电磁波CT成像技术在防水工程场地勘查中的应用

电磁波CT成像技术是基于地下介质的物性差异,利用各种波源透视探测目的体及地质现象的一种地球物理方法,文章介绍了电磁波CT成像技术的原理和工作方法、某防水工程场地电磁波CT成像勘查实例及应用效果.     

定向扫描成像测井技术及其应用

定向扫描成像测井技术，就是按照规定的方向对井壁进行扫描，把井壁展开成一个连续的平面。这种信号不能在磁屏蔽、磁干扰条件下工作，进而不能确定地质信息的方位。然而，当运用陀螺定向技术对人造磁场进行定向，在人造磁场中，转动的线圈感应出来的交变电信号作为图像扫描触发信号，能够测量所形成的超声图像，并快捷、准确地查明井管故障点的位置、损坏的规模大小和方位，从而为维修方案的确定提供了可靠的依据。     

利用背景噪声进行地震成像的新方法

利用背景地震噪声提取格林函数，即通过一对台站记录的地震噪声进行互相关计算，来近似台站间的格林函数，并进一步通过地震成像获取地下结构的认识，成为最近跨学科研究的热点问题之一.本文首先叙述了其发展背景及过程，然后分别从四个角度，简要介绍了目前对其物理原理的解释.如果该方法能得到进一步的发展，将不再依赖于天然地震以及人工地震，而仅仅利用地震台站记录的地震噪声便可获取高分辨率的地下成像.该方法将会大大促进地震学的发展.     

改良FS-3D-TrueFISP序列与传统序列在软骨成像中的对比研究

目的:总结正常软骨在改良脂肪抑制三维真实稳态自由进动序列上的表现,与传统序列对比研究软骨显像的图像质量,探讨经过改良以后的脂肪抑制三维真实稳态自由进动序列应用于软骨成像的可行性.方法:应用脂肪抑制三维快速小角度激发序列、三维双回波稳态序列、脂肪抑制快速自旋回波质子密度加权序列,以及经过改良以后的两个脂肪抑制三维真实稳态自由进动序列,对10名志愿者的膝关节进行扫描.测量各序列软骨及关节滑液的信号强度及背景噪声,计算各种方法所得图像的关节软骨的信噪比、关节软骨与滑液的对比噪声比及对比噪声比效率,比较各序列所得的信噪比、对比噪声比及对比噪声比效率之间有无统计学差异.结果:在改良的序列上软骨信号强度介于关节液与邻近骨质之间.6例信号均匀,4例软骨信号可见与脂肪抑制三维快速小角度激发序列相似的分层现象,各序列的信噪比、对比噪声比及对比噪声比效率差异具有显著性.采集次数为2次的脂肪抑制三维真实稳态自由进动序列的对比噪声比及对比噪声比效率优于其他序列.结论:经过改良后的真实稳态自由进动序列可以在保持关节软骨一定的信噪比的前提下在短时间内获得与关节滑液之间具有良好对比噪声比的图像.真实稳态自由进动序列可以用于关节软骨病变的诊断.     

Imaging Offsets in the Moho: Synthetic Tests using Gaussian Beams with Teleseismic Waves

We carry out a sequence of numerical tests to understand conditions under which rapid changes in crustal thickness can be reliably imaged by teleseismic body waves. Using the finite-difference method over a 2-D grid, we compute synthetic seismograms resulting from a planar P-wavefield incident below the grid. We then image the Moho using a migration scheme based on the Gaussian beam representation of the wavefield. The use of Gaussian beams for the downward propagation of the wavefield is particularly advantageous in certain geologically critical cases such as overthrusting of continental lithosphere, resulting in the juxtaposition of high-velocity mantle material over crustal rocks. In contrast to ray-based methods, Gaussian beam migration requires no special treatment to handle such heterogeneities. Our results suggest that with adequate station spacing and signal-to-noise ratios, offsets of the Moho, on the order of 10 km in height, can be reliably imaged beneath thickened crust at depths of about 50 km. Furthermore, even sharp corners and edges are faithfully imaged when precise values of seismic wave speeds are available. Our tests also demonstrate that flexibility in choices of different types of seismic phases is important, because any single phase has trade-offs in issues such as spatial resolution, array aperture, and amplitude of signals.     

Seismic identification of channel sandbodies in the Fuyang oil layer in North Songliao Basin, China

The Fuyang oil-layer in North Songliao Basin is characterized by thin interbedded sands and shales, strong lateral variation, strong reservoir heterogeniety, and so on. The thickness of individual sand layers is generally 3 - 5 m. Identifying the channel sand-bodies of the Fuyang oil layer using seismic techniques is very difficult due to the low seismic resolution. Taking the GTZ area as an example, we discuss the genetic characteristics of the channel sand-bodies and point out the real difficulty in using seismic techniques to predict the channel sand-bodies. Two methods for the identification of channels are presented： frequency spectrum imaging and pre-stack azimuthal anisotropy. Identifying the channel sand-bodies in Fuyu oil-layer using the two seismic methods results in a success rate up to 80% compared with well data.     

陕西马元地区铅锌矿地质特征及找矿远景

陕西马元地区铅锌矿位于扬子地台北缘碑坝隆起东南缘一带。矿化带长大于60km,宽10～200m,可分为南、东、北3个铅锌矿化带,已圈出了40多条铅锌矿体。其中南矿化带长大于20km,宽20～120m,已圈出了40多条铅锌矿体;东矿化带长大于30km,宽20～200m,地表已发现7条铅锌矿体;北矿化带长大于10km,宽10～100m。矿体一般长100～2560m,厚0.80～10.01m,锌品位1.05%～10.82%,铅品位0.55%～7.54%。主矿体长2560m,厚1.46～32.53m,平均厚约7.60m,最厚28.40m,锌品位1.45%～11.42%,平均4.47%。矿化带主体由震旦系灯影组白云岩组成,产于灯影组的砾状白云质角砾岩带中。矿化主要受地层和构造的控制。经预测,马元地区铅锌矿有较好的找矿远景,具有形成超大型铅锌矿的潜力。     

连续降雨作用下非饱和土边坡的稳定性分析

在边坡稳定性研究中,吸力的影响经常被忽略。基于非饱和土的渗流理论,利用数值分析方法研究了一个由于连续降雨导致的非饱和土边坡失稳的工程实例。研究结果表明:非饱和土的吸力对于维持边坡稳定具有重要影响,而吸力与降雨频率、降雨量、降雨时间、蒸发量等密切相关。对于工程实践而言,吸力的监测对于维持土坡稳定具有重要意义。     

Peatland development at the arctic tree line (Québec, Canada) influenced by flooding and permafrost

In this study, we documented the Holocene history of a peat plateau at the arctic tree line in northern Québec using stratigraphic and macrofossil analyses to highlight the effects of geomorphic setting in peatland development. Paludification of the site began about 6800 cal yr BP. From 6390 to 4120 cal yr BP, the peatland experienced a series of flooding events. The location of the peatland in a depression bounded by two small lakes likely explains its sensitivity to runoff. The proximity of a large hill bordering the peatland to the south possibly favored the inflow of mineral-laden water. The onset of permafrost aggradation in several parts of the peatland occurred after 3670 cal yr BP. Uplifting of the peatland surface caused by permafrost stopped the flooding. According to radiocarbon dating of the uppermost peat layers, permafrost distribution progressed from the east to the west of the peatland, indicating differential timing for the initiation of permafrost throughout the peatland. Most of the peatland was affected by permafrost growth during the Little Ice Age. Picea mariana macroremains at 6450 cal yr BP indicate that the species was present during the early stages of peatland development, which occurred soon after the sea regression.     

Laser Scanning的基本原理及其应用前景

首先介绍了激光测距仪的发展历程,针对应用领域的不同,分别对3维激光成像仪和机载/星载激光测高仪的测量原理进行了阐述,并分别介绍了两种激光测距仪的工作流程以及数据处理流程,最后对两种激光测距仪的应用范围进行了阐述,并把两种激光测距技术和普通摄影测量进行了比较,指出了激光测距技术相对于普通摄影测量的优点,即高精度性、穿透性、实时性。