地壳介质各向异性研究状况,存在问题及进一步研究思路

引言近２０多年来对地球的观测和研究表明地壳介质呈现强烈各向异性。研究地球介质尤其是地壳的各向异性特征,对自然资源开发和地震前兆场演化规律认识都有十分重要的意义。但同时也应看到,地壳介质各向异性研究的各种方法和理论是建立在简化的物理或数学模型上的,因此...     

地壳介质弹性、电性各向异性理论及对地震过程的联合解释

本文共分 1 0章 :第 1章为引论 ;第 2～ 6章为基础理论 ;第 7～ 1 0章为应用研究。主要研究内容可分为 5个方面。1 )第 1章引论部分综述了地壳介质各向异性现象和分类 ,从发展沿革、理论方法及成果、存在的问题等几个方面分别论述了地壳介质弹性各向异性和电性各向异性。在此基础上提出了本文的研究思路和主题 :将地震学中的S波分裂法与电法中的大地电磁测深法联合起来解释地震过程中的各向异性动态特征与发震应力场的关系。围绕这个主题设定了 2个核心 :一是建立地壳介质电性各向异性微观模型 ;二是基于 EDA(广泛扩容各向异性 )裂隙模型…     

重庆及周边地区地壳各向异性研究

根据重庆及周边地区固定地震台站记录的远震资料提取了接收函数,并利用接收函数Pms相到时方差最小方法建立网格搜索,最终获得该区的地壳各向异性参数。结果表明:重庆及周边地区的地壳各向异性延迟时间为0.14～0.91 s,平均为0.4 s;快波偏振方向主要有NEE、NNW和NWW向,并且大部分台站快波方向与所在区域的主压应力方向明显不一致;重庆地区地壳各向异性具有横向不均匀性及分区特征,岩石圈形变特征主要来自地幔各向异性。     

地壳介质各向异性弹性本构关系讨论

论述了地壳介质中存在的各类向异性及其弹性本构关系,推导了应变能变换公式、ＥＤＡ薄层各向异性弹性常数及非对称面上ＥＤＡ构成的单斜对称弹性常数的计算公式;讨论了几种各向异性对称系统的本征方程并给出了弹性波的角散表达式,最后选取合理的参数对波的角散现象作了数值模拟。     

地壳分层各向异性介质接收函数及其粒子群反演

地壳不同深度介质的地震各向异性是研究地壳不同深度范围变形方式的重要依据.鉴于地壳介质的复杂性,如何从远震体波接收函数中提取不同深度的各向异性参数仍是一个有待深入研究的课题.在已有研究的基础上,本文利用广义反射-透射系数矩阵方法计算的合成地震图,研究了复杂地壳分层各向异性介质的接收函数随反方位角（back azimuth）变化及不同层位各向异性参数对接收函数波场的影响,为各向异性介质接收函数的解释提供了新的理论依据.通过引入粒子群优化理论,发展了分层各向异性介质接收函数全局反演算法.数值及观测数据的验证结果表明,在各向同性速度模型确定的前提下,我们的方法能够可靠地提取地壳分层各向异性参数;在反演中引入曲波变换去噪技术,对于正确解析不同层位的各向异性参数具有重要价值.     

延庆—怀来盆地地震预测研究

本文阐述了英国地质调查所与国家地震局地球物理研究所在北京西北延庆－怀来盆地进行地震学合作研究的过程和取得的成果。     

首都圈东南部地区地壳介质各向异性

基于首都圈地震台网2002——2005年的区域地震波形数据,采用剪切波分裂系统分析方法（SAM）, 计算得到首都圈东南部地区(38.5deg;N——39.85deg;N,115.5deg;E——118.5deg;E)24个台站的剪切波分裂参数. 结果表明,首都圈东南部地区快剪切波平均偏振方向与区域最大主压应力方向相近,与华北地区GPS主压应变测量结果一致;但首都圈东南部盆地地区的剪切波分裂观测结果与首都圈西北部的隆起——盆地构造结合区的观测结果不同. 这说明了不同的构造对观测结果具有一定的影响. 研究还表明,台站附近的断层分布状态对观测结果影响很大,复杂的断层分布会加剧剪切波分裂测量结果的离散程度. 本研究区域南部台站与北部台站的快剪切波偏振方向存在较大差异,这可能与该区南北部的构造及应力环境存在较大差异有关.       

地壳介质各向异性电性本构关系讨论

讨论了地壳介质中常见的两类电性各向异性。推导了长波长条件下薄中向异性电导率张量;提出了一种新的电导率物理模型并由此推导了与ＥＤＡ裂隙相适应的各向异性电导率张量。从直流电法和大地电磁测深法的角度分别讨论了这两种电性各向异性所显现的地表视电阻率、阻抗和电位特征。     

各向异性介质中的弹性阻抗及其反演

地震反演已成为油藏描述中的重要组成部分.绝大多数的常规地震反演是叠后地震数据体上进行,很少考虑各向异性存在的情况.随着勘探开发的发展,地震各向异性和叠前地震波阻抗反演引起了人们极大关注.本文在各向同性介质中弹性阻抗研究基础上,推导出了各向异性介质中的弹性阻抗方程,提出了地震各向异性介质中用弹性阻抗进行储层参数描述的技术路线和框架,并对反演过程中存在的问题进行了有益探讨.     

延庆、怀来地区地壳深部磁性构造与地震的研究

应用三维磁性层反演理论和方法，对延庆、怀来地区航磁资料进行了数据处理，反演计算了该区磁性基底埋深、居里等温面埋深和视磁化强度分布。揭示了延庆盆地、矾山盆地、怀来盆地、涿鹿盆地等四个相互联通盆地的磁性基底的定量特征。对该区地震发生的深部原因和地壳内不同特性块体与地震的关系进行了探讨；对该区地震分布的特点进行了研究；初步提出了该区地震的危险区划和今后的重点监测区。     

Crustal seismic anisotropy in southeastern Capital area, China

Shear-wave splitting parameters of 24 stations in southeastern Capital area of North China (38.5°N~39.85°N, 115.5°E ~118.5°E) are obtained with systematic analysis method of shear-wave splitting (SAM) based on the data recorded by Capital Area Seismograph Network (CASN) from 2002 to 2005. The results show that the average polarization of fast shear-wave in southeastern Capital area is consistent with regional maximum horizontal prin- cipal compressive stress in the area, and is also consistent with maximum horizontal principal compressive strain from GPS in North China. The average shear-wave splitting in southeastern Capital area (in basin) is different from that in northwestern Capital area where uplifts and basin exist, which means that tectonics can be related to shear-wave splitting results. Research also shows that the distribution of faults around stations can obviously affect the shear-wave splitting results, and complicated distribution of faults can result in much more scatter of shear-wave splitting. Moreover, in the north and south of the studied area (southeastern Capital area), the polariza- tions of fast shear-wave are not very consistent, which may be related to differences in tectonic and stress for the two areas.     

云南地区地壳各向异性及其动力学意义

本文使用中国地震局地壳应力研究所2010—2011年期间在云南地区布设21个宽频带野外流动地震台记录到的波形资料,经时间域迭代反褶积求取远震接收函数,并挑选高质量Pms （莫霍面转换）震相,利用切向能量最小化方法获得283对高信噪比的径向和切向对应的Pms分裂参数,从而得到云南地区各台下方地壳各向异性. 结果显示,研究区内慢波时间延迟量在0.125 s和0.40 s之间变化,平均为0.25 s,且各向异性强弱与构造分布有一定相关性. 在扬子地台和保山地块表现为相对较强的各向异性,而思茅地块相对弱些,说明这些块体受下地壳流的影响作用各不相同. 从各向异性快波方向分布来看,在扬子地台和思茅地块除红河断裂带和澜沧江断裂带走向变化明显地区（如YNL04和YNL12台）外,各向异性方向均与断裂带走向近似平行,说明研究区内大型断裂带控制着下地壳流的构造变形. 腾冲地区的各向异性与其他三个块体均不相同,在该块体内部各向异性快波方向近似呈现出以火山为中心发散状分布,可能说明腾冲火山下方地幔热物质上涌到达下地壳后受上地壳的阻挡作用向四周发散的原因.     

Preliminary study on characteristics of earthquake precursor of earth resistivity anisotropy degree in East China

Introduction The degree of earth-resistivity anisotropy was described (MAO, et al, 1995, 1998) as follows: S=|1\nn∑I=1(ρSN\ρEW)I|-1|×103 n=6(1) whereρNS and ρEW are monthly mean values of earth resistivity in the direction of NS and EW, respectively, S is the half-year value. Equation (1) shows that if ρNS=ρEW, then S =0 and the electrical property of medium is isotropic; if ρNS≠ρEW, then S≠0 and the electrical property of medium is anisotropic. When S increases, the anisotropy of electrical property of medium is enhanced. Because the rightside of equation (1) is absolute value and the possibility ofρNS＞ρEW and ρNS＜ρEW can be different at different stations, the increase or decrease of S cannot reflect the relative changes between ρNS and ρEW. FENG, et al (2000) defined S as follows:     

华北不同构造块体地壳结构及其对比研究

华北古大陆块体经多期构造运动的改造使地壳构造具有明显的分块特征. 利用华北地区近30条、共约两万公里的深地震测深资料及成果,进一步研究华北各次级块体内部地壳细结构,对比分析各块体的结构差异. 根据不同的地壳结构特征,华北地壳可分为三大类：西部鄂尔多斯盆地地壳结构简单,基底结构完整,为稳定古大陆地壳;华北中部隆起区太行山及北部阴山、燕山隆起区地壳结构相对简单,中部地壳和下地壳局部区域轻微速度逆转,可能与该区域地壳增厚隆升的壳内介质解耦形变有关;华北东部裂陷盆地地壳结构复杂, 基底下陷、破碎,壳内介质松散、速度低,Moho上隆、地壳减薄,横向结构差异明显,显示了新生地壳构造特征. 在此基础上,综合研究、探讨了华北地壳分块构造以及与之相关的动力学演化.     

用剪切波分裂研究台湾北部地壳各向异性

研究主要使用台湾北部13个地震台站记录到的1991年7月～2002年12月的波形数据,采用剪切波分裂SAM分析方法,对台湾北部地区的剪切波分裂特征进行了研究.发现位于宜兰盆地内的台站的快剪切波优势偏振方向为近E-W方向,而位于山脉(西部麓山带、雪山山脉和中央山脉)的台站的快剪切波优势偏振方向为NNE向或NE方向.位于海...     

Crack－induced anisotropy in the crust from shear wave splitting observed in Tangshan region，North China

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Crustal structure and local seismicity in Colombia

Using P-wave travel time data from local seismicity, the crustal structure ofthe central and southern part of Colombia was determined. A very stableand narrow range of possible velocity models for the region was obtainedusing travel time inversion. This range of models was tested with earthquakelocations to select the best velocity model. The 1D velocity modelproposed has five layers over a halfspace, with interfaces at depths of 4,25, 32, 40 and 100 km and P-wave velocities of 4.8, 6.6, 7.0, 8.0, 8.1and 8.2 km/sec, respectively. According to this model the Moho lies at32 km depth on average. For P-waves, the station corrections range from–0.62 to 0.44 sec and for S-wave they range from –1.17 to 0.62 sec.These low variations in station residuals indicate small lateral velocitychanges and therefore the velocity model found should be well suited forearthquake locations and future starting model for 3D tomography studies.Using this new velocity model, the local earthquakes were relocated. Theshallow seismicity, < 30 km, clearly shows the borders betweentectonic plates and also the main fault systems in the region. The deepseismicity, > 80 km, shows two subduction zones in the country: theCauca subduction zone with a strike of N120^°E, dip of 35^°and thickness of 35 km, and the Bucaramanga subduction zone which has,for the northern part, a strike of N103^°E, dip of 27^° andthickness undetermined and, for the southern part, a strike ofN115^°E, dip of 40^° and thickness of 20 km. Based ondifferences of thickness of brittle crust in the subducted slab and spatialdistribution of the seismicity, the Cauca and Bucaramanga subduction zonesseem to represent independent processes. The Cauca subduction seems tobe connected to the process of the Nazca plate being subducted under theNorth Andes Block. In the Bucaramanga subduction zone, the transitionbetween southern and northern parts and changes in geometry of the slabseem to be gradual and there is no evidence of a tear in the slab, howeverthe local seismicity does not allow us to determine which plate or plates arebeing subducted. The Bucaramanga nest appears to be included into thesubducted slab.     

Study on fine structure of crust-mantle transition zone in Yanqing-Hailai basin based on CDP and DSS data

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2-D crustal Poisson's ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region

Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.