芦山M_S7.0与岷县漳县M_S6.6地震前甘肃地区部分台站地电场变化

本文应用2013年芦山MS7.0与岷县漳县MS6.6地震震中周围的平凉等3个地电场台站观测数据,研究地震发生前后地电场在时间域、频率域内的变化。结果表明:1在芦山地震、岷县漳县地震前,位于青藏高原东北缘的平凉台记录到显著的地电场异常变化。2利用最大熵谱估计方法计算平凉、松山、古丰台在芦山地震以及岷县漳县地震发生前后地电场观测数据,得到在上述两次地震前均发生地电场功率谱密度(特别是低于4×10-3 Hz频段的成分)增大的现象,岷县漳县地震发生后,部分测向谱密度增大现象消失。3距离震源区越近,地震发生前后功率谱密度异常变化越明显,长短极距相关性越差,初步分析认为此现象的发生,可能是由于在震源孕育、发生过程中,台站所在位置地下介质形变激发宏观电磁辐射造成的。     

用接收函数方法研究汶川和芦山地震之间未破裂段的地壳结构

芦山与汶川地震之间存在约40 km的地震空区.震源区和地震空区的深部构造背景的研究对深入了解中强地震的深部孕育环境及地震空区的地震活动性具有重要科学意义.利用本小组布设的15个临时观测地震台以及21个芦山科考台站和21个四川省地震局固定台站记录的远震数据,用H-K叠加方法得到各个台站的地壳厚度和平均泊松比,并构建了接收函数共转换点(CCP)偏移叠加图像以及反演得到台站下方的S波速度模型.我们的结果揭示了震源区和地震空区地壳结构特征差异:(1)汶川震源区的地壳平均泊松比为~0.28;芦山震源区为~0.29;而地震空区处于泊松比变化剧烈的区域;(2)汶川地震与芦山地震的震源区以西下方的Moho面呈现深度上的突变(这与前人的研究成果基本一致),分别从~44 km突变到~59 km,~40 km突变到~50 km,而地震空区地壳平均厚度呈现渐变性变化;(3)地震空区Moho面下凹且具有低速的上地壳.综合一维S波速度结构和H-k以及CCP的初步结果,这可能显示汶川地震的发震断裂在深部方向上向西倾斜并形成切割整个地壳的大型断裂;芦山地震则可能是由于上、下地壳解耦引起的;而地震空区处于两种地震形成机制控制区域的过渡带中.     

芦山MS 7. 0 地震前近震源区地形变熵特征研究

2013 年4 月20 日芦山MS7.0地震是继2008年汶川MS8.0地震后发生在龙门山断裂带的又一强震,与汶川地震相似,该震临震前在近震源区未观测到显著的异常变化。为研究其临震前形变特征,本文根据信息熵理论对芦山MS7.0地震前近震源区的连续形变观测资料进行了年变熵率值分析,并研究其时序上的分布特征。结果表明,震前近震源区台站地倾斜形变熵均表现出减熵现象,时序的年尺度熵结果表明,汶川MS8.0地震对芦山MS7.0地震具有一定的触发作用,且震中区的EW 向和NS 向分量具有高度一致的熵变趋势。     

2013年芦山M_s7.0地震震源区横波分裂的变化特征

对2013年芦山Ms7.0级地震序列的横波分裂的时空变化现象进行了研究.通过在横波窗内S波质点运动图的分析,从位于龙门山断裂带南段芦山地震震源区地震台站的记录中提取了S波分裂的快波偏振方向和慢波的到时延迟.在研究区,观测到各台站的快波偏振优势方向从南向北有分区特征,慢波到时延迟的随时间有趋势性变化.空间上,快波偏振优势方向在南部为北东向,与龙门山断裂走向一致,而北部为北西向,与区域主压应力方向一致,位于断裂带上的台站TQU和BAX表现出特殊性,可能受到龙门山断裂带的直接影响,体现了断裂带上的应力场方向变化的特殊性.时间上,慢波到时延迟在主震后迅速增大,持续一段时间后又减小;横波分裂现象主要由台站下方岩层中随应力分布排列的微裂隙控制,本文结果揭示了主震和余震过程中区域应力场的变化,芦山地震震源区的地壳应力在主震后得到了增强,随着余震活动导致的应力释放,后期应力减小.     

基于误差分布的震源区波速比反演及其应用:乳山震群源区介质性质变化研究

本文利用误差分布和概率统计分析改进了波速比计算方法.对于震源位置相对集中的震群活动,对台站震相到时进行两次差分,通过对差分后的震相数据对进行二维高斯分布拟合,可以稳健地估计震群活动震源区波速比.该方法充分利用了不同台站Pg、Sg到时差的所有信息,其优势是不需要地震事件的震源位置,并且不依赖震源区以外的速度变化,有效消除了震源区到台站的传播路径效应的影响;相对于传统的平均波速比,本文方法得到的震源区波速比,更能真实地反映震源区介质的性质.我们将该方法应用到2013—2016年的乳山震群,结果显示:震源区波速比的变化与震群活动过程密切相关,波速比的变化反映了序列活动的阶段性特征.     

基于气枪震源信号的云南漾濞MS6.4地震前后波速变化

本文基于宾川气枪地震信号发射台激发的地震波信号,利用线性叠加和时频域相位加权叠加方法提高信噪比,通过反褶积、插值拟合和波形互相关等方法,获得2021年漾濞M;6.4地震前后气枪震源初至波信号走时变化特征.结果表明两种叠加方法得到的走时变化趋势基本一致,在沿发震断裂带附近的3个台站观测到的初至波走时延迟为7.3~14.4 ms,在射线路径上平均波速降低了0.08%~0.12%,距离震中位置较远的台站走时延迟为2~6 ms.分析认为,观测到的走时变化主要是漾濞M;6.4地震引起强地面运动造成浅层介质疏松、同震破裂导致震源区地下介质裂隙增加和地下流体侵入等共同作用造成,相关研究成果有助于加深和促进对此次地震震源物理过程的认识和了解.     

2013年芦山MS7.0地震序列S波分裂特征

本文测定了2013年4月20日芦山M_S7.0地震震源区及其附近台站的S波分裂参数,包括快波偏振方向和慢波延迟时间,最终得到了40个台站的S波分裂结果．结果显示:在地震主破裂区内观测到的快波优势取向为NE向,与余震分布的长轴方向一致;位于双石—大川断裂以西台站的快波偏振优势方向为NW向,与区域最大主压应力轴方向一致;位于荥经断裂附近台站的快波偏振优势方向为NW向,与该断裂走向一致．快波偏振优势方向随时间的变化结果显示:主震前位于地震破裂区附近的TQU和BAX台站的快波偏振优势方向均呈NE向;主震后TQU台站的快波偏振优势方向为近EW向,而BAX台站的快波偏振优势方向则不突出,反映出芦山地震主震前快波偏振方向受控于龙门山断裂带,而主震后受构造应力场的作用更加明显．此外,各台站的慢波延迟时间为1.25—5.40ms/km,在余震覆盖密集区域,台站的慢波延迟时间均大于3.0ms/km,反映出震源区的各向异性程度较强．芦山主震后,各台站的延迟时间随时间变化持续减小,反映出震源区地壳应力随余震活动逐渐减小．      

体波谱振幅相关系数法在肥东地震序列震后判定中的应用

地震直达体波记录的观测谱包含震源、传播路径和台站信息,而发生在同一震源区的不同地震,如:序列地震,在同一地震台站的记录,受传播路径影响基本相同,地震台站的场地响应、仪器响应也完全相同。因此,序列地震体波观测零频谱的相关系数直接反映震源辐射图型因子的相似性,即震源机制解的相似性。将该方法用于2009年安徽肥东地震序列,与传统方法计算的震源机制解作比较,结果显示,谱振幅相关系数法能反映序列地震震源机制解的变化过程。     

利用断层首波分析2010年玉树M_W6.9地震断裂带的速度差异特征

<正>断层首波是在断裂带两侧介质的地震波速度存在差异,在地震波速度较慢一侧的台站可记录到比直达体波优先到达的初至波。目前,断层首波主要在板块边界附近的断裂带观测到,但没有得到很好的应用。但由于断层首波的存在,对地震初至波识别、地震定位、震源机制解及震源破裂过程的分析研究带来了更大的误差。另外,断裂带两侧介质存在速度差异会影响地震的震源特征,例如,地震破裂的优势方向。对     

2013年四川芦山Ms7.0地震前的重力变化

利用川西地区2010-2012年期间的流动重力观测资料,系统分析了区域重力场变化及其与2013年4月20日四川芦山7.0级地震发生的关系.结果主要表明:①区域重力场异常变化与北东向龙门山断裂带南段和北北西向马尔康断裂带在空间上关系密切,反映沿该两断裂带(段)在2010-2012年期间发生了引起地表重力变化效应的构造活动或变形.②芦山7.0级地震前,测区内出现了较大空间范围的区域性重力异常,而震源区附近产生了局部重力异常,沿龙门山断裂带南段形成了重力变化高梯度带,其中,宝兴、天全、康定、泸定、石棉一带重力差异变化达100×10^-8m·s^-2以上;这些可能反映芦山地震前,区域及震源区附近均产生与该地震孕育、发生有关的构造运动或应力增强作用.③重力场差分动态演化图像和重力场累积变化动态图像均反映芦山7.0级地震孕育过程的最后2~3年出现较显著的流动重力异常变化,可视为该地震的中期前兆信息;本文第一作者等也曾基于该流动重力异常变化在芦山7.0级地震前做过一定程度的中期预测,尤其是地点预测.本文的例子再次证明流动重力观测能较好地捕捉到强震孕育发生过程中,特别是该过程最后阶段的重力异常变化信息.因此,区域流动重力场观测对未来强震的中-长期预测,尤其是在发震地点的判定上具有优势.     

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.     

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.     

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。     

On the use of the autocorrelation method for estimating the depth to the magnetic basement

The depth to the top of magnetic dykes can be estimated from total field aeromagnetic data using the relation between the depth to magnetic sources and the autocorrelation function of magnetic data. By using synthetic anomalies we show that in the ideal case, depth can be determined to an accuracy of 10% or better, when the anomaly sources are two-dimensional dykes. However, the estimated depths depend on the width of the dykes. The estimated depth is about 0.6 times the actual depth to the top of thin dykes, and around the true depth for thick dykes having width-to-depth ratio around 3. The depth is considerably overestimated for very thick dykes (e.g., contacts, which is a special case of the thick dyke). Thus, the autocorrelation method requires that the width-to-depth ratio of the dyke is estimated independently to correctly estimate the depths. Alternatively, it must be assumed that the width-to-depth ratio for the two-dimensional source body is between 1.5 and 4.     

固体潮的地震预测研究与地球动力学研究之分析比较

本文分析了现行固体潮地震研究中的历史影响,对比研究了固体潮地震预测研究和固体潮地球动力学研究二者在振动频率、振动源体积、传输距离与介质等方面的地球物理特点与本质区别,强调了固体潮地震预测研究中最根本的工作是建立地震预测的目标和基本概念.     

On the Mechanism of the Secular Tidal Acceleration of the Solid Inner Core and the Viscosity of the Liquid Core

As is known, the secular deceleration of the Earth's diurnal rotation is explained mainly by the tidal friction in the ocean. Below we consider this mechanism in some detail, taking into account also elastic deformations of the mantle under the action of ocean loading and the interaction between the tide-generating body, ocean tidal wave, liquid outer core, and solid inner core. It is shown that elastic displacements of the core-mantle boundary under the action of ocean loading are of about the same amplitude and phase as the elastic loading displacements of the Earth's outer surface. As a result, side by side with the mechanism of secular deceleration of diurnal rotation of the mantle, there are also (1) the opposite mechanism of secular acceleration of diurnal rotation of the outer liquid core and of the solid inner core and (2) the mechanism of excitation of differential rotation in the liquid core. Taking these effects into account, we compare theoretical and modern observed data on the eastward drift of the solid inner core. It is shown that the best agreement may be obtained if the turbulent viscosity of the liquid core is about 2 × 10 ³ Poise     

Macrobenthic communities of the Pechora Sea: the past and the present on the threshhold of the prirazlomnoye oil-field exploitation

On data of bottom sampling, carried out by means of grab, trawl and underwater photography in August–September of 1993 in the area of the Pechora Sea, quantitative regularities of macrobenthos distribution are described for the ecological monitoring purposes. Maps of -biodiversity and biomass indices, bottom communities and trophic zones, singled out by dominant method, are presented. Assessment of structure changes of the investigated area bottom communities during the last 60–70 years is fulfilled. It is shown that the described communities on the whole are of natural undisturbed character and that the revealed changes are within the natural fluctuations in the abundance of benthic populations or may be interpreted in terms of methodical differences in the data analysis and generalization by different authors.     

动水压力对深水桥墩地震响应影响的研究综述

地震激励下处于深水中的桥墩和周围水体的相互作用将对桥梁结构的动力响应产生较大影响。首先对地震作用下水-桥墩的相互作用理论做了概括,给出了动水压力对桥墩的作用效应及各自的适用范围;对主要的三种考虑流固耦合效应的分析方法做了对比,探讨了地震作用下影响水-结构相互作用的主要因素,并对今后的研究提出了建议。     

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.     

环太平洋俯冲带内双地震带及其成因机制研究进展

俯冲带作为地球最为庞大的循环系统的重要组成部分,已成为地球科学的研究热点之一.很多俯冲带,特别是环太平洋俯冲带内的中深源地震,在空间上呈明显的分层分布,并且各层地震具有不同的震源机制,即所谓的双地震带现象.本文简要介绍了环太平洋双地震带形态特征与震源机制的空间分布,并回顾了双地震带的几种成因模型.根据形态特征和震源机制的差异,中源深度的双地震带可以分为两类,其中,一类双地震带对应上、下二层分别为压缩和张性的地震分布;另一类双地震带的震源分布较浅,且其浅部地震以横向压缩为主.此外,日本本州东北俯冲带的地震分布可能是由三层地震带组成的,而且汤加、伊豆-小笠原地区还发现深源深度的双地震带.通过对双地震带的形态特征以及其热力学条件的研究,人们从抗弯作用、脱水脆化、相变断层等多方面,尝试建立解释双地震带成因的模型.目前,大多数研究利用数值计算结果,结合蛇纹石脱水脆化、相变断层模型,能够不同程度地分别解释中源和深源双地震带成因.不过,这些模型几乎相互独立,并不能同时解释中源和深源双地震带.有人试图尝试用统一模型解释中深源地震成因,例如,先前存在的断层模型,不过该模型还不很具有说服力.也可能是多种因素的联合作用,共同影响着俯冲板内的温度场、应力场分布.