An example of high-pressure low-temperature metamorphic rocks from an island-arc: the Paikon Series (Innermost Hellenides, Greece)

Abstract The Paikon Series is considered to be a volcanic arc sequence with a mainly neritic sedimentary sequence and bimodal tholeiitic volcanism of early Mesozoic age. The metamorphic assemblages are syn- to post-kinematic with respect to a pre-Tithonian tectonic phase and range from the lawsonite-chlorite-albite facies through transitional Na-amphibole-greenschist facies to the chlorite sub-zone of the greenschist facies. The metamorphic imprint of the Paikon Series corresponds to a temperature range from less than 330° C to ± 450° C under a total pressure from 3 kbar to 6–7 kbar. The overprinting of these facies on an earlier blueschist assemblage, related either to a subduction zone or to a tectonic overpressure caused by thrusting, is suspected.     

利用MODIS fAPAR傅立叶时间序列分析研究植被光合作用活动对净辐射和降雨的响应：青藏高原个例研究

气候变化对植被动力学有非常大的影响。为了定量描述气候变化对植被的影响，文章利用MODIS fAPAR 数据和NCEP 的净辐射和降雨再分析数据对青藏高原地区气候变化对植被的影响进行了时间序列分析。研究所用的数据时间跨度为2000年至2005年。首先利用NCEP 再分析数据建立了干旱度因子的时间序列，为了与MODIS fAPAR 具有相同的时间采样间隔，由NCEP的日净辐射和日降雨量得到每8天的平均净辐射和8日降雨的和。根据一定时间间隔的净辐射与降雨量的比可以用来衡量相对于可利用水分的剩余能量，因此该比值也是干旱灾害的度量。其次，对MODIS fAPAR 的傅立叶时间序列分析提供了两个植被光合作用对干旱相应的因子，即fAPAR的年平均值及其年振幅值。在时间和空间尺度上对植被光合作用活动与干旱指数之间的关系进行了定量分析。对湿年和干年之间的响应差异进行了比较。研究表明较干地区对气候变化的响应最为显著。分析应该扩展到更长的时间跨度以便更加有效地在时间和空间尺度上评估气候变化对植被动力学的影响。     

Mechanics of a sandy subsoil subjected to cyclic loadings

A simple model for compaction of a sand, that may be useful in various geotechnical applications is presented. The model has been formulated in terms of the cyclic stress and strain amplitudes. The compaction properties of a dry sand are characterized by a common compaction curve described by two coefficients. The second aim of this paper is to show some applications of the theory proposed. The attention has been restricted to the two extreme cases of practical importance, namely to the behaviour of a dry sand (or a saturated sand but in free draining conditions), and to the behaviour of saturated sand in undrained conditions. Some numerical algorithms showing how to deal with those problems are presented and illustrated on the following examples: settlement and pore pressure generation in a soil stratum subjected to an earthquake, settlement of a foundation, pore pressure generation and liquefaction in a sea-bed. The results obtained suggest that the model proposed, as well as a method of dealing with boundary value problems can serve as a useful tool for the analysis of a sandy subsoil subjected to cyclic loadings.     

塔里木盆地巴楚隆起北缘的吐木休克断裂与巴东断裂

吐木休克断裂位于塔里木盆地西部,巴楚隆起和阿瓦提凹陷之间,是一条大型基底卷入型冲断构造。走向NW‐SE,呈弧形向NEE凸出;倾向巴楚隆起。根据构造变形特征,断裂自NW向SE可以划分为4段。Ⅰ和Ⅲ段为简单基底卷入型冲断构造段;Ⅱ段发育背冲断层,与主干断层呈“y”字型剖面组合关系;Ⅳ段为基底卷入型楔状构造,主冲断层顶部出现一条向巴楚隆起逆冲的反冲断层。断裂上盘发育背斜,下盘有明显的“牵引构造”,显示吐木休克断裂可能是由吐木休克背斜北翼突破形成的,是一条褶皱相关断层。吐木休克断裂形成于中新世晚期至上新世初,持续演化至第四纪。断裂带上发育的上新世末—第四纪初正断层代表印度—亚洲碰撞脉动式远程效应的一个构造间歇期。吐木休克断裂东侧的巴东断裂是巴楚隆起与塔中隆起的过渡构造带,雏形形成于奥陶纪晚期—志留纪,晚新生代复活。     

自适应滤波器

自适应滤波器是一个空间域的数字滤波器。它对不应作滤波处理的点不作滤波,使滤波过程对区域成分的畸变降到最小。它采用一元三点内插法作插值,使滤波公司简单,计算速度快而又能保证精度。判别局部成分的标志及滤波计算都只用局部成分前二个点及后三个点,因而边缘损失小。     

Earthquake source model using strong motion displacement as response of finite elastic media

The strong motion displacement records available during an earthquake can be treated as the response of the earth as the a structural system to unknown forces acting at unknown locations. Thus, if the part of the earth participating in ground motion is modelled as a known finite elastic medium, one can attempt to model the source location and forces generated during an earthquake as an inverse problem in structural dynamics. Based on this analogy, a simple model for the basic earthquake source is proposed. The unknown source is assumed to be a sequence of impulses acting at locations yet to be found. These unknown impulses and their locations are found using the normal mode expansion along with a minimization of mean square error. The medium is assumed to be finite, elastic, homogeneous, layered and horizontal with a specific set of boundary conditions. Detailed results are obtained for Uttarkashi earthquake. The impulse locations exhibit a linear structure closely associated with the causative fault. The results obtained are shown to be in good agreement with reported values. The proposed engineering model is then used to simulate the acceleration time histories at a few recording stations. The earthquake source in terms of a sequence of impulses acting at different locations is applied on a 2D finite elastic medium and acceleration time histories are found using finite element methods. The synthetic accelerations obtained are in close match with the recorded accelerations.     

Design and simulation of a vertical broadband seismometer

In this paper, a new vertical broadband seismometer is designed, simulated, and evaluated. The proposed seismometer has a bandwidth from 40 s to 50 Hz and sensitivity to ground velocity of 1500 V’/m/s. The mechanical suspension used in the proposed design is a mass-leaf spring rotational pendulum. The displacement of the seismic mass is sensed by a laser interferometer and then forwarded to an electronic force feedback system which feeds a linear actuator to keep the mass almost fixed in its position. The current needed to fix the mass in its position is an indication of the ground acceleration. The performance of the simulated seismometer is evaluated by applying a data record of two actual earthquakes to the simulated model and comparing its response to the earthquakes with that of a real seismometer (Trillium-40) having the same bandwidth and sensitivity. The proposed seismometer has performed within 0.4 % residual variance for the local event and 0.03 % residual variance for the regional one compared to Trillium-40.     

Discrete fracture model for coupled flow and geomechanics

We present a fully implicit formulation of coupled flow and geomechanics for fractured three-dimensional subsurface formations. The Reservoir Characterization Model (RCM) consists of a computational grid, in which the fractures are represented explicitly. The Discrete Fracture Model (DFM) has been widely used to model the flow and transport in natural geological porous formations. Here, we extend the DFM approach to model deformation. The flow equations are discretized using a finite-volume method, and the poroelasticity equations are discretized using a Galerkin finite-element approximation. The two discretizations—flow and mechanics—share the same three-dimensional unstructured grid. The mechanical behavior of the fractures is modeled as a contact problem between two computational planes. The set of fully coupled nonlinear equations is solved implicitly. The implementation is validated for two problems with analytical solutions. The methodology is then applied to a shale-gas production scenario where a synthetic reservoir with 100 natural fractures is produced using a hydraulically fractured horizontal well.     

变参数DCD算法在岩土工程位移反分析中的应用

常规DCD(dynamic canonical descent)算法具有全局优化能力且无需考虑目标函数的可微性,只要预先定义优化空间即可,但是该算法的收敛速度有限,为此提出了变参数DCD算法,并建立了其相应的算法迭代格式。在数值试验和工程应用中将该变参数DCD算法与常规的DCD算法进行比较,其结果均表明：变参数DCD算法在全局优化能力和收敛速度上找到了一个均衡点,该算法不仅具有DCD算法的全局优化能力,而且收敛时所需的目标函数评估次数少,在优化过程中该算法展示出了稳定性强且优化结果可靠度高的一面。     

Measurement of vertical environmental-head profiles in unconfined sand aquifers using a multi-channel manometer board

The vertical hydraulic gradient in an unconfined sand aquifer frequently exceeds the horizontal gradient when measured close to a surface discharge boundary, around an abstraction bore or close to a saline interface. The vertical gradient can be efficiently investigated using a multi-channel manometer board connected to a bundled piezometer installed using hollow-stem-auger-drilling techniques. The design and construction of a manometer board is described. Manometer board data from a site in a 30-m-deep fresh-water aquifer adjacent to a pumping bore are described. The bore is screened in the lower part of the aquifer and the impacts of partial penetration are evident on the manometer board results. Data are then described from the centre of a coastal sand spit where fresh water overlies saline water. Fluid electrical conductivity measurements from the individual tubes of the bundled piezometer are used to derive fluid density at each of the bundled piezometer ports. The average fluid density of water above the mini-piezometer port at each depth is then calculated using Gaussian quadrature. The environmental-water head profiles are compared to point-water and fresh-water head profiles and the implications of the incorrect use of point-water or fresh-water head vertical profiles are clearly demonstrated.     

Stochastic Structural Modeling

A consistent stochastic model for faults and horizons is described. The faults are represented as a parametric invertible deformation operator. The faults may truncate each other. The horizons are modeled as correlated Gaussian fields and are represented in a grid. Petrophysical variables may be modeled in a reservoir before faulting in order to describe the juxtaposition effect of the faulting. It is possible to condition the realization on petrophysics, horizons, and fault plane observations in wells in addition to seismic data. The transmissibility in the fault plane may also be included in the model. Four different methods to integrate the fault and horizon models in a common model is described. The method is illustrated on an example from a real petroleum field with 18 interpreted faults that are handled stochastically.     

北京市永定河流域地下水^14C年龄的初步分析

应用同位素方法初步分析北京郊区永定河流域地下水的演化特点。沿永定河冲洪积扇地下水流动方向布置取样剖面，共有取样点14个，对采集的水样进行^14C和氚含量分析，并确定地下水同位素年龄。浅层孔隙水的^14C年龄的变化范围为730～4900a，深层孔隙水为13420-22480a；^14C年龄在垂直方向上由浅部至深部逐渐增大，最大变化幅度为从3010a增至22480a；浅层孔隙水的氚含量都在14．99～30．56TU之间，深层孔隙水大部分在0．51～4．71TU之间。运用地下水^14C和氚年龄在垂向和水平方向变化的结果，验证了地下水的流向并计算了地下水的流速变化范围为5．02～62．63m／a，从山前至平原浅层地下水径流速度逐渐变小，反映了地下水水平径流强度逐渐减弱，地下水交替逐渐变差，浅层孔隙水以垂向交替为主，深层孔隙水以水平径流为主。     

Numerical study on S-wave transmission across a rough,filled discontinuity

This paper presents a numerical simulation of S-wave propagation across a rough, filled discontinuity using the universal distinct element code (UDEC). The ability of UDEC to simulate a stress wave across a smooth and planar discontinuity filled with an elastic material is validated through comparisons with analytical solutions. Next, the effect of the plastic deformation of the fill on the wave propagation is investigated. The model is extended to further study S-wave propagation across a filled discontinuity with rough interfaces, which is described using a sawtooth. The transmission coefficient defined by the energy is used to measure the wave attenuation. Finally, a parametric study is conducted to investigate the influences of the filled thickness, asperity angle, and incident amplitude on the transmission waves and transmission coefficients. The asperity angle and filled thickness together determine the transmitted waveform and transmission coefficient. The transmitted wave may be cut off when the incident wave amplitude exceeds a threshold value. The transmission coefficient decreases with a different trend with the incident wave amplitude increasing when the asperity angle varies. Compared with planar discontinuity, a filled discontinuity with rough interfaces is more sensitive to the amplitude of the incident wave. The causes of these phenomena are analyzed in detail. In addition, the deformation of the fill material is strongly related to the wave attenuation.     

The mechanics of a magma chamber-fault system in trans-tension with application to Coso

The mechanical interaction between an elliptically shaped magma chamber and a fault subject to transtension is investigated with particular reference to the Coso geothermal field. The geologic setting of the Coso field is interpreted as a releasing bend step-over structure formed by the Airport Lake and Owens Valley dextral strike-slip fault system. The role of the Coso volcano-magmatic center in the development of the “over-step” structure is examined by treating the magma chamber as a liquid inclusion in a viscoelastic crust containing a fault (Airport Lake). The problem is numerically solved using a 2D viscoelastic finite element model with thermally activated viscosity to account for thermal weakening of the rock. The temperature distribution around the magma body is calculated based on a 3D steady-state approach and using the mesh-less numerical method. The fault is modeled as a frictionless contact. The simulated distributions of stress and strain around the inclusion display a rotation caused by the shearing component of the applied transtension. The results indicate that the fault tends to overstep the chamber in a geometric pattern similar to a step-over. There is good correspondence between the computed distributions of the maximum shear stress in the vicinity of the magma chamber and the map of earthquake epicenters at a depth of 7–10 km in Coso.     

Constructing a social vulnerability index to earthquake hazards using a hybrid factor analysis and analytic network process (F’ANP) model

Iran is a seismic prone country and has been host to a long series of devastating earthquakes which have resulted in heavy casualties and damages. In order to assess social vulnerability (SV) to earthquake hazards, this paper presents the development of a hybrid factor analysis and analytic network process model for aggregating vulnerability indicators into a composite index of SV to earthquake hazards. The proposed model is then applied in Iran as a case study. The proposed model uses factor analysis (FA) to extract the underlying dimensions of SV. The identified dimensions of SV and their primary variables are then entered into a network model in Analytic Network Process (ANP). The ANP is used to calculate the relative importance of different SV variables, taking into consideration the results obtained from FA and the possible interdependence between variables of the individual dimensions of SV. These weights are then used to compute the factor scores for the individual dimensions of SV and also the composite social vulnerability index (SOVI). The application of the proposed model to a real world case study and its validation show that it is a robust approach for constructing a composite SOVI. Its application to counties in Iran indicates that there exist severe regional differences in terms of SV to earthquake hazards. The pronounced regional variations in SV warrant special attention by both local authorities and the national government to reconsider current natural disaster management strategies.     

Burial and infilling of a karst in Papua New Guinea by road erosion sediments

The anthropogenic impact on karst in Papua New Guinea is briefly introduced and a specific case is presented detailing the effect of road erosion sediments on a small karst. The karst is in the perennially humid tropics and covered with primary rain forest. The road was placed high above the karst on steep friable rock and traverses several of its catchments. The changes to and the rate of burial of parts of the karst and the infilling of the caves are described. The karst drainage has altered, and there is increased water storage. The sediment build-up ceased in less than a year due to vegetation and stabilization of the road embankments. It is concluded that any construction within a catchment leading to a karst should be assessed as to its impact on the karst.     

Estimating the crush zone size under a cutting tool in coal

Summary As part of an effort to understand the mechanics of fine fragment formation in coal, which is important in studies of respirable dust due to mining, fracture toughness measurements and the strain energy density (SED) theory were applied to calculate the crush zone size under a cutting tool in coal. This zone is the major source of fine fragments in the 1 to 10 µm size range. The model used in these calculations is a boundary element program containing a failure criterion based on the SED theory. The boundary element program calculates linear elastic stresses at numerous points in the coal material ahead of a cutting bit. These stresses are then input to a subroutine called critical flaw length and orientation (CFLO) which uses the SED theory to determine the CFLO for a small crack at the boundary element stress computation point. The extent of crushing is based on earlier postulates about the role of inherent flaws in a fragmentation process. To form 1 to 10 µm fragments requires firstly a local stress strong enough to activate flaws with a characteristic length less than 1 to 10 µm and secondly, a flaw density sufficient to provide an average spacing between flaws also on the order of 1 to 10 µm. The locus of active 10 µm flaws represents the maximum possible extent of fine fragmentation in the 10 µm or less size range assuming that a sufficient inherent flaw density exists. The approach offers a first order approximation to the extent of crushing under a tool tip. The size and shape of the crush zone volume is affected by the attack angle and geometry of the tool.     

Stress and displacement analysis of boudinages by the finite-element method

The paper deals with the displacement and stress distribution in boudinage structures. To analyze this, the finite-element method is used. Four models are examined.The first model treats three homogeneous bands. The displacement of the central band produces a barrel-shaped structure. The tension is greatest in the central part of this band and decreases almost continuously towards the shorter edges. If the band ruptures, the rupture will occur in the central part.The second model treats a quarter of a total structure that is already in part a developed boudinage. This development is followed through 19 iterative steps. The displacement analysis demonstrates that the boudin is displaced towards the free short edge and becomes more barrel-shaped, thinner and wider. The mean stress has two, local, tensilestress maxima inside the boudin at the upper boundary: one in the gap area and the other in the matrix at the outer, short edge of the boudin.The third model treats a quarter of a developed boudinage with two materials in the matrix. Displacement analyses demonstrate that the barrel shape of the boudin becomes more pronounced when the competence contrast between boudin and matrix decreases.One axis of principal stress has a direction in every element close to the x-axis of the model. In the area marked PbS (model 6A), this axis shows a local tensile-stress maximum and a local compressive-stress maximum. In model 6B, these points are still extreme points, but the local compressive-stress maximum has changed to a local tensile-stress maximum.The fourth model treats a boudinage in which one boudin is rotated. Displacement analyses demonstrate that the boudins tend to rotate to a position in which they are parallel, diverging a little from a right angle to the angle of the applied pressure. The mean stress demonstrates a pressure shadow in the PbS area, with a slight displacement downwards in the area beside the rotated boudin.The stress distribution corresponds to the mineral distribution of the boudinage from the Udden Mine. The investigation indicates a direct relationship between grain size and stress distribution.     

Transportation and the recent development of the Queensland coal industry

The role of transportation in the development of the Queensland coal industry since 1955 is reviewed in this paper. It is found that transportation has played a concomitant rather than a prerequisite role in the industry's development. The commitment of the Japanese to Queensland coal has been the most important stimulus to the development. The paper ends with a view to future developments, concluding that it would be unwise for Queensland to develop a transportation infrastructure as a stimulus to expanding the coal industry.     

Modelling fluid flow through a single fracture with different contacts using cellular automata

The representation of the surface of a rock fracture and a numerical method to simulate fluid flow in single fractures are the keys to understanding the hydraulic behaviour of rock fractures. In this paper, a cellular automaton (CA) approach is used to generate the single fracture structure, which is assumed to be composed of contacts and voids. We develop a CA evolution rule to produce a contact area, and randomly model a single rock fracture with different contact ratios to reflect natural fracture properties such as dead voids, islands and tortuous flow path. Then, based on the localisation theory of a CA, a numerical method to simulate fluid flow in single fractures with contacts is developed. In this method, the fracture is discretised into a system composed of cell elements. Different apertures, i.e., zero for contacts and non-zero for voids, are assigned to each cell element. Therefore, the contribution of the cell elements in a contact on a cell’s transmissivity can be ignored completely. The local transmissivity is assumed to conform to the cubic law. The fluid flow in a fracture with different contact situations is then modelled using the method established in this paper. The fluid flow path, flow velocity and fluid head distributions as well as the channel flow in the fracture are well-modelled. The flow behaviour of the fracture strongly depends on the effective fluid flow path.