Hierarchical community detection and functional area identification with OSM roads and complex graph theory     

Ye Hong 《International journal of geographical information science》2019,33(8):1569-1587

An in-depth analysis of the urban road network structure plays an essential role in understanding the distribution of urban functional area. To concentrate topologically densely connected road segments, communities of urban roads provide a new perspective to study the structure of the network. In this study, based on OpenStreetMap (OSM) roads and points-of-interest (POI) data, we employ the Infomap community detection algorithm to identify the hierarchical community in city roads and explore the shaping role roads play in urban space and their relation with the distribution of urban functional areas. The results demonstrate that the distribution of communities at different levels in Guangzhou, China reflects the urban spatial relation between the suburbs and urban centers and within urban centers. Moreover, the study explored the functional area characteristics at the community scale and identified the distribution of various functional areas. Owing to the structure information contained in the identification process, the detected community can be used as a basic unit in other urban studies. In general, with the community-based network, this study proposes a novel method of combining city roads with urban space and functional zones, providing necessary data support and academic guidance for government and urban planners.  相似文献   

Impacts of small cascaded hydropower plants on river discharge in a basin in Southern China     

Xu Xiao  Xiaohong Chen  Lilan Zhang  Rouyi Lai  Jie Liu 《水文研究》2019,33(10):1420-1433

The run‐off volume altered by the construction of hydropower plants affects ecohydrological processes in catchments. Although the impacts of large hydropower plants have been well documented in the literature, few studies have been conducted on the impacts of small cascaded hydropower plants (SCHPs). To evaluate the impacts of SCHPs on river flow, we chose a representative basin affected by hydropower projects and, to a lesser degree, by other human activities, that is, the Qiuxiang River basin in Southern China. The observed river discharge and climate data during the period of 1958–2016 were investigated. The datasets were divided into a low‐impact period and a high‐impact period based on the number of SCHPs and the capacities of the reservoirs. The daily river discharge alteration was assessed by applying the Indicators of Hydrologic Alteration. To separate the impact of the SCHPs on the local river discharge from that of climate‐related precipitation, the back‐propagation neural network was used to simulate the monthly average river discharge process. An abnormal result was found: Unlike large reservoirs in large watersheds, the SCHPs regulated the flows during the flood season but were not able to mitigate the droughts during the dry season due to their limited storage and the commonly occurring inappropriate interregulations of the SCHPs. The SCHPs also reduced the annual average river discharge in the research basin. The contribution of the SCHPs to the river discharge changes was 85.37%, much higher than the contributions of climate change (13.43%) and other human activities (1.20%). The results demonstrated that the impacts of the SCHPs were different from those of large dams and reservoirs that regulate floods and relieve droughts. It is necessary to raise the awareness of the impacts of these river barriers.  相似文献   

Hydrological impact of a reservoir network in the upper Gan River Basin,China     

Ningpeng Dong  Zhongbo Yu  Chuanguo Yang  Mingxiang Yang  Wenzhuo Wang 《水文研究》2019,33(12):1709-1723

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Characteristics of the Seismic Waves from a New Active Source Based on Methane Gaseous Detonation   总被引：1，自引：0，他引：1  

WANG Weitao  WANG Xiang  MENG Chuanmin  DONG Shi  WANG Zhigang  XIE Junju  WANG Baoshan  YANG Wei  XU Shanhui  WANG Tao 《中国地震研究》2019,33(2):354-366

Active seismic sources are critical for obtaining high resolution images of the subsurface. For active imaging in urban areas, environment friendly and green seismic sources are required. In present work, we introduce a new type of green active source based on the gaseous detonation of methane and oxygen. When fired in a closed container, the chemical reaction, i.e. gaseous detonation, will produce high pressure air over 150MPa. Seismic waves are produced when high pressure air is quickly released to impact the surroundings. The first field experiment of this active source was carried out in December, 2017 in Jingdezhen, Jiangxi Province, where a series of active sources were excited to explore their potential in mine exploration. In current work, we analyzed the seismic waves recorded by near-field accelerators and a dense short-period seismic array and compared them with those from a mobile airgun source, another kind of active source by releasing high pressure air into water. The results demonstrate that it can be used for high resolution near surface imaging. Firstly, the gaseous detonation productions are harmless CO₂ and water, making it a green explosive source. Secondly, the dominant seismic frequencies are 10-80Hz and a single shot can be recorded up to 15km, making it suitable for local structure investigations. Thirdly, it can be excited in vertical wells, similar to traditional powder explosive sources. It can also act as an additional on-land active source to airgun sources, which requires a suitable water body as intermediate media to generate repeating signals. Moreover, the short duration and high frequency signature of the source signals make it safe with no damage to nearby buildings. These make it convenient to excite in urban areas. As a new explosive source, the excitation equipment and conditions, such as gas ratio, sink depth and air-releasing directions, need further investigation to improve seismic wave generation efficiency.  相似文献   

2017年九寨沟MS7.0地震场地特征分析     

吴效勇  王晓青  袁小祥  窦爱霞  丁香 《地震》2019,39(4):147-157

场地条件对地震动具有较大影响, 研究不同场地条件下的地震动特征对地震动的校正具有重要意义。 本文以九寨沟地震为例, 收集了66个台站的198条三分量强震观测记录和SRTM(Shuttle Radar Topography Mission)公里格网的DEM(Digital Elevation Model)数据, 从多个角度对场地特征进行分析。 首先根据坡度法使用DEM数据对九寨沟特征进行了场地分类, 然后讨论了不同场地类型下的加速度时程、 加速度反应谱、 地震动衰减等地震动特征。 研究表明, 缺少实测资料的情况下, 地形坡度可以作为Vs30(地表以下30 m范围的平均剪切波速度)的一种替代指标, 利用坡度法可以较快速地对场地进行分类; 利用强震观测记录能够从多角度对台站的场地特征进行分析, 不同场地类型对地震动影响不同, 其中, 土层对地震动具有明显的放大效应。 该结论可以为地震动结果的校正提供依据。  相似文献   

滇东北地区地震弱活动前兆异常特征研究     

李利波  付虹  李琼  何德强 《地震》2019,39(3):115-126

以鲁甸M_S6.5地震震中附近的鲁甸大坪子泉水氡、 水质观测资料为基础, 通过对其地震前后的异常特征进行差异性对比, 分析认为震前地震活动丛集, 水氡、 水质异常持续时间较长, 幅度较大, 表现为破年变异常现象; 震后为小震群弱活动, 水氡、 水质异常幅度相对较小, 持续时间较短, 多次出现同步转折, 表现为介质弱化区的前兆异常特征。 从水样测试结果, GNSS位移观测资料、 GPS时间序列曲线及地震活动性等方面分析了鲁甸水氡、 水质的异常机理, 认为鲁甸的水质离子组分群体异常, 与区域的变形活动有关, 局部应力的不断积累, 加剧了地下深部物质活动及构造活动; 近期的同步转折现象属于介质弱化区应力调整状态下的前兆异常。  相似文献   

南北地震带地震震源机制解和现今应力特征     

崔子健  陈章立  王勤彩  李君 《地震》2019,39(1):1-10

基于CAP方法, 使用地震波形资料, 计算得到了2009年1月~2017年8月期间南北地震带及周边区域466个3.5级以上地震震源机制解。 在补充收集1976年1月~2017年8月GCMT公布的259个4.5级以上地震震源机制解的基础上, 分析了南北地震带地震震源机制解和应力特征。 震源机制空间分布显示, 不同断裂带、 块体间表现出不同的震源机制空间分布特征, 该特征与南北地震带不同段落活动构造性质基本吻合。 作为青藏高原东边界的南北地震带, 由于动力环境复杂, 其内部P轴方向具有明显的差异性。 这种差异主要表现为: 南北地震带北段P轴呈NE向分布; 龙门山断裂带及周边除NE段P轴取向为NW—NNW向外, 其他地段P轴近EW向; 川滇菱形块体内部P轴呈NNW向, 而其西边界以西呈NNE向, 东边界以东呈NW向, 应力方向转换带的与川滇菱形块体边界基本一致。 整体而言, 南北地震带及近邻P轴方向由北到南发生了顺时针转动。  相似文献   

2018年9月8日云南墨江5.9级地震预测回顾与资料论证     

杨建文  赵家本  张鹏映  何应文  王军  茶文剑 《中国地震》2019,35(3):509-520

通过分析墨江5.9级地震前预测意见和预测资料，认为云南地区M≥5.5地震平静异常突出，M≥5.0地震连续间隔时间达200天以上，通海2次5.0级地震震级偏小是震前地震活动异常的显著特征；通海地震的指示意义、前兆异常M≥5.7地震中期和M≥5.0地震短临综合预测指标是判断地震短期可能性的主要依据；1900年以来，通海50km范围内M≥5.0地震后云南地区发生M≥5.0地震优势对应关系和GNSS表征的区域面应变变化特征为地点判定提供了线索。墨江5.9级地震的预测经验及资料的论证丰富了对地震孕育复杂性的认识，为震例积累了新的资料。  相似文献   

Erosion probability model of base-soil particle migration into a granular filter under local flow     

《国际泥沙研究》2019,34(5):455-460

To avoid soil erosion, filters often are installed in the downstream cross section of dams. However, the probability of piping failure and the filter effect both are related to the soil pore network. Previous erosion probability models for a base soil-filter system do not consider the effect of local flow. Therefore, in this study, an improved erosion probability model is established, in which the deviation between the main flow direction of the soil and the local flow direction in the filter was considered based on a previous model. The improved model was validated by numerical simulation. The erosion probability was found to affect the reasonable evaluation of filter effects and the optimal selection of filter thickness. The controlling constriction size in a granular filter was increased to D_c^* = D_c5 with a filter thickness of 59 D_m.  相似文献   

地震计保温效能分析     

安全  翟浩  赵铁锁 《地震地磁观测与研究》2019,40(2):131-134

为内蒙古自治区大沁塔拉地震台地震计安装保温罩，利用台基噪声计算软件，计算保温前后地震观测数据PSD概率密度函数，分析保温罩对地震计的效能，结果发现，保温罩安装后，地震计温度变化平稳，地震观测数据质量提高。  相似文献