2016年新疆呼图壁6.2级地震前b值异常特征研究   总被引：1，自引：0，他引：1       下载免费PDF全文

刘子璇  冯建刚  王维桐 《地震工程学报》2020,42(1):150-156

利用2009年以来中国地震台网中心地震编目资料,以2016年新疆呼图壁6.2级地震作为研究对象,采用最大似然法进行b值空间扫描计算,获取震前震中及其邻区地震b值的空间图像。研究结果显示,2016年呼图壁6.2级地震发生在震前显著低b值区域,该异常特征可能反映了地震孕育的应力积累过程,印证了b值的物理意义。  相似文献   

2019年长宁M_S6.0地震邻区分钟采样地电场分析     

王玮铭  谭大诚 《地震》2020,40(3):41-51

2019年6月17日四川宜宾市长宁县发生M_S6.0地震, 分析震中周边600 km内7个地电场台站观测分钟值数据, 获知震前2个月左右红格等6个台站地电场均存在不同方位之间、 同方位长短极距之间的相关系数持续降低, 6月17日这些相关系数基本降至最低, 反映出这6个场地的地电场在此次地震前后发生了非均匀变化; 同时, 这6个台站的地电场优势方位角出现了约45°或90°跃变, 并伴有显著发散或收窄现象。分析表明长宁M_S6.0地震前后, 这6个场地的多种地电场异常现象具有局部场地效应、 时间准同步性。  相似文献   

顾及地形起伏的无人机影像覆盖分析方法     

张衡  李骁  叶朋飞 《测绘通报》2020,(1):102-106

使用无人机实施测绘航空摄影时，由于无人机相对航高较低，地面起伏会对无人机影像的分辨率、覆盖范围、重叠度造成较大的影响，影像成果会出现分辨率不足、重叠度不够、覆盖漏洞等缺陷。针对这一情况，本文提出了一种利用数字微分正解法的计算方法，借助DEM准确计算每张影像的覆盖范围，并使用FME软件高效生成全部影像的覆盖范围。经过实际使用，验证了该方法可以在航线设计阶段准确预测并分析全部影像的覆盖范围、重叠度，因此可及时发现设计问题并调整航线。该方法可以有效减少因地形起伏造成的影像覆盖缺陷，减少返工现象，从整体上提高了作业效率。  相似文献   

资源三号和天绘一号卫星影像无控联合平差精度分析     

郑义  张宏伟  杜晓  张俊辉  周琦  林尚纬  陈利军 《测绘通报》2020,(7):10

近年来国产卫星传感器类型日益丰富，使用自主可控的国产卫星影像进行生产和研究的需求越来越大，多源国产卫星影像联合平差的精度分析显得尤为重要。本文针对在立体测图生产中，资源三号卫星影像在时相较旧、噪声较大、云覆盖和摄影漏洞等特殊困难的条件下，利用天绘一号卫星影像进行补漏生产的情况，最终分析并验证了两者无控联合平差的可行性和成果精度。  相似文献   

X波段高分辨率SAR数据土石坝表面相干性时序变化分析     

单强  姜卫平  李陶  陈露璐 《测绘通报》2020,(10):1-5

本文以深圳公明水库6个中小型土石坝为试验区，利用10景1 m分辨率升降轨X波段TerraSAR影像和坝体附近连续气象站的降雨量数据，研究了坝体表面相干性的时序变化与雷达本地入射角及降雨的关系。试验结果表明，混凝土面板和草坡平均相干性均会随本地入射角增加而减小，同时，草坡表面平均相干性在有微小降雨的情况下就会快速下降0.1~0.2，差分干涉图的噪声增大；混凝土面板对微小的降雨敏感度小，但是在暴雨情况下将导致其表面完全失相干。上述结果表明，针对中小土石坝坡体变形监测应当顾及坝体的坡度及入射角选择合适的雷达成像参数，同时应充分利用降雨资料评估干涉图失相干情况，剔除噪声数据。  相似文献   

基于三维激光扫描技术的钢结构扰度检测及应用     

宋云记  王晓民  王智 《测绘通报》2020,(12):160-163

钢结构在长期荷载及不均匀受力的作用下会产生空间变形，其中扰度是其重要的衡量指标。通常采用全站仪采集钢结构轴线上若干特征点进行分析、计算，由于钢结构特征点难以捕捉，测量存在误差，并且有限的空间离散点难以全面反应钢结构空间变形。本文采用徕卡RTC360三维激光扫描进行钢结构扰度测量；介绍了其作业流程及数据处理方法；利用标靶将各个测站的三维点云拼接成一个整体；采用拟合的方法提取空间特征点及轴线；利用三维点云构建空间模型，并与设计模型进行碰撞分析；可全面地反映钢结构的空间变形情况。  相似文献   

Seismic reliability assessment and the nonergodicity in the modelling parameter uncertainties     

Fatemeh Jalayer  Hossein Ebrahimian 《地震工程与结构动力学》2020,49(5):434-457

Modelling uncertainty can significantly affect the structural seismic reliability assessment. However, the limit state excursion due to this type of uncertainty may not be described by a Poisson process as it lacks renewal properties with the occurrence of each earthquake event. Furthermore, considering uncertainties related to ground motion representation by employing recorded ground motions together with modelling uncertainties is not a trivial task. Robust fragility assessment, proposed previously by the authors, employs the structural response to recorded ground motion as data in order to update prescribed seismic fragility models. Robust fragility can be extremely efficient for considering also the structural modelling uncertainties by creating a dataset of one-to-one assignments of structural model realizations and as-recorded ground motions. This can reduce the computational effort by more than 1 order of magnitude. However, it should be kept in mind that the fragility concept itself is based on the underlying assumption of Poisson-type renewal. Using the concept of updated robust reliability, considering both the uncertainty in ground motion representation based on as-recorded ground motion and non ergodic modelling uncertainties, the error introduced through structural reliability assessment by using the robust fragility is quantified. It is shown through specific application to an existing RC frame that this error is quite small when the product of the time interval and the standard deviation of failure rate is small and is on the conservative side.  相似文献   

Efficient strong motion duration of pulse-like records for nonlinear structural analyses     

Constantinos C. Repapis  Petros P. Mimoglou  Vicky V. Dimakopoulou  Ioannis N. Psycharis  Ioannis M. Taflampas 《地震工程与结构动力学》2020,49(5):479-497

The special interest produced by near-field directivity records and their effect on structural response has given a new significance in the velocity time history, its pulse-like content, and relevant parameters and indices. Recent research has shown that directivity pulses inherent in these records govern the linear and the nonlinear response of a wide range of structures. Based on this observation, it is suggested in this paper that a truncated ground motion, limited to the duration of the predominant velocity pulse, can be efficiently used to predict the structural response, instead of the base motion with the total duration, reducing significantly the required runtimes. The proposed methodology is verified for a series of medium to high rise reinforced concrete buildings, for which nonlinear time-history analyses are performed for a vast suite of pulse-like near-field records applied as base excitations with their total duration and the proposed truncated one. Comparison of the results for the response displacements and forces shows very good agreement, permitting the acceptance of the pulse duration as the efficient strong motion time interval of the original record, which determines the response and, thus, it can be used for nonlinear structural analyses.  相似文献   

Stormflow threshold behaviour in a subtropical mountainous headwater catchment during forest recovery period     

Lezhang Wei  Zhijun Qiu  Guangyi Zhou  Tsuyoshi Kinouchi  Yu Liu 《水文研究》2020,34(8):1728-1740

Forest ecohydrological feedbacks complicate the threshold behaviour of stormflow response to precipitation or wetting conditions on a long-term scale (e.g. several years). In this study, the threshold behaviours in an evergreen-deciduous mixed forested headwater catchment in southern China were examined during 2009–2015, when damaged vegetation was recovering after the great 2008 Chinese ice and snowstorm. The non-uniqueness of the thresholds and the slow and rapid responses of stormflow at the outlet of the catchment in different hydro-climate datasets with different maximum values of gross precipitation (P) and sums of precipitation and antecedent soil moisture index (P + ASI) were assessed. The thresholds of P and P + ASI required to trigger stormflows (i.e. ‘generation thresholds’) and the transition from slow to rapid responses of stormflow (i.e. ‘rise thresholds’) were compared both seasonally and annually. The results indicated significant differences in the analysed datasets, highlighting the need to compare thresholds with care to avoid misinterpretation. Seasonal variations in threshold behaviours in the catchment suggested that vegetation canopy interception contributed to higher rise thresholds, and wetter conditions resulted in higher runoff sensitivity to precipitation during the growing and rainy seasons. Furthermore, the generation thresholds were higher in the dormant season, possibly due to drier soil moisture conditions in the near-channel areas. During the vegetation recovery period, the annual generation thresholds increased, however the rise thresholds did not exhibit a similar trend. The rapid stormflow response above the threshold decreased, possibly due to transpiration and interception of the recovered vegetation. However, the slow stormflow response to small rainfall events below the thresholds was higher in wetter years but lower in drier years, suggesting that the total water input dominated the stormflow response during small rainfall events. In conclusion, the seasonal and annual variations in threshold behaviours highlight that vegetation recovery and hydro-climatic conditions had a notable impact on the stormflow response.  相似文献   

Geostatistical features of streambed vertical hydraulic conductivities in Frenchman Creek Watershed in Western Nebraska     

Olufemi P. Abimbola  Aaron R. Mittelstet  Troy E. Gilmore 《水文研究》2020,34(16):3481-3491

This study evaluated the spatial variability of streambed vertical hydraulic conductivity (K_v) in different stream morphologies in the Frenchman Creek Watershed, Western Nebraska, using different variogram models. Streambed K_v values were determined in situ using permeameter tests at 10 sites in Frenchman, Stinking Water and Spring Creeks during the dry season at baseflow conditions. Measurements were taken both in straight and meandering stream channels during a 5 day period at similar flow conditions. Each test site comprised of at least three transects and each transect comprised of at least three K_v measurements. Linear, Gaussian, exponential and spherical variogram models were used with Kriging gridding method for the 10 sites. As a goodness-of-fit statistic for the variogram models, cross-validation results showed differences in the median absolute deviation and the standard deviation of the cross-validation residuals. Results show that using the geometric means of the 10 sites for gridding performs better than using either all the K_v values from the 93 permeameter tests or 10 K_v values from the middle transects and centre permeameters. Incorporating both the spatial variability and the uncertainty involved in the measurement at a reach segment can yield more accurate grid results that can be useful in calibrating K_v at watershed or sub-watershed scales in distributed hydrological models.  相似文献