Temporal change in permeability of the Nojima fault zone by repeated water injection experiments

Three boreholes were drilled near the Nojima fault, which the 1995 Hyogoken–Nanbu earthquake occurred on. In order to research the properties and the healing process of the fault, water injection experiments were conducted every 3 years. In this report, we researched the permeability of the fault as a measurement of crack density or porosity of the fault zone. Pore water pressure changes in rock due to the water injections at one borehole were observed as discharge changes or groundwater level changes at the other borehole. Using numerical calculations, the permeability of the fault fracture zone was estimated for each experiment. The permeability has been decreasing as time passed, which is thought to show the fault healing process of the Nojima fault after the 1995 Hyogoken–Nanbu earthquake.     

Fault zone characteristics,fracture systems and permeability implications of Middle Triassic Muschelkalk in Southwest Germany

Fault zone structure and lithology affect permeability of Triassic Muschelkalk limestone-marl-alternations in Southwest Germany, a region characterized by a complex tectonic history. Field studies of eight fault zones provide insights into fracture system parameters (orientation, density, aperture, connectivity, vertical extension) within fault zone units (fault core, damage zone). Results show decreasing fracture lengths with distances to the fault cores in well-developed damage zones. Fracture connectivity at fracture tips is enhanced in proximity to the slip surfaces, particularly caused by shorter fractures. Different mechanical properties of limestone and marl layers obviously affect fracture propagation and thus fracture system connectivity and permeability. Fracture apertures are largest parallel and subparallel to fault zones and prominent regional structures (e.g., Upper Rhine Graben) leading to enhanced fracture-induced permeabilities. Mineralized fractures and mineralizations in fault cores indicate past fluid flow. Permeability is increased by the development of hydraulically active pathways across several beds (non-stratabound fractures) to a higher degree than by the formation of fractures interconnected at fracture tips. We conclude that there is an increase of interconnected fractures and fracture densities in proximity to the fault cores. This is particularly clear in more homogenous rocks. The results help to better understand permeability in Muschelkalk rocks.     

Time evolution of hydraulic and electrokinetic parameters around the Nojima fault, Japan, estimated by an electrokinetic method

The Nojima Fault Zone Probe was designed to study the properties and healing processes of the Nojima fault, which is the surface fault rupture of the Hyogo-ken Nanbu earthquake (M7.2) of 1995 (1995 Kobe earthquake). In this project, water injection experiments were conducted in a borehole of 1800 m depth at the Nojima fault. We set up electrodes around the borehole and observed self-potential variations to investigate the magnitude of electrokinetic and hydraulic parameters around the Nojima fault zone. In the 1997 experiment, self-potential variations were in the range of a few to about 20 mV across 320–450 m electrode dipoles with hydraulic pressure variations from 3.5 to 4 MPa. In the 2000 experiment, self-potential variations were in the range of a few to about 85 mV across 160–260 m electrode dipoles with the hydraulic pressure variations from 3 to 4.5 MPa. In the 2003 experiment, self-potential variations were in the range of a few to about 30 mV across 20–80 m electrode dipoles with hydraulic pressure of 4 MPa. These observed self-potential variations were explained well with an electrokinetic effect due to the underground flow of the injected water. From the observed results, we estimated that the ratio of hydraulic parameters (permeability, porosity, and tortuosity) to electrokinetic parameters (zeta potential and dielectric constant) decreased approximately 40% during eight years after the earthquake. This result suggests that the healing process around the fault zone progress.     

鲜水河断裂带康定段雅拉河断裂深部应力应变状态及其孕震环境

鲜水河断裂带位于青藏高原东缘,是中国大陆内部地震活动性最强的大型左行走滑断裂之一,揭示其深部应力状态与应变是认识孕震环境和评估断裂带地震危险性的重要依据。本文选择鲜水河断裂带未来强震危险性较高的康定段作为研究对象,聚焦雅拉河断裂带内的糜棱岩,通过光学显微镜和扫描电镜（SEM）的显微构造分析、粒度统计、石英组构和Ti含量测试,确定石英递进变形过程中差应力的变化和不同阶段的变形温度,构建鲜水河断裂带康定段的地壳强度剖面。观测结果显示,糜棱岩在抬升过程中石英发生颗粒边界迁移（GBM）、亚颗粒旋转（SGR）和膨凸重结晶（BLG）三种类型的变形机制。构建的地壳强度剖面显示,雅拉河断裂带应变速率约为6.08×10^-13~1.62×10^-11s^-1,脆韧性转化带发生在~12.5±2.5km深度,该处岩石极限强度~145.5MPa。实际岩石强度（μ=0.383）小于理论破裂摩尔圆（μ=0.85）的岩石强度发育应变弱化。当韧性变形阶段由位错蠕变形成的应变局部化以及细粒化等机制降低岩石的强度至临界条件时,会导致破裂频次的增强,应力释放发生地震。同时,位错蠕变引起的应变弱化导致岩石强度降低,使高应力无法积累。     

断层破碎带隧道突水突泥灾变演化模型试验研究

为研究断层破碎带隧道开挖扰动作用下突水、突泥灾变演化过程,建立了三维地质模型试验系统,以江西永莲隧道F2断层突水、突泥灾害为例,通过大量的材料配比及物理力学性能参数测试,研制出适用于流-固耦合模型试验的新型断层及正常围岩相似材料,对隧道突水、突泥灾害进行研究。试验结果有效地揭示了无支护条件下断层破碎带隧道的洞周位移、渗流压力、应力-应变以及突出物质量等特征参数对时效性的响应规律。随着时间的增长,渗流压力整体呈上升趋势,越靠近开挖面其波动范围及幅度越大;突出物质量在发生突水、突泥灾害前出现短时减小后迅速增加;洞周围岩拱顶以竖向位移为主,而拱腰以水平位移为主;在相同相应力状态下,拱腰位置应变比拱顶位置大。将试验灾变特征与现场实际演化过程进行对比分析,两者结果较为吻合。该系统可广泛应用于其他地下工程的模型试验研究,其研究方法及结果对类似工程研究具有一定的指导和借鉴意义。     

Gas permeability evolution of cataclasite and fault gouge in triaxial compression and implications for changes in fault-zone permeability structure through the earthquake cycle

We report the results of permeability measurements of fault gouge and tonalitic cataclasite from the fault zone of the Median Tectonic Line, Ohshika, central Japan, carried out during triaxial compression tests. The experiments revealed marked effects of deformation on the permeability of the specimens. Permeability of fault gouge decreases rapidly by about two orders of magnitude during initial loading and continues to decrease slowly during further inelastic deformation. The drop in permeability during initial loading is much smaller for cataclasite than for gouge, followed by abrupt increase upon failure, and the overall change in permeability correlates well with change in volumetric strain, i.e., initial, nearly elastic contraction followed by dilatancy upon the initiation of inelastic deformation towards specimen failure. If cemented cataclasite suffers deformation prior to or during an earthquake, a cataclasite zone may change into a conduit for fluid flow. Fault gouge zones, however, are unlikely to switch to very permeable zones upon the initiation of fault slip. Thus, overall permeability structure of a fault may change abruptly prior to or during earthquakes and during the interseismic period. Fault gouge and cataclasite have internal angles of friction of about 36° and 45°, respectively, as is typical for brittle rocks.     

Modeling of damage,permeability changes and pressure responses during excavation of the TSX tunnel in granitic rock at URL,Canada

This paper presents numerical modeling of excavation-induced damage, permeability changes, and fluid-pressure responses during excavation of a test tunnel associated with the tunnel sealing experiment (TSX) at the Underground Research Laboratory (URL) in Canada. Four different numerical models were applied using a wide range of approaches to model damage and permeability changes in the excavation disturbed zone (EDZ) around the tunnel. Using in situ calibration of model parameters, the modeling could reproduce observed spatial distribution of damage and permeability changes around the tunnel as a combination of disturbance induced by stress redistribution around the tunnel and by the drill-and-blast operation. The modeling showed that stress-induced permeability increase above the tunnel is a result of micro and macrofracturing under high deviatoric (shear) stress, whereas permeability increase alongside the tunnel is a result of opening of existing microfractures under decreased mean stress. The remaining observed fracturing and permeability changes around the periphery of the tunnel were attributed to damage from the drill-and-blast operation. Moreover, a reasonably good agreement was achieved between simulated and observed excavation-induced pressure responses around the TSX tunnel for 1 year following its excavation. The simulations showed that these pressure responses are caused by poroelastic effects as a result of increasing or decreasing mean stress, with corresponding contraction or expansion of the pore volume. The simulation results for pressure evolution were consistent with previous studies, indicating that the observed pressure responses could be captured in a Biot model using a relatively low Biot-Willis’ coefficient, α ≈ 0.2, a porosity of n ≈ 0.007, and a relatively low permeability of k ≈ 2 × 10⁻²² m², which is consistent with the very tight, unfractured granite at the site.     

The role of Pan-African structures in intraplate seismicity near the termination of the Romanche fracture zone, West Africa

The distribution of epicenters of both historic earthquakes and recent seismic events in southeastern Ghana, compiled from local and teleseismic networks, show strong correlation with the Pan-African structures onshore and indicate an alignment with disruptions on seismic sections offshore. The seismic reflection sections reveal basement structures of the external zone of the Pan-African Dahomeyide orogen and these structures can be traced to offsets of shelf strata and seabottom reflectors, providing direct evidence, for the first time, for neotectonic activity that may be responsible for seismicity in the area. The deep structure of the external zone consists of moderately-dipping reflectors inferred to represent high-strain zones in the variably deformed margin of the West African craton. Taken together, the available data suggest that active tectonics in this intraplate environment may involve inversion of the Pan-African thrust structures but that this activity is apparently not related to reactivation of the nearby Romanche Fracture Zone.     

Discrete element simulation of the effect of particle size on the size of fracture process zone in quasi-brittle materials

Experimental tests performed on quasi-brittle materials show that a process zone develops ahead of a crack tip. This zone can affect the strength and the deformation pattern of a structure. A discrete element approach with a softening contact bond model is utilized to simulate the development of the fracture process zone in the three-point bending tests. Samples with different dimensions and particle sizes are generated and tested. It is shown that as the material brittleness decreases, the width of the process zone becomes more dependent on the specimen size. Furthermore, the increase in the particle size, results in increase in the width of the process zone. A dimensional analysis together with the numerical results shows that the width of process zone is a linear function of particle size (radius). This finding is discussed and compared with published experimental data in the literature.     

Diurnal soil water dynamics in the shallow vadose zone (field site of China University of Geosciences,China)

Because of the relatively low soil moisture in arid or semi-arid regions, water vapour movement often predominates in the vadose zone and affects the partitioning of energy among various land surface fluxes. In an outdoor sand bunker experiment, the soil water content at 10 and 30 cm depth were measured at hourly intervals for 2.5 days during October 2004. It was found that the soil moisture reached the daily maximum value (5.9–6.1% at 10 cm and 11.9–13.1% at 30 cm) and minimum value (4.4–4.5% at 10 cm and 10.4–10.8% at 30 cm) at midday (0–1 p.m. for 10 cm and 2–3 p.m. for 30 cm) and before dawn (2–3 a.m. for 10 cm and 4–5 a.m. for 30 cm), respectively. The modified HYDRUS-1D code, which refers to the coupled water, water vapour and heat transport in soil, was used to simulate the moisture and water vapour flow in the soil. The numerical analyses provided insight into the diurnal movement of liquid water and water vapour driven by the gradients of pressure heads and temperatures in the subsurface zone. The simulated temperature and water content were in good agreement with the measured values. The spatial–temporal distribution of liquid water flux, water vapour flux and soil temperature showed a detailed diurnal pattern of soil water dynamics in relatively coarse sand. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

韧性剪切带糜棱岩中不对称旋转碎斑系剪切指向模拟实验韧性剪切带糜棱岩中不对称旋转碎斑系剪切指向模拟实验研究现状及其问题

韧性剪切带是大陆变形过程中形成于地壳深层次的重要构造变形形迹,是重建构造变形温压环境、变形几何学、运动学及动力学的重要研究对象。剪切变形方向的确定是韧性剪切带研究的基础环节之一。尽管指示韧性剪切带剪切方向的标志很多,但是由于韧性剪切带变形过程的复杂性,实际工作中往往很难准确地限定剪切方向,甚至常常会发现同一条韧性剪切带中发育指向相反的剪切标志。在变形岩石中,不对称旋转碎斑系被认为是判断韧性剪切带剪切方向的可靠标志。根据有拖尾的旋转碎斑系判断剪切指向要比“云母鱼”、“多米诺”等组构可靠得多。总结前人的理论和模拟试验成果,可以清楚地认识到,碎斑系的演化是其形态、轴率、初始方位、基质及其界面性质、运动学涡度、剪应变强度、剪切带的厚度、碎斑短轴比等因素综合作用的结果。深刻认识不对称旋转碎斑系在韧性剪切带形成过程中的发育过程、限制条件、影响因素,将有助于准确地运用它们来判断韧性剪切变形的构造指向,以便进一步研究与该韧性剪切变形相关的大陆动力学。     

包气带中温度变化对水分分布影响的实验研究

笔者在高180cm、宽50cm的砂槽中,做了温度对水分运移影响的模拟试验。试验结果表明,在包气带一定深度以下,孔隙相对封闭,孔隙内液态水与气态水处于动态平衡,相对湿度接近或达到饱和状态。在此条件下,砂柱内温度场的任何微小变化都会导致孔隙系统内的水分发生蒸发或凝结。当包气带内温度场发生变化时,气态水在温度梯度作用下,向最低温度界面运移,蒸发或是凝结取决于最低温度界面的性质。在不发生聚集的开放性界面上出现蒸散,消耗包气带内水分。在聚集性封闭界面上则出现凝结,使包气带内水分增加。在温度场控制下,包气带中气态水凝结或蒸发是水分运移的另一重要形式,它在一定程度上决定着水分的分布状态,尤其在温差巨大的地区,这种作用显得十分重要。     

地质温度计在郯庐断裂带南段低温糜棱岩中的尝试

在缺少糜棱岩形成温度资料的情况下,糜棱岩的形成深度、与所叠加岩石的关系、变质演化、抬升-剥露历史、矿物的变形机制、同位素年龄数据的解释等一系列问题就很难得到正确合理的解释.适用于低温条件下的白云母-绿泥石地质温度计、白云母-黑云母地质温度计和绿泥石成分温度计仅在区域变质岩中应用过,从未在糜棱岩中使用.本文利用郯庐断裂带南段（安徽段）韧性剪切带内糜棱岩中同构造新生的白云母、黑云母和绿泥石,首次尝试上述3种地质温度计在糜棱岩中的应用.糜棱岩中新生矿物组合及长石变形行为显示,糜棱岩的变形温度为350℃～450℃.利用白云母-黑云母地质温度计和绿泥石地质温度计获得的温度值分别为672℃～1116℃和470℃～520℃,高于糜棱岩的形成温度,指示这2个地质温度计不适用于计算低温糜棱岩的形成温度.而利用白云母-绿泥石地质温度计获得的温度值与糜棱岩的形成温度相吻合,这表明在上述3种低温地质温度计中,只有白云母-绿泥石地质温度计适用于低温糜棱岩的形成温度测定.     

Do tides affect water quality in the upper phreatic zone of a small oceanic island, Sipadan Island, Malaysia?

 Sipadan Island is a small oceanic island with limited storage of fresh groundwater. A study was carried out to determine the effect of tidal change on the groundwater quality of such an island using temperature, dissolved oxygen content, conductivity, salinity, and pH values as indicators. Overall, the results indicated that the groundwater quality changes with tides, but the trends of fluctuation differs between the observed parameters. It was found that the percentages of changes during the period of study were 0.8% (temperature), 53% (dissolved oxygen), 61% (conductivity), 58% (salinity), and 1.7% (pH) at the centre of the island; and 0.9% (temperature), 33% (dissolved oxygen), 40% (conductivity), 42% (salinity), and 9% (pH) at a station 120 m from the coast, based on 2.9-m and 2.8-m tidal ranges at each station. Received: 5 July 1995 · Accepted: 6 November 1995     

Suggestion of a method for landslide early warning using the change in the volumetric water content gradient due to rainfall infiltration

An early warning system can be an effective measure to reduce the damage caused by landslides by facilitating the timely evacuation of residents from a landslide-prone area. Early detection of landslide triggering across a broad range of natural terrain types can be accomplished by monitoring rainfall and the physical property changes of soils in real time or near-real time. This study involved the installation of a real-time monitoring system to observe physical property changes in soils in a valley during rainfall events. This monitoring included the measurement of volumetric water content, which was compared with the results of laboratory flume tests to identify landslide indicators in the soils. The response of volumetric water content to rainfall events is more immediate than that of pore-water pressure, and volumetric water content retains its maximum value for some time before slope failure. Therefore, an alternative method for landslide monitoring can be based on the observation of volumetric water content and its changes over time at shallow soil depths. Although no landslide occurred, the field monitoring results showed a directly proportional relationship between the effective cumulative rainfall and the gradient of volumetric water content per unit time (t/t _max). This preliminary study thus related slope failure to the volumetric water content gradient as a function of rainfall. Laboratory results showed that a high amount of rainfall and a high gradient of volumetric water content could induce slope failure. Based on these results, it is possible to suggest a threshold value of the volumetric water content gradient demarcating the conditions for slope stability and slope failure. This threshold can thus serve as the basis of an early warning system for landslides considering both rainfall and soil properties.     

Radial growth of Tamarix ramosissima responds to changes in the water regime in an extremely arid region of northwestern China

The response of radial growth of tamarisk (Tamarix ramosissima) growing on the shore of West-Juyan Lake, on the Heihe River in northwestern China, to changes in the lake’s water regime was studied using tree-ring chronologies, principal components (PC) analysis, and classical correlation analysis. The first PC accounted for 53.3% of the total variance and reflected a common growth response at different sites. Correlation analysis indicated that fluctuations in the lake’s water level during the growing season (May–August) was primarily responsible for variations in the radial growth of tamarisk and explained more of the variance at low-lying sites than at higher sites. The second PC accounted for 30.7% of the total variance and revealed distinct differences in growth response between low-lying sites and those on higher ground. Total annual precipitation played an important role in radial growth of tamarisk at the higher sites. The spatial pattern in the tree-ring chronologies for different sites was performed in the temporal pattern of the tree-ring chronology at the same site. Other factors such as microtopography, soil salinity, sand activity, and browsing by herbivores also affected the radial growth of tamarisk. The diversity in responses to the maximum water table depth for tamarisk in the study area appears to have been caused by local variations in precipitation, which can compensate to some degree for the inability of a plant’s roots to reach the water table.     

滇西南2014年景谷中-强震群的地质构造成因——茶房-普文断裂带贯通过程的构造响应

2014年10—12月期间,云南景谷接连发生了Ms6.6、Ms5.8、Ms5.9三次中-强地震。为确定地震的地质构造成因,在地表调查的基础上,综合该区的地质构造情况、烈度与余震分布、震源机制解等资料,确定此次震群活动的宏观震中位于永平盆地东南侧山地,发震断层为地质与地貌表现不显著的NW向右旋走滑断层。此次震群活动及余震迁移过程指示,由于断层斜接部位岩桥的临时阻碍,Ms6.6地震破裂在向南东扩展过程中发生短暂停滞,突破障碍后进一步引发了Ms5.8和Ms5.9地震,这符合震源破裂沿NW向发震断裂分段破裂的行为。区域活动断裂的遥感解译结果发现,发震断层位置恰好处于NW向右旋走滑的茶房断裂与普文断裂之间,区域上属于该断裂带的不连贯部位,指示此次中-强震群活动应该是茶房-普文断裂带贯通过程的构造活动表现。结合思茅地块的历史地震资料发现,思茅地块地震活动多以小于等于6.8级为主,发震构造多为NW向断裂。指示在现今构造应力场作用下,该区NW向断裂的活动性相对NE向断裂更加显著,属于该区主要控震构造,应在今后的地震地质工作中给予更多关注。     

丘陵油田三间房组注水开发效果影响因素分析

利用岩石铸体薄片、压汞和物性分析资料等,对丘陵油田三间房组储层岩石学特征、沉积特征、微观孔隙结构以及成岩相进行了深入研究。在此基础上,从多角度出发分析了影响丘陵油田三间房组储层注水开发效果的因素。研究表明:1)不同沉积微相储层注水开发效果存在较大差异;2)油藏注水开发效果在一定程度上受区域局部构造的控制;3)孔隙结构越复杂,孔径越小,注水开发效果越差;4)不同成岩相组合控制了储层发育特征和储集物性,其注水开发效果不同。因此,丘陵油田三间房组储层注水开发效果是主力微相、微构造、微观非均质性、成岩相等多因素共同作用的结果。     

上海开展工业开发区土地利用绩效评估的意义

随着工业化和城镇化建设进程加快,土地供需矛盾日益突出。作为城镇发展和土地开发利用的重点区域,开发区在促进经济高速发展中发挥了举足轻重的作用,通过对工业开发区土地绩效评估实践,建立健全开发区土地节约集约利用考核制度与长效机制,增强土地参与宏观调控的能力,对构建资源节约型社会具有重要意义。     

GPS-derived strain in northwestern California: Termination of the San Andreas fault system and convergence of the Sierra Nevada–Great Valley block contribute to southern Cascadia forearc contraction

GPS-derived velocities (1993–2002) in northwestern California show that processes other than subduction are in part accountable for observed upper-plate contraction north of the Mendocino triple junction (MTJ) region. After removing the component of elastic strain accumulation due to the Cascadia subduction zone from the station velocities, two additional processes account for accumulated strain in northern California. The first is the westward convergence of the Sierra Nevada–Great Valley (SNGV) block toward the coast and the second is the north–northwest impingement of the San Andreas fault system from the south on the northern California coastal region in the vicinity of Humboldt Bay. Sierra Nevada–Great Valley block motion is northwest toward the coast, convergent with the more northerly, north–northwest San Andreas transform fault-parallel motion. In addition to the westward-converging Sierra Nevada–Great Valley block, San Andreas transform-parallel shortening also occurs in the Humboldt Bay region. Approximately 22 mm/yr of distributed Pacific–SNGV motion is observed inland of Cape Mendocino across the northern projections of the Maacama and Bartlett Springs fault zones but station velocities decrease rapidly north of Cape Mendocino. The resultant 6–10 mm/yr of San Andreas fault-parallel shortening occurs above the southern edge of the subducted Gorda plate and at the latitude of Humboldt Bay. Part of the San Andreas fault-parallel shortening may be due to the viscous coupling of the southern edge of the Gorda plate to overlying North American plate. We conclude that significant portions of the upper-plate contraction observed north of the MTJ region are not solely a result of subduction of the Gorda plate but also a consequence of impingement of the western edge of the Sierra Nevada–Great Valley block and growth of the northernmost segments of the San Andreas fault system.