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1.
 5.12汶川大地震发生后,在龙门山断裂带东北段,开展了6个钻孔的原地应力测量工作.测量钻孔分别位于龙门山中央断裂带上下两盘的平武、北川、江油和广元等地.钻孔孔深在200~500 m之间,共取得了72个测试段的地应力测量数据,以及其中33个测段的印模定向试验数据,由此获得了每个测点处地应力的赋存状态,包括地应力量值随孔深的变化以及地应力作用方向.根据库仑准则,结合Byerlee定律对各测点实测数据进行分析,可以看出,龙门山断裂带上盘现今地应力的作用强度高于下盘.其上、下两盘现今地应力赋存状态特征及其差异性显示出该区域处于不均衡的应力环境,容易导致断裂失稳而产生新的活动;印模定向试验数据表明,龙门山断裂带东北段的北川、江油、平武的最大水平主应力优势方向为NEE向;广元附近为NWW或近东西方向.结合已有的研究成果,初步得到龙门山断裂带现今地应力作用方向的分段性特征,即大致以北川为界,龙门山断裂带东北段应力方向显示了与西南段不同的特征.其西南段现今地应力的优势作用方向为北西方向,而龙门山断裂带东北段,自江油、北川、平武一带至广元、青川附近,其现今地应力的最大水平主压应力的优势作用方向呈现了NEE→NWW的赋存状态和变化趋势.本文获得的研究结果对于认识5.12汶川特大地震的动力学机制具有一定的借鉴和启示作用.  相似文献
2.
山西煤矿矿区井下地应力场分布特征研究   总被引:1,自引:1,他引:9       下载免费PDF全文
采用煤矿井下专用的小孔径水压致裂地应力测量装置,在山西省的晋城、潞安、汾西、华晋、阳泉、平朔、大同等矿区,完成了160个测点的地应力测量,测点地质条件涵盖了山西省煤矿大部分条件.基于实测数据,分析了地应力与测点埋深的关系,不同深度条件下煤矿矿区井下地应力状态;绘制出山西省煤矿矿区井下地应力分布图,并与震源机制解的分析结果进行了比较,得出山西省煤矿矿区井下地应力场分布特征与变化规律.煤矿井下水平应力总体上随着埋深增加而增大,但由于各矿区地质条件差异较大,导致地应力测试数据离散性也较大;埋深小于250 m的岩层应力状态主要为σHhV型,埋深处于250~500 m的岩层应力状态以σHVh型为主,埋深较大的矿区主要为σVHh型;最大水平主应力与垂直主应力的比值绝大部分集中在0.5~2.0之间,而且随着埋深增加,侧压比呈现减小的趋势,并向1附近集中;最大水平主应力与最小水平主应力的比值主要集中在1.5~2.0之间;平均水平主应力与垂直主应力的比值大多处于0.5~1.5,尤以0.5~1.0之间最多;山西省煤矿矿区从北到南,最大水平主应力方向发生了较大变化.北部最大水平主应力方向为NE,往南发生偏转到NNW;靠东部与西部偏向NW;靠东南部出现了多变的方向.井下实测数据与震源机制解相比在部分区域一致性较好,而在另一些区域存在明显的差异.特别是在受较大地质构造影响的区域,水平主应力方向往往发生明显的扭转和变化.  相似文献
3.
北京地区地应力测量与主要断裂稳定性分析   总被引:1,自引:0,他引:1       下载免费PDF全文
 2008年汶川地震后,为查明北京地区现今地应力状态、评价断裂稳定性,相继在北京地区开展了5个深孔(600~1000 m)的水压致裂法地应力测量,并在适宜深度安装了地应力相对变化监测探头,建立了地应力变化监测台站.本文首先利用实测地应力数据分析了北京地区地壳浅表层应力状态,结果表明:(1)北京地区千米深度内,最大、最小水平主应力随深度增加梯度系数分别为0.0328和0.0221,侧压系数Kav和KHv值,最大、最小水平主应力之比KHh值与国内外已有认识基本一致,而水平向剪应力相对强度参数μm值较低;(2)北京地区最大水平主应力优势方向为近EW向,与华北地区构造应力场方向基本一致,同时受区内断裂活动等影响,存在与区域主应力方向偏差的局部应力场;(3)实测数据揭示的应力结构显示,北京地区地壳浅表层最大主应力(σ1)总体为最大水平主应力(σH),受区域构造演化以及测点附近断裂的影响,中间主应力(σ2)与最小主应力(σ3)所对应的实测地应力存在变化,但总体来讲,实测地应力数据揭示的应力结构与北京地区主要断裂性质基本相吻合.其次,基于实测应力数据,采用库仑摩擦滑动准则,结合拜尔定律,并取摩擦系数为0.2~1.0,初步评价了北京地区主要断裂稳定性,结果显示:(1)在摩擦系数取0.6~1.0条件下,北京地区现今应力状态尚未达到导致断裂失稳滑动水平,断裂不会出现失稳滑动现象;(2)摩擦系数弱化到0.4时,西峰寺钻孔应力状态满足断裂失稳滑动条件,揭示出八宝山断裂存在失稳滑动可能性,而夏垫-马坊断裂和黄庄-高丽营断裂附近测点应力状态将趋近满足断裂失稳滑动条件,表明这两条断裂有趋向失稳滑动可能性;(3)只有当摩擦系数弱化到0.2时,北京地区主要断裂才可能在现今应力状态出现断裂失稳滑动.本文的认识对北京地区乃至华北地区构造应力场、地震地质研究有重要参考意义.  相似文献
4.
根据黄河上游某水电站地下厂房区工程地质勘探资料和原地应力测量资料,用Marc Mentat软件建立了有限元计算模型。利用应力回归分析方法模拟该地区地应力场:首先确定自重和构造应力因素为待回归因素,然后采用回归法原理计算待回归因素的系数,从而模拟出工程区地应力场。对比实测值和模拟值,表明两者在数值和方位上差距均不大。厂房区附近最大主应力值为8MPa左右,最大水平应力近东西向。重力作用对该区地应力的影响要大于构造应力的作用。反演获得的规律与预先推测的结果基本一致。反演结果表明该水电站地下厂房的稳定性较好。  相似文献
5.
2008年5月12日汶川Ms8.0级地震后,为了解发震断裂附近地应力分布特征,于2009年10月-12月期间,在龙门山断裂带东北段江油、北川地区3个200 m钻孔中开展水压致裂地应力测量工作;本文首先依据研究区域内3个200m钻孔的水压致裂地应力测量结果,分析了汶川8.0级地震发生1年后,龙门山断裂带东北段附近现今地应力状态分布特征;其次,基于龙门山断裂带基础地质、地球物理等研究资料,采用线弹性有限元模拟方法,运用ANSYS有限元模拟软件,模拟得到了地震后研究区内现今地应力状态;再次,综合研究区内地应力测量结果和应力场的三维有限元数值模拟结果,揭示了断裂带附近江油~北川剖面现今应力场的变化规律;文章最后探讨了龙门山断裂带东北段江油和北川地区的地震危险性.  相似文献
6.
Scientists and water users are concerned about the potential impact on water resources, particularly during low-flow periods, of freshwater withdrawals for hydraulic fracturing (fracking). Therefore, the objective of this paper is to assess the potential impact of hydraulic fracturing on water resources in the Muskingum watershed of Eastern Ohio, USA, especially due to the trend of increased withdrawals for hydraulic fracking during drought years. The Statistical Downscaling Model (SDSM) was used to generate 30 years of plausible future daily weather series in order to capture the possible dry periods. The data generated were incorporated in the Soil and Water Assessment Tool (SWAT) to examine the level of impact due to fracking at various scales. Analyses showed that water withdrawal due to hydraulic fracking had a noticeable impact, especially during low-flow periods. Clear changes in the 7-day minimum flows were detected among baseline, current and future scenarios when the worst-case scenario was implemented. The headwater streams in the sub-watersheds were highly affected, with significant decrease in 7-day low flows. The flow alteration in hydrologically-based (7Q10, i.e. 7-day 10-year low flow) or biologically-based (4B3 and 1B3) design flows due to hydraulic fracking increased with decrease in the drainage area, indicating that the relative impact may not be as great for higher order streams. Nevertheless, change in the annual mean flow was limited to 10%.  相似文献
7.
利用水压致裂原地应力测试技术,在乌鲁木齐市区碗窑沟断裂东段、雅玛里克断裂东段和西山断裂带中、东段开展了断层附近原地应力测量研究,得到了地表浅部构造应力的大小、方向和分布特征。钻孔HFZK3位于碗窑沟断裂东段的南侧,孔深62.13m;钻孔HFZK5位于雅玛里克断裂东段的南侧,孔深30.00m;钻孔HFZK9和HFZK12都位于西山断裂带的中、东段,孔深分别为34m和54.5m。根据实测的地应力资料,断层附近最大水平主压应力方向为NE—NEE向,与区域构造应力SN—NNE向主压方向有一些差异,说明受断层活动影响,断层附近的应力状态与区域应力场明显不同。利用地应力实测资料研究了断层的活动性,在测量深度域内水平和垂直应力的关系为σH>σh>σV,该应力状态有利于逆断层活动,与地质资料反映的以逆断层活动为主基本一致。利用库仑摩擦滑动准则,摩擦强度取0.6~1.0进行分析,断层附近的现今地应力状态达到或超过产生逆断层摩擦滑动的临界值,表明测区现今构造活动以逆断层为主。研究区的3条断层不具备发生走滑断层活动的可能性,其中雅玛里克断裂东段、西山断裂带中段和东段具有发生逆断层活动的可能性,相比而言,西山断裂带中段危险性更大  相似文献
8.
Natural heat stored in the earth's interior represents an essentially inexhaustible energy supply which, at usefully high temperatures, is accessible at practical drilling depths from almost anywhere on the earth's land surface. The problems of extracting and using this heat are those of engineering and economics, and can be expected to vary with the local geology and value of thermal energy. The first major experimental system designed to investigate these problems in one common type of geologic environment has recently been completed in the crystalline rock underlying the Jemez Plateau of northern New Mexico. It consists principally of two boreholes connected at a depth of about 2.7 km by a system of hydraulic fractures produced in granitic rock at a temperature of approximately 185°C. Cool water injected through one hole is heated as it flows through the fractures, and is recovered through the second hole as pressurized, superheated water. In a surface heat-exchange system now being completed, this heat will be extracted and the cool water reinjected to maintain a continuous, closed, pressurized-water energy-extraction loop.  相似文献
9.
The Bridgman ring experiment, in which a hard rubber ring slipped over a steel rod was observed to split when subjected to a hydrostatic confining pressure, was repeated with Pyrex glass rings. Three cases were studied, in which (a) both ring and rod were unjacketed, (b) the inner wall of the ring was sealed from the pressure medium and (c) both rod and ring were completely jacketed. In the first two cases the ring was observed to split abruptly, with a single axial crack when confining pressure reached a critical level. In the third case no abrupt failure occurred, but a number of axial cracks were found to have formed, grown stably, but not penetrated the outer wall of the ring. The first two cases are explained by hydraulic fracturing of the ring. Observations and analysis indicate that in the third case the cracks started at flaws on the inner surface of the ring and propagated outwards in a stable manner. This case, in which a tensile crack propagates in an all-around compressive stress field, provides some insight into axial cracking of rock in triaxial compression and tensile failure of rock under radial shock loading.  相似文献
10.
Fluid infiltration into fault zones and their deeper-level counterparts, brittle-ductile shear zones, is examined in diverse tectonic environments. In the 2.7 Ga Abitibi greenstone belt, major tectonic discontinuities, with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism. During reverse motion on the structures, accommodating shortening of the belt, these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids. Such fluids were characterised by 18O=+6±2, D=–50±20, 13C=–4±4, and temperatures of 270 to 450°C, probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism. Hydrothermal fluids were more radiogenic (87Sr/86Sr=0.7010 to 0.7040) and possessed higher than did contemporaneous mantle, komatiites or tholeiites, and thus carried a contribution from older sialic basement. A provinciality of87Sr/86Sr and 13C is evident, signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres. Mineralised faults possess enrichments of large ion lithophile (LIL), LIL elements, including K, Rb, Ba, Cs, B, and CO2, and rare elements, such as Au, Ag, As, Sb, Se, Te, Bi, and W. Fluids were characterised by XCO 20.1, neutral to slightly acidic pH, low salinity 3 wt-%, K/Na=0.1, they carried minor CH4, CO, and N2, and they underwent transient effervescence of CO2 during decompression. Clastic sediments occupy graben developed at fault flexures. The40Ar/39Ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years.At the Grenville front, translation was accommodated along two mylonite zones and an intervening boundary fault. The high-temperature (580°C) and low-temperature (430 to 490°C) mylonite zones, formed in the presence of deep-level crust-equilibrated fluids of metamorphic origin. Late brittle faults contain quartz veins precipitated from fluids with extemely negative 18O (–14 per mil) at 200 to 300°C. The water may have been derived from downward penetration into fault zones of precipitation of low18O on a mountain range induced by continental collision, with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults.Archean gneisses overlie Proterozoic sediments along thrust surfaces at Lagoa Real, Brazil; the gneisses are transected by brittle-ductile shear zones locally occupied by uranium deposits. Following deformation at 500 to 540°C, in the presence of metamorphic fluids and under conditions of low water-to-rock ratio, shear zones underwent local intense oxidation and desilication. All minerals undergo a shift of –10 per mil, indicating discharge of meteoric-water-recharged formation brines in the underlying Proterozoic sediments up through the Archean gneisses, during overthrusting; 1000 km3 of solutions passed through these structures. The shear zones and Proterozoic sediments are less radiogenic (87Sr/86Sr=0.720) than contemporaneous Archean gneisses (0.900), corroborating the transport of fluids and solutes through the structure from a large external reservoir.Major crustal detachment faults of Tertiary age in the Picacho Cordilleran metamorphic core complex of Arizona show an upward transition from undeformed granitic basement through mylonitic to brecciated and hydrothermally altered counterparts. The highest tectonic levels are allochthonous, oxidatively altered Miocene volcanics. This transition is accompanied by an increase of 12 per mil in 18O, from +7 to +19, and a 400°C decrease in temperature. Lower tectonic levels acted as aquifers for the expulsion of large volumes of higher-temperature reduced metamorphic fluids and/or evolved formation brines. The Miocene allochthon was influenced by a lower-temperature reservoir inducing oxidative potassic alteration; mixing occurred between cool downward-penetrating thermal waters and the hot, deeper aqueous reservoir.In general, flow regimes in these fault and shear zones follow a sequence, from conditions of high temperature and pressure with locally derived fluids at low water-to-rock ratios, during initiation of the structures, to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs. Later in the tectonic evolution and at shallower crustal levels there was incursion of oxidising fluids from near-surface reservoirs into the faults. In general, magmatism, tectonics, and fluid motion are intimately related.  相似文献
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