四川盆地深部地壳结构——深地震反射剖面探测

四川盆地位于扬子地块的西北部,被褶皱构造带所围绕,受周缘构造带的侧向挤压作用,盆地卷入了多期次和多边界的构造变形,为开展盆山耦合作用及多边界、多期次构造叠加与复合关系的研究提供了不可多得的理想野外实验室.为揭示四川盆地地壳结构,本文通过对3条不同时间采集的深地震反射剖面数据进行拼接联线处理,获得跨越四川盆地的330 km深地震反射偏移成果剖面,揭示了四川盆地地壳上地幔细结构:沉积层从西北向东南逐渐变薄,在龙门山前沉积层厚度超过15 km,在华蓥山下沉积层减薄到~8 km,且褶皱变形形成华蓥山薄皮褶皱冲断带;莫霍面出现在13~15 s(双程走时),埋深约40~45 km;并发现从下地壳延伸至地幔的东南向的倾斜反射,从13 s向下延伸至18 s,结合四川盆地及其周边地区其他地球物理和地球化学花岗岩同位素年龄等资料,我们认为这些倾斜反射层是扬子克拉通地台西北缘发生的新元古代俯冲的遗迹.     

羌塘盆地中部地区地壳S波速度结构及构造意义

羌塘盆地是我国最大的海相盆地.本文根据在羌塘盆地内布设的27个宽频带地震观测台站记录的远震波形数据,利用非线性复谱比反演算法得到各台站下方100 km深度范围内S波速度结构.结果表明.羌塘地区Moho深度较为平缓,平均深度为61 km;北羌塘地壳内低速层广泛分布;北羌塘具有两个较大的沉积盆地,龙尾错和白滩湖坳陷,沉积厚度分别有10 km和15 km.尽管北羌塘下地壳受到强烈的新生代火山岩作用改造,但是这种深部岩浆热作用会加速烃源岩中有机质的热演化历程.北羌塘两个盆地具有很好的油气前景.与北羌塘低速层分布相比,南羌塘下低速层更深,可能与班公怒江洋于中生代的俯冲消减及拉萨地体北向俯冲有关.     

辽阳灯塔M_S5.1地震震源深度分析

对不同震中距台站的记录采用入射角法、s PL-Pg等震相到时差,对辽宁地震台网记录采用单纯形法研究了辽阳灯塔5.1级地震的震源深度。结果表明,该地震震源深度应为14km,略大于目录给出的10km。利用四川松潘台、青海湟源台的远台记录也得到同样的结果。通过对辽宁1970年以来5.0级以上地震进行分析发现,辽宁地震的震源分布存在东西两侧偏深、中部偏浅、中部地区南浅北深的统计规律,灯塔地震震源深度符合该统计规律。     

利用接收函数方法研究中国东北东南部地区不同构造体的地壳特征

基于我们布设的探测深俯冲的中国东北地震台阵NECsaids台阵和固定地震台长时段的观测记录及NECESSArray流动台阵共计152个台站数据提取得到的33752条P波接收函数,采用H-κ叠加分析和共转换点（CCP）叠加成像等方法进行统一分析处理,并汇集他人接收函数研究结果得到中国东北东南部地区迄今为止最高分辨率的地壳厚度和平均波速比分布图像.对中国东北东南部地区不同构造体的地壳特征综合分析研究表明：研究区不同陆块的地壳属性存在明显差别,张广才岭地块中南部的地壳厚度和波速比与华北克拉通东北缘相当,地壳厚度同地表地形之间显示有明显的正相关关系;松辽地块东南缘地壳最薄、波速比最高,地壳厚度同壳内波速比之间显示出明显的负相关关系;兴凯地块西部地区的地壳结构表现为稍厚的地壳厚度和研究区内最低的壳内波速比,其地壳厚度同壳内波速比之间亦显示出明显的负相关关系;佳木斯地块西南缘在具有"正常"的壳内波速比同时地壳最厚.研究区内的郯庐断裂带北延段在切穿其下Moho面的同时表现出南北分段的特征：北段（44.4°N—47°N）两分支之下的Moho面整体下凹,而南段（41.5°N—43.3°N）两分支之下的Moho面则整体上隆.长白山天池火山下方表现为Moho面下凹沉落及高壳内波速比特征,推测其壳内岩浆囊很可能存在于火山口东北隅至少10 km的范围内.     

冀中坳陷中部现今热岩石圈厚度及地热学意义探讨

热岩石圈厚度是研究盆地的构造演化和板块动力学的重要参数,本文通过实测数据构建地壳分层模型,根据热传导的基本原理,计算了冀中坳陷中部的Moho面温度以及热岩石圈厚度,并探讨其地热学意义。结果表明:冀中坳陷中部的Moho面温度分布在500～600℃,西南侧整体温度较东北部高,热岩石圈厚度介于102～122km,其平面展布特征与华北克拉通热岩石圈厚度西厚东薄的特征相吻合,为华北克拉通受太平洋板块西向俯冲导致东部遭受破坏提供了依据,并且较薄的岩石圈使热流更易传导到地壳浅部,成为了该地区热异常的成因背景。     

基于混合聚类的岩体结构面优势分组方法

提出一种基于凝聚层次法和模糊C均值法的混合聚类法,用于对岩体结构面的优势组划分。该方法将结构面投放到在单位球面上,并使用欧式距离作为极点的相似性度量准则。先剔除结构面数据中的孤值产状,然后用凝聚层次法得到初步聚类结果,并将其作为FCM法的初始聚类中心,最后用FCM法划分优势组。通对人工生成产状样本的分组,验证了该法的正确性。将该方法应用于大藤峡坝址区实测的结构面数据的划分。在实测数据中寻找到两个孤值产状,成功将大藤峡D1y^1-3地层岩体结构面划分为两组,得到了符合实际的分组结果。     

CHARACTERISTICS OF SATELLITE GRAVITY FIELD AND SEISMOGENIC MECHANISM IN THE LONGMENSHAN FAULT ZONE

Longmenshan fault zone is a famous orogenic belt and seismic zone in the southeastern Tibetan plateau of China. The Wenchuan M_S8.0 earthquake on May 12, 2008 and the Ya'an M_S7.0 earthquake on April 20, 2013 occurred in the central-southern part of Longmenshan fault zone. Because of its complex geological structures, frequent earthquakes and special geographical locations, it has attracted the attention of many scholars around the world. Satellite gravity field has advantages in studying gravity field and gravity anomaly changes before and after earthquake. It covers wide range, can be updated regularly, without difficulty in terms of geographical restrictions, and is not affected by environmental factors such as weather, terrain and traffic. Therefore, the use of high-precision Earth satellite gravity field data inversion and interpretation of seismic phenomena has become a hot topic in earth science research. In order to understand satellite gravity field characteristics of the Longmenshan earthquake zone in the southeastern Tibetan plateau and its seismogenic mechanism of earthquake disasters, the satellite gravity data was used to present the terrain information of the study area. Then, by solving the regional gravity anomaly of the Moho surface, the crustal thickness of the study area was inverted, and the GPS velocity field data was used to detect the crustal deformation rate and direction of the study area. Combining the tectonic setting of the Longmenshan fault zone and the existing deep seismic sounding results of the previous researchers, the dynamic characteristics of the gravity time-varying field after the earthquake in the Longmenshan earthquake zone was analyzed and the mechanism of the earthquake was explored. The results show that the eastward flow of deep materials in the eastern Tibetan plateau is strongly blocked at the Longmenshan fault zone. The continuous collision and extrusion process result in a "deep drop zone" in the Moho surface, and the long-term stress effect is conducive to the formation of thrust-nappe and strike-slip structures. The Longmenshan earthquake zone was in the large-scale gradient zone of gravity change before the earthquake, the deep plastic fluid material transport velocity differed greatly, the fluid pressure was enhanced, and the rock mechanical strength in the seismic source region was weakened, which contributed to the intrusion of crustal fluid and the upwelling of the asthenosphere. As a result, the continuous accumulation of material and energy eventually led to continuous stress imbalance in the deep part and shear rupture of the deep weak structure, causing the occurrence of the thrust-nappe and strike-slip earthquake.     

Two-dimensional scattering of in-plane body waves due to a discontinuity in bedrock

The direct boundary integral equation technique is used to study in-plane surface amplification of in-plane seismic body waves for the case of an inhomogeneity in a bedrock half-space. In the studied soil configuration, a soil layer rests on a rock half-space which includes a rock inclusion. The rock inclusion considered is a semi-infinite horizontal rock layer in which its upper boundary borders the soil layer. Materials in the soil–rock configuration are considered viscoelastic except for the section of the rock half-space below the level of the rock inclusion which is considered elastic. A parametric study is performed to determine controlling factors for surface displacement due to in-plane body waves. The study investigates varying the stiffness and the thickness of the rock inclusion for a range of frequencies and wave incidence angles. Anti-plane waves for this type of soil-rock configuration have been addressed in a previous article by Heymsfield (Earthquake Engng. Struct. Dyn. 28 : 841–855 (1999)). Copyright © 1999 John Wiley & Sons, Ltd.     

Numerical modelling for clays with internal discontinuity surfaces

A numerical model capable of performing deformation analysis of a medium containing discontinuity surfaces is presented. The discontinuity can be either a crack, which can be open or closed, or a shear band. The model consists of two separate numerical algorithms, which are coupled together by means of the principle of superposition. In particular, an integral equation scheme based on the theory of dislocations is adopted for modelling the discontinuity, while a finite element discretization is used for the continuous medium. In this paper the discontinuity modelling is illustrated in detail, together with the specific formulation of the principle of superposition adopted, and some simple examples of application are presented. The well-known modelling approach based on Fracture Mechanics theory is also briefly discussed. The two models are compared and some advantages and drawbacks of each are pointed out, comments are made regarding their applicability in the specific case of soil mechanics, and conclusions are drawn as regards the conditions under which one or the other is appropriate. Finally, a full-scale example of deformation analysis using the proposed model is presented. Copyright © 1999 John Wiley & Sons, Ltd.     

利用接收函数反演青藏高原西部地壳S波速度结构

相对于宽阔的腹地,青藏高原西部南北向宽度仅约600km,却记录了印度和欧亚板块汇聚的深部过程及其响应.本文用22台宽频带流动地震台站在西缘构建了一条南北向探测剖面(~80°E,TW-80试验).利用接收函数反演剖面下方S波速度结构,综合西部已有的宽频带探测结果,分析认为:印度板块向北俯冲可能已到达班公湖—怒江缝合带附近,俯冲过程中下地壳发生榴辉岩化;喀拉昆仑断裂带、班公湖—怒江缝合带、阿尔金断裂带均为切穿地壳的深断裂,莫霍面发生错断;喀拉昆仑断裂带和龙木错断裂带之间的中上地壳没有发现连续的S波低速体,说明可能缺乏解耦层,支持青藏高原西部地壳为整体缩短增厚模式.