区域和全球地磁场模型

本文叙述了计算区域地磁场模型的各种数学方法，给出了选择计算区域模型数学方法的判据，讨论了改善区域地磁场模型边界效应的方法，研究了确定区域地磁场模型截断阶数的判据，另外，简单介绍了第六代国际地磁参考场，１９９０年世界地磁图，国际地磁参考场的精度和使用。     

三维井间电磁场的正反演计算

提出了一种计算体积分方程的方法－改进型局域非线性迭代（MLNI），并用其对三维井间电磁场进行反演计算，该方法将井间大尺度散射体分为近场和远场区域两部分，它们的位置和尺寸均随场点位置的变化而改变，采用局域非线性近似计算近场区域的影响，将远场区域的影响作为外部激励源，采用迭代方法计算，该方法具有计算速度快，所需内存量少，收敛性好的优点，在反演中采用基于MLNI的非线性反演方法，利用这种方法可以将成像区域集中于一定范围内而不是整个三维空间，该反演方法由于考虑到了雅可比矩阵元素的非线性项，因而与传统的Born迭代反演方法相比更为精确和稳定，考虑到信息量和计算机内存的限制，第1次成像采用双重体元分割法进行较粗略的成像，然后缩小成像范围进行第2次较精确的成像，数值计算结果表明，MLNI是一种有效的计算井间大尺度异常体散射场的方法，将该方法用于反演过程能够得到较高分辨率的三维井间电导率图像。     

利用第七代IGRF计算1995.0年中国及邻区地磁场

本文介绍了第七代国际地磁参考场，利用ＩＧＲＦ１９９５计划并绘制１９９５．０年中国及邻区地磁图，考虑了地球扁率对计算结果的影响。     

山西省地震危险性计算与制图

地震危险性计算是山西省地震灾害风险普查工程的基础工作内容之一，文章基于概率地震危险性分析方法对山西省地震危险性进行计算。简述地震危险性计算的原理、数据处理与图件制作流程，将计算结果与第五代地震区划图潜源模型的计算结果进行对比分析，结果表明基于风险普查潜源模型的晋西北、晋东南山区计算结果稍有增大；汾渭断陷带内的计算结果略有降低，但差距很小，可认为结果基本一致。同时对产生差异的原因进行初步分析。     

地震灾害经济学研究

本专辑所述内容是《地震灾害经济学研究》（第一部分已发表在《国际地震动态》１９９５年第４期上）课题的第二部分。作者简要地介绍了防御地震危险的方法（省略计算部分），地震危险减轻的选址方法，地震灾害的统计分析，公用设施财产损失及其应急反应的经济分析，地震工程投资的经济分析，以及地震灾害管理的经济分析。     

鲜水河断裂带区域第四纪构造应力场的分期研究

利用断层滑动方向资料反演构造应力张量的分期计算方法，获得鲜水河断裂带区域第四纪以来两期主要构造应力作用：第１期为早～中更新世，构造应力作用以北东－南西向挤压为特征；第Ⅱ期自晚更新世至今，构造应力作用以近东西向挤压和近南北向拉张为特征     

基于第三类边界条件的大地电磁三维矢量有限元任意各向异性正演

地球内部介质的各向异性对地球物理场解译有很大影响,研究各向异性介质中大地电磁响应具有重要的意义.边界条件是影响电磁场正演精度的一个关键因素,其中第一类边界条件需要将底面边界设置在离异常体足够远的地方,面临着计算规模大、求解速度慢的问题.相比第一类边界条件,第三类边界条件具有计算规模更小、计算精度更高的优点,在三维各向同性正演中被广泛使用.然而,各向异性使得第三类边界条件理论变得更为复杂,目前尚未见到采用第三类边界条件的大地电磁三维各向异性正演.本文推导出各向异性介质中三维矢量有限元底界面的第三类边界条件,通过模型计算对算法的可靠性和精度进行了验证.结果表明,当精度相同时,第三类边界条件的计算规模可以更小;而当底界面离异常体较近时,第三类边界条件有着更高的精度.     

球面波的反射P波AVO分析

本文对球面波反射P波反射系数计算公式进行了推导,根据推导公式计算出第I类AVO和第Ⅲ类AVO介质中反射系数及相位随入射角的变化,并与基于平面波的Zoeppritz方程计算的结果进行对比.结果显示,对于第I类AVO介质,球面波反射系数在临界角附近较基于平面波的Zoeppritz方程计算结果更精确;同时受界面深度的影响较大,随深度的增加,球面波AVO趋势接近平面波AVO.最后,通过数值模拟技术,对模型数据和实际数据进行模拟,对平面波AVO道集和球面波AVO道集进行了验证分析.浅层的第I类AVO现象,在近临界角和超临界角处折射引起反射系数与相位的变化较大,对于第Ⅲ类AVO现象,由于不存在临界角问题,球面波模拟结果与基于平面波的Zoeppritz计算结果差别较小.上述计算分析,可为实际资料的大偏移距道集的AVO分析提供理论基础.     

高层结构-桩-土共同作用的地震反应分析

采用边界元特解样条函数提出了桩－土与上部结构共同作用的动力分析方程，分析了土桩刚度与阻抗的计算方法；指出在共同作用下，结构的动力特性发生了变化，结构自振频率减小，上部结构的位移、加速度分布不同于传统的以第1振型为主的倒三角形分布，而随着地基土软弱程度的加重越来越接近K型分布的特性。     

基于MLS形函数处理边界的电阻率法有限单元正演模拟

电阻率法有限单元正演模拟中,采用第三类边界条件时为保证精度仍要求较大范围的计算域.无单元法为地球物理领域的新兴正演模拟方法,其计算效率低,但其中采用的移动最小二乘(MLS)形函数相比于有限单元法形函数具有良好的连续性,模拟精度高.本文将MLS形函数应用于电阻率法有限单元2.5维正演的第三类边界条件处理,提出电阻率法有限单元-移动最小二乘(FEM-MLS)耦合正演方法.通过不同正演方法的模型算例模拟结果对比,验证了本文算法的有效性,并讨论了各个参数选择对模拟结果的影响.本文数值模拟结果表明采用第三类边界条件时,在同等计算精度前提下,FEM-MLS耦合法相比于有限单元法可进一步缩小计算域并提高了计算效率,相比于采用较大计算域满足边界条件的有限单元法计算效率提高了约一倍,相比于采用相同小范围计算域的有限单元法平均精度提高了约一倍.     

On the synchronism in the events within the core and on the surface of the earth: the changes in the organic world and in the polarity of the geomagnetic field in the phanerozoic

The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes in the organic world.     

On the gravimetric undulations of the geoid and the deflections of the vertical

Summary The author mentions the aims of the World-wide gravity project he established in the Ohio State University in Columbus, in 1950. He outlines the practical procedure of the gravimetric computations of the undulationsN and the vertical deflection components and and emphasizes that only by the global international cooperation and additional gravity observations at sea carried out during the last decade it has been possible to gather to Columbus the needed gravity material. Since there exist still large gravimetrically unsurveyed areas it is of vital significance to study what gravity anomalies are best to be used for these regions. The given figures concerning the accuracy of theN, and , estimated theoretically and obtained in practice, indicate that in the gravimetrically well surveyed parts of the world like in Europe and the United States we can get gravimetrically on basis of existing gravity material theN-values with accuracy of about 5–10 meters, and and with the accuracy of about 1. The geoid undulationsN are already computed in Columbus for more than 6000 points of the northern hemisphere. The sample maps show the interesting geoid of Europe and vicinity between the latitudes 60° and 30° and longitude 5° W and 30° E, drafted on basis of more than 1000N-values computed at the corners of 1°×1° squares. It is interesting to realize that the geoid undulations in all this area are positive, the extreme values being between 40 and 50 meters. The geophysical significance of the geoid maps of this kind is pointed out.     

On the maintenance of the axisymmetric part of the flow in the atmosphere

Summary The maintenance of the axisymmetric component of the flow in the atmosphere is investigated by means of a steady-state, quasi-geostrophic formulation of the meteorological equations. It is shown that the meridional variations in the time-averaged axisymmetric variables can be expressed as the sum of three contributions, one being due to the eddy heat transport, another to the eddy momentum transport, and a third to the convective-radiative equilibrium temperature which enters the problem through the specification of a Newtonian form of diabatic heating. The contributions by the large scale eddies are evaluated through the use of observed values for the eddy heat and momentum transports.The contributions from each of the three forcing mechanisms to the temperature and zonal wind fields are invstigated individually and found to be of about equal importance. The sum of the three contributions are also presented for the temperature, the zonal wind, the stream function associated with the mean meridional circulation and the corresponding vertical motion. Although the results fail to reproduce the main observed features of the lower stratosphere, they are found to be in good agreement with observations in the middle latitude troposphere. At any pressure level, for example, the computed mean zonal wind has a jet-like profile and the axis of the jet is found to slope to the south with height, as observed in the atmosphere.Based in part on a thesis submitted by the first author as partial fulfillment of the requirements for the Ph.D. degree at the University of Michigan. — Publication No. 194 from the Department of Meteorology and Oceanography, The University of Michigan.     

太平洋中部地磁台11年周期变化的研究

综合APIA、HONOLULU、PAMATAI 3个地磁台三分量的11年周期变化的形态后,可定性地提出该变化源于内场。如内源为核幔边界的电涡流,则其中心点应位于3台之间。     

Comparison Between the Nutations of the Planet Mars and the Nutations of the Earth

The nutations of the planets Mars andEarth are investigated and compared. Alarge number of interior structureparameters are involved in the nutationcomputations. The comparison between the observations and the computationsprovides several constraints on these parmeters andtherefore allows a better understanding of the physics of the interior of theplanet. For the Earth, the high precision of the observations of the nutationshas led to a very good determination of interior properties of the planet. ForMars, observations of nutations are not yet available, and we review how theamplitude of the Martian nutations depends on the hypotheses consideredfor its interior. Although Mars is very similar to the Earth, its interior is not well known;for example, we don't knowif its core is liquid or solid. Only if the core is liquid,the Free Core Nutation (FCN) normal mode exists and can alter the nutationswhich are close to the resonance. From the observed geoids, it is known thatboth planets are not in hydrostatic equilibrium. The departure is larger forMars than for the Earth, and consequently, the implication of considering a convective mantle instead of a mantle in hydrostatic equilibrium described byClairaut's equation for the initial equilibrium state of the planet is largeron the Martian nutations than on the Earth nutations. The consequences of theuncertainty in the core dimensions are also examined and shown to be of a veryhigh influence for Mars if the core is liquid, due to the potential changes inthe FCN resonance. The influence of the presence of an inner core, which isknown to exist for the Earth, could be more important for Mars than for theEarth if the inner core is large. Due to the presence of Tharsis on Mars, thetriaxiality of this planet has, additionally, larger effects than on Earth.     

Magnetic stratigraphy of the Ordovician in the lower reach of the Kotuy River: the age of the Bysy-Yuryakh stratum and the rate of geomagnetic reversals on the eve of the superchron

Until recently, the existing data prevented the geophysicists from accurately dating the Bysy-Yuryakh stratum, which outcrops in the middle reach of the Kotuy River, constraining the time of its formation to a wide interval from the end of the Late Cambrian to the beginning of the Silurian. The obtained paleomagnetic data unambiguously correlate the Bysy-Yuryakh stratum to the Nyaian regional stage and constrain its formation, at least a considerable part of it, by the Tremadocian. This result perfectly agrees with the data on the Bysy-Yuryakh conodonts studied in this work and yields a spectacular example of the successful application of paleomagnetic studies in solving important tasks of stratigraphy and, correspondingly, petroleum geology. Within the Bysy-Yuryakh stratum, we revealed a large normal-polarity interval corresponding to the long (>1 Ma) period when the geomagnetic reversals were absent. This result, in combination with the data for the Tremadocian and Middle–Upper Cambrian sequences of the other regions, indicates that (1) the rate of occurrence of the geomagnetic reversals on the eve of the Ordovician Moyero superchron of reversed polarity was at most one reversal per Ma; (2) the superchron does not switch on instantaneously but is preceded by a certain gradual change in the operation conditions of the dynamo mechanism which, inter alia, manifests itself by the reduction of the frequency of geomagnetic reversals with the approach of the superchron. This finding supports the views according to which a process preparing the establishment of the superchrons takes place at the core–mantle boundary.     

On the variation in the geomagnetic dipole over the geological history of the Earth

The global database on the paleointensity, containing determinations of the virtual dipole moment (VDM) for a stable (normal) regime of the geomagnetic field in a time interval of up to 3.5 Ga, is supplemented by new VDM determinations and analyzed. The field generation process started no later than 3–3.5 Ga (earlier data are absent) at the stage of the Earth’s core formation. Since that time, the dipole value has differed from its present value by no more than an order of magnitude, and the deviations that have already been detected tend toward smaller values. The distribution of VDM values in the time interval 0–400 Ma is bimodal, which apparently reflects the presence of two different generation levels of the geomagnetic field distinguished by a relatively large value (close to the present field value) and a relatively small value (approximately half as large as the present value). The total duration of decreased VDM values appreciably exceeds that of increased VDM values (179.1 and 28.6 Myr, respectively). On the whole, data on the paleointensity do not contradict the hypothesis about the dipole nature of the field over the last 400 Myr; however, the number of determinations at high paleolatitudes is too small to draw decisive conclusions on the validity (or invalidity) of the dipole field approximation based solely on paleointensity data.     

Structure of the poleward wall of the trough and the inclination of the geomagnetic field above the EISCAT radar

A special high-resolution routine of the EISCAT radar has been used to investigate the structure and development of the poleward wall of a deep trough in electron density. The feature was tracked by the radar during a 7-hour period under very quiet geomagnetic conditions. The field-aligned nature of the structure enabled an estimate to be made of the inclination of the geomagnetic field above EISCAT that was in good agreement with the current model. Observations of narrow field-aligned enhancements in electron temperature demonstrated that the wall of this trough is a dynamic feature, reforming regularly as the electron density responds on a time scale of tens of minutes to energy input from soft-particle precipitation.