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1.
We introduce new estimators for fracture trace intensity, trace density and mean trace length that exploit the use of circles as efficient sampling tools. A fracture trace is the commonly observed surface expression of a fracture, i.e. the intersection of a fracture with an exposed surface such as a rock pavement or a mine drive wall. Trace intensity, trace density and mean trace length estimators are derived and shown to form a self-consistent set of two-dimensional fracture abundance measures. The intensity estimator n/4r uses the number, n, of intersections between fracture traces and a circular scanline of radius r. The density estimator m/2πr2 uses the number, m, of trace endpoints inside a circular window. The mean trace length estimator (n/m)πr/2 uses the ratio of the number of trace intersections on the circle to the number of endpoints in the circle.The circular sampling tools and estimators described here eliminate most sampling biases due to orientation and also correct many errors due to censoring and length bias that plague established scanline and areal measurement techniques. Performance of the estimators is demonstrated by comparison with areal samples of a synthetic fracture trace population with known intensity, density and mean trace length. The estimators are also applied successfully to a natural rock pavement with two orthogonal fracture sets, one of which is severely censored. Because the new circle-based estimators only require counts of trace–circle intersections and/or trace endpoints, they are more time-efficient than current methods for estimating geometric characteristics of fracture traces.  相似文献   

2.
Fracture network modeling is an essential part of the design, development and performance assessment of Enhanced Geothermal Systems. These systems are created from geothermal resources, usually located several kilometers below the surface of the Earth, by establishing a network of connected fractures through which fluid can flow. The depth of the reservoir makes it impossible to make direct measurements of fractures and data are collected from indirect measurements such as geophysical surveys. An important source of indirect data is the seismic event point cloud generated by the fracture stimulation process. Locations of these points are estimated from recorded micro-seismic signals generated by fracture initiation, propagation and slip. This point cloud can be expressed as a set of three-dimensional coordinates with attributes, for example Se ijk ={(x,y,z);?a|x,y,z∈R,?a∈I}. We describe two methods for reconstructing realistic fracture trace lines and planes given the point cloud of seismic events data: Enhanced Brute-Force Search and RANSAC. The methods have been tested on a synthetic data set and on the Habanero data set of Geodynamics’ geothermal project in the Cooper Basin of South Australia. Our results show that the RANSAC method is an efficient and suitable method for the conditional simulation of fracture networks.  相似文献   

3.
Numerical and experimental studies were performed on a new fracture test configuration called the edge cracked triangular (ECT) specimen. Using several finite-element analyses, the fracture parameters (i.e., K I, K II, and T-stress) were obtained for different combinations of modes I and II. The finite-element results show that the ECT specimen is able to provide pure mode I, pure mode II, and any mixed-mode loading conditions in between. Also, a series of mixed-mode fracture experiments were conducted on Neiriz marble rock using the proposed specimen. Furthermore, the generalized maximum tangential stress (GMTS) criterion was used to predict the experimental results. The GMTS criterion makes use of a three-parameter model (based on K I, K II, and T) for describing the crack tip stresses. Due to the significant positive T-stresses that exist in the ECT specimen, typical minimum fracture toughness values were expected to be obtained when the ECT specimen is used. The direction of fracture initiation and the path of fracture growth were also obtained theoretically using the GMTS criterion, and good agreement was observed between the experimental fracture path and theoretical simulations. The fracture study of this specimen reveals that the ECT specimen can be also used in mixed-mode fracture studies of rock materials in addition to the conventional circular or rectangular beam test samples.  相似文献   

4.
Creation of a geological fracture network model conditioned to in situ geometric measurements is of great importance to geoprofessionals, as fractures dominate pathways for fluid flow, a major concern for many engineering applications. This paper introduces and applies the Stochastic Nelder Mead simplex method to automatically calibrate stochastic parameters of geometric characterisations of a discrete fracture network model. This method can overcome the non-convergence of a previous exploratory approach on the classic Nelder Mead method by others, and is an effective substitution to the manual trial-and-error method and is complementary to existing conditional simulation approaches. The procedure to integrate the Stochastic Nelder Mead with a discrete fracture network is presented in detail, and a case study was conducted. Results show that the improved model can better handle the stochastic nature of the underlying system and effectively simulates the observed number and mean trace length of these fractures, although the model results underestimate its standard deviation. Simulated distributions of trace lengths and spacings are within acceptable ranges except for some small offsets, which can be adjusted during model runs.  相似文献   

5.
The observed fractal nature of both fault length distributions and earthquake magnitude-frequency distributions suggests that there may be a relationship between the structure of active fault systems and the resulting seismicity. In previous theoretical work, a positive correlation between the exponent D from the fracture length distribution, and the seismic or acoustic emission (AE) b-value has been inferred from a simple dislocation model of the seismic source. Here, we present the first experimental evidence for a correlation between D and b from a series of tensile fracture mechanics tests on crystalline rock, carried out in different environmental conditions, both air-dry and water-saturated, and at ambient temperature and pressure. The microseismic acoustic emissions were monitored during subcritical crack growth under controlled conditions of constant stress intensity, KI, and quantitative analyses of the resulting fracture patterns were carried out on the same specimens. It is found that AE b-values, ranging from 1.0 to 2.3, correlate negatively with the normalized stress intensity KI/KIC, where KIC is the fracture toughness of the specimen. The microcrack length distribution exponent D, ranges from 1.0 to 1.7. Fluid presence has a first-order influence on both the AE and structure produced in these experiments. For experiments at low stress intensity or high fluid content, the activation of the stress corrosion mechanism for KI < KIC leads to a greater relative proportion both of small cracks and of low amplitude acoustic emissions, reflected in higher values of D and b. The exponent D is found to correlate positively with the AE b-value.  相似文献   

6.
In order to generate early warning for landslides, it is necessary to address the spatial and temporal aspects of slope failure. The present study deals with the temporal dimension of slope failures taking into account the most widespread and frequent triggering factor, i.e. rainfall, along the National Highway-58 from Rishikesh to Mana in the Garhwal Himalaya, India. Using the post-processed three-hourly rainfall intensity and duration values from the Tropical Rainfall Measuring Mission-based Multi-satellite Precipitation Analysis and the time-tagged landslide records along this route, an intensity–duration (I–D)-based threshold has been derived as I?=?58.7D ?1.12 for the rainfall-triggered landslides. The validation of the I–D threshold has shown 81.6 % accuracy for landslides which occurred in 2005 and 2006. From this result, it can be inferred that landslides in the study area can be initiated by continuous rainfall of over 12 h with about 4-mm/h intensity. Using the mean annual precipitation, a normalized intensity–duration relation of NI?=?0.0612D ?1.17 has also been derived. In order to account for the influence of the antecedent rainfall in slope failure initiation, the daily, 3-day cumulative, and 15- and 30-day antecedent rainfall values associated with landslides had been subjected to binary logistic regression using landslide as the dichotomous dependent variable. The logistic regression retained the daily, 3-day cumulative and 30-day antecedent rainfall values as significant predictors influencing slope failure. This model has been validated through receiver operating characteristic curve analysis using a set of samples which had not been used in the model building; an accuracy of 95.1 % has been obtained. Cross-validation of I–D-based thresholding and antecedent rainfall-based probability estimation with slope failure initiation shows 81.9 % conformity between the two in correctly predicting slope stability. Using the I–D-based threshold and the antecedent rainfall-based regression model, early warning can be generated for moderate to high landslide-susceptible areas (which can be delineated using spatial integration of preconditioning factors). Temporal predictions where both the methods converge indicate higher chances of slope failures for areas predisposed to instability due to unfavourable geo-environmental and topographic parameters and qualify for enhanced slope failure warning. This method can be verified for further rainfall seasons and can also be refined progressively with finer resolutions (spatial and temporal) of rainfall intensity and multiple rain gauge stations covering a larger spatial extent.  相似文献   

7.
The resonance bond number n, as defined in this paper, is designed to describe the strength of an XO bond as a function of the kinds of atoms present and which atoms are bonded. The calculation of n is made on a fragment extracted from the crystal encompassing the XO bond. If this fragment consists of only the X atom and its coordinating O atoms, then n is numerically equal to the Pauling bond strength, s. In this study a graph-theoretic algorithm is developed permitting the calculation of n using fragments including up to 50 atoms. This algorithm was used to calculate n for all of the bonds in ten silicate crystals. Since bond strength is be inversely related to bond length, we examined the relationship between these two variables and found that n can be used to explain over 70 percent of the variation of XO bond lengths from their average values in the crystals. A fit of the parameter n/r, where r is the row number in the periodic table of the metal atom X, to the observed bond lengths in these crystals yielded the equation R(XO)=1.39(n/r)?0.22 which explains over 95.5 percent of the variation of bond lengths in the crystals. The fact that the same formula with s replacing n was found in an earlier study to be a good estimator of average bond lengths in crystals shows that n relates to individual variations in bond lengths in crystals in the same way that s relates to average bond lengths in crystals. Using minimum energy SiO, AlO and MgO bond lengths and harmonic force constant data calculated for these bonds in hydroxyacid molecules, theoretical equations similar to those used by Pauling to explain bond length variations in hydrocarbons are derived. Bond lengths calculated with these equations for the 10 crystals shows that 95 percent of the variation of the observed bond lengths in these crystals can be explained in terms of n by this purely theoretical model.  相似文献   

8.
Orogens are spatiotemporal expressions of instabilities in materials under load, constrained by thermodynamics, and preserved in the cold outer shell of the planet. Their pressure–temperature–time histories are consistent with the predictions of differential grade-2 (DG-2) materials in pure shear. We place the statistically invariant shear localization mechanism of these materials in a coherent thermodynamic context using an analysis of strained elastic materials. This prototype system exhibits non-classical thermodynamic symmetry-breaking, where the potentials are all functions of a single variable and the distinction between heat and work fades from view. Consequently, internal energy must be described by a monotonically decreasing function of the entropy in order for heat capacity and absolute temperature to be positive. The entropy itself exhibits an inverse dependence on length. These constraints are satisfied by the overall shape and slope of the distributed deformation threshold ψD for DG-2 materials, and its noted 1/length correlation with naturally observed folds as a function of thermomechanical competence κ/χ. We predict that temperature in this non-linear elastic material will vary in proportion to the slope of ψD, being high at low competence, and low at high competence. Similar constraints apply to a self-gravitating body, where the energy function varies inversely with radius. Assigning zero pressure at the surface of the body, we also predict that pressure, the tensor trace of its stress–energy density, will vary inversely with radius. Thus, the body force of gravity will be expressed in this elastic self-gravitating system through the interplay of elastic and thermal lengths. Deformation localization in DG-2 materials arises due to the dynamic rescaling of lengths in response to a spike in the intrinsic energy ψI at κ/χ = ½. While the intrinsic ψI and localization ψL thresholds are monotonically decreasing for κ/χ > ½, they exhibit positive slopes at lower competence, signaling a return to classical thermodynamics and Joule heating in this transitional domain. Numerous structural and tectonic observations can be correlated using this remarkably simple model, beginning with the thickness and mechanical character of the brittle crust and oceanic lithosphere. In effect, this model projects the kinematic theory of plate tectonics into four-dimensional spacetime.  相似文献   

9.
Four isolated cervical vertebrae from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of Abingdon, Oxfordshire, England are identified as from a pliosaurid plesiosaurian sauropterygian on account of their shortness relative to width and height, their near platycoelous nature and the location of tall rib facets on the centrum body. They are noteworthy for their size, with a maximum width of 269 mm, maximum height of 222 mm and maximum length of 103 mm. Simple scaling and comparisons with cervical vertebrae of Mid Jurassic pliosaurs Peloneustes and Liopleurodon, and the Early Cretaceous Stenorhynchosaurus and Sachicasaurus suggest a total body length of between ~ 9.8 m and 14.4 m for the Abingdon Kimmeridge Clay pliosaur. Likely the true length was towards the higher end of this range.A genus and species cannot be confidently determined on the basis of the described material, but they likely belong to Pliosaurus sp. or a similar animal, for which a precise neck length is not known. We estimate a neck length of 0.77 m for Pliosaurus ?brachyspondylus based on the average cervical lengths provided for specimen CAMSM J.35991.  相似文献   

10.
Numerical and experimental investigation of symmetric fracture bifurcation (Kalthoff, 1972), has shown that for forks with small branch angles α<αc, where αc is approximately 14°, the propagation of the branches tends to enlarge the angle. For forks with larger branch angles, α>αc, the propagation of the branches tends to diminish the angle. Forks with the critical angle αc will propagate in their original direction. Kalthoff theorized that the branch angle changes as a function of KI/KII, where KI and KII are the stress intensity factors for tensile and shear (sliding) modes, respectively, and KI is considerably larger than KII. In this study I test the hypothesis that this fracture mechanic theory applies to the analysis of fault bifurcation in the crust, particularly in cases of rapid fracture.Fractures produced during the 1968 earthquake at the Coyote Creek fault in California are intensively branched and an example of rapid rupture. The angular behaviour of the branching ruptures in eight forks follows Kalthoffs theory unusually well. This implies that fracture at the surface was dominated by the tensile mode. Additional observations that support this implication are: series of prominent ruptures which show openings (of 20–30 mm per rupture), the symmetrical and bilateral forking, the high-intensity and angular shapes of individual branches, the opening of grabens associated with several bifurcations, lack of bifurcation in the southern break of the Coyote Creek fault, and the patterns of en echelon fractures which reflect mixed mode surfacial rupture.Hence, contrary to previous interpretations, according to field evidence and fracture mechanic theory, the fault bifurcation and opening along the Coyote Creek fault are not compatible with local tension caused by the primary shear. Fracture probably occurred by different mechanical modes at depth and at the surface. While faulting may have originated by shear at depth, rupture at the surface was dominated by far-field tension associated with NE-SW extension in South California. The present model predicts the directions of fracture propagation along the fault.  相似文献   

11.
The effect on positron annihilation lifetime spectra, measured at room temperature, of the dehydration of single crystals of beryl and cordierite was studied. In each case, the spectra were satisfactorily fitted to three lifetime components. For the beryls, the dehydration considerably enhanced the intensity of the intermediate-lifetime component (I 2) and reduced the intensity of the longest-lived component (I 3). I 2 is attributed to positron annihilation in the empty cages in the channels of the beryl structure and I 3 to annihilation by a pick-off process via unknown foreign molecules. However, for the cordierites, the main effect of the dehydration was a slight (～10%) increase in the lifetime of the intermediate component, τ2. Here I 2 was relatively high both before and after dehydration and the increase in τ2 is attributed to Si-Al ordering. No changes in the lifetime spectra were produced by γ irradiation.  相似文献   

12.
利用激光诱导离解光谱检测铍铝元素区分透闪石白玉产地   总被引：2，自引：1，他引：1  
涂彩  袁心强  周钊 《岩矿测试》2012,31(2):301-305
利用自行搭建的激光诱导离解光谱仪分析54块新疆、青海、俄罗斯产地的透闪石白玉样品,提出通过检测Be、Al元素来区分白玉产地的方法。使用波长1064 nm的激光器激发样品,4CCD光谱仪采集光谱,为避免外界条件干扰,以透闪石白玉中含量比较固定的Si元素作为内标元素测量原子谱线强度比值IBe/ISi、IAl/ISi,分别代表Be、Al元素的含量变化,重复测量10次的相对标准偏差(RSD)<3%。结果表明,新疆白玉的IBe/ISi为0.3～0.6,IAl/ISi为0.1～0.4;青海白玉IBe/ISi<0.1,IAl/ISi<0.2,显示出低Be低Al的明显特征;俄罗斯白玉的IBe/ISi分为高值和低值两个区域,部分样品的IBe/ISi>0.7,指示Be的含量较高,另一部分样品的IBe/ISi为0.1～0.5,略低于新疆白玉。研究显示Be、Al元素特别是Be元素具有较好的产地指示意义,激光诱导离解光谱技术用于鉴别白玉产地有着较好的推广前景。  相似文献   

13.
Numerous supernova outbursts that are correlated in time and space are the main mechanism for the formation of powerful galactic winds and supershells of ionized hydrogen. Information about the dynamics and thermal properties of the gas in shells (bubbles) can be obtained from spectral observations, including those of optical recombination lines. The emission properties of the Hα and Hβ recombination lines and the velocity dispersion of the gas in bubbles formed by numerous supernova outbursts are studied. The appearance of the intensity vs. velocity dispersion (I(H α)?σ) diagram depends on the supernova rate and the age of the bubble. The temperature dependence of the I(Hα)/I(H β) line-intensity ratio (the Balmer decrement) can be used to obtain additional constraints on the evolutionary status of a collective remnant formed by numerous supernova outbursts.  相似文献   

14.
X-ray diffraction and microprobe analyses of pseudomonocrystalline fragments of pyrrhotite from Bodenmais, Bavaria, revealed continuous gradients in composition and phase distribution. The gradients extend from the well-developed (0001) cleavage surfaces 15–30 μm into the bulk of the crystals. The phase gradient is made up two low-temperature pyrrhotites with monoclinic (4C) and hexagonal (5C) symmetry. The fraction of monoclinic pyrrhotite, expressed on the basis of recorded X-ray intensities, I, decreases exponentially according to I (mon)/[I (hex)+I (mon)] = EXP (aX+b) where a is a constant ranging from ?0.04 to ?0.25, X is the depth from the (0001) cleavage surface in μm, and b is a constant determined by the intensity ratios obtained from the untreated cleavage surfaces. The phase gradient developed during retrograde reactions from a continuous composition gradient. This primary gradient was caused by the extraction of iron from a disordered, high-temperature hexagonal pyrrhotite during oxidation of the cleavage surfaces at temperatures above 254° C (upper stability limit of 4C pyrrhotite), probably above 308° C. The length of the c axis of the monoclinic superstructure slightly increases with the increase in iron and decrease in vacancy content of the bulk. This expansion is probably due to a minor compositional variation of the monoclinic phase controlled by the availability of vacancies during the transition to low-temperature phases.  相似文献   

15.
Landslides triggered by moderate to major earthquakes are a recognized seismic hazard. Arias Intensity (I a) is a key intensity measure of the ground motion, but significant duration is widely used to define strong motion duration. We calculate Newmark’s displacements using earthquake records bracketing a broad range of Arias Intensity and significant duration employing Newmark’s rigid block method and a number of yield accelerations. Total landslide displacement increases with the increase in the energy content of the ground motion (I a) above a threshold. Such threshold may be expressed as a function of yield acceleration of the slope regardless of the ground motion characteristics. Newmark displacement decreases with increasing duration for earthquakes with similar energy content. The wide scatter in the results converges when using formal dimensional analysis. Self-similar symmetry may facilitate the assessment of the performance of slopes during earthquakes. The mathematical framework for probabilistic determination of landslides displacement may be a useful aid to estimate the likelihood of landslide hazards provided that the geotechnical properties of the slopes are known.  相似文献   

16.
Based on the fracture trace length distribution, conditions for the existence, uniqueness, and correctness of the fracture diameter distribution are given using Warburton’s fracture model. In particular, a solution for the fracture diameter distribution exists and is unique for all trace length probability density functions, h A (y), such that \(h_{A}(y)/\sqrt{y^{2}-x^{2}}\) is Lebesgue integrable on [x,∞). This condition is met by the uniform, exponential, gamma, lognormal, and power-law trace length distributions as well as by the trace length distributions that arise from a deterministic fracture diameter or from a discontinuous fracture diameter length distribution. Exponential, gamma, lognormal, and power-law trace length distributions satisfy necessary conditions for the diameter distribution to be non-negative, and necessary and sufficient conditions for the distribution to have unit integral over the real line. Negative values of the fracture diameter distribution arise when the trace has a uniform distribution and the lower bound of the fracture trace is greater than zero.  相似文献   

17.
We estimate the absolute intensity of the Hα emission line in M17 based on spectroscopic observations with the 70 cm telescope of the Fesenkov Astrophysical Institute and the 1.25 m telescope of the Sternberg Astronomical Institute’s Crimean Laboratory. The visual extinction, A v , is derived for about 250 regions in the nebula via a comparison of the optical (Hα) and radio (21 cm continuum) emissions. The A v values for the eastern, optically bright, part of the nebula are 2–6m. For the western part, which is covered by a dark cloud, the extinction is A v = 7?14.5m. We derived I(Hα)/I([NII] λ6584) ratios and estimated the degree of ionization of nitrogen in the nebula; we find that most nitrogen is in the [NIII] state.  相似文献   

18.
Results of polarization observations of gas-dust condensations obtained on the Nançay radio telescope in the 1665 and 1667 MHz OH lines in all four Stokes parameters are reported. Seven OH maser sources associated with methanol masers were selected for this study. The goal was to estimate the magnetic fields in methanol condensations from the Zeeman splitting of OH maser lines associated with the methanol masers. The Gaussian parameters of features in the OH spectra are presented, and their polarization parameters are estimated: the degree of circular polarization m C , flux density in linear polarization p, and degree of linear polarization m L . The magnetic field intensity B has been estimated from the Zeeman splitting of the OH lines and approximation of the Stokes parameter V from the derivative of Stokes parameter I. B varies from ≤0.5 to 1.4 mG for different sources. The association of OH masers with methanol emission has been analyzed; the magnetic fields of OH masers in interstellar condensations associated with Class I methanol masers can be determined more reliably than the fields in interstellar condensations with OH masers associated with Class II methanol emission, and have higher values. The sizes of the studied regions suggest they may be bound structures such as Bok globules, small IRDC clouds, or protoplanetary disks.  相似文献   

19.
Ulf Hålenius  Klaus Langer 《Lithos》1980,13(3):291-294
Six natural chloritoid crystals with Fe2+ and Fe3+ contents ranging from 4.15 to 12.81 and from 0.411 to 0.849g-atoms/l, respectively, as determined by means of microprobe and Mössbauer techniques, served as reference material to develop non-destructive microscope-spectrophotometric methods for quantitative Fe2+ – Fe3+ determinations in chloritoids from unpolarized spectra of (001) platelets. Fe2+ concentrations in g-atom/l can be obtained from [ [Fe3+]=C1xD1/t where D1 = log10(I0/I at 28,000 cm-1 and t=crystal thickness in cm; C1 is a conttant that may be influenced somewhat by experimental conditions and is found to be 0.002289 with the experimental set-up used in this study. Fe2+ concentrations in g-atom/l can be obtained from [Fe2+]=C1xD1/D1-C3 with D2=log10(I0/I) at 16,300 cm?1 and constants C4 = 45.36 and C5 = 3.540. Due to the uncertainties in absorbance measurements, D1 and D2 and the thickness measurements, the accuracies are ±0.05 and ±0.15 g-atom/l for [Fe3+] and [Fe2+], respectively. The determinations may be carried out on chloritoid grains in normal thin sections with an areal resolution of ～10 μm.  相似文献   

20.
An advanced hypoplastic constitutive model is used in probabilistic analyses of a typical geotechnical problem, strip footing. Spatial variability of soil parameters, rather than state variables, is considered in the study. The model, including horizontal and vertical correlation lengths, was calibrated using a comprehensive set of experimental data on sand from horizontally stratified deposit. Some parameters followed normal, whereas other followed lognormal distributions. Monte-Carlo simulations revealed that the foundation displacement uy for a given load followed closely the lognormal distribution, even though some model parameters were distributed normally. Correlation length in the vertical direction θv was varied in the simulation. The case of infinite correlation length was used for evaluation of different approximate probabilistic methods (first order second moment method and several point estimate methods). In the random field Monte-Carlo analyses with finite θv, the vertical correlation length was found to have minor effect on the mean value of uy, but significant effect on its standard deviation. As expected, it decreased with decreasing θv due to spatial averaging of soil properties.  相似文献   

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