基于WebGIS构建航空物探资料综合查询系统

通过对现有海量航空物探、遥感及其他相关资料进行整理分类,引入Geodatabase模型对资料中涉及的相关空间信息进行空间数据库存储,构建基于WebGIS的航空物探资料综合查询系统.根据用户需求设计了实用的空间查询工具,实现对于原有分散的、多类型的、不同专业的实测数据和资料基于同一地理底图的综合空间查询和网络共享,提高了航空物探资料综合查询服务能力.     

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.     

西南印度洋洋中脊热液活动区综合地质地球物理特征

西南印度洋洋中脊(SWIR)是超慢速扩张洋脊的代表,是海洋地学研究热点.本文从SWIR多波束水深数据、重、磁数据和地震结构等几方面,阐述了SWIR热液活动区(49°39′E)的综合地质地球物理特征.SWIR热液活动不仅与扩张速率有关,构造作用更是一个重要控制因素;热液活动区位于Indomed和Gallieni转换断层之间,从水深地形上看,该区段洋脊是SWIR上水深最浅的区域之一,水深与MBA存在良好的镜像关系,MBA和RMBA低值意味着较厚的地壳厚度与较高的地幔温度,洋脊段27地壳厚度大于9km,可能是受到Crozet热点的影响;磁条带数据表明,此区段洋脊南北两翼呈不对称扩张,形成南翼的浅离轴域比北翼宽;在洋脊段28发现的活动热液喷口刚好位于热液蚀变形成的低磁强区内,具有良好的硫化物资源.这些认识必将为在该区首次实施的三维地震探测研究的地质地球物理解释及活动热液喷口的动力学机制研究打下坚实基础.     

利用多源地球物理图像融合方法识别物性异常——以航空电磁和航磁数据为例

对于同一地质模型, 将不同地球物理数据分别进行反演, 通常得到多个不同的反演结果, 研究多源地球物理数据综合解释, 有助于实现复杂地形环境下目标体的精确识别和定位.本文采用一种基于非下采样轮廓波变换(Non-Subsampled Contourlet Transform, 简称NSCT)的多源地球物理信息融合方法, 以美国阿拉斯加库克湾西南部的Iliamna火山地区的实测数据(公开数据)为例, 通过对多源地球物理图像数据进行综合分析, 实现了磁化率和电阻率模型的融合.首先, 利用NSCT将不同地层的多源图像分解为低频子带图像和高频子带图像; 然后, 设计了基于加权平均和新度量参数(New Metric Parameter, 简称NMP)的融合规则, 并分别对低频子带图像和高频子带图像进行融合; 最后利用NSCT反变换得到包含磁化率和电阻率信息的融合图像.将融合结果与先验资料进行对比, 结果显示两者具有较高的一致性, 表明这一方法有效可靠, 为目标体精确识别和快速定位提供了一种新的解决思路.

     

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.     

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.     

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.     

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.     

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.     

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.     

The energetics of internal tides at the Luzon Ridge

Ocean Dynamics - Three-dimensional simulations of the M2 and K1 internal tides using the MIT General Circulation Model (MITgcm) configured for the Luzon Ridge are presented. The energetics of M2...