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1
Janetzki, Nathan, Kirsten Benkendorff, and Peter G. Fairweather. "Rocks of different mineralogy show different temperature characteristics: implications for biodiversity on rocky seashores." PeerJ 9 (January 26, 2021): e10712. http://dx.doi.org/10.7717/peerj.10712.
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As some intertidal biota presently live near their upper tolerable thermal limits when emersed, predicted hotter temperatures and an increased frequency of extreme-heat events associated with global climate change may challenge the survival and persistence of such species. To predict the biological ramifications of climate change on rocky seashores, ecologists have collected baseline rock temperature data, which has shown substrate temperature is heterogenous in the rocky intertidal zone. A multitude of factors may affect rock temperature, although the potential roles of boulder surface (upper versus lower), lithology (rock type) and minerology have been largely neglected to date. Consequently, a common-garden experiment using intertidal boulders of six rock types tested whether temperature characteristics differed among rock types, boulder surfaces, and whether temperature characteristics were associated with rock mineralogy. The temperature of the upper and lower surfaces of all six rock types was heterogeneous at the millimetre to centimetre scale. Three qualitative patterns of temperature difference were identified on boulder surfaces: gradients; mosaics; and limited heterogeneity. The frequency of occurrence of these temperature patterns was heavily influenced by cloud cover. Upper surfaces were generally hotter than lower surfaces, plus purple siltstone and grey siltstone consistently had the hottest temperatures and white limestone and quartzite the coolest. Each rock type had unique mineralogy, with maximum temperatures correlated with the highest metallic oxide and trace metal content of rocks. These baseline data show that rock type, boulder surface and mineralogy all contribute to patterns of heterogenous substrate temperature, with the geological history of rocky seashores potentially influencing the future fate of species and populations under various climate change scenarios.
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Turra, A., and M. R. Denadai. "Microhabitat use by two rocky shore gastropods in an intertidal sandy substrate with rocky fragments." Brazilian Journal of Biology 66, no. 1b (February 2006): 351–55. http://dx.doi.org/10.1590/s1519-69842006000200017.
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Sandy beaches in some areas of the São Sebastião Channel in southeastern Brazil have unremittingly undergone a variety of impacts, including the deposition of rock fragments in the intertidal region. Consequently, these environments support a rich fauna comprising both sandy beach and rocky shore organisms. Two rocky shore gastropods, Tegula viridula and Morula nodulosa, are particularly abundant in such environments. An evaluation of the use of microhabitats by these two species revealed that they occupy the available microhabitats in different proportions and the presence of one species is associated with the absence of the other. Morula nodulosa is randomly dispersed, occupying mostly areas with rock fragments covered with sediment and branching brown algae. Tegula viridula shows a clumped dispersion associated with the patchiness of the microhabitats used: the presence of encrusting green algae and absence of sediment and branching brown algae covering the rocks. These findings suggest T. viridula has a lower tolerance than M. nodulosa to sand inundation of the rocky fragments, a stochastic event common to the environment in question.
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Yu, Zhenzi, Ang Li, Bo Zhang, Hongyue Li, Qian Mu, Yonggen Zhou, and Shuai Gao. "Particle Flow Analysis on Mechanical Characteristics of Rock with Two Pre-Existing Fissures." Sustainability 14, no. 22 (November 10, 2022): 14862. http://dx.doi.org/10.3390/su142214862.
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Many research results show that under any stress state the rock mass is most likely to crack, swell, bifurcate, and infiltrate from the fissure tip, resulting in rock engineering instability and failure. In order to study the influence of double fissure angles on rock mechanical characteristics, five rock numerical models with different fissure angles were established by numerical simulation software. Uniaxial compression tests were carried out, and the variation characteristics of rock stress, strain, failure, microcrack, and acoustic emission (AE) were recorded. The test results show that: With increases in the fissure angles, the elastic modulus of rock increased, while the peak strength decreased first and then increased. The number of microcracks in rock was greater at 15° and 75° than at other angles. The microcracks in rock were mainly tensile cracks, and relatively few were shear cracks. The angles of microcracks were mostly concentrated between 0 and 180°, most of which were between 60 and 110°. The failure of rock was relatively light when the fissure angle was15° or 75°, but it produced more and smaller fragments, and the failure was the most serious when the fissure angle was 30°. The angles of the fissures affected the maximum number of AE events, the strain values for the initial AE event, and the maximal AE event. This research can provide some reference for disasters caused by rocks with pre-existing fissures.
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Liu, Yang, Cai-Ping Lu, and Heng Zhang. "Mutation effect of acoustic and electromagnetic emissions of hard rock impact failure." International Journal of Distributed Sensor Networks 15, no. 1 (January 2019): 155014771882447. http://dx.doi.org/10.1177/1550147718824473.
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To reveal acoustic emission and electromagnetic emission effects during hard rock impact failure is a crucial issue for monitoring and warning rockburst risk induced by hard roof fracture and fall. The presented research focuses on acoustic emission and electromagnetic emission and microseismic effects detected during laboratory tests and by in situ multi-parameter observations, and the field observations agreed satisfactorily with the experimental evidences. The following main conclusions were drawn: (1) the stress level, frequency of micro-cracks, and impact failure regularity of hard rocks can be revealed with electromagnetic emission and acoustic emission/microseismic parameters, respectively; (2) acoustic emission/microseismic event counts can directly reveal the cracks change in rocks, and the initiation, propagation, and coalescence of micro-cracks can be presented as first increase, followed by decrease in acoustic emission/microseismic event counts; (3) in most cases, only when stress suddenly decreases or the rock final collapses, acoustic emissions show obviously abnormal; and (4) acoustic emission/microseismic can be more effectively applied to warn rockburst danger. The above conclusions may shed light on the effective monitoring and warning methods of rockburst triggered by hard roof fall, and events contribute to some interpretations to originally transient precursors of hard rock fracturing.
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JASTRZĘBSKI, MIROSŁAW, BARTOSZ BUDZYŃ, and WOJCIECH STAWIKOWSKI. "Cambro-Ordovician vs Devono-Carboniferous geodynamic evolution of the Bohemian Massif: evidence from P–T–t studies in the Orlica–Śnieżnik Dome, SW Poland." Geological Magazine 156, no. 3 (November 16, 2017): 447–70. http://dx.doi.org/10.1017/s0016756817000887.
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AbstractThe pressure–temperature–deformation–time (P–T–d–t) record of metagranitic rocks and adjacent diverse rocks of the metavolcano-sedimentary group from the Orlica–Śnieżnik Dome (OSD) in SW Poland is examined. The study aims to better understand the course of the break-up of northern Gondwana and the overprinting Variscan tectonometamorphism in the NE Bohemian Massif. We test the existing hypotheses that explain the Cambro-Ordovician thermal event recorded in the meta-supracrustal group by (i) syn-deformational regional metamorphism or (ii) the contact metamorphism of the (meta)sedimentary rocks around the intruding ~490–500 Ma granitic magmas. In addition, we check the extent and timing of the Variscan prograde and retrograde medium-pressure metamorphism in the OSD. The results imply that Early Palaeozoic monazites, rarely preserved in both rock groups, document ~490–500 Ma volcanic and plutonic events related to the Gondwana's break-up and following disturbance of the Th–U–Pb system during younger, Variscan events. The monazite geochronology reveals no distinct Cambro-Ordovician thermal aureole around the post-granitic orthogneisses. However, no large-scale Variscan juxtaposition is evident between the two main OSD rock groups or within the meta-supracrustal rocks. Consistent P–T–d–t results for the meta-supracrustal rocks and the orthogneisses suggest that their precursors contacted before the Variscan tectonometamorphism. The directly contiguous ortho- and paragneisses together experienced tectonometamorphic processes at maximum depths that correspond to 7.5–8.0 kbar and maximum temperatures of ~600–620°C, as a result of the Variscan collision of Gondwana and Euramerica. The continental collision-related events intensified at ~360 Ma and ~330–340 Ma.
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Alber, M., R. Fritschen, and M. Bischoff. "Strength constraints of shallow crustal strata from analyses of mining induced seismicity." Solid Earth Discussions 5, no. 1 (June 3, 2013): 737–65. http://dx.doi.org/10.5194/sed-5-737-2013.
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Abstract. Stress redistributions around large underground excavations such as coal mines may lead to failure of the surrounding rock mass. Some of these failure processes were recorded as seismic events. In this paper the different failure processes such as rock mass failure or the reactivation of faults are delineated from the seismic records. These are substantiated by rock mechanical analyses including laboratory strength tests on coal measure rocks obtained from underground drilling. Additionally, shear tests on discontinuities in coal measure rocks (slickensides in shale and rough sandstone joints) were conducted to grasp the possible variation of strength properties of faults. Numerical modeling was employed to evaluate the state of stress at the locations where seismic events did occur.
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Anderson, John G., and James N. Brune. "Methodology for using precarious rocks in Nevada to test seismic hazard models." Bulletin of the Seismological Society of America 89, no. 2 (April 1, 1999): 456–67. http://dx.doi.org/10.1785/bssa0890020456.
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Abstract Fields of precariously balanced rocks indicate that strong earthquake motions have not occurred at that site since the precarious rocks developed. These fields can be characterized with an estimate of the peak acceleration that would be sufficient to topple the rocks and an estimate of how long the rocks have been precarious. This article uses this information to test the input to probabilistic seismic hazard analysis. The fundamental assumption is that the probability of exceeding a ground motion capable of toppling a precarious rock during a time period equal to the age of the rock is equal to the confidence level at which the inputs to the probabilistic seismic hazard analysis can be rejected. We performed a probabilistic seismic hazard analysis for 26 sites of observed precarious rocks in Nevada, using preliminary estimates of the toppling acceleration and the age of the features. Two standard models are rejected with over 95% confidence by most of the precarious rock observations. We consider several possible explanations for the inconsistency. A probabilistic seismic hazard analysis that eliminates the area sources and only includes faults is consistent with the precarious rock observations at most of the sites. Spatial clustering of small-magnitude events could maintain this effect without contradicting the precarious rock observations. However, it may not be necessary to completely reject the area sources from our probabilistic seismic hazard analysis. The physics of rock stability may allow increasing the minimum magnitude to 6.0 in the area sources, because the short duration of high-frequency accelerations in smaller events may not topple all precarious rocks. The precarious rocks could generally have small site effects. Attenuation models may overestimate ground motions on the foot wall of normal faults, and a different attenuation model in general might decrease the ground-motion predictions. The ergodic assumption that is made in estimating the uncertainty in attenuation models may be contributing to overestimate the hazard. Individually, each of these effects might allow more of the precarious rock sites to be consistent with the area source zones.
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Jenkin, Gawen R. T., Paul Mohr, John G. Mitchell, and Anthony E. Fallick. "Carboniferous dykes as monitors of post-Caledonian fluid events in West Connacht, Ireland." Transactions of the Royal Society of Edinburgh: Earth Sciences 88, no. 4 (1997): 225–43. http://dx.doi.org/10.1017/s0263593300006969.
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AbstractThe causes of hydrothermal alteration in dolerite dykes intruding Caledonian rocks of W Connacht are investigated using stable isotope, water content and K–Ar data for whole rocks and mineral separates. Using an isochron approach the Logmór dyke in the north is re-dated to 308±4 Ma; previously determined older whole-rock ages reflect excess 40Ar. The ∼ 305 Ma age previously proposed for the Teach Dóite suite in the south is reinforced by a 305 Ma age on a pyroxene separate, although the severe resetting of most samples is emphasised by other pyroxene and plagioclase ages of ∼210 Ma. Pyroxene δ18O values for these Upper Carboniferous dykes are mostly 5·5 to 6·1%, indicating negligible crustal contamination. Logmór whole-rock samples have water contents of 1·7–2·1 wt.%, δ5D= 59 to –47‰ and δ18O = 9·4 to 9·6‰; plagioclase shows little mineralogical alteration but its δ18O is 9·7‰. Hydrothermal alteration involving a local formation or metamorphic water took place at high fluid/rock ratios and high temperature during cooling after intrusion, most probably in a thermally-driven convection system. Teach Dóite dykes have water contents of 2·0–4·2 wt.%. δD= –58 to –38‰ and δ18O = 3·6 to 9·2‰, and were mostly altered in two stages; hydration upon intrusion to ∼ 2 wt.% water by contemporaneous meteoric water at low fluid/rock ratios was followed by extensive chemical and isotopic alteration at ∼210 Ma (Upper Triassic) by surface waters. This latter event could also have caused the extensive alteration observed in the host rocks.
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Lorenz, R. D., J. M. Norris, B. K. Jackson, R. D. Norris, J. W. Chadbourne, and J. Ray. "Trail formation by ice-shoved "sailing stones" observed at Racetrack Playa, Death Valley National Park." Earth Surface Dynamics Discussions 2, no. 2 (August 28, 2014): 1005–22. http://dx.doi.org/10.5194/esurfd-2-1005-2014.
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Abstract. Trails in the usually-hard mud of Racetrack Playa in Death Valley National Park attest to the seemingly-improbable movement of massive rocks on an exceptionally flat surface. The movement of these rocks, previously described as "sliding stones", "playa scrapers", "sailing stones" etc., has been the subject of speculation for almost a century but is an exceptionally rare phenomenon and until now has not been directly observed. Here we report documentation of multiple rock movement and trail formation events in the winter of 2013–2014 by in situ observation, video, timelapse cameras, a dedicated meteorological station and GPS tracking of instrumented rocks. Movement involved dozens of rocks, forming fresh trails typically of 10s of meters length at speeds of ~5 cm s−1 and were caused by wind stress on a transient thin layer of floating ice. Fracture and local thinning of the ice decouples some rocks from the ice movement, such that only a subset of rocks move in a given event.
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Yao, Chi, Sizhi Zeng, and Jianhua Yang. "Failure Process Simulation of Interlayered Rocks under Compression." Advances in Civil Engineering 2018 (August 1, 2018): 1–13. http://dx.doi.org/10.1155/2018/9615457.
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Anisotropy in strength and deformation of rock mass induced by bedding planes and interlayered structures is a vital problem in rock mechanics and rock engineering. The modified rigid block spring method (RBSM), initially proposed for modeling of isotropic rock, is extended to study the failure process of interlayered rocks under compression with different confining pressures. The modified rigid block spring method is used to simulate the initiation and propagation of microcracks. The Mohr–Coulomb criterion is employed to determine shear failure events and the tensile strength criterion for tensile failure events. Rock materials are replaced by an assembly of Voronoi-based polygonal blocks. To explicitly simulate structural planes and for automatic mesh generation, a multistep point insertion procedure is proposed. A typical experiment on interlayered rocks in literature is simulated using the proposed model. Effects of the orientation of bedding planes with regard to the loading direction on the failure mechanism and strength anisotropy are emphasized. Results indicate that the modified RBSM model succeeds in capturing main failure mechanisms and strength anisotropy induced by interlayered structures and different confining pressures.
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Chen, Guoqing, Yan Zhang, Runqiu Huang, Fan Guo, and Guofeng Zhang. "Failure Mechanism of Rock Bridge Based on Acoustic Emission Technique." Journal of Sensors 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/964730.
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Acoustic emission (AE) technique is widely used in various fields as a reliable nondestructive examination technology. Two experimental tests were carried out in a rock mechanics laboratory, which include (1) small scale direct shear tests of rock bridge with different lengths and (2) large scale landslide model with locked section. The relationship of AE event count and record time was analyzed during the tests. The AE source location technology and comparative analysis with its actual failure model were done. It can be found that whether it is small scale test or large scale landslide model test, AE technique accurately located the AE source point, which reflected the failure generation and expansion of internal cracks in rock samples. Large scale landslide model with locked section test showed that rock bridge in rocky slope has typical brittle failure behavior. The two tests based on AE technique well revealed the rock failure mechanism in rocky slope and clarified the cause of high speed and long distance sliding of rocky slope.
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Tucker, Gregory E., Scott W. McCoy, and Daniel E. J. Hobley. "A lattice grain model of hillslope evolution." Earth Surface Dynamics 6, no. 3 (July 17, 2018): 563–82. http://dx.doi.org/10.5194/esurf-6-563-2018.
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Abstract. This paper describes and explores a new continuous-time stochastic cellular automaton model of hillslope evolution. The Grain Hill model provides a computational framework with which to study slope forms that arise from stochastic disturbance and rock weathering events. The model operates on a hexagonal lattice, with cell states representing fluid, rock, and grain aggregates that are either stationary or in a state of motion in one of the six cardinal lattice directions. Cells representing near-surface soil material undergo stochastic disturbance events, in which initially stationary material is put into motion. Net downslope transport emerges from the greater likelihood for disturbed material to move downhill than to move uphill. Cells representing rock undergo stochastic weathering events in which the rock is converted into regolith. The model can reproduce a range of common slope forms, from fully soil mantled to rocky or partially mantled, and from convex-upward to planar shapes. An optional additional state represents large blocks that cannot be displaced upward by disturbance events. With the addition of this state, the model captures the morphology of hogbacks, scarps, and similar features. In its simplest form, the model has only three process parameters, which represent disturbance frequency, characteristic disturbance depth, and base-level lowering rate, respectively. Incorporating physical weathering of rock adds one additional parameter, representing the characteristic rock weathering rate. These parameters are not arbitrary but rather have a direct link with corresponding parameters in continuum theory. Comparison between observed and modeled slope forms demonstrates that the model can reproduce both the shape and scale of real hillslope profiles. Model experiments highlight the importance of regolith cover fraction in governing both the downslope mass transport rate and the rate of physical weathering. Equilibrium rocky hillslope profiles are possible even when the rate of base-level lowering exceeds the nominal bare-rock weathering rate, because increases in both slope gradient and roughness can allow for rock weathering rates that are greater than the flat-surface maximum. Examples of transient relaxation of steep, rocky slopes predict the formation of a regolith-mantled pediment that migrates headward through time while maintaining a sharp slope break.
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Cheng, Guoqiang, Xiaohui Sun, and Jiangong Li. "Study on the Precursors of Coal-Rock Fracture Based on the Maximum Lyapunov Exponent of Acoustic Emission Parameters." Geofluids 2022 (March 18, 2022): 1–10. http://dx.doi.org/10.1155/2022/3280185.
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In this paper, the relationship between acoustic emission (AE) parameters and coal-rock fracture is investigated by using the discrete element particle flow simulation software PFC. PFC is used to simulate the coal-rock uniaxial compression test for extracting the time series of AE event number, calculate the maximum Lyapunov exponent of the time series, and analyze the chaotic characteristics of AE event number. Combined with the relationship between the maximum point of the Lyapunov exponent and the peak point of the stress-strain curve, the coal-rock fracture precursor model was developed. The results indicate that during the uniaxial compression of coal-rock, the number of AE events first increases and then decreases, while the maximum point appears after the peak point of the stress-strain curve. The lower the coal-rock homogeneity, the earlier is the initial occurrence time of AE events. The AE event number has chaotic characteristics. In most cases, the chaotic characteristics of the number of AE events are the most evident before the specimen is completely destroyed. When the maximum Lyapunov exponent of AE event number time series mutates, it indicates that the specimen is about to be destroyed entirely, which can be used as a precursor criterion for coal-rock fracture.
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Sun, Lihui, Yaxin Long, Xing Li, Zhixin Jiang, Yu Fan, Zongze Wang, and Xiangang Han. "Effect of Loading Rate on the Mechanical Properties of Weakly Cemented Sandstone." Sustainability 15, no. 3 (February 2, 2023): 2750. http://dx.doi.org/10.3390/su15032750.
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Weakly cemented rocks are characterized by low strength, loose structure, and easy disintegration. High-intensity mining activities can damage and rupture such rock bodies and induce damage, such as flaking and roofing on roadways. To reveal the mining intensity influence on the weakly cemented rocks’ deformation and damage, a numerical particle flow model of weakly cemented sandstone was established based on particle flow theory. Uniaxial compression simulation tests were conducted at four loading rates of 0.01, 0.1, 0.5, and 1 mm/min to study the weakly cemented sandstone’s stress–strain relationship, damage rupture, acoustic emission, and energy evolution. The results show that, with an increased loading rate, the uniaxial compressive strength of weakly cemented sandstone increases exponentially, and the rupture mode transforms from brittle damage to ductile damage; the greater the loading rate, the greater the degree of damage and crushing range of the rock. Further, with an increased loading rate, the peak hysteresis of rock acoustic emission events decreases, and the number of events increases; the energy accumulated in the rock increases, thus intensifying the degree of rock damage. Therefore, the possibility of engineering disasters should be considered when conducting high-speed underground mining activities.
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Zhang, Wenlong, Tianhong Huo, Chen Li, Cunwen Wang, Xiaocheng Qu, and Chongwei Xin. "Characteristics of Valuable Microseismic Events in Heading Face of an Underground Coal Mine Using Microseismic System." Shock and Vibration 2021 (March 26, 2021): 1–10. http://dx.doi.org/10.1155/2021/6683238.
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Rock burst monitoring of heading face is a weak aspect of rock burst monitoring in China; acoustic emission (AE) monitoring is one of the few monitoring technologies used in heading face, but its target signals are small energy events which are easy to be disturbed. Researchers usually focus on the weak AE events but ignore the microseismic (MS) events (different from AE event and caused by a larger scale of coal fracture), while this kind of events can also reflect the pressure situation of heading face and have higher energy value which may become a better indicator for rock burst monitoring of heading face. So, the basic characteristics of MS events in heading face are studied based on a running vibration signal acquisition system, including the occurrence position, main frequency range, maximum amplitude (MA) range, event duration, and relationship with geological structure. This paper provides a development basis of the monitoring method for rock burst monitoring of heading face by using MS events.
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Lee, K. Kh, and V. V. Ivanov. "Studies of Changes in the Electrical Resistivity of Rocks of the Tashtagol Mine in a Critical Rock-bump Hazardous State Based on the Kinetic Concept of Solids Destruction." Occupational Safety in Industry, no. 12 (December 2020): 19–25. http://dx.doi.org/10.24000/0409-2961-2020-12-19-25.
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Main hypotheses of the occurrence of seismic events centers, including rock bumps are presented. Equations of kinetic theory of strength are given. A two-stage kinetic model of crack accumulation and catastrophic destruction of rocks is formulated. It consists in the fact that at the first stage of the rock bump preparation there is a diffuse accumulation of cracks, and at the second — merging of cracks, appearance of enlarged cracks and formation of the destruction center. The results are presented concerning the theoretical and laboratory measurements of change of specific electric resistance of the host rocks and ores of iron ore deposit at mechanical loading and destruction. It has been shown that the relative change of specific electrical resistance of the low conductive rocks depends significantly on the ratio of electrical resistance of the rock itself and charged zones near the surface of the incipient cracks during rock loading. With the accumulation of cracks in the process of mechanical loading of the host rocks of the Tashtagol mine, the number of charged point defects of the structure on the crack edges increases. Specific electrical resistance of such rocks decreases with the accumulation of the number of cracks. In the ore bodies and magnetic iron ores, on the contrary, with increasing disturbance, the electrical resistance increases. There is regular change in the electrical resistance of rocks in the intermediate and limit states. For ores and magnetic iron ores, the critical change is 40 %, and for the host rocks with high electrical resistance — 28–37 %. Obtained values of change of the specific electric resistance in the rock critical state can be used for prediction of the rock bumps.
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Lule, Arjol. "Rockfall Analyses at Km 13+550 in the New Road of Vlora, Albania." European Journal of Engineering and Formal Sciences 4, no. 1 (May 15, 2021): 40. http://dx.doi.org/10.26417/473cvm79a.
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Rockfall dynamics is a complex function of the location of the detachment point and the geometry and mechanical properties of both the block and the slope. Theoretically, knowing the initial conditions, the slope geometry, and the relationships describing the energy loss at impact or by rolling, it should be possible to compute the position and velocity of a block at any time. Nevertheless, relevant parameters are difficult to ascertain both in space and time, even for an observed event. Usually, the geometrical and geomechanically properties of the blocks (size, shape, strength, fracturing) and the slope (gradient, length and roughness, longitudinal and transversal concavities and convexities, grain size distribution, elastic moduli, water content, etc.), and the exact location of the source areas are unknown. In this paper, the sources of potential rock fallings involve a rocky area including between km 13+550 and km 13+600 in the new road of Vlora city in Albania. The area is characterized by a rock ridge, shaped like a dome, located few tens of meters above the design road. The purpose of this paper is the rock slope analysis. This analysis consists mainly of defining the sources of falling rocks, estimating the causes (by toppling, rock slides, single blocks) the size, the geometry, and type of blocks, the structural arrangement of joints, etc.
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Wang, Yalei, and Jinming Xu. "Particle Flow Analysis of Acoustic Emission Features of Rock under Rock Burst Stress Path." Geofluids 2022 (November 19, 2022): 1–17. http://dx.doi.org/10.1155/2022/6534034.
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The AE (acoustic emission) features could reflect the process of fracture initiation and propagation in rocks. Taking Lalin railway tunnel granite as an example, a three-dimensional particle flow numerical model of rock was established based on the PFC (particle flow code). The mechanical properties between particles were simulated using parallel bond. The rock burst stress path was simulated using the movement of the wall in the particle flow model. The results of uniaxial compression tests in a laboratory were used to calibrate the mesoscale mechanical parameters of the particle flow model. AE features of rock deformation and failure under different confining pressures were then studied. It shows that the unloading direction of rock may produce strong dilatation deformation during rock burst; with the increase of confining pressure, the more obvious dilatation deformation and the more possibility of serious rock burst to occur; the unloading failure of rock reveals that rock burst is a mixed failure of tensile and shear, and the tensile cracks account for about 70%; the number of AE events of rock unloading failure occur at the top and bottom of the rock first and then expand rapidly to the middle part until the rock is completely destroyed; in the process of rock burst, AE rupture strength is relatively concentrated, the number of AE events surge obviously, and the number of AE events in surge period account for more than 80% of all AE events. The results presented herein may be referable in analyzing the mechanism of rock burst.
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Mineo, Simone, and Giovanna Pappalardo. "Advances in Engineering Geology of Rocks and Rock Masses." Applied Sciences 13, no. 3 (January 18, 2023): 1322. http://dx.doi.org/10.3390/app13031322.
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Slope instability phenomena are among the most hazardous natural events affecting our society, and therefore the physical–mechanical behavior of rock masses with reference to these is a relevant topic for engineering geological practice, as it conditions the realization and functionality of structures and infrastructures, as well as the quality of life and economy [...]
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Balestra, Valentina, Adriano Fiorucci, and Bartolomeo Vigna. "Study of the Trends of Chemical–Physical Parameters in Different Karst Aquifers: Some Examples from Italian Alps." Water 14, no. 3 (February 1, 2022): 441. http://dx.doi.org/10.3390/w14030441.
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The results of a series of continuous characterizations of physical parameters (flow, temperature, water conductivity) and chemical analyses in water springs fed by karst aquifers located in the Piedmont region (northwestern Italy) are presented in this work. Rock masses in carbonate rocks, characterized by very different hydrogeological situations, linked to a different degree of karstification, fracturing, and development of the saturated zone, were examined. A series of data-loggers were installed, operating for several years, and different water sampling missions and subsequent chemical analyses (main ions, metals, and rare earth elements) under different hydrodynamic conditions were carried out. The results show very different trends of chemical–physical water parameters, particularly following significant infiltrative events. Aquifers characterized by a high karstification and reduced saturated zone highlight water mineralization decreases, even within a few hours, as a result of significant flow rate increases (prevalent substitution). Aquifers with a well-developed saturated zone, during an entire flood event, highlight an increase in mineralization linked to the remobilization of water present in the less permeable sectors of the aquifer (piston flow phenomenon). Lastly, aquifers fed by very fractured rocky masses and reduced karstification have a water flow rate with mild annual variations and constant chemical–physical parameters over time (homogenization phenomenon).
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Chen, Feng, Tianhui Ma, Chun’an Tang, Yanhong Du, Zhichao Li, and Fei Liu. "Research on the Law of Large-Scale Deformation and Failure of Soft Rock Based on Microseismic Monitoring." Advances in Civil Engineering 2018 (July 17, 2018): 1–8. http://dx.doi.org/10.1155/2018/9286758.
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Based on the existing Canadian ESG microseismic monitoring system, a mobile microseismic monitoring system for a soft rock tunnel has been successfully constructed through continuous exploration and improvement to study the large-scale nucleation and development of microfractures in the soft rock of the Yangshan Tunnel. All-weather, continuous real-time monitoring is conducted while the tunnel is excavated through drilling and blasting, and the waveform characteristics of microseismic events are analysed. Through the recorded microseismic monitoring data, the variation characteristics of various parameters (e.g., the temporal, spatial, and magnitude distributions of the microseismic events, the frequency of microseismic events, and the microseismic event density and energy) are separately studied during the process of large-scale deformation instability and failure of the soft rock tunnel. The relationship between the deterioration of the rock mass and the microseismic activity during this failure process is consequently discussed. The research results show that a microseismic monitoring system can be used to detect precursors; namely, the microseismic event frequency and energy both will appear “lull” and “active” periods during the whole failure process of soft rock tunnel. Two peaks are observed during the evolution of failure. When the second peak occurs, it is accompanied by the destruction of the surrounding rock. The extent and strength of the damage within the surrounding rock can be delineated by the spatial, temporal, and magnitude distributions of the microseismic events and a microseismic event density nephogram. The results of microseismic analysis confirm that a microseismic monitoring system can be used to monitor the large-scale deformation and failure processes of a soft rock tunnel and provide early warning for on-site construction workers to ensure the smooth development of the project.
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Sun, Yongshuai, Fei Yu, and Jianguo Lv. "Experimental Study on Acoustic Emission Characteristics of Granite and Sandstone under Uniaxial Compression." Geofluids 2023 (February 13, 2023): 1–11. http://dx.doi.org/10.1155/2023/2944871.
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In order to better apply acoustic emission technology to engineering practice, this paper carried out indoor acoustic emission test, and uniaxial compression tests of granite and sandstone under monotonic loading and grading loading were carried out and monitored. The influencing factors of the acoustic emission characteristics of the two rock samples were discussed and the characteristics of the acoustic emission signals corresponding to different stages of rock failure were analyzed. The analysis of the test results includes the curve fitting relationship between the AE event count rate, energy rate, and stress time and the changes of AE event count rate and energy rate under different loading methods. The results of the study are as follows: there is a quiet zone in the acoustic emission event before the rock is destroyed and destabilized, and the higher the rock strength, the more obvious the quiet zone; this important feature can be used as a precursor feature of rock mass failure for prediction, and the rock acoustic emission energy rate is more obvious in the quiet area before destruction than the acoustic emission event rate; rock acoustic emission has experienced initial compaction zone, rising zone, peak zone, and descending zone, whether different rocks go through each stage and how long each stage lasts is related to the nature of the rock; under different loading methods, the failure mechanism of rock is different; the different loading rates of monotonic loading and grading loading will affect the change rate of acoustic emission.
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Kern, Dominik, Fabien Magri, Victor I. Malkovsky, and Thomas Nagel. "Hydro-mechanical effects of seismic events in crystalline rock barriers." Safety of Nuclear Waste Disposal 1 (November 10, 2021): 179–80. http://dx.doi.org/10.5194/sand-1-179-2021.
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Abstract. Under ideal conditions, owing to its extremely low matrix permeability, crystalline rock can constitute a suitable hydro-geological barrier. Mechanically, its high strength and stiffness provide advantages when constructing a repository and for long-term stability. However, crystalline rock usually occurs in a fractured form, which can drastically alter hydromechanical (HM) barrier functions due to increased permeability and decreased strength. Seismic events have the potential to alter these HM properties by activating faults, increasing their transmissibility, creating new fractures or altering network connectivity (De Rubeis et al., 2010). Therefore, it is of high importance to build computational models to allow assessment of the HM effects of seismic events in a Deep Geologic Repository (DGR) in crystalline rock, as illustrated in Fig. 1. For this purpose, we consider a DGR in Russia (Yeniseysky site) for high-level waste in crystalline rock (Proterozoic and Archaean gneiss complexes) that is located close to a potentially seismically active area (Jobmann, 2016). Here, we present a coupled HM simulation, using OpenGeoSys (Kolditz et al., 2012), of a large-scale, three-dimensional finite-element model of the Yeniseysky site to assess the consequences of seismically induced stress-field changes on the local stress field and the fluid flow. This research also provides an outlook of current model development geared towards a more detailed assessment of seismically induced hydro-mechanical processes in porous and fractured rocks.
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Williams, Megan A., David E. Kelsey, Martin Hand, Tom Raimondo, Laura J. Morrissey, Naomi M. Tucker, and Rian A. Dutch. "Further evidence for two metamorphic events in the Mawson Continent." Antarctic Science 30, no. 1 (December 4, 2017): 44–65. http://dx.doi.org/10.1017/s0954102017000451.
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AbstractIn this study,in situand erratic samples from George V Coast (East Antarctica) and southern Eyre Peninsula (Australia) have been used to characterize the microstructural, pressure–temperature and geochronological record of upper amphibolite and granulite facies polymetamorphism in the Mawson Continent to provide insight into the spatial distribution of reworking and the subice geology of the Mawson Continent. Monazite U-Pb data shows thatin situsamples from the George V Coast record exclusively 2450–2400 Ma ages, whereas most erratic samples from glacial moraines at Cape Denison and the Red Banks Charnockite record only 1720–1690 Ma ages, consistent with known ages of the Sleaford and Kimban events, respectively. Phase equilibria forward modelling reveals considerable overlap of the thermal character of these two events. Samples with unimodal 1720–1690 Ma Kimban ages reflect either formation after the Sleaford event or complete metamorphic overprinting. Rocks recording only 2450–2400 Ma ages were unaffected by the younger Kimban event, perhaps as a result of unreactive rock compositions inherited from the Sleaford event. Our results suggest the subice geology of the Mawson Continent is a pre-Sleaford-aged terrane with a cover sequence reworked during the Kimban event.
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Tzamos, Evangelos, Micol Bussolesi, Giovanni Grieco, Pietro Marescotti, Laura Crispini, Andreas Kasinos, Niccolò Storni, Konstantinos Simeonidis, and Anastasios Zouboulis. "Mineralogy and Geochemistry of Ultramafic Rocks from Rachoni Magnesite Mine, Gerakini (Chalkidiki, Northern Greece)." Minerals 10, no. 11 (October 22, 2020): 934. http://dx.doi.org/10.3390/min10110934.
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The importance of magnesite for the EU economy and industry is very high, making the understanding of their genesis for the exploration for new deposits a priority for the raw materials scientific community. In this direction, the study of the magnesite-hosting ultramafic rocks can be proved very useful. For the present study, ultramafic rock samples were collected from the magnesite ore-hosting ophiolite of the Gerakini mining area (Chalkidiki, Greece) to investigate the consecutive alteration events of the rocks which led to the metallogenesis of the significant magnesite ores of the area. All samples were subjected to a series of analytical methods for the determination of their mineralogical and geochemical characteristics: optical microscopy, XRD, SEM, EMPA, ICP–MS/OES and CIPW normalization. The results of these analyses revealed that the ultramafic rocks of the area have not only all been subjected to serpentinization, but these rocks have also undergone carbonation, silification and clay alteration. The latter events are attributed to the circulation of CO2-rich fluids responsible for the formation of the magnesite ores and locally, the further alteration of the serpentinites into listvenites. The current mineralogy of these rocks was found to be linked to one or more alteration event that took place, thus a significant contribution to the metallo- and petrogenetic history of the Gerakini ophiolite has been made. Furthermore, for the first time in literature, Fe inclusions in olivines from Greece were reported.
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Chen, Hongran, Mengyang Zhai, and Lei Xue. "Energy Characteristics of Acoustic Emission at the Volume-Expansion Point of a Rock Bridge: A New Insight into the Evolutionary Mechanism of Coastal Cliff Collapse." Journal of Marine Science and Engineering 9, no. 12 (November 28, 2021): 1338. http://dx.doi.org/10.3390/jmse9121338.
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The recession of a coast can destabilize coastal cliffs. The stability of a cliff is controlled by a rock bridge. Identifying the volume-expansion point of rock bridges is crucial to assess cliff stability, but currently there are few identifying methods. Using a numerical analytical tool, we investigate the acoustic emission characteristics during shear tests on rock bridges. Acoustic emission events with a high energy level, i.e., characteristic events which occur at the volume-expansion point of rock bridges, can indicate this point. The characteristic events, the mainshock (the maximum event corresponding to rock-bridge rupture), and the smaller events between them constitute a special activity pattern, as the micro-seismicity during the evolutionary process of a coastal cliff collapse in Mesnil-Val, NW France showed. This pattern arises in rock bridges with different mechanical properties and geometry, or under different loading conditions. Although the energy level of characteristic events and mainshocks changes with the variation of the conditions, the difference of their energy level is approximately constant. The spatial distribution of characteristic events and mainshocks can indicate the location of rock bridges. These findings help to better understand the evolutionary mechanism of collapses and provide guidelines for monitoring the stability of coastal cliffs.
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Sokolov, S. D., S. A. Silantyev, A. V. Moiseev, M. I. Tuchkova, and V. E. Verzhbitsky. "Amphibolites of the metamorphic basement of Wrangel island: age, nature of the protolite and conditions of metamorphism." Геохимия 64, no. 12 (December 20, 2019): 1222–46. http://dx.doi.org/10.31857/s0016-752564121222-1246.
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New data on petrography, geochemistry and geochronology of metamorphic rocks sampled from Neoproterozoic basement of Wrangel Island are presented. Oceanic affinity for mafic rocks underwent greenschist to amphibolite facies conditions (350600C) has been established by geochemical data. Protolith of this rock belongs to products of the evolution of magmatic melts parental for MORB. Protoliths age is 61713 and 69812 Ma was determined by U-Pb isotope dating of Zircons from these rocks (SHRIMP II and La-ICP MS). There are two main stage of metamorphism could be established: Neoproterozoi Early Paleozoi (amphibolite and greenschist facies conditions) and Middle Cretaceous (greenschist facies condition only), Last stage of metamorphism related to Chukcha deformation events accompanied by formation of folded nappes structure and consequent extension. An comparison of studied rocks with samples dredged at Chukcha Borderland evidenced for certain similarity existing between these rock assemblages judging by their petrography and chemistry.
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Xu, Rongchao, Yiding Jin, and Yumin Zhang. "Experimental Research on Brittleness and Rockburst Proneness of Three Kinds of Hard Rocks under Uniaxial Compression." Advances in Civil Engineering 2021 (July 1, 2021): 1–10. http://dx.doi.org/10.1155/2021/8891633.
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Rockburst is a highly destructive geological disaster caused by excavation and unloading of hard and brittle rock mass under high geostress environment. Quantitative evaluation of rock brittleness and rockburst proneness is one of the important tasks in potential rockburst assessment. In this study, uniaxial compression and acoustic emission tests were carried out for basalt, granite, and marble, and their brittleness and rockburst proneness were quantitatively evaluated. The acoustic emission evolution characteristics of the three rocks during uniaxial compression were analyzed, and the differences of fracture mechanism of the three rocks were compared. The results show that (1) based on the brittleness evaluation index, basalt is the most brittle rock, followed by granite, and marble is the weakest; (2) based on the rockburst proneness evaluation index, combined with the macroscopic failure phenomenon and morphology of the samples, the rockburst proneness of basalt is the strongest, followed by granite, and marble is the weakest; (3) there exists a positive correlation between rockburst proneness and brittleness, and the fitting results show that they are approximately exponential; and (4) brittleness has an important influence on the rock fracture mechanism. Unlike marble, basalt and granite with strong brittleness continuously present high-energy acoustic emission signals in the stage of unstable crack propagation, and large-scale fracture events continue to occur; from the calculation results of the acoustic emission b value, the stronger the brittleness of rock, the larger the proportion of large-scale fracture events in the failure process.
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Grozdev, Valentin, Rossitsa Vassileva, and Irena Peytcheva. "The rare earth elements in zircons as pathfinder of geological events." Review of the Bulgarian Geological Society 83, no. 3 (December 2022): 93–96. http://dx.doi.org/10.52215/rev.bgs.2022.83.3.93.
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The usual main purpose of the zircon investigation is to determine the precise age of particular rocks, applying the U-Pb isotope method. In this study we attempt to reveal the vast potential of zircons in understanding the magmatic and modification processes, as well as the structure of the deeper Earth’s interior, using the analysis of the zircon population of the major volcanic variety in the Ruen tectono-magmatic zone, Kyustendil area, SW Bulgaria. The ascending magmas crosscut different rock types and units along their path to the Earth’s surface. Using the zircon crystal analysis, we may make consideration about the age and chemical characteristics of these units. The trace and rare earth element (REE) content of the zircons brings insights for the rock formation time and discloses characteristics of the deeper parts of the Earth’s crust.
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Giacomini, Anna, Klaus Thoeni, Marina Santise, Fabrizio Diotri, Shaun Booth, Stephen Fityus, and Riccardo Roncella. "Temporal-Spatial Frequency Rockfall Data from Open-Pit Highwalls Using a Low-Cost Monitoring System." Remote Sensing 12, no. 15 (July 31, 2020): 2459. http://dx.doi.org/10.3390/rs12152459.
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In surface mining, rockfall can seriously threaten the safety of personnel located at the base of highwalls and cause serious damage to equipment and machinery. Close-range photogrammetry for the continuous monitoring of rock surfaces represents a valid tool to efficiently assess the potential rockfall hazard and estimate the risk in the affected areas. This work presents an autonomous terrestrial stereo-pair photogrammetric monitoring system developed to observe volumes falling from sub-vertical rock faces located in surface mining environments. The system has the versatility for rapid installation and quick relocation in areas often constrained by accessibility and safety issues and it has the robustness to tolerate the rough environmental conditions typical of mining operations. It allows the collection of synchronised images at different periods with high-sensitivity digital single-lens reflex cameras, producing accurate digital surface models (DSM) of the rock face. Comparisons between successive DSMs can detect detachments and surface movements during defined observation periods. Detailed analysis of the changes in the rock surface, volumes and frequency of the rocks dislodging from the sub-vertical rock surfaces can provide accurate information on event magnitude and return period at very reasonable cost and, therefore, can generate the necessary data for a detailed inventory of the rockfall spatial-temporal occurrence and magnitude. The system was first validated in a trial site, and then applied on a mine site located in NSW (Australia). Results were analysed in terms of multi-temporal data acquired over a period of seven weeks. The excellent detail of the data allowed trends in rockfall event to be correlated to lithology and rainfall events, demonstrating the capability of the system to generate useful data that would otherwise require extended periods of direct observation.
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Jinqiang, Wang, Prabhat Basnet, and Shakil Mahtab. "Review of machine learning and deep learning application in mine microseismic event classification." Mining of Mineral Deposits 15, no. 1 (2021): 19–26. http://dx.doi.org/10.33271/mining15.01.019.
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Purpose. To put forward the concept of machine learning and deep learning approach in Mining Engineering in order to get high accuracy in separating mine microseismic (MS) event from non-useful events such as noise events blasting events and others. Methods. Traditionally applied methods are described and their low impact on classifying MS events is discussed. General historical description of machine learning and deep learning methods is shortly elaborated and different approaches conducted using these methods for classifying MS events are analysed. Findings. Acquired MS data from rock fracturing process recorded by sensors are inaccurate due to complex mining environment. They always need preprocessing in order to classify actual seismic events. Traditional detecting and classifying methods do not always yield precise results, which is especially disappointing when different events have a similar nature. The breakthrough of machine learning and deep learning methods made it possible to classify various MS events with higher precision compared to the traditional one. This paper introduces a state-of-the-art review of the application of machine learning and deep learning in identifying mine MS events. Originality.Previously adopted methods are discussed in short, and a brief historical outline of Machine learning and deep learning development is presented. The recent advancement in discriminating MS events from other events is discussed in the context of these mechanisms, and finally conclusions and suggestions related to the relevant field are drawn. Practical implications. By means of machin learning and deep learning technology mine microseismic events can be identified accurately which allows to determine the source location so as to prevent rock burst. Keywords: rock burst, MS event, blasting event, noise event, machine learning, deep learning
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Daly, L., M. R. Lee, S. Piazolo, S. Griffin, M. Bazargan, F. Campanale, P. Chung, et al. "Boom boom pow: Shock-facilitated aqueous alteration and evidence for two shock events in the Martian nakhlite meteorites." Science Advances 5, no. 9 (September 2019): eaaw5549. http://dx.doi.org/10.1126/sciadv.aaw5549.
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Nakhlite meteorites are ~1.4 to 1.3 Ga old igneous rocks, aqueously altered on Mars ~630 Ma ago. We test the theory that water-rock interaction was impact driven. Electron backscatter diffraction demonstrates that the meteorites Miller Range 03346 and Lafayette were heterogeneously deformed, leading to localized regions of brecciation, plastic deformation, and mechanical twinning of augite. Numerical modeling shows that the pattern of deformation is consistent with shock-generated compressive and tensile stresses. Mesostasis within shocked areas was aqueously altered to phyllosilicates, carbonates, and oxides, suggesting a genetic link between the two processes. We propose that an impact ~630 Ma ago simultaneously deformed the nakhlite parent rocks and generated liquid water by melting of permafrost. Ensuing water-rock interaction focused on shocked mesostasis with a high density of reactive sites. The nakhlite source location must have two spatially correlated craters, one ~630 Ma old and another, ejecting the meteorites, ~11 Ma ago.
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Zhang, Jinliang, Jiaqi Guo, Jinshui Liu, Wenlong Shen, Na Li, and Guangchen Xu. "3D-Basin Modelling of the Lishui Sag: Research of Hydrocarbon Potential, Petroleum Generation and Migration." Energies 12, no. 4 (February 17, 2019): 650. http://dx.doi.org/10.3390/en12040650.
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The Lishui Sag is located in the southeastern part of the Taibei Depression, in the East China Sea basin, where the sag is the major hydrocarbon accumulation zone. A three dimensional modelling approach was used to estimate the mass of petroleum generation and accumulated during the evolution of the basin. Calibration of the model, based on measured maturity (vitrinite reflectance) and borehole temperatures, took into consideration two main periods of erosion events: a late Cretaceous to early Paleocene event, and an Oligocene erosion event. The maturation histories of the main source rock formations were reconstructed and show that the peak maturities have been reached in the west central part of the basin. Our study included source rock analysis, measurement of fluid inclusion homogenization temperatures, and basin history modelling to define the source rock properties, the thermal evolution and hydrocarbon generation history, and possible hydrocarbon accumulation processes in the Lishui Sag. The study found that the main hydrocarbon source for the Lishui Sag are argillaceous source rocks in the Yueguifeng Formation. The hydrocarbon generation period lasted from 58 Ma to 32 Ma. The first period of hydrocarbon accumulation lasted from 51.8 Ma to 32 Ma, and the second period lasted from 23 Ma to the present. The accumulation zones mainly located in the structural high and lithologic-fault screened reservoir filling with the hydrocarbon migrated from the deep sag in the south west direction.
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Zhang, Zhiyong, Diego Arosio, Azadeh Hojat, and Luigi Zanzi. "Reclassification of Microseismic Events through Hypocenter Location: Case Study on an Unstable Rock Face in Northern Italy." Geosciences 11, no. 1 (January 15, 2021): 37. http://dx.doi.org/10.3390/geosciences11010037.
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Passive seismic methods are increasingly used in monitoring unstable rock slopes that are likely to cause rockfalls. Event classification is a basic step in microseismic monitoring. However, the classification of events generated by the propagation of fractures and rockfalls is still uncertain due to their similar features in the time and frequency domains. Hypocenter localization might be a powerful tool to distinguish events generated by fracture propagation from those caused by rockfalls. In this study, a classification procedure based on hypocenter location was validated using a selected subset of high-quality data recorded by a five-geophone network installed on a steep rock slope in Northern Italy. Considering the complexity and heterogeneity of the rock mass, a 3D velocity model that was derived from a tomographic experiment was used. We performed the localization using the equal differential time method. The location results fairly fit our expectations on suspected rockfall events because most signals were located near the rock face. However, only 4 out of 20 suspected fracture events were unquestionably confirmed as fractures being located inside the rock mass and far enough from the rock face. Further improvements in location accuracy are still necessary to distinguish suspected fracture events located close to the rock face from rockfalls. This study demonstrates that hypocenter location is a promising method to improve the final classification of microseismic events.
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Powell, Wayne. "Greenschist-facies metamorphism of the Burgess Shale and its implications for models of fossil formation and preservation." Canadian Journal of Earth Sciences 40, no. 1 (January 1, 2003): 13–25. http://dx.doi.org/10.1139/e02-103.
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Metamorphosed silty mudstones of the Burgess Shale and Stephen Shale formations record a poly metamorphic history. An early greenschist-facies event associated with burial by Paleozoic strata produced a nearly ubiquitous bedding-parallel cleavage (S1). Tectonic exhumation during the formation of the southern Canadian Rocky Mountains produced a domainal subgreenschist-facies retrograde overprint in which a high-angle crenulation cleavage (S2) was developed. Whereas all rocks have experienced these two events, the degree of deformation and fossil pre servation varies with position relative to the Cathedral Escarpment. This paleosubmarine cliff resulted in a zone of reduced deformation within adjacent strata by buttressing them during burial and deflecting deformation during orogenesis. Fossil-bearing strata are composed of a typical greenschist assemblage of muscovitechloritequartzalbite, are devoid of clays, and contain an average of 0.28% organic carbon. This typical metamudstone assemblage is consistent with the typical whole-rock composition of these rocks which tends to be richer in K and Al and poorer in Fe relative to the Post-Archean Average Shale. These mineralogicalcompositional characteristics suggest that the premetamorphic clay assemblage was likely illitesmectitekaolinite, with no evidence of highly reactive species such as nontronite or Na-montmorillonite. This is contrary to the required conditions for taphonomic models involving organic preservation due to clay-related suppression of decomposition-related reactions. Metamorphism of the Burgess Shale has also re duced the total organic carbon content to <20% of initial values. This must be considered in any models that involve interpretation of organic carbon in diagenetic processes (e.g., fossil formation and determination of paleoredox conditions).
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Kim, J. S., Wooil M. Moon, Ganpat Lodha, Mulu Serzu, and Nash Soonawala. "Imaging of reflection seismic energy for mapping shallow fracture zones in crystalline rocks." GEOPHYSICS 59, no. 5 (May 1994): 753–65. http://dx.doi.org/10.1190/1.1443633.
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The high‐resolution reflection seismic technique is being used increasingly to address geologic exploration and engineering problems. There are, however, a number of problems in applying reflection seismic techniques in a crystalline rock environment. The reflection seismic data collected over a fractured crystalline rock environment are often characterized by low signal‐to‐noise ratios (S/N) and inconsistent reflection events. Thus it is important to develop data processing strategies and correlation schemes for the imaging of fracture zones in crystalline rocks. Two sets of very low S/N, high‐resolution seismic data, previously collected by two different contractors in Pinawa, Canada, and the island of Äspö, Sweden, were reprocessed and analyzed, with special emphasis on the shallow reflection events occurring at depths as shallow as 60–100 m. The processing strategy included enhancing the signals hidden behind large‐amplitude noise, including clipped ground roll. The pre‐ and poststack processing includes shot f-k filtering, residual statics, careful muting after NMO correction, energy balance, and coherency filtering. The final processed seismic sections indicate that reflected energy in these data sets is closely related to rock quality in Äspö data and fracturing in Atomic Energy of Canada, Ltd. (AECL) data. The lithologic boundaries are not clearly mappable in these data. When thickness of the reflection zone is of the order of a wavelength, the top and bottom of the zone may be resolved. The major fracture zones in crystalline rocks correlate closely with the well‐log data and are usually characterized by very low velocity and produce low‐acoustic‐impedance contrasts compared to those of surrounding rocks. Because the incidence angles vary rapidly for shallow‐reflection geometries, segments of major fracture zones can effectively be analyzed in terms of reflectivity. Reflection images of each fracture zone were investigated in the common‐offset section, where each focused event was associated with a consistent incidence angle on the reflectivity map. The complex attributes of the data indicate that strong reflectors at shallow depth coincide with intensely fractured zones. These correlate well with instantaneous amplitude plots and instantaneous frequency plots. The instantaneous phase plot also identifies the major and minor fractures.
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Elmi, Chiara, Anna Cipriani, Federico Lugli, and Giampaolo Sighinolfi. "Insights on the Origin of Vitrified Rocks from Serravuda, Acri (Italy): Rock Fulgurite or Anthropogenic Activity?" Geosciences 11, no. 12 (December 1, 2021): 493. http://dx.doi.org/10.3390/geosciences11120493.
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In this study, twenty five partially vitrified rocks and four samples of vitrified rocks collected on the top hill called Serravuda (Acri, Calabria, Italy) are analyzed. The goal is to shed light on the origin of these enigmatic vitrified materials. The analyzed vitrified rocks are a breccia of cemented rock fragments (gneiss, granitoid, and amphibolite fragments) which extends for more than 10 m, forming a continuous mass along the northern and north-west border of the flat top hill. Surrounded by the vitrified accumulation, exposed Paleozoic granitoid substrate rocks show limited melting or heat-alteration processes. By mapping minerals embedded in the glass matrix via X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM), an interpretation of source rock material, reactions, and thermometric indications to form vitrified materials on the top hill of Serravuda, Acri (Italy), is provided. The mineralogical composition of heated or partially vitrified samples is heterogeneous owing to the effects of heating events, but it mostly recalls the parent rock composition (gneiss, granitoid, and amphibolite). The presence of quartz, cristobalite, tridymite, mullite, plagioclase, hercynite, cordierite, and olivine in Serravuda partially vitrified rocks and glasses suggests that samples were subjected to pyrometamorphism and the temperature range at which the glass formed was about 1000–1100 °C in the presence of hydrous gas, burning organic material (e.g., wood), and assuming thermodynamic equilibrium. Lithologies of the heated or partially vitrified rock fragments are a mixture of parent rocks not outcropping on the top of the hill such as gneiss and amphibolite. Data suggest that Serravuda vitrified rocks are most likely the result of anthropic activities and could represent remnants of vitrified fort walls. The mineral assemblage of partially vitrified rocks and glasses suggests that the fort walls were made of slabs derived from the local metamorphic rocks with the addition of Serravuda substrate Paleozoic granitoid rocks to improve the strength and insulation of the fort walls.
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Senfaute, G., A. Duperret, and J. A. Lawrence. "Micro-seismic precursory cracks prior to rock-fall on coastal chalk cliffs: a case study at Mesnil-Val, Normandie, NW France." Natural Hazards and Earth System Sciences 9, no. 5 (October 2, 2009): 1625–41. http://dx.doi.org/10.5194/nhess-9-1625-2009.
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Abstract. Erosion of rock cliffs has been considered to be relatively unpredictable. This perceived stochastic nature of the erosional processes often occurs through collapses along fractures in the rock-mass. The prediction of catastrophic cliff failures and collapses remains very difficult. For advancing in this field, it is important to understand the processes through which a crack is initiated, how it develops and propagates until the final failure. This paper examines the micro-seismic signals recorded 15 h prior to a rock-fall located at Mesnil-Val, France. The results lead to the hypothesis that several phases of failure mechanisms contribute to rock-fall occurrence. The most important phases were associated with micro-seismic event families identified by multiplet selection. Each event family contained one specific frequency spectrum showing a progressive decrease of the frequencies as the rock approached failure suggesting the following phases: 1) the micro-seismic events recorded 15 h before the rock-fall were characterised by the highest frequencies in a large spectrum-band, between ~100 and 1000 Hz (family 1), suggesting a crack initiation mechanism or the opening of existing fractures; 2) the micro-seismic events recorded several minutes before the rock-fall were associated with a clear decrease in the highest frequency components (family 2) suggesting that the mechanism was related to the growing and development (or coalesce) of existing micro-cracks into larger fractures; 3) micro-seismic events recorded just before the rock-fall were associated with a lower frequency spectrum than families 1 and 2, the highest frequency components were absent (family 3), the frequency emission source mechanism could be related to the shearing or opening of the existing large fractures permitting the complete detachment of the blocky rock-mass; 4) finally, micro-seismic events with a very low frequency spectrum (lower than 100 Hz) characterized the rock-fall impact on the ground. These encouraging results offer the possibility of using the micro-seismic system to monitor high risk sections of coastline and to advance understanding of cliff failure mechanisms.
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Mines, Aine, Darren Beckstrand, Paul D. Thompson, Bret Boundy, Scott Helm, and Jeff Jackson. "Estimating Event Likelihood for Rock Slope Assets on Transportation Networks." Transportation Research Record: Journal of the Transportation Research Board 2672, no. 52 (June 13, 2018): 316–24. http://dx.doi.org/10.1177/0361198118777622.
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Recent federal regulations require states to develop risk-based transportation asset management (TAM) plans for bridge and pavement assets. These requirements are making TAM principles, and their related benefits and tools, familiar to a variety of sections within Departments of Transportation (DOTs) and prompting select DOTs to apply them to select geotechnical assets. The Montana Department of Transportation (MDT) recently completed a multi-year project to update its previous Rockfall Hazard Rating System (RHRS) into a Rock slope Asset Management Program (RAMP), incorporating some of these new tools. Incorporating risk into decision-making is important, but risk posed by deteriorating geotechnical assets is difficult for departments to quantify. Adverse event data are often collected in an ad-hoc fashion, with only the worst events attracting attention. As part of the RAMP project, an MDT-administered adverse event survey was combined with a statewide dataset of detailed rock slope assessments. These data were used to develop initial relationships between rock slope condition and adverse event likelihood per unit area of rock slope face. Annual likelihood of both service disrupting events and accidents was calculated for each rock slope in MDT’s database and used to identify high-risk corridors. Using established AASHTO methods, event likelihood was combined with traffic and detour data, generating site-specific estimates of annual safety and mobility risks, expressed in dollars, which can be incorporated into benefit/cost tools at various planning levels and permits dollar-to-dollar comparisons of the risks posed by rock slope assets to other actively managed assets.
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Chhatkuli, S., K. Kawamura, K. Manno, T. Satoh, and K. Tachibana. "AN APPROACH TO AUTOMATIC DETECTION AND HAZARD RISK ASSESSMENT OF LARGE PROTRUDING ROCKS IN DENSELY FORESTED HILLY REGION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B3 (June 9, 2016): 195–99. http://dx.doi.org/10.5194/isprs-archives-xli-b3-195-2016.
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Rock-fall along highways or railways presents one of the major threats to transportation and human safety. So far, the only feasible way to detect the locations of such protruding rocks located in the densely forested hilly region is by physically visiting the site and assessing the situation. Highways or railways are stretched to hundreds of kilometres; hence, this traditional approach of determining rock-fall risk zones is not practical to assess the safety throughout the highways or railways. In this research, we have utilized a state-of-the-art airborne LiDAR technology and derived a workflow to automatically detect protruding rocks in densely forested hilly regions and analysed the level of hazard risks they pose. Moreover, we also performed a 3D dynamic simulation of rock-fall to envisage the event. We validated that our proposed technique could automatically detect most of the large protruding rocks in the densely forested hilly region. Automatic extraction of protruding rocks and proper risk zoning could be used to identify the most crucial place that needs the proper protection measures. Hence, the proposed technique would provide an invaluable support for the management and planning of highways and railways safety, especially in the forested hilly region.
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Chhatkuli, S., K. Kawamura, K. Manno, T. Satoh, and K. Tachibana. "AN APPROACH TO AUTOMATIC DETECTION AND HAZARD RISK ASSESSMENT OF LARGE PROTRUDING ROCKS IN DENSELY FORESTED HILLY REGION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B3 (June 9, 2016): 195–99. http://dx.doi.org/10.5194/isprsarchives-xli-b3-195-2016.
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Rock-fall along highways or railways presents one of the major threats to transportation and human safety. So far, the only feasible way to detect the locations of such protruding rocks located in the densely forested hilly region is by physically visiting the site and assessing the situation. Highways or railways are stretched to hundreds of kilometres; hence, this traditional approach of determining rock-fall risk zones is not practical to assess the safety throughout the highways or railways. In this research, we have utilized a state-of-the-art airborne LiDAR technology and derived a workflow to automatically detect protruding rocks in densely forested hilly regions and analysed the level of hazard risks they pose. Moreover, we also performed a 3D dynamic simulation of rock-fall to envisage the event. We validated that our proposed technique could automatically detect most of the large protruding rocks in the densely forested hilly region. Automatic extraction of protruding rocks and proper risk zoning could be used to identify the most crucial place that needs the proper protection measures. Hence, the proposed technique would provide an invaluable support for the management and planning of highways and railways safety, especially in the forested hilly region.
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Ririe, G. Todd. "A comparison of alteration assemblages associated with Archean gold deposits in Western Australia and Paleozoic gold deposits in the southeast United States." Canadian Journal of Earth Sciences 27, no. 12 (December 1, 1990): 1560–76. http://dx.doi.org/10.1139/e90-168.
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A comparison of high-alumina mineral assemblages spatially associated with the Haile and Brewer gold deposits in the Paleozoic Carolina slate belt (CSB) of the southeast United States and the Sons of Gwalia and Mount Celia gold deposits in the Archean Norseman–Wiluna greenstone belt (NWGB) in Western Australia suggests a similar hydrothermal origin and subsequent metamorphic and deformational history. A common hydrothermal origin is supported by the striking similarity in whole-rock chemistry, even though there were probably significant variations in original unaltered protoliths. An analysis of rocks from each of the deposits that contain high-alumina minerals demonstrates that the protoliths were leached of alkalis with respect to aluminum and have a ratio of Al2O3/Na2O + CaO + K2O greater than three. Although the rocks contain abundant high-alumina minerals, the aluminum content in these rocks is not unusually high, and it does not appear that there has been any significant transport of aluminum either into or out of the rocks that were altered.The most common high-alumina minerals found in rocks affected by the feldspar destructive alteration event include andalusite, kyanite, pyrophyllite, kaolinite, and sericite. Other minerals present in variable amounts include diaspore, chloritoid, alunite, natroalunite, paragonite, and topaz. It is possible that some of these minerals formed during the early hydrothermal alteration event and were recrystallized during metamorphism. Regardless of when the high-alumina minerals formed, textural relations suggest that the rocks had been hydrothermally altered by the time the metamorphic minerals formed. A comparison of alteration from the deposits studied in the CSB and the NWGB suggests there are many similarities to acid-sulfate alteration associated with geothermal areas, such as Yellowstone Park, Wyoming, and with acid-sulfate gold deposits, such as Goldfield, Nevada. Thus, it is possible that the protolith of the metamorphosed rocks in the CSB and NWGB contained an alteration assemblage that included alunite, pyrophyllite, and kaolinite.A generalized paragenetic sequence determined from petrographic and field observations, beginning with regional metamorphism, follows: (i) formation of andalusite, kyanite, chloritoid, and topaz during prograde metamorphism, depending on whole rock chemistry, (ii) formation of pyrophyllite and quartz-rich pods during silicification of aluminosilicate-bearing rocks, (iii) bedding parallel schistosity and fracturing produced by a deformational event, (iv) fractures filled by quartz, sericite, pyrophyllite, or calcite, (v) folding of early layering in the rocks to form a crenulation cleavage accompanied by introduction of quartz veins at high angles to foliation; and (vi) retrograde metamorphism of andalusite–kyanite-pyrophyllite to produce an assemblage of kaolinite ± diaspore.The spatial association of the acid-sulfate alteration with gold mineralization, together with comparison of analogous alteration associated with younger unmetamorphosed acid-sulfate gold deposits, suggests that at least some of the gold was introduced during the early premetamorphic alteration event. The present location of gold in each deposit is a result of local changes brought about by later metamorphic and deformational events.
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Ding, Ke, Lianguo Wang, Mei Yu, Wenmiao Wang, and Bo Ren. "Study on Microseismic Monitoring, Early Warning, and Comprehensive Prevention of a Rock Burst under Complex Conditions." Shock and Vibration 2020 (September 19, 2020): 1–12. http://dx.doi.org/10.1155/2020/8863771.
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Rock bursts in coal mines are usually unpredictable. In view of this problem, the energy–frequency relationship and spatial distribution characteristics of microseismic events during the mining of 5305 working face in Xinhe Coal Mine under complex geological conditions were analyzed in this study. Besides, the law and precursors of rock burst occurrence in this working face were discussed. The following research results were obtained. Before the rock burst occurred in 5305 working face, the energy and frequency of microseismic events vary in the following order: “peak-drop-rise-rock burst.” The analysis on spatial characteristics of microseismic events suggests that microseismic events were mainly concentrated at the boundary between the roof and the coal seam or at the hard roof near the coal seam within 0–160 m in front of the working face, and most of the events lay on the goaf side. Moreover, the energy and frequency of microseismic events both decrease in the above region before the rock burst occurred. This “microseismic event absence” phenomenon can be regarded as one of the precursors of rock burst occurrence. In addition, a multilevel antiburst scheme was proposed for the complex conditions: (1) to adopt large-diameter boreholes pressure relief technology and key layer high-level pressure relief technology for adjusting the stress distribution in the surrounding rock of crossheading in front of the working face and dissipating elastic strain energy; (2) to determine the advance speed to be 1.5 m/d for reducing the mining disturbance; (3) to adopt full-section reinforced support of the roadway for enhancing the antiburst capacity of surrounding rock. After the implementation of this scheme, the energy and frequency of microseismic events monitored on-site changed gently, and 5305 working face was safely recovered to the stop line position. The scheme boasts a remarkable rock burst prevention and control effect.
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Zhao, Yongqiang, Quansheng Li, Kai Zhang, Yingming Yang, Dongxiao Zhang, Weilong Zhang, and Xiaojun Ding. "Experimental Study on Mechanical Properties and Failure Mechanism of Damaged Sandstone." Sustainability 15, no. 1 (December 28, 2022): 555. http://dx.doi.org/10.3390/su15010555.
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Solid materials such as rocks can contain primary defects, and internal defects are activated in the event of mining disturbance, which causes rock damage and destruction. Therefore, it is of great significance for rock engineering to study the mechanical properties and failure mechanism of damaged rock. In this study, damaged prefabricated crack sandstone specimens were prepared with the cyclic loading-unloading test, and the uniaxial loading test was carried out with damaged specimens. The evolution law of peak strength, elastic modulus, and peak strain of specimens with different damage degrees was studied, the quantitative relationship between the P-wave velocity and the damage degree was obtained, and the acoustic emission (AE) count and energy evolution characteristics of specimens with different damage degrees were analyzed. The energy evolution law of damaged specimens was revealed, and with the increase in damage degree, the elastic energy stored in the specimens can be converted into crack propagation more quickly, and the dissipated energy density increases rapidly, resulting in complete rock failure. The research results can provide theoretical support for the stability analysis and control of underground engineering rock mass in the event of multiple disturbances.
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Wieczorek, G. F., G. M. Stock, P. Reichenbach, J. B. Snyder, J. W. Borchers, and J. W. Godt. "Investigation and hazard assessment of the 2003 and 2007 Staircase Falls rock falls, Yosemite National Park, California, USA." Natural Hazards and Earth System Sciences 8, no. 3 (May 6, 2008): 421–32. http://dx.doi.org/10.5194/nhess-8-421-2008.
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Abstract. Since 1857 more than 600 rock falls, rock slides, debris slides, and debris flows have been documented in Yosemite National Park, with rock falls in Yosemite Valley representing the majority of the events. On 26 December 2003, a rock fall originating from west of Glacier Point sent approximately 200 m3 of rock debris down a series of joint-controlled ledges to the floor of Yosemite Valley. The debris impacted talus near the base of Staircase Falls, producing fragments of flying rock that struck occupied cabins in Curry Village. Several years later on 9 June 2007, and again on 26 July 2007, smaller rock falls originated from the same source area. The 26 December 2003 event coincided with a severe winter storm and was likely triggered by precipitation and/or frost wedging, but the 9 June and 26 July 2007 events lack recognizable triggering mechanisms. We investigated the geologic and hydrologic factors contributing to the Staircase Falls rock falls, including bedrock lithology, weathering, joint spacing and orientations, and hydrologic processes affecting slope stability. We improved upon previous geomorphic assessment of rock-fall hazards, based on a shadow angle approach, by using STONE, a three-dimensional rock-fall simulation computer program. STONE produced simulated rock-fall runout patterns similar to the mapped extent of the 2003 and 2007 events, allowing us to simulate potential future rock falls from the Staircase Falls detachment area. Observations of recent rock falls, mapping of rock debris, and simulations of rock fall runouts beneath the Staircase Falls detachment area suggest that rock-fall hazard zones extend farther downslope than the extent previously defined by mapped surface talus deposits.
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Dussauge-Peisser, C., A. Helmstetter, J. R. Grasso, D. Hantz, P. Desvarreux, M. Jeannin, and A. Giraud. "Probabilistic approach to rock fall hazard assessment: potential of historical data analysis." Natural Hazards and Earth System Sciences 2, no. 1/2 (June 30, 2002): 15–26. http://dx.doi.org/10.5194/nhess-2-15-2002.
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Abstract. We study the rock fall volume distribution for three rock fall inventories and we fit the observed data by a power-law distribution, which has recently been proposed to describe landslide and rock fall volume distributions, and is also observed for many other natural phenomena, such as volcanic eruptions or earthquakes. We use these statistical distributions of past events to estimate rock fall occurrence rates on the studied areas. It is an alternative to deterministic approaches, which have not proved successful in predicting individual rock falls. The first one concerns calcareous cliffs around Grenoble, French Alps, from 1935 to 1995. The second data set is gathered during the 1912–1992 time window in Yosemite Valley, USA, in granite cliffs. The third one covers the 1954–1976 period in the Arly gorges, French Alps, with metamorphic and sedimentary rocks. For the three data sets, we find a good agreement between the observed volume distributions and a fit by a power-law distribution for volumes larger than 50 m3 , or 20 m3 for the Arly gorges. We obtain similar values of the b exponent close to 0.45 for the 3 data sets. In agreement with previous studies, this suggests, that the b value is not dependant on the geological settings. Regarding the rate of rock fall activity, determined as the number of rock fall events with volume larger than 1 m3 per year, we find a large variability from one site to the other. The rock fall activity, as part of a local erosion rate, is thus spatially dependent. We discuss the implications of these observations for the rock fall hazard evaluation. First, assuming that the volume distributions are temporally stable, a complete rock fall inventory allows for the prediction of recurrence rates for future events of a given volume in the range of the observed historical data. Second, assuming that the observed volume distribution follows a power-law distribution without cutoff at small or large scales, we can extrapolate these predictions to events smaller or larger than those reported in the data sets. Finally, we discuss the possible biases induced by the poor quality of the rock fall inventories, and the sensibility of the extrapolated predictions to variations in the parameters of the power law.
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Mack, Greg H., and T. Jerzykiewicz. "Provenance of post-Wapiabi sandstones and its implications for Campanian to Paleocene tectonic history of the southern Canadian Cordillera." Canadian Journal of Earth Sciences 26, no. 4 (April 1, 1989): 665–76. http://dx.doi.org/10.1139/e89-057.
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Late Campanian to Early Paleocene sandstones of the Alberta Foothills were derived from three types of rocks: (i) andesitic–dacitic volcanic rocks that were presumably comagmatic with middle to late Mesozoic plutons in the Omineca Crystalline Belt; (ii) low-grade metamorphic rocks in the suprastructure of the Omineca Crystalline Belt; and (iii) sedimentary rocks in die Rocky Mountain Thrust Belt, principally pelitic rocks in the western Main Ranges and carbonates and chert-arenites in the eastern Main and Front ranges. A paucity of quartzo-feldspathic rocks fragments and potassium feldspar indicates that the core of the Omineca Crystalline Belt was not extensively exposed at that time.Vertical trends in composition of the sandstones reveal five petrographic stages. Stage I is dominated by volcanic rock fragments and plagioclase, suggesting that initial progradation of the sediment was largely a response to coeval volcanism or tectonic emplacement of older volcanic rocks. Stages III and V are characterized by a significant decrease in the relative proportion of metamorphic detritus and an increase in the proportion of carbonate and chert detritus. These stages may represent periods of thrusting in the eastern Main Ranges or Front Ranges. In contrast, stages II and IV display increases in metamorphic detritus and stage II shows a concomitant decrease in carbonate and chert detritus, trends that indicate wearing down of the eastern Main Ranges or Front Ranges thrust sheet(s) and reintegration of the Omineca Crystalline belt and the western Main Ranges into the drainage basin. The compositional stages indicative of thrust events are associated with coarse facies, including the Entrance and High Divide Ridge conglomerates, whereas those stages indicative of tectonic quiescence are associated with fine-grained facies including coal.
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Supakulopas, R., and S. M. Tikoo. "The remanent magnetisation recorded in the Chesapeake Bay impact crater, Virginia." Journal of Physics: Conference Series 2145, no. 1 (December 1, 2021): 012051. http://dx.doi.org/10.1088/1742-6596/2145/1/012051.
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Abstract During impact events, planetary crusts experience high pressures that can impart rocks with shock remanent magnetisation (SRM) if an ambient magnetic field or demagnetise rocks if a field is absent. If rocks experience substantial impact heating or are pressurised above ~40 GPa (inducing melting and recrystallisation) they may instead record a thermo-viscous remanent magnetisation (TVRM) as they cool below their Curie temperatures. Understanding impact re-magnetisation is crucial for studying terrestrial impact craters, but also unraveling the history of long-lived core dynamo fields on other planetary bodies. In this research we studied impact-related re-magnetisation recorded in natural rock samples from the Chesapeake Bay impact crater, Virginia. As a case study, here we discuss the natural remanent magnetisation (NRM) of two samples of different rock types: a suevite (sample I9-UI, depth 1.40 km beneath the ground) and a schist (sample S32, depth 1.67 km beneath the ground) using thermal and alternating field demagnetisation. The suevite represents a sample that contains material that experience impact remelting, whereas the schist represents an unmelted rock. From the NRM spectra, we found that the sample ITH9-UI was remagnetised by TVRM due to impact-related heating, while the sample STH32 shows the indication of shock deformation of magnetic minerals.
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Minnitt, R. C. A., and K. H. Esbensen. "Geochemical evolution of magmatic rocks in the Vioolsdrif Domain, Namibia." South African Journal of Geology 126, no. 1 (March 1, 2023): 49–74. http://dx.doi.org/10.25131/sajg.126.0001.
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Abstract Geological, lithological, petrographical, geochemical, and geochronological data in the Palaeoproterozoic Richtersveld Subprovince/Magmatic Arc (RMA) of Precambrian basement rocks of the Vioolsdrif Domain in southern Namibia, strongly support linkages in the history of formation between the volcanic rock types of the Orange River Group (ORG) and the plutonic rocks of the Vioolsdrif Suite (VS). Previous age dating indicates volcanics of the ORG are more-or-less synchronous with granitic phases of the VS. Geochemical, mineralogical, and comprehensive field and petrological characteristics of the volcanic and granitic rocks suggest genetically linked, parallel igneous-effusive rock suites through processes of fractional crystallisation. Intermittent tapping of evolving residual magmas produced an extrusive carapace of volcanic rocks covering the granitic rocks in a classic magmatic differentiation context of parallel geochemical and lithological evolution. As the magma chamber fractionated plutonic phases of the VS at depth, it extruded residual liquids as volcanic flows and ejecta at surface to form the ORG. A first principal model, based on Ba, Rb and Sr trace element and SiO2, MgO, Al2O3, TiO2 major element behaviour, is supported by multivariate modelling of 28 major and trace elements in 129 rock analyses using Principal Component Analysis (PCA). PCA indicates the first four components account for more than 80% of the total compositional variance in all rock types lending comprehensive support for a linked geochemical differentiation model for both the igneous and the volcanic suites. Strong evidence for the magmatic co-evolution of the plutonic and effusive series includes the Cu-mineralisation event, which manifests itself as a resolvable, orthogonal fifth principal component, geochemically overprinting the intermediate ‘porphyry monzogranite’ differentiation stages, but not related to the terminal leuco-granites. The full spectrum of geochemical relationships is consistent with current models of a direct genetic relationship between evolving high Sr/Y magmas and hydrothermal porphyry Cu deposits, in overall agreement with the full context of field, rock, mineralogical, geochemical, and economic geology interpretations presented here.
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Bucholz, Claire E., and Christopher J. Spencer. "Strongly Peraluminous Granites across the Archean–Proterozoic Transition." Journal of Petrology 60, no. 7 (June 7, 2019): 1299–348. http://dx.doi.org/10.1093/petrology/egz033.
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Abstract Strongly peraluminous granites (SPGs) form through the partial melting of metasedimentary rocks and therefore represent archives of the influence of assimilation of sedimentary rocks on the petrology and chemistry of igneous rocks. With the aim of understanding how variations in sedimentary rock characteristics across the Archean–Proterozoic transition might have influenced the igneous rock record, we compiled and compared whole-rock chemistry, mineral chemistry, and isotope data from Archean and Paleo- to Mesoproterozoic SPGs. This time period was chosen as the Archean–Proterozoic transition broadly coincides with the stabilization of continents, the rise of subaerial weathering, and the Great Oxidation Event (GOE), all of which left an imprint on the sedimentary rock record. Our compilation of SPGs is founded on a detailed literature review of the regional geology, geochronology, and inferred origins of the SPGs, which suggest derivation from metasedimentary source material. Although Archean and Proterozoic SPGs are similar in terms of mineralogy or major-element composition owing to their compositions as near-minimum melts in the peraluminous haplogranite system, we discuss several features of their mineral and whole-rock chemistry. First, we review a previous analysis of Archean and Proterozoic SPGs biotite and whole-rock compositions indicating that Archean SPGs, on average, are more reduced than Proterozoic SPGs. This observation suggests that Proterozoic SPGs were derived from metasedimentary sources that on average had more oxidized bulk redox states relative to their Archean counterparts, which could reflect an increase in atmospheric O2 levels and more oxidized sedimentary source rocks after the GOE. Second, based on an analysis of Al2O3/TiO2 whole-rock ratios and zircon saturation temperatures, we conclude that Archean and Proterozoic SPGs formed through partial melting of metasedimentary rocks over a similar range of melting temperatures, with both ‘high-’ and ‘low-’temperature SPGs being observed across all ages. This observation suggests that the thermo-tectonic processes resulting in the heating and melting of metasedimentary rocks (e.g. crustal thickening or underplating of mafic magmas) occurred during generation of both the Archean and Proterozoic SPGs. Third, bulk-rock CaO/Na2O, Rb/Sr, and Rb/Ba ratios indicate that Archean and Proterozoic SPGs were derived from partial melting of both clay-rich (i.e. pelites) and clay-poor (i.e. greywackes) source regions that are locality specific, but not defined by age. This observation, although based on a relatively limited dataset, indicates that the source regions of Archean and Proterozoic SPGs were similar in terms of sediment maturity (i.e. clay component). Last, existing oxygen isotope data for quartz, zircon, and whole-rocks from Proterozoic SPGs show higher values than those of Archean SPGs, suggesting that bulk sedimentary 18O/16O ratios increased across the Archean–Proterozoic boundary. The existing geochemical datasets for Archean and Proterozoic SPGs, however, are limited in size and further work on these rocks is required. Future work must include detailed field studies, petrology, geochronology, and constraints on sedimentary source ages to fully interpret the chemistry of this uniquely useful suite of granites.