Tidal Stress/Strain and the b-values of Acoustic Emissions at the Underground Research Laboratory, Canada     

Takaki Iwata  R. Paul Young 《Pure and Applied Geophysics》2005,162(6-7):1291-1308

The correlation between the b-values of acoustic emissions (AEs) and the phase of the moon was investigated at the Underground Research Laboratory (URL) in Canada. The same data as those used in Iwata (2002) were examined, which showed that the occurrence of AEs is correlated with the phase of the moon. It was expected, therefore, that the b-value of the AEs would also be sensitive to tidal stress/strain fluctuations. We investigated the variation of the b-values as a function of the phase of the moon. Results show that b-values immediately following the times of full/new moon are higher than those at other times. Using AIC (Akaike Information Criterion) and random (Monte Carlo) simulations, it was confirmed that this feature is statistically significant. We also investigated whether or not there was a change in the b-values immediately before the times of full/new moon, but no statistically significant change was observed. The results suggest that the effect of stress/strain fluctuations on AE occurrences at the URL is asymmetric to the times of full/new moon.All authors are members of the Academic Robotics Group. In listing The Academic Robotics Group, the authors are endeavoring to place each of the participant institutions on an equal footing in terms of effort and authorship. M. A. Talamini is serving as presenter.  相似文献   

形变数字化观测曲线畸变与处理——兼论资料预处理中遇到的一些问题     

黄晓华 《福建地震》2005,(4)

数字化形变台站日常下载、处理直至管理数据,都应用《数字化通讯控制软件》、《形变前兆台站(网)数据处理系统》及《形变前兆数据库服务软件(台站版)》等三个软件交互进行,在实际使用过程中会遇到一些棘手的问题。本文结合我台的观测工作的实践,总结经验,以供台站同行共享。  相似文献   

浅析福建地倾斜潮汐因子γ及其组合动态特征     

傅再扬  危福泉  吴绍祖  陈光 《福建地震》2005,(Z1)

本文计算了福建自1992年至2004年以来的地倾斜EW和NS两分量的固体潮潮汐因子,并进行动态组合,绘制组合动态三种特征量:ΔγEW ΔγNS(表征扩容)、ΔγEW-ΔγNS(表征剪切应变)、ΔγEW/ΔγNS(表征介质各向异性)的时序曲线图,并进行固体潮特征分析,寻找中、强地震发生前远场块体和近场块体地倾斜突变性形变异常与之对应关系。结果表明:在福建沿海,海潮是决定倾斜固体潮特征的主要因素;福建发生5级上的中强地震、台湾发生7级以上强烈地震时,福建地倾斜固体潮潮汐因子及其动态组合特征存在明显的渐进式突变性形变异常现象,异常量和异常持续时间与震级和震中距有较好的对应关系。  相似文献   

小动力旋挖钻机用嵌岩短螺旋钻头结构形式的改进          下载免费PDF全文

刘南昌  胡继良  黄玉文  翁炜  张宏智 《探矿工程》2005,32(2):43-43,46

采用小动力无加压旋挖钻机在粒径较大的卵砾石地层和泥页岩地层中进行1500 mm以上大口径钻孔灌注桩施工，由于钻机动力小且不能加压，用常规嵌岩短螺旋钻头钻进出现进尺慢或不进尺现象。通过对河南西峡县宛西制药责任有限公司新厂房桩孔施工过程中出现此种现象的分析和处理，提出了嵌岩短螺旋钻头针对性的改进措施，并取得了良好效果。  相似文献   

Prediction of creep characteristic of rock under varying environment   总被引：2，自引：0，他引：2  

T. N. Singh  A. K. Verma 《Environmental Geology》2005,48(4-5):559-568

The strain developed due to creep is mainly proportional to the logarithm of the time under load, and is mostly proportional to the stress and temperature. At higher temperature the creep rate falls slowly with respect to time, and the creep strain is proportional to a fractional power of time, with the exponent increasing as the temperature increases and reaching a value approximately one-third at temperatures of about 0.5°C. At these temperatures, the creep increases with stress according to a power greater than unity and possibly exponentially. It increases with temperature as (−U/kT), where U is an activation energy and k is Boltzman’s constant. There are different methods to determine the creep strain and the energy of Jog (B) including experimental methods, multivariate regression analysis, and by numerical simulation. These methods are less cumbersome and time consuming. In the present investigation, artificial neural network technique has been used for prediction of the creep strain and energy of Jog (B). Two different networks have been tested and validated. Both the networks have four input neurons and one hidden layer with five neurons, and one output neuron. The data for different rocks at temperatures up to 750°C under conditions of compressive or tortional stress are taken from the literatures. The training and testing data sets used were 163 and 14, respectively. To deal with the problem of overfitting of data, Bayesian regulation has been used and network is trained with suitable training epochs. The coefficients of correlation among the predicted and observed values are found high and they improve the confidence of the users. The mean absolute percentage error obtained are also very low.  相似文献   

Experimental determination of REE partition coefficients between zircon,garnet and melt: a key to understanding high‐T crustal processes          下载免费PDF全文

R. J. M. Taylor  S. L. Harley  R. W. Hinton  S. Elphick  C. Clark  N. M. Kelly 《Journal of Metamorphic Geology》2015,33(3):231-248

The partitioning of rare earth elements (REE) between zircon, garnet and silicate melt was determined using synthetic compositions designed to represent partial melts formed in the lower crust during anatexis. The experiments, performed using internally heated gas pressure vessels at 7 kbar and 900–1000 °C, represent equilibrium partitioning of the middle to heavy REE between zircon and garnet during high‐grade metamorphism in the mid to lower crust. The D_REE (zircon/garnet) values show a clear partitioning signature close to unity from Gd to Lu. Because the light REE have low concentrations in both minerals, values are calculated from strain modelling of the middle to heavy REE experimental data; these results show that zircon is favoured over garnet by up to two orders of magnitude. The resulting general concave‐up shape to the partitioning pattern across the REE reflects the preferential incorporation of middle REE into garnet, with D_Gd (zircon/garnet) ranging from 0.7 to 1.1, D_Ho (zircon/garnet) from 0.4 to 0.7 and D_Lu (zircon/garnet) from 0.6 to 1.3. There is no significant temperature dependence in the zircon–garnet REE partitioning at 7 kbar and 900–1000 °C, suggesting that these values can be applied to the interpretation of zircon–garnet equilibrium and timing relationships in the ultrahigh‐T metamorphism of low‐Ca pelitic and aluminous granulites.  相似文献   

Dynamic analysis of strain localization in water‐saturated clay using a cyclic elasto‐viscoplastic model     

B. Shahbodagh Khan  M. Mirjalili  S. Kimoto  F. Oka 《国际地质力学数值与分析法杂志》2014,38(8):771-793

A computational framework is presented for dynamic strain localization and deformation analyses of water‐saturated clay by using a cyclic elasto‐viscoplastic constitutive model. In the model, the nonlinear kinematic hardening rule and softening due to the structural degradation of soil particles are considered. In order to appropriately simulate the large deformation phenomenon in strain localization analysis, the dynamic finite element formulation for a two‐phase mixture is derived in the updated Lagrangian framework. The shear band development is shown through the distributions of viscoplastic shear strain, the axial strain, the mean effective stress, and the pore water pressure in a normally consolidated clay specimen. From the local stress–strain relations, more brittleness is found inside the shear bands than outside of them. The effects of partially drained conditions and mesh‐size dependency on the shear banding are also investigated. The effect of a partially drained boundary is found to be insignificant on the dynamic shear band propagation because of the rapid rate of applied loading and low permeability of the clay. Using the finer mesh results in slightly narrower shear bands; nonetheless, the results manifest convergency through the mesh refinement in terms of the overall shape of shear banding and stress–strain relations. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Modeling the 2D behavior of dry‐stone retaining walls by a fully discrete element method          下载免费PDF全文

James J. Oetomo  Eric Vincens  Fabian Dedecker  Jean‐Claude Morel 《国际地质力学数值与分析法杂志》2016,40(7):1099-1120

The dry‐stone retaining walls (DSRW) have been tipped as a promising solution for sustainable development. However, before recently, their behavior is relatively obscure. In this study, discrete element method (DEM) approach was applied to simulate the plane strain failure of these walls. A commercial DEM package (PFC2D™) was used throughout this study. The authors used a fully discrete approach; thus, both the wall and the backfill were modeled as discrete elements. The methodology for obtaining the micromechanical parameters was discussed in detail; this includes the three mechanical sub‐systems of DSRWs: wall, backfill and interface. The models were loaded progressively until failure, and then the results were compared with the full‐scale experimental results where the walls were loaded, respectively, with hydrostatic load and backfill. Despite its complexity and its intensive calculation time, DEM model can then be used to validate a more simplified approach. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

The tectono‐metamorphic evolution of the very low‐grade hangingwall constrains two‐stage gneiss dome formation in the Montagne Noire (Southern France)          下载免费PDF全文

M. P. Doublier  S. Potel  K. Wemmer 《Journal of Metamorphic Geology》2015,33(1):71-89

The Montagne Noire in the southernmost French Massif Central is made of an ENE‐elongated gneiss dome flanked by Palaeozoic sedimentary rocks. The tectonic evolution of the gneiss dome has generated controversy for more than half a century. As a result, a multitude of models have been proposed that invoke various tectonic regimes and exhumation mechanisms. Most of these models are based on data from the gneiss dome itself. Here, new constraints on the dome evolution are provided based on a combination of very low‐grade petrology, K–Ar geochronology, field mapping and structural analysis of the Palaeozoic western Mont Peyroux and Faugères units, which constitute part of the southern hangingwall of the dome. It is shown that southward‐directed Variscan nappe‐thrusting (D₁) and a related medium‐P metamorphism (M₁) are only preserved in the area furthest away from the gneiss dome. The regionally dominant pervasive tectono‐metamorphic event D₂/M₂ largely transposes D₁ structures, comprises a higher metamorphic thermal gradient than M₁ (transition low‐P and medium‐P metamorphic facies series) and affected the rocks between c. 309 and 300 Ma, post‐dating D₁/M₁ by more than 20 Ma. D₂‐related fabrics are refolded by D₃, which in its turn, is followed by dextral‐normal shearing along the basal shear zone of both units at c. 297 Ma. In the western Mont Peyroux and Faugères units, D₂/M₂ is largely synchronous with shearing along the southern dome margin between c. 311 and 303 Ma, facilitating the emplacement of the gneiss dome into the upper crust. D₂/M₂ also overlaps in time with granitic magmatism and migmatization in the Zone Axiale between c. 314 and 306 Ma, and a related low‐P/high‐T metamorphism at c. 308 Ma. The shearing that accompanied the exhumation of the dome therefore was synchronous with a peak in temperature expressed by migmatization and intrusion of melts within the dome, and also with the peak of metamorphism in the hangingwall. Both, the intensity of D₂ fabrics and the M₂ metamorphic grade within the hangingwall, decrease away from the gneiss dome, with grades ranging from the anchizone–epizone boundary to the diagenetic zone. The related zonation of the pre‐D₃ metamorphic field gradients paralleled the dome. These observations indicate that D₂/M₂ is controlled by the exhumation of the Zone Axiale, and suggest a coherent kinematic between the different crustal levels at some time during D₂/M₂. Based on integration of these findings with regional geological constraints, a two‐stage exhumation of the gneiss dome is proposed: during a first stage between c. 316 and 300 Ma dome emplacement into the upper crust was controlled by dextral shear zones arranged in a pull‐apart‐like geometry. The second stage from 300 Ma onwards was characterized by northeast to northward extension, with exhumation accommodated by north‐dipping detachments and hangingwall basin formation along the northeastern dome margin.  相似文献   

Reaction softening by dissolution–precipitation creep in a retrograde greenschist facies ductile shear zone,New Hampshire,USA          下载免费PDF全文

R. J. McAleer  D. L. Bish  M. J. Kunk  K. R. Sicard  P. M. Valley  G. J. Walsh  B. A. Wathen  R. P. Wintsch 《Journal of Metamorphic Geology》2017,35(1):95-119

We describe strain localization by a mixed process of reaction and microstructural softening in a lower greenschist facies ductile fault zone that transposes and replaces middle to upper amphibolite facies fabrics and mineral assemblages in the host schist of the Littleton Formation near Claremont, New Hampshire. Here, Na‐poor muscovite and chlorite progressively replace first staurolite, then garnet, and finally biotite porphyroblasts as the core of the fault zone is approached. Across the transect, higher grade fabric‐forming Na‐rich muscovite is also progressively replaced by fabric‐forming Na‐poor muscovite. The mineralogy of the new phyllonitic fault‐rock produced is dominated by Na‐poor muscovite and chlorite together with late albite porphyroblasts. The replacement of the amphibolite facies porphyroblasts by muscovite and chlorite is pseudomorphic in some samples and shows that the chemical metastability of the porphyroblasts is sufficient to drive replacement. In contrast, element mapping shows that fabric‐forming Na‐rich muscovite is selectively replaced at high‐strain microstructural sites, indicating that strain energy played an important role in activating the dissolution of the compositionally metastable muscovite. The replacement of strong, high‐grade porphyroblasts by weaker Na‐poor muscovite and chlorite constitutes reaction softening. The crystallization of parallel and contiguous mica in the retrograde foliation at the expense of the earlier and locally crenulated Na‐rich muscovite‐defined foliation destroys not only the metastable high‐grade mineralogy, but also its stronger geometry. This process constitutes both reaction and microstructural softening. The deformation mechanism here was thus one of dissolution–precipitation creep, activated at considerably lower stresses than might be predicted in quartzofeldspathic rocks at the same lower greenschist facies conditions.  相似文献