Three-dimensional arbitrarily anisotropic modeling for time-domain airborne electromagnetic surveys

Electrically anisotropic strata are abundant in nature, so their study can help our data interpretation and our understanding of the processes of geodynamics. However, current data processing generally assumes isotropic conditions when surveying anisotropic structures, which may cause discrepancies between reality and electromagnetic data interpretation. Moreover, the anisotropic interpretation of the time-domain airborne electromagnetic (TDAEM) method is still confined to one dimensional (1D) cases, and the corresponding three-dimensional (3D) numerical simulations are still in development. In this study, we expanded the 3D TDAEM modeling of arbitrarily anisotropic media. First, through coordinate rotation of isotropic conductivity, we obtained the conductivity tensor of an arbitrary anisotropic rock. Next, we incorporated this into Maxwell’s equations, using a regular hexahedral grid of vector finite elements to subdivide the solution area. A direct solver software package provided the solution for the sparse linear equations that resulted. Analytical solutions were used to verify the accuracy and feasibility of the algorithm. The proven model was then applied to analyze the effects of arbitrary anisotropy in 3D TDAEM via the distribution of responses and amplitude changes, which revealed that different anisotropy situations strongly affected the responses of TDAEM.     

活动断层探察数据的信息编码优化研究

从20世纪90年代起,研究人员就开始探索活动断层探察数据的制作、存储与管理。迄今为止,已经获得了大量的活动断层探察数据,建成了一套系统的数据组织体系,为减轻地震灾害的相关研究提供了数据和技术支撑。近年来,随着活动断层数据库信息的扩充,初期设计的部分属性信息编码已不适用。为了形成适应当前工作的属性信息编码体系,本文以活动断层数据库建设体系为基础,对数据库属性值代码进行信息分类和编码优化。文章将数据库属性值代码分为字符型单一含义值、数值型单一含义值及复合含义值,分别进行编码规则设计,最终优化了数据库属性信息编码体系,提高了从建库到数据应用的数据录入、检测、制图自动化、数据分析等环节的效率。     

河北省数字水位短临异常特征研究——以2016年唐山4.2级地震为例

2016年9月10日河北唐山发生M_S 4.2地震,以该震为例,研究河北省地下流体观测井水位震前异常变化特征。结果表明：①震中区域观测井水位异常变化形态一般为缓变型,震中外围观测井水位异常变化形态一般为骤变型;②距离震中越近,观测井水位异常出现越早,异常持续时间越长;③临近地震震中时,观测井水位异常有从震中向外围扩散的趋势;④观测井水位异常最大幅度与井震距关系不大。     

河北北部地区平均波速比分析

河北省北部地区地质构造较为复杂,历史上多次发生破坏性地震。基于河北数字地震台网震相到时报告数据,使用和达法,计算2006年1月至2015年10月河北省北部地区平均波速比,分析部分地震前波速比时序变化特征,发现震前波速比数值呈现正常—低值异常—恢复—发震的异常演变特征,为地震波速比变化与地震前兆相关性研究提供一定参考信息。     

柱脚可更换的地下结构抗震截断柱技术性能分析

基于功能可快速恢复的抗震韧性设计目标,结合提升中柱水平变形能力的地下结构抗震截断柱技术,提出了可有效避免由于柱脚应力集中产生的破坏和震后可快速更换的地下结构中柱设计思路,其中复合截断中柱与顶、底纵梁采用剪力销栓连接,柱脚部采用局部增强或增韧可更换材料进一步替代。采用数值模型分析了复合柱的承载力、变形能力以及柱脚采用不同材料时对复合柱变形和承载力的影响规律,并与整体现浇柱进行了对比。结果表明:一般截断柱的承载能力明显低于整体现浇柱,但其变形能力远远优于整体现浇柱。随着中柱变形的增加,一般截断柱中柱柱脚位置出现明显的“应力集中”现象,局部增强或增韧材料的采用可有效避免复合截断柱脚部因应力集中而产生的破坏,提高了复合截断柱的水平变形能力。     

水平分层土层系统等效阻尼比的简化计算方法

在实际工程场地中,很多土层可视为水平分层,各层土的物理和力学性质存在差异,其中包括土的振动阻尼比。本文讨论水平分层土层系统的等效阻尼比的近似计算方法,基于5个不同的加权函数推导了10种等效阻尼比的计算公式。通过2个算例,分别以等效阻尼比为参数计算水平分层土层的地震反应,并与准确解相比较,分析了不同等效阻尼比近似计算方法的计算精度。数值结果表明,若等效阻尼比计算方法选择不恰当,会导致土层地震反应的计算结果出现较大误差。针对2种不同类型的水平分层土层,建议采用基于三角形分布的加权函数来计算土层系统的等效阻尼比。     

Major advances in studies of the physical geography and living environment of China during the past 70 years and future prospects

The natural environment provides material essentials for human survival and development. The characteristics,processes, regional differentiation and forcing mechanisms of the elements of the natural environment(e.g. geomorphology,climate, hydrology, soil, etc.) are the main objects of research in physical geography. China has a complex natural environment and huge regional differentiation and therefore it provides outstanding reserach opportunities in physical geography. This review summarizes the most important developments and the main contributions of research in the physical geography and human living environment in China during the past 70 years. The major topics addressed are the uplift of the Tibetan Plateau and the evolution of its cryosphere, the development of fluvial systems, the acidification of the vast arid region of the Asian interior, variations in the monsoon and westerly climate systems on multiple timescales, the development of lakes and wetlands, the watershed system model, soil erosion, past human-environment interactions, biogeography, and physical geographic zonality. After briefly introducing international research developments, we review the history of research in physical geography in China, focusing on the major achievements and major academic debates, and finally we summarize the status of current research and the future prospects. We propose that in the context of the national demand for the construction of an ecological civilization, we should make full use of the research findings of physical geography, and determine the patterns and mechanisms of natural environmental processes in order to continue to promote the continued contribution of physical geography to national development strategies, and to further contribute to the theory of physical geography from a global perspective.     

柴达木盆地北缘反S形褶皱冲断带变形机制的物理模拟研究

阿尔金断裂走滑变形的侧向传递十分有限,难以解释柴达木盆地北缘反S形褶皱冲断带的形成。本文设计的一组具有不同性质基底条件的弧形边界砂箱实验表明:刚性块体边界形态控制了褶皱冲断带走向和构造格局,同时基底力学性质也有部分影响作用,因而可用“刚性块体弧形边界联合作用”来解释其形成,即:1)冷湖反S形褶皱冲断带的形成是赛什腾山前弧形边界与昆特依凹陷弧形边界联合作用的结果;2)鄂博梁反S形褶皱冲断带的形成是昆特依凹陷与一里坪凹陷弧形边界联合作用的结果;3)位于一里坪凹陷南侧、与阿尔金断裂左行走滑变形呈反牵引关系的褶皱冲断带则与该凹陷西南侧向南西突出的弧形边界有关。     

基于无人机摄影测量技术的地震地表破裂带定量参数提取 ——以1709年中卫南M7½地震为例

本文首先介绍了无人机摄影测量技术获取数字高程模型(digital elevation model,缩写为DEM)和地貌数据(正射影像)的作业流程,对比分析了三种不同质量密集点云生成的DEM在水平位置和高程上的差异;然后以1709年中卫南M7?大地震的主体地表破裂带为例,提取其上地震断层的垂直位错量和水平位移量.研究结果...     

Using Sr isotopes to trace the geographic origins of Chinese mitten crabs

Identifying the geographic origins of Chinese mitten crabs is important for food safety and fair market competition. In this study, we used strontium (Sr) isotopes as a tool to trace the geographic origins of Chinese mitten crabs. Chinese mitten crabs, water, and different types of crab feed were collected from four different lakes for Sr isotope analyses. The results showed that the Sr isotope compositions of the different parts from one single crab were consistent within error, indicating that any piece of a crab could be used to represent the Sr isotope characteristics of the whole crab. The Sr isotope compositions of Chinese mitten crabs from the same lake were consistent within the analytical error, and the values were similar to the Sr isotope composition of the water from the same lake. However, the Sr isotope compositions of water and crabs from different lakes are significantly different. Therefore, the Sr isotope compositions of Chinese mitten crabs are mainly controlled by lake water composition, while the impact of feed is limited. This study provides an effective method for tracing the geographic origins of Chinese mitten crabs.