河南及邻区瑞利波群速度噪声层析成像

本文选取河南及邻区39个宽频带和甚宽频带地震台站记录的2014年1月～2015年12月垂直分量的连续波形资料,通过波形互相关和叠加运算得到台站间的经验格林函数,并用时频分析方法提取了498条瑞利波群速度频散曲线,进而采用噪声层析成像方法反演获得了河南及邻区8～25s的瑞利波群速度分布图像。结果表明,8s周期的群速度分布与地表构造特征密切相关,平原地区表现为低速异常,而基岩出露的山区呈现为高速异常;14s、20s周期的群速度在山区表现的高速异常与8s相似,说明中上地壳与地壳浅部结构有一定的相关性和继承性;8～20s周期的群速度在华北平原地区存在低速异常范围随周期增加而减小的现象。华北平原地区在下地壳表现出的低速异常,可能与大陆地壳减薄有关。大致以太行-武陵重力梯度带为界,下地壳表现出的西部低速、东部至研究区中部高速异常差异,体现了地壳东薄西厚的结构特征。     

Effects of snow-depth change on spring runoff in cryosphere areas of China

Based on snow-depth and measured runoff data in the 19 river basins of the cryosphere areas of China, changes in cold season snow depth (CSSD) and spring runoff, and the relationship between CSSD and spring runoff were analysed. Decreasing trends in CSSD were detected mainly in the plains (plateaus), while increasing trends were found mainly in the mountainous regions. Different combinations of precipitation and temperature may be responsible for these results. The response of spring runoff to CSSD change varied greatly under climate warming. The runoff in April and May was commonly affected by CSSD, while the runoff in March was less affected by CSSD, but more by the increasing temperature causing more snowmelt in March. Due to relatively greater snow accumulation in spring, the runoff during spring was less affected by CSSD in the southern Tienshan Mountains.     

Automated watershed subdivision for simulations using multi-objective optimization

A qualitative trial-and-error approach is commonly used to define watershed subdivisions through varying a single topographic threshold value. A methodology has been developed to quantitatively determine spatially variable threshold values using topography and a user-defined landscape reference layer. Optimization and topographic parameterization algorithms were integrated to create solutions that minimize the number of sub-watersheds and maximize the agreement between the discretized watershed and the reference layer. The system was evaluated using different reference datasets such as soil type, land management, and landscape form. Comparison of simulated results indicated that the scenario using land management as the reference layer yielded results closer to the scenario subdivided using a constant topographic threshold but with approximately 10 times more sub-catchments and therefore indicating customization of the watershed subdivision to the user-defined reference layer. The proposed optimization technology could be used in adequately applying watershed modeling technology in developing conservation practice implementation plans.     

Laboratory and theoretical evaluation of impact of packing density,particle shape,and uniformity coefficient on erodibility of coarse-grained soil particles

Sedimentation – including erosion, transport, and deposition of coarse-grained particles – is a primary and growing environmental, engineering, and agricultural issue around the world. Soil erosion occurs when the hydrodynamic force induced by flowing water exceeds the geotechnical resistance of soils, as measured by critical shear stress for initiation of soil-particle motion. Even though various quantitative methods have been suggested with respect to different types of soil, the most widely accepted formula to estimate critical shear stress for coarse-grained soil is a direct function of the median grain size of the soil particles; however, the erosion resistance of soils also varies with other geotechnical properties, such as packing density, particle shape, and uniformity coefficient. Thus, in this study, a combined rolling–lift model for particle detachment was derived based on theoretical analysis. A series of experimental flume tests were conducted with specimens prepared with standard soil types, as well as laboratory-prepared mixtures of coarse-grained soil to validate the theoretical model and determine the effect of other geotechnical properties on the erosion characteristics of coarse grains, coupled with the effect of median particle size. The results indicated that the median grain size is the primary variable determining the resistance of coarse grains, but the critical shear stress also varies with the packing density of the soil matrix. In addition, angular particles show more erosion resistance than rounded particles, and the erosion potential of a soil decreased when the grain is well graded (higher value of uniformity coefficient). Additionally, regression analysis was performed to quantify the effect of each parameter on the critical shear stress of coarse grains. © 2020 John Wiley & Sons, Ltd.     

多维地震激励下曲线梁桥简化模型及最不利输入方向研究

曲线梁桥只有在某一特定方向输入地震动时,结构某点或某截面的内力(或应力)才能达到最大值,需要沿多个可能方向输入计算才能确定地震动最不利输入方向。根据隔震曲线梁桥受力特点,将桥梁上部结构和桥墩简化均具有两个水平自由度和一个围绕质量中心轴扭转自由度的堆积质量模型,建立双质点六自由度简化分析模型,通过求解曲线梁桥的动力学方程研究结构的动力特性和地震动行为。算例表明,双质点模型计算结果与传统的有限元模型基本一致,且计算方法简单,可以考虑各种敏感因素的影响,借助编程更适合提出规律性的设计方法。进而在双质点模型基础上应用MATLAB编程探讨多维地震作用下曲线梁桥地震波最不利输入方向的问题,针对不同参数的隔震曲线梁桥,改变相关参数后只需运行一次就可以实现最不利输入角度的确定,可为有限元法最不利地震波输入方向的确定提供参考,并大大减少多个方向输入试算的工作量。     

甘东南地区水氡浓度的临界慢化现象研究

本文将临界慢化理论应用于甘东南地区水氡浓度观测资料的处理中,以2008年5月12日汶川M_S8.0地震、2013年7月22日甘肃岷县—漳县M_S6.6地震为例,计算表征临界慢化现象的自相关系数和方差。计算结果表明,甘东南地区多个台站的水氡浓度观测资料在两次地震前均存在较明显的临界慢化现象。并从空间分布、持续时间、变化形态方面分析了异常点水氡浓度变化的临界慢化特征,结合水氡异常的水动力学机制和异常点所在构造,认为2次地震前的临界慢化现象与地震的发生有一定关系。     

平原农区贫困地理格局及其分异机制——以安徽省利辛县为例

以安徽省利辛县为例,运用空间自相关分析和地理探测器模型,验证了平原农区是否存在空间贫困陷阱,定量探测了平原农区农村贫困化主导因子,揭示了平原农区贫困化地域分异机制。结果表明：①平原农区农村贫困化存在明显的地域分异规律和空间集聚性,张庄村、贾桥村、徐田村、刘染村、陆楼村长期处于贫困发生率的“高高集聚”区,空间上存在贫困陷阱现象;②区位条件、公共服务等第二地理要素对平原农区贫困化分异起主导作用,自然环境、资源禀赋等第一地理要素的影响作用较弱,到县城中心距离、到主干道距离、公共服务点数量和人均耕地面积是利辛县农村贫困化的主导因子;③交互探测的结果显示,主导因素交互作用的驱动力呈非线性增强。平原农区在精准扶贫的实践中,应重视第二地理要素对贫困分异的增强作用,加强交通设施投入,合理布局公共服务点,促进基本公共服务均等化,为平原农区减贫提供基础保障。为了实现这一目标,亟待强化贫困地理学的贫困发生机制、贫困地理格局和减贫路径研究。     

基于高速公路流的东北大都市区边界识别与结构特征研究

利用高速公路收费站数据分析东北大都市区的空间边界与中心-外围结构特征。研究发现,① 中心城市高速公路流随距离的分布符合距离衰减规律,随规模位序的累积分布符合“二八定律”,但在具体的指标阈值上却表现出显著差异。② 四大都市区在空间上相连,以较小的国土面积承载了区域主要的社会经济活动。沈阳都市区和大连都市区在城镇关联体系中已实现融合;沈阳都市区、长春都市区、哈尔滨都市区间的空间联系则相对松散。③ 高速公路流空间下,各大都市区中心-外围空间结构表现出空间圈层、功能廊道和边界切割的典型特征。     

桂西北喀斯特山区人口分布特征及其与自然因素的关系

选择第六次全国人口普查的最小行政单位——乡（镇）为基本单元,利用Lorenz曲线和空间相关分析方法分析桂西北喀斯特山区乡（镇）级尺度下的人口空间分布特征,运用地理探测器方法探测自然因素单独和叠加作用后对区域人口空间分布的影响强度。结果表明： 乡（镇）级研究尺度下的人口空间分布具有不均衡性特征,呈现一般显著正相关和一定的聚集性; 各自然因素空间分布对人口分布的影响呈现显著差异,研究区西北和中南部没有喀斯特分布的乡镇,人口密度随有利于人类居住因素的增加而增加,但平均人口密度仅79人/km ²。东部和南部有喀斯特分布的乡镇,人口密度与自然因素空间分布并非简单的增减关系,其随喀斯特分布面积的变化呈现起伏波动。 地理探测器的因子探测结果显示对人口空间分布的影响强度最大的为海拔高度,交互探测结果显示,任意两个自然因素叠加交互作用后的影响强度呈现非线性增强和双因子增强。可见,桂西北喀斯特山区与其他地区类似,海拔高度是影响人口空间分布的最主要因素之一,但喀斯特山区的河网密度及特有的地质地貌等因素对其人口的空间分布具有较强的催化作用,与其他因素叠加交互作用可进一步加强对人口分布的影响。     

连片特困地区物流业发展的减贫效应测度

为科学测度连片特困地区物流业发展的减贫效应,基于熵权-TOPISIS模型对贫困程度进行评估,并以综合贫困指数为被解释变量,表征物流业发展水平的6个指标(货物周转量、物流业增加值、公路网密度、规模以上工业产值、社会消费零售总额和货物平均运距)为解释变量,引入空间杜宾模型(SDM)计量县域尺度下物流业发展对区域减贫的直接影响和空间溢出效应。研究表明：物流业增加值、路网密度和规模以上工业产值对区域减贫具有显著的直接效应,物流业增加值每增加10⁸元,本县(区)的综合贫困指数将降低0.060;货物周转量、公路网密度和规模以上工业产值对区域减贫的间接(空间溢出)作用明显,本县(区)货物周转量每增加10⁸ t·km^-1,毗邻县(区)的综合贫困指数将降低0.020。均衡物流产业的空间分布、完善物流基础设施和调动贫困县(区)物流需求,是发挥物流减贫效应的有效措施。