地球物理研究的国际动态

1卫星低频电磁辐射效应的研究 自从20世纪70-80年代利用卫星进行地球固有磁场测量以来,全球地磁场及其变化的测量中断了20余年时间.直到1999年2月丹麦航天局发射了奥尔斯太特2号卫星,又掀起地球磁场重力场测量热潮,推动了国际地球位场研究10年的活动(1998-2008年).     

我国航空地球物理野外试验场建设方法

"十一五"期间,在国家863重大计划项目支持下,开展了我国航空地球物理野外试验场建设.在总结国内外航空地球物理试验场建设情况基础上.以加拿大Reid-Mahaffy航空电磁地球物理场为例,从试验场场址选择和试验场建设两方面,分析了国外航空地球物理试验场建设方法,总结了相关经验和借鉴意义.在此基础上.根据我国航空地球物理试验场建设目标,综合考虑不同航空地球物理测量系统的特点,制定了我国航空地球物理试验场建设的基本条件.根据这些条件,采用"先选区后选场,区中选场"的原则,进行了试验场场址的选择,最终确定大井坡航空地球物理试验场为我国首个航空重、磁、电磁等测量系统的野外综合检测平台(简称为大井坡试验场).根据试验场建设思路,在分析大井坡试验场现有条件基础上,从岩石物性测量与研究、地球物理测量、地质填图与剖面测制以及试验场数据信息管理等方面提出了试验场的建设内容与方法.     

苏联石油工业中地球物理勘探方法的发展情况

地球物理工作在石油工业中已获得了公认,并在普查和勘探油田的综合地质勘探工作中居于牢固而称职的地位.三十七年前,苏联就开始了第一次勘探地球物理工作,最初是用来研究库尔斯克磁力异常上的鉄矿床.1919年根据列宁的指示在库尔斯克地区开始了磁力测量.1925年在乌拉尔-恩巴油区开始了第一次用地球物理勘探石油的工作,旨在寻找盐丘构造.     

高温高压下矿物和岩石电导率的测量

地球及行星内部物质的电导率与温度有着密切的依赖关系.在实验室创造代表地球内部不同温度的物理及化学条件,可直接测量物质的电导率,矿物和岩石电导率的测量和研究可获得地球内部(地幔)物质传输过程的信息,这不仅提供对地球物理测量结果的解释,同时也提供了地球和行星内部温度分布     

高压下岩石弹性波速度几种测量方法的比较实验研究

在高压高温条件下测量岩石弹性波速是获得岩石在地球内部的各种力学和热力学数据的主要途径, 也是研究地球内部物质结构和组成的重要手段. 近年来, 用固体作为传压介质的高压高温岩石弹性波速测量方法发展较快, 然而目前各个实验室在高温高压条件下所测量出的岩石弹性波数据, 还没有进行过严格的对比. 为了对比各实验室的实验测量结果, 对3种测量方法进行了比较实验研究, 并与流体传压介质透射法的测量结果进行了对比. 实验表明, 3种测量方法在其适用压力范围内的测量结果都能相互对比. 其中Kern所使用的六面体样品脉冲透射法适用于压力温度较低的地壳类岩石样品的测量. 柱状样品脉冲反射-透射法在适用压力范围、加热温度和测量精度方面均有一定优势. 柱状样品脉冲透射法虽然在压力较低时测量精度较低, 但样品长度大, 组装简便, 适用于样品量大, 要求压力较高的实验. 因此在实际应用中, 后两种方法可进行相互校正和相互补充.     

1996-2003年中国大陆高精度绝对重力观测

近十年间利用自由落体式绝对重力仪(FG5/112)对分布在全国55个测点进行了绝对重力测定,观测精度均优于5×10-8 ms-2,对其中80%以上的测点还作了重复观测,文中给出了观测精度及其测量结果的互差.上述的测量极大地改善了我国目前重力网的精度和覆盖率,并为研究重力场的变化提供了重要的基础资料.本文还对观测结果和存在问题作了初步分析并提出有关建议.     

卫星重力梯度测量与地球引力场的精度研究

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V_rr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△V_i3（i=3,2,1）至少可分别在1/4和1/3弧圈内达到△V_i3≤σ（仪器精度）.     

锡霍特-阿林—日本海—本州岛—太平洋地学断面

在苏日合作期间,进行了太平洋到亚洲大陆的过渡区内地壳与上地幔结构和动力学的地质-地球物理研究,本文是这一研究的结果。经过地震、地质、岩相学、重力测量、磁测、大地电磁法和热流测量资料的综合解释,编绘了深达300km的构造圈地质-地球物理剖面(地学断面)。并计算了沿地学断面的深部温度场以及部分熔融面的深度,后者可被视为软流圈的上界。     

地球内部结构及其密度分布特征研究综述

地球内部密度结构是了解其构造特征及性质的重要参数.根据全球性模型的回顾分析可了解地球内部密度的基本特征,垂向的分层性和横向不均一是全球性的密度特征.对地球浅层地壳特别是沉积层,岩石采样的密度测试和速度-密度关系研究为揭示其密度特征提供了重要依据.在总结和分析前人速度-密度关系研究的基础上,本文进一步给出了具有更好适用性...     

南北地震带北段地壳微动态变化的初步研究

本文根据应力台站和水平形变的实际观测结果,研究了南北地震带北段1970—1983年间的区域地壳微动态变化特征及其与同时期中强地震活动的关系,得出1970—1983年本区地壳微动态变化与地球自转角速率的长期变化有关的初步结论。     

基于热点参考系的板块绝对运动模型

本文在最新一代板块相对运动模型(MORVEL模型)的基础上,通过最小二乘反演观测热点方向数据建立板块绝对运动模型.经过对前人用于约束板块绝对运动模型的所有热点数据与MORVEL模型的一致性作系统的统计学检验,发现存在离群数据.相应地,提出两种系统剔除离群数据的新方法:逐一剔除法和全局搜索法.结合对总残差的卡方检验和对残差频率分布的正态检验,逐步筛选最优模型,最终得到一个基于热点参考系的板块绝对运动新模型(T87模型).该模型能够合理拟合全球分布的87个热点方向数据,而模型预测的板块绝对运动速率比观测热点火山的迁移速率系统偏小,最大偏差达到4 cm·a~(-1).这样的偏差可由观测热点速率的系统误差或地幔返回流造成的热点间运动解释.不论是哪种解释成立,本文结果表明热点方向数据能够独立、有效地定义全球热点参考系.这样定义的热点参考系可方便地应用于板块绝对运动、地幔对流及真极移的研究.     

Geodetic constraints on active tectonics of the Western Mediterranean: Implications for the kinematics and dynamics of the Nubia-Eurasia plate boundary zone

We present GPS observations in Morocco and adjacent areas of Spain from 15 continuous (CGPS) and 31 survey-mode (SGPS) sites extending from the stable part of the Nubian plate to central Spain. We determine a robust velocity field for the W Mediterranean that we use to constrain models for the Iberia-Nubia plate boundary. South of the High Atlas Mountain system, GPS motions are consistent with Nubia plate motions from prior geodetic studies. We constrain shortening in the Atlas system to <1.5 mm/yr, 95% confidence level. North of the Atlas Mountains, the GPS velocities indicate Nubia motion with respect to Eurasia, but also a component of motion normal to the direction of Nubia-Eurasia motion, consisting of southward translation of the Rif Mountains in N Morocco at rates exceeding 5 mm/yr. This southward motion appears to be directly related to Miocene opening of the Alboran Sea. The Betic Mountain system north of the Alboran Sea is characterized by WNW motion with respect to Eurasia at ～1–2 mm/yr, paralleling Nubia-Eurasia relative motion. In addition, sites located in the Betics north of the southerly moving Rif Mountains also indicate a component of southerly motion with respect to Eurasia. We interpret this as indicating that deformation associated with Nubia-Eurasia plate motion extends into the southern Betics, but also that the Betic system may be affected by the same processes that are causing southward motion of the Rif Mountains south of the Alboran Sea. Kinematic modeling indicates that plate boundary geometries that include a boundary through the Straits of Gibraltar are most compatible with the component of motion in the direction of relative plate motion, but that two additional blocks (Alboran-Rif block, Betic Mountain block), independent of both Nubia and Eurasia are needed to account for the motions of the Rif and Betic Mountains normal to the direction of relative plate motion. We speculate that the southward motions of the Alboran-Rif and Betic blocks may be related to mantle flow, possibly induced by southward rollback of the subducted Nubian plate beneath the Alboran Sea and Rif Mountains.     

板块绝对运动及地幔热对流

本文以板块绝对运动AM1-2模型为边界条件探讨了不同的瑞利数下地幔热对流模型.结果表明,瑞利数小于10000（529.41）时,地幔对流呈现以板块驱动图式,运动的极型场和环型场由板块运动激发,两种场占有差不多相同的功率.当瑞利数增加到接近或略超过最低临界值时（约1.5倍）,对流呈现出复杂状态:1.板块运动速率小于下伏地幔对流速率;2.区域性的双层对流环出现;3.对流谱成分发生变化;4.环型场仅在地幔很浅的区域中起作用,而在地幔深部对流图式中影响很小.     

Horizontal and vertical components of earthquake ground motions at liquefiable sites

Field observations on ground motions from recent earthquakes imply that current knowledge is limited with regard to relating vertical and horizontal motions at liquefiable sites. This paper describes a study with the purpose of clarifying this emerging issue to some extent. A series of numerical analyses is carried out on a liquefiable soil deposit with a verified, fully coupled, nonlinear procedure. It is shown that the transformation of vertical motions in the deposit differs considerably from the transformation of horizontal motions. Both the amplitude and frequency content of the horizontal motions are strongly dependent on the shaking level or the associated nonlinear soil behavior. The transfer function for vertical motions is however likely to be independent of the intensity of input motions; no reduction in the amplitude occurs even in the case of strong shaking. The results are shown to be in consistence with the laboratory observations on shaking table tests and recent field observations that less nonlinearity exists for vertical motions. It is also shown that the possibility exists for using information on spectral ratios between the horizontal and vertical surface motions to quickly identify in situ soil behavior and liquefaction that are not readily covered by conventional field or laboratory experimentation procedures.     

采用剪切波分裂方向约束的板块绝对运动模型研究

板块绝对运动(即岩石圈板块相对于深部地幔的运动)导致软流圈深度存在较强的剪切作用,为软流圈呈现较强的地震波速各向异性提供了一种物理解释.相应地,软流圈地震各向异性的实测数据为反演板块绝对运动提供了一种定量的约束.本文利用前人发表的由474个剪切波分裂数据组成的全球软流圈地震各向异性方向数据集,结合板块相对运动模型MORVEL,通过加权最小二乘法反演板块绝对运动.计算结果表明,由实测数据约束的板块绝对运动模型不能将观测数据拟合到原始数据测量误差要求的统计水平上,反映出以地震各向异性方向指示板块绝对运动方向存在原始数据测量误差之外的系统性误差.该误差或可归因于板块绝对运动控制软流圈地震各向异性的物理机制复杂性以及小尺度地幔流动的区域复杂性.因此,地震各向异性方向只能从统计平均的意义上约束板块绝对运动方向,两者间的差别除了测量误差外还应包含复杂物理成因的模型误差.在原始数据测量误差的基础上增加20°的模型误差并且剔除一个离群数据后,本文得到了最优拟合剪切波分裂数据集的SKS473模型,并与由热点数据反演得到的板块绝对运动模型进行对比.由于约束板块绝对运动的地震各向异性数据和热点数据都存在误差较大、地理分布不均的局限性,结合两类数据的联合反演或可成为未来建立更高精度板块绝对运动模型的有效途径.     

Simulations of Seismic Hazard for the Pacific Northwest of the United States from Earthquakes Associated with the Cascadia Subduction Zone

-- We investigate the impact of different rupture and attenuation models for the Cascadia subduction zone by simulating seismic hazard models for the Pacific Northwest of the U.S. at 2% probability of exceedance in 50 years. We calculate the sensitivity of hazard (probabilistic ground motions) to the source parameters and the attenuation relations for both intraslab and interface earthquakes and present these in the framework of the standard USGS hazard model that includes crustal earthquakes. Our results indicate that allowing the deep intraslab earthquakes to occur anywhere along the subduction zone increases the peak ground acceleration hazard near Portland, Oregon by about 20%. Alternative attenuation relations for deep earthquakes can result in ground motions that differ by a factor of two. The hazard uncertainty for the plate interface and intraslab earthquakes is analyzed through a Monte-Carlo logic tree approach and indicates a seismic hazard exceeding 1 g (0.2 s spectral acceleration) consistent with the U.S. National Seismic Hazard Maps in western Washington, Oregon, and California and an overall coefficient of variation that ranges from 0.1 to 0.4. Sensitivity studies indicate that the paleoseismic chronology and the magnitude of great plate interface earthquakes contribute significantly to the hazard uncertainty estimates for this region. Paleoseismic data indicate that the mean earthquake recurrence interval for great earthquakes is about 500 years and that it has been 300 years since the last great earthquake. We calculate the probability of such a great earthquake along the Cascadia plate interface to be about 14% when considering a time-dependent model and about 10% when considering a time-independent Poisson model during the next 50-year interval.     

Sea-floor positioning with global positioning system–acoustic link system

The present study describes a new system designed and developed for observing crustal deformation on the sea floor. The system consists of two parts, the kinematic positioning by global positioning system (GPS) and acoustic ranging techniques. Since the location of a site at the ocean bottom relative to a reference site on land cannot be determined directly, the procedure was divided into two steps. First, the position of a vessel was determined using differential and kinematic GPS techniques, and then the position of a reference point at the ocean bottom was located relative to the vessel using the acoustic ranging technique. Thus, the location of the ocean-bottom station is determined relative to the reference sites on land in the global reference system. The accuracy was tested in several ways. In one experiment, a buoy was used as the surface station which linked the positions of a GPS receiver to the acoustic transponder. Assuming a simple sound velocity profile of the seawater, the position of an ocean-bottom reference point was estimated with an accuracy of several meters. Thus, with the present system, it is difficult to observe ocean-bottom crustal deformations generated by typical plate motions. Methods are being investigated to improve the observation system for more accurate sea floor positioning.     

东亚北部地区现代板块构造的运动学分析

从原欧亚板块划出阿穆利亚微板块,并建立一个包括太平洋、北美、欧亚、鄂霍次克及菲律宾海等板块在内的６板块系统,利用地震滑移矢量,转换断层走向,洋中脊扩展速率,以及最新的ＧＰＳ观测资料,采用Ｍｏｎｔｅ－Ｃａｒｌｏ盒子法,反演得到该６板块系统的欧拉运动矢量．本文得到的有关欧拉矢量为：ＡＭ-ＥＵ（６０．４２°Ｎ,１２３．２５°Ｅ,０．０２５°／Ｍａ）,ＡＭ-ＯＫ（５３．２０°Ｎ,１４１．９５°Ｅ,０．４７６°／Ｍａ）以及ＡＭ-ＰＨ（５０．８４°Ｎ,１５８.１３°Ｅ,１.２０４°／Ｍａ）,ＡＭ－ＥＵ的欧拉运动极点位于贝加尔隆起的东北及斯塔诺夫山脉的西北,并给出在贝加尔隆起有０．４－０．７ｍｍ／ａ的扩张,与从地质学证据得到的估计结果一致;由ＡＭ－ＯＫ及ＡＭ－ＰＨ欧拉运动矢量可以分别得到日本海东缘的６-１５ｍｍ／ａ及日本南海地槽带的５１－６６ｍｍ／ａ收敛速率,与最新的ＧＰＳ观测结果并不一致．因此,东亚北部地区存在独立的南中国微板块及其它亚尺度的微板块,可以更好地描述该地区现今板块构造的运动规律．     

低纬度环球带和环太平洋带大地震的幕式活动分析

统计分析低纬度环球带(E带)和环太平洋带(P带)在1900～2008年间M_W≥7.5地震的时空分布,进一步证实两者本身和两者之间都存在15～18年的幕式交替活动. 将这两大地震带分别划分为5个地震区,发现这些分区地震幕式活动互不相同, 但E带各区奇数幕与偶数幕年均地震数之比OER均大于1.58, 而P带各区的OER均小于0.93, 显示出前者以奇数幕活跃为特征, 后者以偶数幕活跃为特征. 对这些地震区的组合分析进一步证明,从幕式活动的共性看, 中太平洋地区宜纳入E带. 本文推论:低纬度环球带是另一条全球尺度地震带;大地震幕式活动的成因应归因于板块运动有几十年时间尺度的非平稳幕式运动;未来5～8年, E带的大地震还会比P带多.     

Earth Rotation Parameters 1899.7–:1992.0 After Reanalysis Within The Hipparcos Frame

Earth rotation parameters (ERP) in the interval 1899.7–1992.0 are obtained from re-analysis of the observed latitude/universal time variations by optical astrometry. Hipparcos Catalogue is used to define the celestial reference frame, within which the ERP are described, with special care devoted to 'problematic' double and/or multiple stars. The terrestrial reference frame is defined by the adopted latitudes/longitudes of participating instruments and their secular motions as given by the NUVEL-1 NNR model of plate motions, and it is chosen to be very close to the International Terrestrial Reference Frame (ITRF). More than four million observations made with 48 different instruments at 31 observatories, located all over the world, are utilized to determine polar motion, celestial pole offsets and (after 1956) universal time UT1, all at 5-day intervals. Along with these parameters, the combinations of Love and Shida numbers, governing the tidal variations of the local verticals at individual observatories, are also determined. The analysis of the results covering almost a century, namely the long-periodic polar motion and length-of-day changes, is presented.