Subsurface Disposal of Liquid Low-Level Radioactive Wastes at Oak Ridge, Tennessee

Liquid low-level radioactive wastes have been disposed of by subsurface injection at Oak Ridge, Tennessee, for the last two decades. The process entails mixing the wastes with cement and other additives, then pumping the slurry under pressure into a highly impermeable shale; the pressure is sufficient to create bedding plane fractures in which the grout, containing the wastes, sets. Research is being conducted to develop an understanding of the hydrology of the site and monitoring methods. The present regulatory climate regarding injection wells has created an uncertain future for this technique.     

A near-bottom geophysical traverse of the Reykjanes Ridge

We report here the results of a near-bottom geophysical survey of the Reykjanes Ridge, a mid-ocean ridge that is oriented obliquely to the perpendicular spreading direction. From a combination of the bathymetric profiles, side-scan sonar data, and regional bathymetric maps we infer that the present center of spreading is made up of a number of N15°E-trending en echelon ridge segments in the southern half of our survey area. Insufficient data prevent the identification of the spreading pattern in the northern half. The side-scan records show that the ridge flanks are highly fractured by inward-facing faults displaced 40 m or less and trending in a N21°E direction. The lack of side-scan features parallel to the spreading direction except in the southernmost portion of the survey area suggests that the ridge segments are not connected by transform faults in the usual sense. Although the mechanism by which en echelon ridge segments can be maintained during sea-floor spreading over time is unclear, similar patterns of crustal accretion have been reported on Iceland. It appears that the accretionary processes along the Reykjanes Ridge are more related to those of Iceland than to those of typical mid-ocean ridges.     

Structure of hydrothermal plumes at the Logatchev vent field, 14°45′N, Mid-Atlantic Ridge: evidence from geochemical and geophysical data

In the Seventh cruise of R/V “Professor Logatchev” anomalies of natural electric field (EF), Eh and pS were discovered using a towed instrument package (RIFT) at 14°45′N on the MAR (Logatchev hydrothermal field). The anomalous zone (AZ) is situated close (10–35 m) to two low-temperature venting areas of degrading sulphides and a black smoker (Irina-Microsmoke) forming a distinct buoyant plume. Over or close to the main area of high-temperature venting situated to the south-east from the AZ, no EF or Eh anomalies were observed. According to the results of Mir dives the highly mineralised solutions from smoking craters at the main mound mostly form non-buoyant plumes (reverse-plumes). The buoyant plume structure shows the differentiation of the electrical and Eh fields within the plume. Maxima of the EF, Eh and E_H2S anomalies were revealed in the lower part (15 m) of the plume. The negative redox potential plume coupled with a sulphide anomaly is more localized in comparison with the EF. This observation indicates a distinct change in the composition of buoyant plume water, which may be due to the formation and fallout of early formed Fe sulphide particles soon after venting.     

Geostatistical integration of near-surface geophysical data

Accurate statics calculation and near‐surface related noise removal require a detailed knowledge of the near‐surface velocity field. Conventional seismic surveys currently are not designed to provide this information, and 3D high‐resolution reflection/refraction acquisition is not feasible for large survey areas. Satellite images and vibrator plate attributes are dense low‐cost data, which can be used in spatially extrapolating velocities from sparse uphole data by geostatistics. We tested this approach in two different areas of Saudi Arabia and found that the optimal recipe depends on the local geology.     

Resolution of airborne VLF data

The interpretation of airborne VLF data represents an important aspect of geophysical mapping of the upper few hundred meters of the Earth's crust, especially in areas with crystalline rocks. We have examined the ability of the single frequency VLF method to provide quantitative subsurface resistivity information using two generic models and standard airborne parameters with a flight altitude of 70 m and a frequency of 16 kHz. The models are long thin conductor (10 m thick, 10 Ω m resistivity and 1 km long) and a wider buried conductive dike (100 Ω m resistivity and 500 m wide). Using standard regularized inversion it turned out that for both models the conductivity of the conductors are underestimated and the vertical resolution is rather poor. The lateral positions of the minimum of the resistivity distributions coincide well with the true positions of the shallow conductors. For deeper conductors the position of the minimum resistivity moves from the edges of the conductor into the conductor. The depth to the minimum of the resistivity anomalies correlates well with the true depth to the top of the conductors although the latter is always smaller than the former.Interpretation of field airborne data collected at 70 m flight height resolved both small scale and large scale near surface conductors (conductance ∼1 S). Deeper conductors show up in the VLF data as very long wavelength anomalies that are particularly powerful in delineating the lateral boundaries of the conductors. Many of the VLF anomalies in the Stockholm area are dominated by these deep conductor responses with some near surface conductors superimposed. The deep conductors often follow topographic lows coinciding with metasediments. We interpret the frequent absence of near surface responses at 70 m flight height as a result of weak coupling between the primary VLF wave and the small scale (in all three dimensions) near-surface conductors.Radio magnetotelluric (RMT) ground measurements were carried out along a short profile coinciding with part of an airborne profile. Using data at 9 frequencies (14–250 kHz) small scale conductors in the upper few tens of meters, not identified from the airborne data, could be well resolved. Large scale deeper conductors could be identified by both methods at nearly the same positions.     

Constraining potential earthquake sources from the geophysical data

The spatial models describing the physico-mechanical properties of the rocks within the seismically active segment of the Altai–Sayan region are constructed from the ground-based geophysical data. The comparative analysis of their probability density functions at the nodes of the spatial grid covering the studied domain and at the hypocenters of the previous earthquakes shows that the bulk and shear moduli are the most efficient markers of the weakened crustal zones, which are prone to earthquakes. The algorithm for constraining the potential earthquake sources based on the spatial distributions of the elastic moduli of the rocks is suggested. When applied to the Taellin segment of the Altai–Sayan region, this algorithm has localized four echelons of the potential source zones of earthquakes at different depths in the crust. The horizontal positions of two of these zones were delineated by the previous studies based on the ground observations of seismicity, whereas the other two zones have been identified by the suggested algorithm for the first time.     

Multifractal characterization of Vesuvio lava-flow margins and its implications

The digitized lava-flow margins of well-defined extended eruptions occurring at Vesuvio in 1760, 1794, 1861, 1906, 1929 and 1944 are found to follow fractal behaviours inside a scaling region enclosed between 50 and 400 m. Although the invariance region is well respected, the fractal dimension D varies from one lava flow to another: the more irregular the lava-flow margin, the larger the value of D. The ascertained dependence of D on the duration of premonitory activity, preceding the emission of lavas, might provide some insight into the inner volcanic processes before the eruption and into the dynamical processes operating during flow emplacement.     

Bicubic spline smoothing of two-dimensional geophysical data

Summary A computational method for fitting smoothed bicubic splines to data given in a regular rectangular grid is suggested. The one-dimensional spline fit has well defined smoothness properties. These are duplicated for a two-dimensional approximation by solving the corresponding variational problem. The complete algorithm for computing the functional values and its derivatives at arbitrary points is presented. The posibilities of the method are demonstrated on an example from geomagnetic surveys.     

Methods of data compression in geophysical research

The urgent geophysical research problem of seismic data storage is considered. To reduce the volume of the stored data, it is suggested to compress data, i.e., to eliminate the information redundancy using algorithms of reversible compression (compression without data loss, nondistorting compression). A review of modern compression algorithms is given. Recommendations on using compression algorithms for accumulation as well as storage of seismic data are offered.     

航空重力测量数据的滤波与处理

我国首套航空重力测量系统(CHAGS)于2002年研制成功.本文设计了CHAGS观测数据的滤波处理流程,着重讨论了比力及各项改正的滤波计算方法,提出了'两步滤波法'.基于某航空重力测量实测数据,对测线重力异常的计算精度作了比较和分析,重复测线计算结果表明,CHAGS确定测线重力异常的内符合精度优于±3mGal,相应的波长分辨率为8km;与地面实测数据向上延拓数值比较表明,对于同样的波长分辨率,外部符合精度优于±4mGal.     

反插值法实现地球物理数据快速网格化

本文借鉴反演理论，采用反插值法实现地球物理数据的快速网格化.首先由已知点与未知网格点的反距离拓扑关系建立反演方程，用已知点值直接计算出其所在网格的未知网格点值，再利用Laplacian算子滤波，使得模型光滑，且能量最小化.利用预条件共轭梯度法求解网格化方程组，并结合螺旋坐标系思想和Wilson\|Burg谱分解法，将二维数据的滤波处理转换到一维空间进行处理，实现二维数据快速滤波.另外，引入了阻尼约束，保证求解稳定、迭代收敛.最后，应用该方法对合成数据和实际资料进行了试验.     

野外实验场地球物理电磁数据采集与分析

地球物理电磁数据观测实验场的建立在国内仍属空白,根据开展电磁法的方法技术要求,我们率先选择具备条件的已知矿区作为实验场地,开展了包括国内、外多种型号电磁法仪器(GDP 32Ⅱ、V8、DEM-V、DJS-8A)的相同装置下的同剖面同点位对比试验.对野外实验场上所开展的不同方法每种仪器的数据采集方式与取得结果进行比较分析,并与地质资料进行了结合分析;通过地球物理电磁数据的综合观测研究,形成标准化的数据,将对电磁法仪器开发、仪器引进提供实验检测场地与标准的检测数据,促进地球物理电磁探测技术的研究与发展.     

频率域航空电磁数据变维数贝叶斯反演研究

传统的梯度反演方法已经广泛应用于频率域航空电磁数据处理中,然而此类方法受初始模型影响较大,且容易陷入局部极小.为解决这一问题,本文采用改进的变维数贝叶斯反演方法实现航空电磁数据反演.该方法根据建议分布对反演模型进行随机采样,并依据接受概率筛选合理的候选模型,最终获得反演模型的概率分布和不确定度信息.为解决贝叶斯反演方法对深部低阻层反演效果不佳的问题,本文通过引入合理加权系数,调整对反演模型约束强度,在很大程度上改善了反演效果.通过对模型统计方法进行改进,在遵循原有模型采样方法和接受标准的基础上,将满足数据拟合要求的模型纳入统计范围,削弱不合理模型对统计结果的干扰.本文最后通过对含有高斯噪声的理论数据和实测数据进行反演,并与Occam反演结果进行对比,验证了该方法的有效性.     

Optical filtering of airborne and ground magnetic data

Summary An optical processor has been used to filter ground and aeromagnetic or gravimetric maps in order to obtain information on magnetic or causative bodies buried in the ground. This is accomplished by directional filtering in the Fourier spectrum of the magnetic or gravimetric intensity as displayed on a contour map. Despite certain difficulties inherent to the use of contour maps instead of density maps, some promising results were obtained.The great advantage of this optical filtering technique resides in the fact that no digitization (which is a lengthy and expensive process) is required for the analysis. The optical processor used may carry out the Fourier transform of over ten million points almost instantaneously, and at a very low unit cost, because the required optical system is much cheaper and much faster than a digital system.     

Dimension of the phase space of a dynamic system from geophysical data

The possibility of determining parameters of complex geophysical processes is considered in terms of nonlinear dynamics. In accordance with modern approaches in the theory of nonlinear dynamic systems, the number of independent parameters controlling the behavior of a nonlinear system can be estimated from the available time realization of only one of these parameters. Model calculations showed that the dimension of the phase space of a dynamic system can be estimated from a sample of one variable. Experimental data on variations in the apparent electric resistivity (AER) and the relative vertical movement of the surface (RVMS) in a seismically active region are analyzed and the dimension of the dynamic system determining its behavior in the phase space is estimated. The resulting estimates of the embedding dimension m = 7?8 for AER variations and m = 6 for RVMS variations possibly characterize the complexity of the dynamic system describing the given fields. The method presented in the paper is also applied to the analysis of the degree of connectivity of different dynamic systems and their parameters. By the connectivity we mean the number of independent parameters simultaneously involved in the formation of the dynamic behavior of various physical fields. The model estimates demonstrate the possibility of such an approach. It is shown that variations in the AER in perpendicular directions are described by a general system of dynamic equations, whereas dynamic systems controlling the AER field and the RVMSs are interconnected only partially. The resulting dimension m = 12 estimated for the AER-RVMS system provides an estimate for the number of common controlling parameters: n = (8 + 6)?12 = 2. The methods and results presented in the paper are applicable to the construction of models of complex geophysical processes and the development and the development of new approaches and methods of identification of prognostic characteristics for the behavior of physical fields of various origins.     

The deep structure of the southern kamchatka volcanic zone from geophysical data

We discuss the interpretation method and results of magnetotelluric soundings in combination with other geological and geophysical data. The interpretation method was developed by studying possible distortions in MTS curves using 3D-numerical modeling of the magnetotelluric field. Deep conductivity was studied by using longitudinal MTS curves below a period of 400 s, which are nearly unaffected by the induction effect due to marine electrical currents. Transverse curves were used to obtain more detail for the geoelectric model. Inversion of average longitudinal MTS curves resulted in a geoelectric section of the lithosphere down to a depth of 60 km. Anomalies of high conductivity in the lithosphere were detected and were found to produce certain effects in gravity and seismic velocities. MTS and seismic tomography data were used to determine the possible origin of the high conductivity anomaly and to estimate rock porosity and the concentration of magma melts.