青藏高原东北缘祁连山中部精细地壳结构研究

现今的青藏高原东北缘祁连山地区是在早古生代构造格架的基础之上,于新生代在欧亚大陆与印度大陆碰撞拼合的远程影响下,重新活化进而隆起成为高原的组成部分.因此,该区域地壳结构的揭示不仅可以获得高原地壳变形方式的关键信息,而且也能对该区域早古生代晚期北祁连洋闭合时的相关构造演化提供重要证据.本文以一条穿过青藏高原东北缘祁连山中部地区的深地震反射剖面为基础,结合前人地质、地球物理资料,通过细致的地质构造解译,获得了青藏高原东北缘祁连山中部地区的精细地壳结构.反射剖面图像揭示了海原断裂西段的深部延伸形态、中地壳的双重构造、以及中下地壳的祁连逆冲断裂系等精细的深部构造.结合前人的地质以及地球物理资料,我们提出早古生代晚期北祁连闭合时的南向俯冲以及新生代以来祁连山地区两次陆内俯冲作用可能造就了现今的祁连山.     

昆仑山口西8.1级地震后青藏高原北部地区地震活动初步研究

利用相关震例分析了昆仑山口西8．1级地震后青藏高原北部地区未来1～3年地震活动特征．结果表明,沿东昆仑构造带及邻近地区发生Ms≥7．0地震后青藏高原北部地区中强地震活动有增强的趋势,祁连山地震带和东昆仑地震带的地震活动具有交替发生的特征,未来1～3年中强地震主体活动区为大型走滑活动断裂上应力转换部位和挤压会聚构造区,如东昆仑断裂带中东段和祁连山地震带中东段和西段。     

祁连山构造带的新构造变形机制

论述了祁连山构造带新生代以来的变形过程及形成机制。研究表明： 祁连山构造带的变形过程是在欧亚大陆与印度大陆碰撞汇聚作用下发生和发展的, 其变形过程与整个青藏高原的隆升过程同步进行。其中阿尔金断裂在其东段的走滑贯通对祁连山－ 河西走廊地区的构造运动影响很大。上新世末或第四纪初阿尔金断裂东段的走滑导致了祁连山地区应力场的旋转, 进而增大了沿 Ｎ Ｗ Ｗ 向主断裂的水平走滑分量。它是引起主断裂发生走滑的重要原因之一。     

祁连山—河西走廊黑河流域地貌特征及其构造意义

采用定量化的地貌因子研究区域构造活动及其演化已成为构造地貌学的一种常用手段。祁连山—河西走廊位于青藏高原东北部边缘,是高原向NE方向挤压扩展的前缘部位,该区河流水系的地貌发育过程记录了高原隆升与挤压扩展及其气候环境效应的重要信息。位于祁连山北部山前的黑河流域向N穿过河西走廊和北山地区,其河流地貌的发育与祁连山的构造隆升直接相关。基于诸多地貌因子(面积-高程积分、地貌信息熵以及河流纵剖面)的研究结果均显示黑河流域所涉及的祁连山东、西段的构造活动存在明显差异,具有西强东弱的特点,如西段流域的平均面积高程积分值(HI)为0.541而东段仅为0.4661;并且根据河流纵剖面分析得到的差异隆升值西段为754m,也远高于东段的219m;而降雨等气候因素则存在东强西弱的特点。综合对比分析发现,本区岩性与降水条件等对研究区地貌因子的影响有限;构造活动是地貌演化发育的主控因素,控制着该区现今的构造变形、地貌发育及其演化历史。     

祁连山构造带的新构造形机制

论述了祁连山构造带新生代以来的变形过程及形成机制。研究表明：祁连山构造带的变形过程是在欧亚大陆与印度大陆碰撞汇聚作用下发生和发展的,其过程与整个青藏高原的隆升过程同步进行。其中阿尔金断裂在其东段的走滑贯通对祁连山－河西走廊地区的构造运动影响很大。上新世末或第四纪初阿尔金断裂东段的走滑导致了祁连山地区的应力场的旋转,进而增大了沿ＮＷＷ向主断裂的水平走滑分量。它是引起主断裂发生走滑的重要原因之一。     

地貌参数揭示的三危山构造活动性差异及其原因探讨

三危山断裂位于青藏高原北缘,沿三危山西北麓展布,全长约175 km.根据其几何特征,可以将断裂分为三段:西段(西水沟—树沟子段)、中段(树沟子—十工口子段)和东段(十工口子—双塔段),其构造活动强度与地貌发育程度各段存在明显差异.根据断层陡坎测量和区域年代对比,三危山断裂西段垂直滑动速率约0.1 mm/a,中东段则较低...     

青藏高原北部东昆仑-羌塘地区的岩石圈结构及岩石圈剪切断层

通过横穿青藏高原北部东昆仑-羌塘地区的格尔木-唐古拉山口(西段)和共和-玉树(东段)两条天然地震探测剖面的综合研究, 揭示东昆仑-羌塘地区岩石圈结构的如下特征: (1)地壳厚度自南往北由70~75 km减小至55~60 km, 西段厚度变化幅度(10 km)较东段(20 km)小; (2)地壳具高速与低速转换界面相间组成的层状结构, 东段中地壳为透镜状低速层; (3)在150 km深度范围内岩石圈的物理状态具高速体和低速体相间特征; (4)岩石圈结构不连续性表明地体边界及地体内部存在150~250 km深度的3条主要的岩石圈剪切断层带: 昆南-阿尼玛卿岩石圈剪切断裂带、金沙江岩石圈剪切断裂带和鲜水河岩石圈剪切断裂带. 推测青藏高原北部存在岩石圈规模的向东挤出作用.     

青藏高原北部地区地震统计区划分及地震活动特征

地震统计区的划分是研究地震活动性的重要前提和基础,通过对青藏高原北部地区构造地质背景的分析,依据地球物理特征和强震活动特点,讨论和划分该区地震活动统计区,探讨研究区地震活动的复发特点、地震构造特征、潜在地震危险性及强度,分析研究区未来强震发生的强度和可能地点,结果表明,目前青藏高原北部地区处于第8个活跃期,仍存在发生强震的可能,且未来数年存在发生7级以上地震的可能,应密切东昆仑断裂带东段和祁连山中西段地区。     

青藏高原东北缘及周边地区基于程函方程的面波层析成像

利用"中国地震科学台阵探测"在南北地震带北段布设的670套宽频带地震台站记录到的面波资料,使用新近发展的程函方程面波层析成像方法,获得了青藏高原东北缘及周边地区12~60 s周期范围比以往成像结果具有更高分辨率的瑞利面波相速度分布图像.青藏高原东北缘的祁连褶皱系西段、秦岭褶皱系西段和松潘一甘孜褶皱系,在16~60s周期范围内均显示出明显的低速异常分布,表明该地区的地壳力学强度较低,在强烈的构造应力作用下易发生形变.与西段不同,祁连褶皱系东段和秦岭褶皱系中段的相速度分布特征揭示,其中下地壳的速度明显高于高原内部区域.鄂尔多斯块体整体上表现为稳定块体具有的高速特征,但其西部边缘在中上地壳的速度比块体中部地区偏低,且存在一定的不均匀性.鄂尔多斯块体西北缘的临河断陷盆地和西缘的银川断陷盆地,在较短的周期范围内(12~20 s)表现为局部低速特征,但与银川断陷盆地不同,临河断陷盆地的低速特征可一直延续至60 s周期以上,表明该盆地下方地壳及上地幔速度明显偏低,可能与深部热作用有关.阿拉善块体与其北部地区的速度差异主要表现在中上地壳,这一现象值得今后进一步探讨.基于程函方程面波层析成像方法给出了青藏高原东北缘及周边地区高分辨率的成像结果,揭示了以往面波层析成像难以获得的深部细节特征,为该地区的深部构造研究提供了新的信息.     

藏北地壳东西向结构与“下凹”莫霍面——来自宽角反射剖面的启示

根据藏北色林错-雅安多510余公里长地震剖面上纵横波特征所识别的来自于莫霍反射及壳内反射震相,通过正演拟合解释了该纵剖面地壳纵横波速度与Poisson比结构.研究结果显示,雅鲁藏布江与班公湖-怒江两条缝合带之间地壳结构东西向变化剧烈,岩石圈结构在剖面中部厚度最深,达到80余公里;莫霍面东西向变化呈现“下凹”特征,自莫霍面“下凹”处沿剖面东西方向呈阶梯状抬升,且西向抬升速度较东向大;地壳内纵横波速度纵向（深度域）与横向（东西方向）均存在非均一性现象,且上地壳内27～34km深度处存在厚度约5～7km的低速层.上地壳内,剖面中段介质的Poisson比较剖面东段与剖面西段的低;下地壳内,剖面东段的Poisson比较剖面西段的Poisson比低.上地壳内介质的刚性变化特征不同于下地壳内介质的刚性变化特征,剖面东段下地壳内物质较剖面西段的刚度小,并蕴含着藏北地区下地壳物质伴随欧亚与印度板块碰撞而东向流动.藏北地区地壳结构东西向变化趋势与莫霍面“下凹”特征可能源于多期构造作用的叠加效应.     

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 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.     

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.     

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。     

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.     

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.     

Evolutionary Changes in the Configuration of the Magnetic Field of the Solar Corona in the Epoch of the Minimum

Geomagnetism and Aeronomy - The evolution of the magnetic configuration in the solar corona is studied. The curvature of the K-corona helmets obtained from an analytical approximation of the...