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1.
An underground gravity study was carried out under extreme conditions of the Alpine regions. The lead–zinc mine Bleiberg, Carinthia, was selected as an example to show the possibilities and limitations of the subsurface gravity method. For in situ density determinations, gravity measurements were made in two vertical mine shafts passing through Triassic sedimentary rocks of the Bleiberg Unit. The main prblem in gravity data reduction in extremely rugged topography is the accurate calculation of the terrain effect on underground stations. A general discussion of the various corrections required for the gravity measurements in the mine is presented. The mean interval densities in the two shafts, in limestone, dolomite, and schists formations, were determined as 2.76 and 2.77 g/cm3, respectively, with an accuracy of better than 0.01 g/cm3 for a depth interval of 50 m. The interval densities provide valuable information about the lithological and structural changes in the shaft surroundings and also agree well with the representative hand sample densities. In the second part, the applications of subsurface horizontal gravity surveys in exploration are discussed. Since the influence of topography is less underground because of the greater distance to the surface, subsurface surveys have definite advantages over surface surveys and can be very helpful in locating anomalous density zones in the mines. An example of gravity survey with a station spacing of 10 m at a depth of about 540 m is presented. 相似文献
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对首都圈地区由不同施测单位用不同仪器或不同方法获得的三组重力测量数据，通过绝对和相对测量的联合平差、相对测量结果的系统差消除，建立起绝对的、统一的重力时变体系；在此基础上分析了非构造因素地壳沉降的影响，并进行了测点位移改正，消除了长波干扰；实现了绝对和相对测量方法优势互补、消除矛盾和环境干扰、扩大信息量、加密时域采样间隔等目的，提高了识别构造活动过程的能力．结果表明，两组相对测量数据之间以及其中的10期观测资料中存在系统误差，研究区东南部的非均匀性局部地壳下沉导致10个点重力值线性上升，本文用回归分析的方法进行了改正．改正后的重力时变图对1995年10月6日古冶5.0级地震有明显而完整的反映． 相似文献
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M. BLÍKOVSKÝ 《Geophysical Prospecting》1979,27(4):848-861
An economic and precise processing system for microgravity surveys is presented. Three computer processing modes covering areal ground and underground measurements, measurements in vertical shafts, and measurements of vertical gravity gradients with a 3 m high tower are dealt with. Diagrams for manual calculation of gravity effects of prismatic walls, vertical shafts, and horizontal galleries, as well as programs for calculation of accurate terrain corrections and corrections for gravity effects of bodies with complicated ground-plan are proposed. The method of processing microgravity data is two to three times quicker than any traditional way, with maximum accuracy preserved in resulting gravity micro-anomalies. Applications from the field of mining geophysics and archaeology are included. 相似文献
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为了检验体潮与海潮的理论模型,分析了中国东西重力潮汐剖面（1981年9月-1985年1月）。同时,为研究LaCoste ET-20和ET-21重力仪的格值系统,建立了一条由17台LaCoste G型和2台LaCoste D型重力仪观测的重力垂直基线。在基线上标定的结果表明,ET-21重力仪的格值大了1％。由标定得到的格值计算剖面上各测站的潮汐因子,经海潮改正后,接近Wahr模型值,振幅因子的残差:O1波小于0.3μGal,M2波小于0.4μGal。但是上海和拉萨的观测经海潮改正后,相位迟后有很大的改善,振幅因子却更偏离于模型值,其潮汐异常主要是近海的海潮模型不完善,以及在海潮计算中,所采用的地球模型未考虑地壳与上地幔的横向不均匀性所引起。 相似文献
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Several new features are described which facilitate an automatic, more meaningful, and more accurate interpretation of gravity anomalies associated with approximately two-dimensional mass distributions. These include a provision for fixed points on the bounds of a distribution, outward dipping boundaries, calculation of the gravity effect at individual elevations of stations, smoothing of models and end-corrections for distributions of limited strike length. It is possible to obtain distributions about a median plane; these distributions are sensitive to shape and allow estimates of optimum depths and minimum density contrasts for the anomalous masses. 相似文献
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文中对腾冲火山区1998—2004年水准及重力观测资料进行了分析,发现垂直形变量大多在±10mm之内,重力变化为几十μGal,火山锥体和断层附近点位活动异常较大,可综合应用多源mogi模型和断层模型解释,断层的活动可使相邻测点的形变方向相反;垂直形变和重力的逐年变化表明火山岩浆处于一种活动状态。将火山区点位各时间段的重力梯度展布在形变-重力关系解释图中,发现数据主要落在Ⅰ、Ⅱ、Ⅳ和Ⅴ区,结合形变量对压力源等效体积的估算,初步认为火山区岩浆目前活动程度较低,暂没有喷发的危险 相似文献
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连续重力观测和GPS的技术结合能够监测到物质迁移和地壳垂直形变之间的量化关系.和相对重力测量以及绝对重力测量技术相比,其避免了时间分辨率和观测精度低,无法精细描述观测周期内的物质迁移过程问题.本文利用武汉九峰地震台超导重力仪SGC053超过13000 h连续重力观测数据;同址观测的绝对重力仪观测结果;气压数据;周边GPS观测结果;GRACE卫星的时变重力场;全球水储量模型等资料,采用同址观测技术、调和分析法、相关分析方法在扣除九峰地震台潮汐、气压、极移和仪器漂移的基础上,利用重力残差时间序列和GPS垂直位移研究物质迁移和地壳垂直形变之间的量化关系.结果表明:在改正连续重力观测数据的潮汐、气压、极移的影响后,不仅准确观测到2009年的夏秋两季由于水负荷引起的约(6~8)×10-8m·s-2短期的重力变化.而且在扣除2.18×10-8(m·s-2)/a仪器漂移和水负荷的影响后,验证了本地区长短趋势垂直形变和重力变化之间具有一致的负相关性规律.同时长趋势表明该地区地壳处于下沉,重力处于增大过程,增加速率约为1.79×10-8(m·s-2)/a.武汉地区重力梯度关系约为-354×10-8(m·s-2)/m. 相似文献
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Pierre Keating 《Geophysical Prospecting》1995,43(4):569-580
Gravity data are often acquired over long periods of time using different instruments and various survey techniques, resulting in data sets of non-uniform accuracy. As station locations are inhomogeneously distributed, gravity values are interpolated on to a regular grid to allow further processing, such as computing horizontal or vertical gradients. Some interpolation techniques can estimate the interpolation error. Although estimation of the error due to interpolation is of importance, it is more useful to estimate the maximum gravity anomaly that may have gone undetected by a survey. This is equivalent to the determination of the maximum mass whose gravity anomaly will be undetected at any station location, given the data accuracy at each station. Assuming that the maximum density contrast present in the survey area is known or can be reasonably assumed from a knowledge of the geology, the proposed procedure is as follows: at every grid node, the maximum mass whose gravity anomaly does not disturb any of the surrounding observed gravity values by more than their accuracies is determined. A finite vertical cylinder is used as the mass model in the computations. The resulting map gives the maximum detection error and, as such, it is a worst-case scenario. Moreover, the map can be used to optimize future gravity surveys: new stations should be located at, or near, map maxima. The technique is applied to a set of gravity observations obtained from different surveys made over a period of more than 40 years in the Abitibi Greenstone Belt in eastern Canada. 相似文献
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Mean annual sea level (MASL) data for 25 Greek stations were analyzed for the time period 1969–1982. The data from 4 of these were unacceptably poor, and the record of 3 stations showed unexplained step functions that were interpreted as errors. Relative MASL between stations showed crustal stability at 10 of the 18 useful stations. The standard deviation from the long-term average of these stations was ±1.8 cm. We conclude that if station records are carefully kept in this area crustal movements in excess of 5 cm can be detected by relative MASL. A comparison of MASL data with gravity changes measured in the Peloponnese and Central Greece suggests that vertical movements occurred along a gradient equal to or larger than the free air gradient. We conclude that the gravity network should be reoccupied frequently such that the non-tectonic effects to be determined from the probable observed gravity changes, and the tectonic vertical movements may be better understood. A co-seismic subsidence of about 5 cm is inferred to have taken place near Korinth during the 1981,M s =6.8, earthquake, which occurred 20 km N of this tide gauge (Posidonia). During 2.5 years before the 1968 Thessaloniki,M s =6.6, earthquake, sea level was lower than average suggesting possible crustal elevation of 3.6 cm at about 28 km epicentral distance. Because of the small amplitude of this change we are not certain that it represents crustal uplift. At station Myrina (on Limnos) a strong and consistent trend of subsidence accumulated a 15 cm change between 1975 and 1980. Chios showed a trend of emergence (total accumulation about +5 cm), while Volos showed a trend of subsidence (approximately ?5 cm total). Kefalinia appears to have subsided about 10 cm during the data period. The six stations along the Hellenic arc plate boundary showed nearly constant MASL, suggesting that crustal stability existed there during the last 14 years. We conclude that MASL data in Greece can be useful for understanding tectonic processes, especially if these data are gathered carefully and at numerous locations, and are cross-correlated to high precision repeat gravity measurements, and geodetic releveling. Also, MASL data on active volcanic islands have excellent potential for detecting uplift before future eruptions. 相似文献
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Extraction of groundwater or hydrocarbons causes pore pressure gradients and soil deformation due to poroelastic coupling. Recent studies show that high-resolution engineering tiltmeters installed at shallow depth between 2 and 10 m resolve this deformation. Models using poroelasticity can describe the relationship between fluid extraction, pore pressure gradients and induced tilt for homogeneous and layered sedimentary half spaces. Faults intersecting a stack of sedimentary layers, for example in the Lower-Rhine-Embayment, are of fundamental impact to the groundwater flow system of an area. However, the fault’s hydromechanical effect on pump induced tilt and the pore pressure regime is still poorly investigated. We chose a comparatively simple approach to quantify anomalous pump induced tilt and pore pressure observed near a fault and close to the surface in a sedimentary subsoil. A PC-based Finite Element software is used to model poroelastic deformation, i.e. modelling vertical tilt and excess pore pressure in response to fluid extraction through a singular well. We compare numerical solutions for models with and without faults and show that a fault can modify symmetry and amplitude of the deformation field by more than a magnitude. We conclude that tilt and pore pressure measurements also at shallow depth can thus be biased by large subsurface structures like faults. Vice versa, these measurements may provide means to quantify hydromechanical effects caused by subsurface structures. However, depending on the geological setting, i.e. if pathways are established by a fault, the anomaly caused by the fault can also be small and hard to detect. Therefore, faults and geological structures like material boundaries have to be considered in poroelastic models carefully. For tilt surveys with a limited number of instruments in geologically well constrained areas these models allow the preselection of potential positions for tiltmeters where prominent field anomalies are expected. 相似文献
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H. GRANSER 《Geophysical Prospecting》1987,35(1):71-82
A numerical method for calculating the topographic reduction of gravity measurements is developed which follows the approximation of the topography by a single valued function. The method involves the conversion of the volume integral for the gravity effect into a two-dimensional definite integral. The definite integral is partly solved by explicit, and partly by numerical, integration, using the Gauss-Legendre quadrature formula. This method is well suited to calculating the topographic reduction of 50 to approximately 1000 m from the station–especially for microgravimetric surveys in areas of steeply sloping terrain. To test the method in practice it was applied in an area of rough relief in Keban (East Turkey). 相似文献
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Gary Barnes 《Geophysical Prospecting》2014,62(3):646-657
When anomalous gravity gradient signals provide a large signal‐to‐noise ratio, airborne and marine surveys can be considered with wide line spacing. In these cases, spatial resolution and sampling requirements become the limiting factors for specifying the line spacing, rather than anomaly detectability. This situation is analysed by generating known signals from a geological model and then sub‐sampling them using a simulated airborne gravity gradient survey with a line spacing much wider than the characteristic anomaly size. The data are processed using an equivalent source inversion, which is used subsequently to predict and grid the field in‐between the survey lines by means of forward calculations. Spatial and spectral error analysis is used to quantify the accuracy and resolution of the processed data and the advantages of acquiring multiple gravity gradient components are demonstrated. With measurements of the full tensor along survey lines spaced at 4 × 4 km, it is shown that the vertical gravity gradient can be reconstructed accurately over a bandwidth of 2 km with spatial root‐mean square errors less than 30%. A real airborne full‐tensor gravity gradient survey is presented to confirm the synthetic analysis in a practical situation. 相似文献
15.
重力方法在地震预报中的作用 总被引：1，自引：0，他引：1
利用重力方法研究地球的潮汐和非潮汐变化。通过它们的变化规律了解地下介质的质量变化和密度分布以及地球弹性模量与地震的关系。２０多年地震预报实践表明，重力方法在地震预报中有其特殊作用。根据目前在台站或测点按波速异常所圈定的孕震区内发生的地震统计检验：台站监测能力为４４％，重力重复测量的监测能力可达５６％。 相似文献
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山区重力测量工作中,用现有方法计算总均方误差,往往使均方误差偏小,异常的可信程度降低。这主要原因是山区重力工作中,忽略了影响较大的岩石密度的误差。而要准确的测定各部分岩石密度又是十分困难的。据此,本文分析了山区重力测量总均方误差的来源,提出了各项误差分配的方法。 相似文献
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The magnetic and gravity field produced by a given homogeneous source are related through Poisson's equation. Starting from this consideration, it is shown that some 2D interpretation tools, widely applied in the analysis of aeromagnetic data, can also be used for the interpretation of gravity gradiometric data (vertical gradient). This paper deals specifically with the Werner deconvolution, analytic signal and Euler's equation methods. After a short outline of the mathematical development, synthesized examples have been used to discuss the efficiency and limits of these interpretation methods. These tools could be applied directly to airborne gravity gradiometric data as well as ground gravity surveys after transformation of the Bouguer anomalies into vertical gradient anomalies. An example is given of the application of the Werner deconvolution and Euler's equation methods to a microgravity survey. 相似文献
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The use of the gravity method to predict rock bursts in mines is based on the relationship between the development of a dilatancy process in the exploited rock mass and the time-dependent gravity anomalies induced by this phenomenon. The differences between successive observations of anomalies and the time behaviour of their trend amplitudes as precursors of preceding changes of rock stability are interpreted. The centres of zones of induced rock density variation are determined by computing the position of singular points of the differences between anomalies. Two gravity surveys have been carried out in the Radbod coal mine (Germany). The first survey took place at the level of the Dickebank seam (depth 1030 m), the second in the Sonnenschein seam (depth 1090 m). The observations were made with Worden and LaCoste-Romberg (D-type) gravimeters. The differences between successive anomalies were less than 100 μGal. In the case of the Dickebank seam, the position of singular points demonstrates the effect of two approaching longwalls on a previously mined-out seam and on the gallery in which the gravity observations were made. In the case of the Sonnenschein seam, the trend amplitudes show distinct variations in the formation of the approaching longwall below the edges of all previously mined-out seams. In particular, the effect of a remnant pillar has caused the largest gravity gradients. This result corresponds to the existence of a zone of rock-burst hazard known from test drilling. The computed singular points are grouped together under the remnant pillar indicating two local hazard zones. Both results, the observed development of rock instability with time and the information about the position of the disturbed rock mass relative to the mine workings, are of importance, subsurface gravity surveying can therefore be a valuable tool for predicting rock-bursts. 相似文献
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卫星重力梯度测量与地球引力场的精度研究 总被引：1，自引：0，他引：1
本文根据地球引力位的球谐函数展开式,利用重力梯度张量各分量导出了位系数模型的精度估计公式.从三方面进行了研究:假定卫星重力梯度仪测量精度,探讨用重力梯度数据确定地球重力场模型的精度;求出位系数模型和大气阻力引起的重力梯度卫星的轨道误差;最后,反求轨道误差和位系数误差对重力梯度测量值的影响.数值计算表明,与地面技术和常规卫星方法相比,卫星梯度测量可使重力场模型的精度至少提高3-5倍;利用重力梯度张量全分量求得的重力值精度比单用径向分量Vrr的结果提高40％以上;若仅顾及位系数模型和大气阻力误差,则轨道误差对梯度测量值的影响△Vi3（i=3,2,1）至少可分别在1/4和1/3弧圈内达到△Vi3≤σ（仪器精度）. 相似文献
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1975年2月4日海城7.3级地震前后在震中以西不远的一条长约250公里的北西—南东向剖面上进行了五次重力测量,震前三次,震后两次.剖面上相邻两个测点的重力差的测量均方误差小于40微伽.自1972年6月至1973年5月的一年期间的三次观测结果表明,剖面东南段重力值显著下降,最大达352微伽.地震以后,1975年3月的第四次重力测量发现,剖面东南段的重力值回升到第一次测量时的水平.1975年7月的第五次测量则表明剖面东南段的重力值继续上升.1976年7月28日唐山7.8级地震前后也观测到重力的变化,不过地震前重力是增加而不是减少.震前和震后,在震中以北不远的一条长约270公里的东西向剖面上各进行过两次重力测量.结果表明,主震后整个剖面,特别是靠近唐山的那些测点的重力也有逐渐恢复到震前第一次测量时的数值的趋势.由这些结果可以看到,重力的变化与地震的发生似有密切的关系.根据重复大地水准测量资料估计的地面高程变化所能引起的重力变化远比所观测到的变化为小.因此,我们推测某些大地震可能与地壳和上地幔内的质量迁移有关,认为所观测到的重力变化大部份是质量迁移引起的.我们对质量迁移的重力效应作了理论分析,但是,对迁移的物理过程我们还很不清楚. 相似文献