全球地幔垂直流动速度研究

用高分辨率地震体波速度成像以及相关的地球物理资料,计算地幔垂直流动形式及流动速度,得到全球地幔流垂直运动模式.从全球尺度来看,地幔流基本可划分为以下几个区域：欧亚大陆—澳大利亚、北美洲—南美洲为两个大规模下降流区域,西印度洋—非洲及大西洋、中南太平洋及东太平洋为两个大规模地幔上升流区域.地幔上升流起源于核幔边界,主要表现在地幔中部和上地幔下部.地幔垂直流动速度约每年1～4cm.地幔流动对地表板块运动、海洋中脊和中隆、俯冲带和碰撞带的分布起着控制作用.地幔上升流与地表现代热点有密切关系.从东亚尺度看,地幔流大体分为三个区域：东亚边缘裂谷系和西太平洋边缘海为上升流、西伯利亚地幔深度表现为物质下降流、青藏高原—缅甸—印度尼西亚特提斯俯冲带地幔下降流,这三个区域地幔流动与地表的西太平洋构造域、亚洲构造域和特提斯构造域相吻合.勾勒出南海地区构造特征：从上到下的大体结构是上部呈“工"字型、中间为圆柱型、底部呈盾形的地幔上升流.     

Bender Elements在测试土样剪切波速中的应用

本文以作者在香港理工大学土木与结构工程系设计制作的一套BenderElements为例,介绍了BenderElements的原理、发展历史、应用范围、使用方法和注意事项等。BenderElements是由压电陶瓷材料制成的,在拉伸、压缩作用下,会产生正、负电荷,反过来,给它施加正、负电荷后,它又可产生弯曲振动,正是利用它的这一特性,将其作成接收和发射装置,来测试土样的剪切波速Vs。BenderElements在安装使用时,防水和静电屏蔽十分关键。Vs可在场地地震反应、液化判别、动力基础设计、检测地基改良效果等方面获得应用。震相识别的原则是接收信号的第一个峰值为到时。     

青藏高原及邻近区域的S波三维速度结构

本文收集了WWSSN台网和我国台网中13个地震台站的长周期地震记录,用140条10-90s瑞利波频散曲线和作者提出的Tarantola-Backus面波频散层析成象方法,作了青藏高原及邻区的速度反演,得出该地区岩石层速度结构的三维图象.结果表明,1.在10-110km深度范围内,速度结构出现与大地构造特征相关的分区性,显示出四个构造单元:青藏块体、柴达木-巴颜喀拉-三江块体、塔里木块体和印度块体.2.高原内部,深度为10-70km内速度较低,莫霍界面呈不对称盆形分布,藏北那曲附近地壳厚度超过70km,高原边缘壳厚为45-50km,90-110km为高速异常,表明高原内部存在上地幔盖层.3.高原北部的班公湖断裂和东部的三江断裂系是该区重要的分界线,是岩石层结构存在明显差异的重要接触部位,可能是冈瓦纳古陆与欧亚古陆的缝合带.4.柴达木-巴颜喀拉-三江块体内部速度分布不均匀,地壳厚度由北向南从45km加深到60km;在深度90-110km存在一低速层.5.塔里木地块内速度随深度均匀增加,从地壳到上地幔110km内没有发现低速层.地壳厚度约50km.     

Modelling and inversion of single-ended refraction data from the shot gathers of multifold deep seismic reflection profiling—an approach for deriving the shallow velocity structure

A multifold crustal-scale deep seismic near-vertical reflection profile generates a large number of single-ended shot gathers, which provide redundant data sets because of overlapping coverage of the shallow refractors. We present an approach for deriving the shallow velocity structure by modelling and inversion of single-ended seismic refraction first arrival traveltime data. We apply this method to a data set acquired with a 12-km long spread with 100 m spacing of shots and receivers, of the Neoproterozoic Marwar basin in the NW Indian shield. The approach is shown to be quite successful for delineating the shallow refractor depths, steep dips and velocities, even in the absence of regular reverse refraction profiles. The study reveals two-layered sedimentary formations, Malani volcanics and a complicated basement configuration of the Marwar basin, and provides a measure of resolution and uncertainty of the estimated model parameters. A seismic section of the near-trace gather is found to be qualitatively consistent with the derived structural features of the basin. The relative highs and lows, observed in the Bouguer gravity profile, further corroborate the derived velocity model. The present approach can be especially useful in offshore areas and elsewhere, where the single-ended multifold seismic profiles are the only available data sets.     

地震立体层析成像的实现方法及效果分析

立体层析成像是一种新的地震反射波层析成像方法, 能为叠前深度偏移提供较为精确的宏观速度模型。本文研究了立体层析成像的实现方法, 包括斜率与走时数据的拾取、离散速度模型构建和初始化、射线参数的确定、斜率和走时及射线计算以及反演问题解法等, 建立立体层析成像的算法流程。并通过对Marmousi模型试验, 对立体层析成像运行所需的主要参数, 如初始速度模型、拾取数据量、离散网格尺寸、速度平滑权重等进行测试和分析, 总结这些不同参数对立体层析反演结果的影响规律, 用以指导生产实践。     

广东沿海地区现代地壳垂直运动研究

对３０多年来１万多ｋｍ精密水准复测数百个重合点资料进行了综合研究，结果表明，广东沿海岸段的地壳平均以－０．５ｍｍ／ａ幅度沉降，表现出粤西抬升，粤东沉降，珠江三角洲大面积下沉的格局。粤西岸段平均以＋０．６ｍｍ／ａ速率上升，粤东沿海岸段平均以－０．７ｍｍ／ａ速率下降；珠江三角洲以－１．８ｍｍ／ａ速率下沉，桂东南岸段则以＋３．４ｍｍ／ａ的速上升。     

定点式声学多普勒流速仪的应用难点与误差分析

定点式声学多普勒流速仪(简称"HADCP")在国内已较为普及,但对其应用却多停留在表面,鲜有人研究其测验误差控制及参数优化方法,影响HADCP测流精度。为解决HADCP使用中的一些疑难问题,从流速仪测验误差表现的三方面对HADCP的测流误差开展讨论。以测验误差为控制指标,对HADCP在使用中各个环节的误差来源及应用难点进行分析,并以多个实例阐明提高仪器应用精度的优化设置方法。按照所论及方法进行对照检查并合理优化,可减小测流误差,提高HADCP测流方案的整体精度。     

干旱环境下氯盐和硫酸盐对遗址土体强度的影响

为了探讨氯盐和硫酸盐对遗址土体强度的影响,本文通过室内试验,对洗盐后的素土分别以0.2%的梯度加入NaCl和Na2SO4两种可溶盐,测试特定盐分含量和类别的含盐土在干旱环境下的单轴抗压强度、抗拉强度、弹性波速以及抗风蚀能力的变化。试验结果表明：在室内环境条件下,盐分的存在对土体起着一定的胶结固化作用,使得土体的强度表现出相应程度的增大,并且硫酸盐对土体的胶结固化作用比氯盐显著。随着盐分含量的增加,含盐试样的单轴抗压强度、抗拉强度呈现出指数形式的增大; 垂直于压制方向和平行于压制方向的弹性波速均呈现出增大的趋势; 随着挟沙风速的增大,试样的风蚀损失量增加,同时在18ms-1的挟沙风速作用下,随着盐分含量的增加,试样的风蚀损失量逐渐减小,含盐试样表现出渐进破坏的形式。     

南京长江第二大桥桥位风速观测及设计风速的计算

本文给出适用于大桥设计风速计算的方法,并利用南京长江第二大桥桥位风速观测资料、南京小教场40年的实测风资料及两处的同步风速观测资料,经统计学分析计算得到南京长江第二桥设计风速的计算值.     

Seismic wave velocity and anisotropy of serpentinized peridotite in the Oman ophiolite

Shallow seismic measurements in harzburgite from the Oman ophiolite performed in a zone where the maximum horizontal anisotropy is expected (vertical foliation and horizontal lineation) point to a dominant dependence of seismic properties on fracturing.

Optical microscopy studies show that microcracks are guided by the serpentine (lizardite) penetrative network oriented subparallel to the harzburgite foliation and subperpendicular to the mineral lineation, and that serpentine (lizardite) vein filling has a maximum concentration of (001) planes parallel to the veins walls. The calculated elastic properties of the oriented alteration veins filled with serpentine in an anisotropic matrix formed by oriented crystals of olivine and orthopyroxene are compared with seismic velocities measured on hand specimens.

Laboratory ultrasonic data indicate that open microcracks are closed at 100 MPa pressure, e.g. (J. Geophys. Res. 65, (1960) 1083) and (Proc. ODP Sci. Results Leg 118, (1990) 227). Above this pressure, laboratory measurements and modeling show that P-compressional and S-shear wave velocities are mainly controlled by the mineral preferred orientation. Veins sealed with serpentine are effective in slightly lowering P and S velocities and increasing anisotropy. The penetrative lizardite network does not affect directly the geometry of seismic anisotropy, but contributes indirectly in the fact that this network controls the microcrack orientations.

Comparison between seismic measurements of peridotite and gabbro in the same conditions suggest that P- and S-waves anisotropies are a possible discriminating factor between the two lithologies in the suboceanic lithosphere.