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1.
The paper deals with the mechanical origin and rules ofen echelon folds and their secondary fractures by means of elastic stability theory and nonlinear fracture criterion. Obtains the quantitative relations amongen echelon angles ofen echelon folds, ratios of boundary stresses anden echelon pitches of shear zone under an action of general boundary forces (tension shear, pure shear or compression shear). As an applied example, the paper researches the displacement field, stress field, distortion energy distribution, state of secondary fractures and energy released by fracturing ofen echelon fold structure developed at the east foot of Taihang Mountain. The results of research show that maximum principal (compressive) stresses, maximum shear stresses, high value area of distortion energy are in the nuclear parts ofen echelon folds. In these parts compressive fractures were easily developed in approximately parallel with fold axis. So it is verified that the secondary fracture ofen echelon folds is a mechanism controlling a strong earthquake. 相似文献
2.
Mechanical analysis of en echelon structure and its significance of controlling earthquakes 总被引：1，自引：0，他引：1
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3.
Yonghong Zhao Haihua Liang Jiefan Huang Jinda Geng Ren Wang 《Pure and Applied Geophysics》1995,145(3-4):759-773
Uniaxial compression tests on marble plates containing two prefabricateden echelon fractures were performed in this study. Photographs showing the typical characteristics of subcrack development were taken under direct scanning electron microscope (SEM) observation during the test. From these photographs, the effects of the lengthL of a single fracture, the separation distanced and overlapping proportiona/L between two prefabricateden echelon fractures on the development of subcracks were analyzed. The results show that the interaction betweenen echelon fractures strengthened with decreasingd. FordL, there was little interaction and the development of subcracks near one of theen echelon fractures was unaffected by the existence of the other. Whereas ford, the number of subcracks in the area intermediate betweenen echelon fractures tended to increase with increasinga and decreasingd. In order to ascertain whether the experiment can furnish some implications for research on earthquake prediction and neotectonic activity, the test results were compared with the spatial-temporal development of foreshocks and ground-water anomalies before the 1975 Haicheng earthquake and the structural framework of the Ganzi pull-apart basin. The results of the comparison are encouraging. According to the similarity between the test results in the laboratory and the natural phenomena in the field, the fault on which the Haicheng earthquake would occur, could be inferred immediately from the relative geometry of the two sub-parallel active faults in the area. Thus, it is considered that the test results would advance our understanding of the process of neotectonic activities and give us inspiration for earthquake prediction. 相似文献
4.
A preliminary study of b value of rocks with two kinds of structural models has been made on the base of a new acoustic emission recording system.
It shows that b value of the sample decreases obviously when the sample with compressive en echelon faults changes into a tensile one after interchange occurs between stress axis σ
1 and σ
2. A similar experiment is observed when the sample with tensile en echelon faults changes into that with a bend fault after two segments of the en echelon fault linking up. These facts indicate that the variation of b value may contain the information of the regional dominant structural model. Therefore, b-value analyses could be a new method for studying regional dominant structural models.
Foundation item: National Natural Science Foundation of China (Grant No. 40072067) and Minister of Science and Technology of China (2004BA601B01). 相似文献
5.
Topographic stress and rock fracture: a two‐dimensional numerical model for arbitrary topography and preliminary comparison with borehole observations 
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下载免费PDF全文 Theoretical calculations indicate that elastic stresses induced by surface topography may be large enough in some landscapes to fracture rocks, which in turn could influence slope stability, erosion rates, and bedrock hydrologic properties. These calculations typically have involved idealized topographic profiles, with few direct comparisons of predicted topographic stresses and observed fractures at specific field sites. We use a numerical model to calculate the stresses induced by measured topographic profiles and compare the calculated stress field with fractures observed in shallow boreholes. The model uses a boundary element method to calculate the stress distribution beneath an arbitrary topographic profile in the presence of ambient tectonic stress. When applied to a topographic profile across the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania, the model predicts where shear fractures would occur based on a Mohr–Coulomb criterion, with considerable differences in profiles of stresses with depth beneath ridgetops and valley floors. We calculate the minimum cohesion required to prevent shear failure, Cmin, as a proxy for the potential for fracturing or reactivation of existing fractures. We compare depth profiles of Cmin with structural analyses of image logs from four boreholes located on the valley floor, and find that fracture abundance declines sharply with depth in the uppermost 15 m of the bedrock, consistent with the modeled profile of Cmin. In contrast, Cmin increases with depth at comparable depths below ridgetops, suggesting that ridgetop fracture abundance patterns may differ if topographic stresses are indeed important. Thus, the present results are consistent with the hypothesis that topography can influence subsurface rock fracture patterns and provide a basis for further observational tests. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
6.
It is deduced on the basis of field investigation that the total length of the stratigraphic fault associated with the great
Haiyuan 8.5 magnitude earthquake of 1920 was 225 km. This fault was formed by 6 secondary faults with different geometric
parameters, which align regularly inen echelon arrangement. Each secondary fault can be divided into three segments with different characteristics of deformation where
the middle segment was mainly of the horizontal strike—slip fault while another two segments the vertical deformation as shown
by the features of reverse or normal faults. It is also shown by the data of vertical and horizontal displacements that the
horizontal displacement approached a maximum at the middle segment for each secondary fault and gradually decreased toward
and finally disappeared at both ends of each segment while in contrast the vertical displacement was minimum at the middle
and became large at both ends of the segment. The feature of the multiple peaks appeared in the deformation as shown by the
earthquake displacements along the whole fault. This feature indicates that the 6 secondary faults associated with the great
Haiyuan earthquake were the horizontal interrupted planes (i.e., dislocation surface) which were independent on each other, and hence each dislocation surface may represent an independent
secondary fracture event of the earthquake. We thus think that the 6 relatively independent secondary events which occurred
successfully might result in the great 8.5 magnitude Haiyuan earthquake.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 21–31, 1991.
This project is sponsored by the Chinese Joint Seismological Science Foundation. 相似文献
7.
Jeremy R. Henderson Ian G. Main Calum Maclean Michael G. Norman 《Pure and Applied Geophysics》1994,142(3-4):545-565
We present a cellular automaton model which simulates the process of seismogenesis using rules for evolution which are derived from the field of fracture mechanics, and include an interplay of positive and negative feedbacks. We describe the implementation of this model, and its analysis, in a massively parallel environment using the Connection Machine. Starting from a lattice with a fractal distribution of fracture toughnesses, theb value evolves in a way which closely mimics both the evolutions ofb value observed in the laboratory and derived from earthquake catalogues, reaching a broad and irregular maximum in the period preceding a major event, and declining rapidly during catastrophic failure. We conclude that the processes modelled are a reasonable representation of those occurring in Nature, and that the cellular automaton paradigm is a valuable way of simulating these processes on a large scale in an economical manner. 相似文献
8.
Based on the observation data, it is found that the Lancang-Gengma earthquake sequence is resulting from the propagation of
a nonuniform fracture system in which the lengths and strikes of fractures are different from each other, the stress field
and medium condition around fractures are also heterogeneous. Therefore, a mechanical model simulating suitably the fracture
processes of the Lancang-Gengma earthquake sequence is suggested in this paper. The fracture criterions and computation method
for elastic fracture and elasto-plastic fracture are studied. The stress intensity factor, strain energy release rate and
J-integral are evaluated respectively. The forward and inverse method jointing a variety of observation data to determine
the earthquake fracture processes is also developed in this paper.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 463–471, 1992.
This project was sponsored by the Chinese Jonit Seismological Science Foundation. 相似文献
9.
Stephen E Laubach Jon E Olson Julia F.W Gale 《Earth and Planetary Science Letters》2004,222(1):191-195
Fluid flow in fractured rock is an increasingly central issue in recovering water and hydrocarbon supplies and geothermal energy, in predicting flow of pollutants underground, in engineering structures, and in understanding large-scale crustal behaviour. Conventional wisdom assumes that fluids prefer to flow along fractures oriented parallel or nearly parallel to modern-day maximum horizontal compressive stress, or SHmax. The reasoning is that these fractures have the lowest normal stresses across them and therefore provide the least resistance to flow. For example, this view governs how geophysicists design and interpret seismic experiments to probe fracture fluid pathways in the deep subsurface. Contrary to these widely held views, here we use core, stress measurement, and fluid flow data to show that SHmax does not necessarily coincide with the direction of open natural fractures in the subsurface (>3 km depth). Consequently, in situ stress direction cannot be considered to predict or control the direction of maximum permeability in rock. Where effective stress is compressive and fractures are expected to be closed, chemical alteration dictates location of open conduits, either preserving or destroying fracture flow pathways no matter their orientation. 相似文献
10.
Fangquan Li 《Pure and Applied Geophysics》1995,145(3-4):775-787
In situ stress measurements are one of the important methods for studying the recent tectonic stress field and stress state. In this paper, the stress state and variation of stresses with depth in Mainland China are presented and analyzed on the basis ofin situ stress data measured by both hydrofracturing and overcoring techniques. 相似文献
11.
基于云南省内及邻区2009—2020年GNSS观测数据解算结果,在各个测点时间序列和速度场的基础上,采用克里金插值方法估计区域应变率场;以连续基准站时间序列为约束,获取漾濞MS6.4地震近场区域的块体应变时间序列。分析发现:漾濞地震发生在前期最大剪应变高值区以及面应变高梯度带的张压转换区,发震的时间处于区域应变积累速率逐渐降低的过程之后。震中近场区域均以NW向断层的右旋走滑应变积累为主,且大多呈现持续增强趋势,与漾濞地震的发震断层走向及其破裂特征一致。震前震区东部块体出现了短期应变趋势转折及反向加速的异常现象,反映了应力-应变积累在接近临界破裂状态时的非线性调整。 相似文献
12.
2022年1月8日,青海省海北藏族自治州门源县发生MS6.9地震,震中位于青藏高原东北缘地区祁连—海原断裂带的冷龙岭断裂和托勒山断裂构造转换区域(37.77°N,101.26°E)。震后野外现场考察结果表明,此次地震形成的同震地表破裂带总长度约为26 km,整体走向NWW向,破裂性质以左旋走滑局部逆冲为主。断层错动造成的破坏形式以雁列式组合的张裂隙、张剪裂隙、挤压鼓包、断层陡坎等为主。其中,道河至硫磺沟段地表破裂最为强烈,规模大且连续性好,造成的震害最为显著,地表破裂规模向东、西两端逐渐衰减。破裂带穿过区域内多条河流,造成显著的冰面破裂变形,并沿河岸形成一系列的边坡崩塌、滚石等地质灾害。综合破裂带及震害规模分析,宏观震中位于道河至硫磺沟地区。 相似文献
13.
腾冲火山区地震构造应力场研究 总被引：5，自引：2，他引：3
通过对腾冲火山区强震和中小地震震源机制制解分析,对火山区构造应力场方向空间分布,以及震源类型和破裂特征作了研究。利用腾冲火山区中小地震地震波资料,计算得到的地震震源处剪应力强度值,对火山区应力场强度或初始应力状态进行了研究。腾冲火山区构造庆力场主要为北北东－北东－北东东向,接近水平的压应力场。腾冲火山区凛环境剪应力场高值区所包围的低剪应力值分布区。腾冲火山区地震震源具有多种类型,震源破裂具有多种形 相似文献
14.
The dynamics of theCeratium hirundinella population and the abundance of dinocysts in the plankton and sediments were studied in Lake Sempach in 1988. In 1987, a rich population ofCeratium (380 cells ml–1) accompanied byPeridinium spp. developed in the lake. The dinocysts were found entrapped in a kind of flocs, in the deepest part of the lake, in the upper flocculent layer. The number of viable cysts ofCeratium in the sediments decreased gradually from April to July 1988. TheCeratium population increased slowly starting in April, and reached a maximum number in August (31 cells ml–1).Peridinium willei reached 100 cells ml–1. Newly formed cysts ofCeratium were recorded in the plankton and sediments at the end of July — beginning of August. They appear in the sediments as separate cells. Their number increased gradually, reaching a maximum of 600 cysts l–1 at the end of October.Ceratium formed more cysts than didPeridinium, but the rate of survival of theCeratium cysts appears to be lower than that ofPeridinium cysts. In addition to their biological functions, the cysts also have an impact on the ecosystem as carriers of nutrients from down to up and from up to down. 相似文献
15.
The problem of physical essence of theb value forAE of rock tests and natural earthquakes has been a controversial topic during the past two decades. In the present paper the
order and energy of each microfracturing of the microcrack system existing in a rock specimen is discussed from the viewpoint
of fracture mechanics, then the whole series ofAE and subsequently the value ofb are determined. The order of microfracturing depends on the parametersKei/Kci whereKei is the effective stress intensity factor of thei-th microcrack andKci is the fracture toughness in the site of thei-th crack. The energy of eachAE can be expressed asηi ∫
loili
Gids whereG is the energy release rate of microcarck,loi andli are the original and final crack lengths respectively andηi is the emanating efficiency for thei-th crack. If we assume that the distribution density function of microcrack lengthl isp(l)=Bl−v whereB andγ are constants, then the expressionb=3γ/2 can be deduced. Hence, we have come to the conclusion that the value ofb mirrors essentially the “crack-system-configuration” of the material, which means the distribution of the sizes, shapes and
orientations of microcracks over space as well as the distribution of the other relevant physical parameters such as fracture
toughness, friction coefficient, etc. Our conclusion is somewhat similar in character to Mogi’s. He concluded thet the heterogeneity
of the material plays the most important role in determining the value ofb. The term heterogeneity of course covers the idea of “crack-system-configuration, but we think that our view has a little
bit deeper insight to the problem than that of Mogi.
This subject is supported by Chinese Joint Seismological Science Foundation. 相似文献
16.
A model has been developed to simulate the statistical and mechanical nature of rupture on a heterogeneous strike-slip fault. The model is based on the progressive failure of circular asperities of varying sizes and strengths along a fault plane subjected to a constant far-field shear displacement rate. The basis of the model is a deformation and stress intensity factory solution for a single circular asperity under a unidirectional shear stress. The individual asperities are unified through the fault stiffness and the far-field stress and displacement. During fault deformation asperities can fail and reheal, resulting in changes in the local stresses in the asperities, stress drops, and changes in the stiffness of the fault. Depending on how the stress is redistributed following asperity failure and on the strenghts of the neighboring asperities an earthquake event can be the failure of one or more asperities. Following an earthquake event seismic source parameters such as the stress drop, energy change, and moment magnitude are calculated. Results from the model show a very realistic pattern of earthquake rupture, with reasonable source parameters, the proper magnitude-frequency behavior, and the development of characteristic earthquakes. Also the progression ofb-values in the model gives some insight into the phenomenon of self-organized criticality. 相似文献
17.
Frictional sliding experiments were conducted on two types of simulated quartz gouge (with median particle diameters 5 m and 25 m, respectively) at confining pressures ranging from 50 MPa to 190 MPa in a conventional triaxial configuration. To investigate the operative micromechanical processes, deformation texture developed in the gouge layer was studied in samples which had accumulated different amounts of frictional slip and undergone different stability modes of sliding. The spatial patterning of shear localization was characterized by a quantitative measurement of the shear band density and orientation. Shear localization in the ultrafine quartz gouge initiated very early before the onset of frictional sliding. Various modes of shear localization were evident, but within the gouge zoneR
1-shears were predominant. The density of shear localization increased with cumulative slip, whereas the angle subtended at the rock-gouge interface decreased. Destabilization of the sliding behavior in the ultrafine quartz gouge corresponded to the extension ofR
1-shears and formation of boundaryY-shear segments, whereas stabilization with cumulative slip was related to the coalescence ofY-shear segments to form a throughgoing boundary shear. In the coarse quartz gouge, the sliding behavior was relatively stable, probably because shear localization was inhibited by distributed comminution. Two different models were formulated to analyze the stress field within the gouge zone, with fundamentally different predictions on the orientations of the principal stresses. If the rock-gouge interface is assumed to be bonded without any displacement discontinuity, then the maximum principal stress in the gouge zone is predicted to subtend an angle greater than 45° at the interface. If no assumption on displacement or strain continuity is made and if the gouge has yielded as a Coulomb material, then the maximum principal stress in the gouge zone is predicted to subtend an angle less than 45°. If the apparent friction coefficient increases with overall slip (i.e., slip-hardening), then the Riedel shear angle progressively decreases with increasing shear strain within the gouge layer, possibly attaining a zero value which corresponds to a boundaryY-shear. Our quantitative data on shear localization orientation are in reasonable agreement with this second model, which implies the coefficient of internal friction to be about 0.75 for the ultrafine quartz gouge and 0.8 for the coarse gouge. The wide range of orientations for Riedel shear localization observed in natural faults suggests that the orientations of principal stresses vary as much as in an experimental gouge zone. 相似文献
18.
A preliminary study of b value of rocks with two kinds of structural models has been made on the base of a new acoustic emission recording system. It shows that b value of the sample decreases obviously when the sample with compressive en echelon faults changes into a tensile one after interchange occurs between stress axis σ 1 and σ 2. A similar experiment is observed when the sample with tensile en echelon faults changes into that with a bend fault after two segments of the en echelon fault linking up. These facts indicate that the variation of b value may contain the information of the regional dominant structural model. Therefore, b-value analyses could be a new method for studying regional dominant structural models. 相似文献
19.
The parameterm in Ishimoto-Iida's relation was investigated for acoustic emissions (AEs) occurring in rock samples under uniaxial compression. In the experiment, we found: 1) The large AEs are counted without serious error but the number of small AEs is systematically underestimated at high AE rates, 2) the frequency distribution of maximum AE amplitudes becomes nonlinear in logarithmic scale with increasing AE rate, and 3) there exists a strong negative correlation betweenm-value and AE rate. The miscount of small AEs was interpreted as due to overlap of the large and small AEs. We call the miscount masking effect. A statistical analysis based on the masking effect showed that them-value decreases more effectively as the AE rate increases, and thus the masking effect is a possible origin both for the nonlinear frequency distribution of maximum AE amplitudes and for the negative correlation ofm-value with AE rate. We emphasize that one should be careful of the masking effect to examine correctly the change, ofm-value. In order to eliminate the masking effect, AEs should be measured by a measurement system with low sensitivity. Even if the masking effect is eliminated, them-value decreases before the main fracture of a rock sample. Them-value is a key parameter to predict the main fracture. 相似文献
20.
The compression wavefield is efficiently converted to shear-wave energy at post-critical angles in areas of high impedance contrast at the sea floor. We have analysed mode-converted shear waves in a data set acquired with a hybrid marine/land geometry in Isfjorden, Svalbard. Through a kinematic 2D ray-tracing modellingV
p/Vs ratios for part of the uppermost 5km of the crust are obtained. Low values (V
p
/V
s
=1.65) are tentatively associated with the section of Devonian sandstones which appears to attain a minimum thickness of 1.5km below 3 km depth about 10km west of Kapp Thorden. 相似文献