. We quantify and analyse fracture networks in the escarpment using a combined field- and numerical-modelling-based approach. The location, orientation and aperture of fractures were documented from local outcrops using scanline and area survey methods. Clusters of poles describing the orientation of geological discontinuities were identified in spherical projections, defining three sets: (1) a sub-vertical stratabound set striking N–S, (2) a sub-vertical stratabound set striking E–W, and (3) a set parallel to horizontal sedimentary bedding planes which we infer controlled sub-vertical fracture geometry. Discrete fracture network modelling of fracture sets highlights their high degree of connectivity, and contribution to local geohazards, and quantifies their role in controlling fluid flow through escarpment strata, which is dependent on fracture aperture. Additionally, bedding planes have the potential to act as free surfaces, facilitating stress conditions in which approximately cuboid blocks are produced, and increasing the risk of rockfalls. We conclude that fractures present a first-order control on the fluid-flow properties and stability of the Niagara Escarpment.

Estimating size of finite fracture networks in layered reservoirs

Conductive fractures in petroleum reservoirs may be totally isolated or fully interconnected. There is an intermediate state between the two extremities. Partially fractured reservoirs include finite fracture networks (FFN), which are bundles of interconnected fractures embedded in a sea of isolated fractures. Devising measures for sizes of FFNs is crucial in estimating critical engineering aspects such as productivity index, production decline rate and expected ultimate recovery of wells especially in reservoirs with low matrix porosity and permeability. Here, we present results of statistical evaluation of FFN size in relation to fracture connectivity which is in essence the number of fracture intersections per fracture. The analysis is based on a large number of stochastic 2-dimensional (2D) Poisson models of sub-vertical layer bound fractures. Fracture length in the models has log normal or truncated power distribution and fracture strike has circular normal distribution. The models may have single or multiple fracture sets and various truncation modes with different probabilities.The analysis shows that number of fracture intersections per fracture can be accurately estimated by a fracture connectivity index, which is defined as product of facture scan-line density, average fracture length and sine of strike standard deviation. The statistically significant finding of this study is that the number of fractures within a FFN is an exponential function of fracture connectivity index. All three fracture properties defining the index can be measured on borehole image logs. Hence it should be possible to estimate fracture connectivity and corresponding FFN size from borehole image data. The analysis pertains to 2D fracture connectivity which is always the lower bound of number of fracture intersections in 3-dimensions. Therefore the exponential relationships must also hold for actual 3-dimensional layer-bound fractures with variable dips.

Predictors of Physical Abuse in Elder Patients With Fracture.

Introduction:Elder abuse is a public health issue requiring attention. Unlike abuse in the pediatric population, predictors of elder abuse in patients with fracture have not been well defined.Methods:Elderly patients with physical abuse and fracture were abstracted using the 2007 to 2017 National Emergency Department Sample database. Univariate comparisons, multivariate regression, and adjusted odds ratios were used to determine independent predictors of elder abuse compared with nonabuse fracture controls.Results:Thirteen percent of elder physical abuse patients presenting to the emergency department had fracture. Of all patients with fracture, elder abuse patients tended to be younger; be female; belong to lower income quartiles; and have codiagnoses of volume depletion, mental disorders, dementia, and intellectual disability. Presentation with other forms of elder abuse, such as psychological abuse, neglect, and sexual abuse, and multiple fractures were also associated with elder physical abuse. Multivariate regression found elder abuse to be more likely in the setting of skull and rib fractures and less likely in the setting of femur and foot and ankle fractures.Discussion:This study identified predictors of elder physical abuse in fracture patients older than 60 years. As with pediatric abuse, heightened awareness of potential physical abuse should be considered, especially in higher risk patients.

Poster 267: The Impact of Posterior Malleolar Fixation on Syndesmotic Stability

Objectives:Trans-syndesmotic fixation with suture buttons, posterior malleolar fixation (PMF) with screws and anterior inferior tibiofibular ligament (AITFL) augmentation with suture tape have all been suggested as potential treatments in the setting of a malleolar fracture. However, there is no consensus on the optimal treatment for small vs. large malleolar fractures. The purpose of this study was to determine which combination of: 1) posterior malleolar screw fixation, 2) syndesmotic fixation with suture button (SB), and 3) AITFL augmentation with suture tape (ST) best restored native tibio-fibular and ankle joint kinematics following a small and large posterior malleolar fracture.Methods:Twenty fresh frozen cadaveric lower leg specimens were divided into two groups and underwent biomechanical testing using a 6-degrees-of-freedom robotic arm in 7 states: 1) Native, 2) Syndesmosis Injury + Malleolar Fracture (Group 1: small fracture, Group 2: large fracture) 3) Screw fixation, 4) Screw + Suture Tape Augmentation, 5) Screw + Suture Tape Augmentation + Suture Button, 6) Suture Button + Suture Tape Augmentation, 7) Suture Button. Four biomechanical tests were performed at neutral and at 30 degrees of plantarflexion: 1) Internal Rotation, 2) External Rotation, 3) Lateral Drawer, 4) Posterior Drawer. The position of the tibia, fibula and talus were continuously recorded using a 5-camera motion capture system.Results:No differences were found in the efficacy of treatments between the small fracture and large fracture groups. In the external rotation test, screws with ST augmentation resulted in best stability of the fibula and ankle joint. In the internal rotation test, all repairs that included posterior malleolar screws stabilized the fibula and ankle. Posterior and lateral drawer of the foot resulted in only small differences between the intact and malleolar fracture states.Conclusions:Posterior malleolar fixation resulted in higher syndesmotic stability compared to trans-syndesmotic fixation with SBs. AITFL augmentation with ST provided additional external rotation stability when combined with screw fixation. Posterior malleolar screw fixation with AITFL augmentation using ST may be the preferred surgical method when treating patients with acute ankle injury involving an unstable syndesmosis injury and a posterior malleolar fragment.Figure 1.Sample of Syndesmosis Injury With Repair.Figure 2.Experimental Specimen Set-Up With the 6 D.O.F.Robotic Arm.

The Use of Headless Screws in the Setting of an Acute Posterior Calcaneal Avulsion Fracture in the Pediatric Population: A Case Report

Background: Sever’s is the most common cause of heel pain in the pediatric population and increases the risk of calcaneal apophyseal avulsion fractures. This is an uncommon fracture that faces problems with tenuous soft tissue coverage and high shear forces at the fracture site. Multiple fixation techniques have been employed in addressing this injury, with no one method standing out as superior. Case Presentation: We present a case of a 13-year-old male with a calcaneal apophyseal avulsion fracture in which cannulated headless compression screws were used for fixation. This was found to provide adequate compression across the fracture with minimal hardware prominence. This also allowed for the injection of radiopaque solution through the cannulated screw to rule out subtalar intraarticular penetration. We believe this represents a novel method of addressing these injuries. Conclusion: Cannulated headless compression screws are a suitable fixation technique for pediatric apophyseal avulsion fractures that provide the added benefit of assessment of intra-articular penetration of the subtalar joint by the injection of radiopaque solution through the cannulated screw.

Routine Histopathologic Analysis of Hip and Knee Bone Specimens After Total Joint Arthroplasty.

Total hip and total knee arthroplasties (THA/TKA) are some of the most common elective surgeries done in the United States. Routine histopathologic analysis of hip and knee bone specimens after total joint arthroplasty commonly occurs to identify unexpected pathologic findings and serves as a quality assurance measure. As the most common indication for THA and TKA is osteoarthritis, the practice of routine histopathologic analysis may not be routinely warranted. There is no clear consensus on the cost-effectiveness of this practice, and the literature has questioned both the clinical relevance of discrepancies between surgeon diagnosis and histopathological diagnosis and raised concerns about variance in the histological evaluation of resected specimens by pathologists. Femoral head analysis in the setting of femoral neck fractures has been previously reported, yet there is no clear overview for this topic in the setting of elective THA. The histopathologic features of bone specimens during routine total joint arthroplasty, the cost-effectiveness, and current recommendations will be reviewed.

3D digital outcrop model-based analysis of fracture network along the seismogenic Mt. Vettore Fault System (Central Italy): the importance of inherited fractures

The Mt. Vettore area is located in the Central Apennines (Italy), a region characterized by intense seismic activity that has recorded multiple moderate-to-high magnitude seismic sequences. The seismic activity is due to the presence of normal fault systems, among which is the Mt. Vettore Fault System (VFS), which was last activated during the 2016-17 Central Italy seismic sequence.. Moreover, the region has experienced three major tectonic phases over geological history, thus it is important to unravel their contribution to the current fracture network. Based on the integration of field observation with Unmanned Aerial Vehicle - Digital Photogrammetry data, we aim to analyze the fracture network on eight different outcrops located at different structural positions with respect to VFZ. Results show that the Late Miocene−Early Pliocene compressional phase deeply affected the present-day fracture pattern, which is especially related to the evolution of the Mt. Sibillini regional thrust and its related anticline. The present-day Quaternary extensional phase, and the associated normal faults, mostly reactivate some of the pre-existing fracture sets.

Multiscale physical–chemical analysis of the impact of fracture networks on weathering: Application to nickel redistribution in the formation of Ni-laterite ores, New Caledonia

Supergene processes related to downward water migration and dissolution of primary minerals in the New Caledonian peridotites result in Ni enrichment at the bottom of the lateritic profile near bedrock. However, the combined effects of relief, lateral fluid flow, and complex inherited discontinuity networks filled by serpentine generate a more complex Ni distribution than a simple flat horizon. In surficial environments, fluid flow and mass transfer are not limited to the vertical scale; they can also be related to lateral fluid circulation and local drainage along damage zones in the vicinity of faults. In this study, we present new structural, petrophysical and geochemical data for core samples to shed light on the impact of a fracture network on the alteration and progression of the Ni-enrichment front during weathering. The analysis of element redistribution by XRF mapping coupled with fracture extraction from computed tomography (CT) establishes that the serpentine fracture network comprises sets of sub-orthogonal fractures whose orientations are potentially determined by pre-existing magmatic foliation. The progression of the olivine dissolution front leads to the redistribution and concentration of Ni into the serpentine fracture network as secondary Mg-Ni talc-like phases. The increase in porosity from < 1 % in the bedrock to > 10 % in the saprock is mainly driven by the formation of nanopores. Nanoporosity may control the development of the weathering front and the redistribution of Ni by small-scale diffusion. Structural and geochemical characteristics identified at the sample scale are analogous to those observed on the larger scale of the outcrop and deposit. Scale invariance in the structural organization and geochemical evolution indicates the potential upscaling of the processes involved in the redistribution of Ni.

An analytical solution of equivalent elastic modulus considering confining stress and its variables sensitivity analysis for fractured rock masses

The equivalent elastic modulus is a parameter for controlling the deformation behavior of fractured rock masses in the equivalent continuum approach. The confining stress, whose effect on the equivalent elastic modulus is of great importance, is the fundamental stress environment of natural rock masses. This paper employs an analytical approach to obtain the equivalent elastic modulus of fractured rock masses containing random discrete fractures (RDFs) or regular fracture sets (RFSs) while considering the confining stress. The proposed analytical solution considers not only the elastic properties of the intact rocks and fractures, but also the geometrical structure of the fractures and the confining stress. The performance of the analytical solution is verified by comparing it with the results of numerical tests obtained using the three-dimensional distinct element code (3DEC), leading to a reasonably good agreement. The analytical solution quantitatively demonstrates that the equivalent elastic modulus increases substantially with an increase in confining stress, i.e. it is characterized by stress-dependency. Further, a sensitivity analysis of the variables in the analytical solution is conducted using a global sensitivity analysis approach, i.e. the extended Fourier amplitude sensitivity test (EFAST). The variations in the sensitivity indices for different ranges and distribution types of the variables are investigated. The results provide an in-depth understanding of the influence of the variables on the equivalent elastic modulus from different perspectives. • A new analytical solution of the equivalent elastic modulus for rock masses is proposed. • The confining stress is considered in the analytical solution. • The sensitivity of the variables in the analytical solution is analyzed.

Continuous versus punctuated vein widening in the Marcellus Formation, USA: the fine line between pressure fringes and hydraulic fractures

AbstractCalcite veins are common in organic-rich mudrocks, but their genesis and ability to transmit fluids are debated. A combined microstructural and isotopic investigation of an array of calcite veins recovered in core from the Marcellus Formation reveals that the veins grew via a combination of continuous fibrous growth and punctuated fracture-opening increments. Continuous opening is the result of pressure-solution creep and involves no mechanical fracturing, but rather the growth of a pressure fringe around a pre-existing, sealed fracture. In contrast, incremental opening is accomplished by overpressured, mineral-saturated fluid, which repeatedly ruptures the rock at the cement / host-rock interface. Punctuated growth increments occurred repeatedly throughout an otherwise protracted, continuous growth history, indicating that the present structures preserve hybrid deformation conditions between brittle, fluid-assisted cracking and plastic strain. Stable isotopic signatures match those of a regional opening-mode fracture set that formed in response to catagenetic fluid overpressures amid a tectonically imposed (Alleghanian) stress field. It is concluded that calcite veins form as opening-mode hydraulic fractures and are susceptible to increments of brittle reactivation, even while inelastic growth processes widen and fill the veins with fibrous cement.

Abstract No. 21 Transcatheter arterial embolization outcomes in pediatric pelvic fractures: a National Trauma Data Bank analysis

Traumatic pelvic fractures are associated with high morbidity and mortality due to the presence of life-threatening hemorrhage. While transcatheter arterial embolization is an established therapy for pelvic hemorrhage control in the adult trauma population, large scale studies supporting its application to pediatric patients remain sparse. This population-based study thus aims to assess the efficacy of transcatheter arterial embolization in the setting of pediatric pelvic fractures.