Variation in reach‐scale thalweg‐migration intensity in a braided reach of the lower Yellow River in 1986–2015          下载免费PDF全文

Jie Li  Junqiang Xia  Meirong Zhou  Shanshan Deng  Xiaolei Zhang 《地球表面变化过程与地形》2017,42(13):1952-1962

Thalweg migration of an alluvial river plays a key role in channel evolution, which may influence the effect of existing river training works and biodiversity on floodplains, and cause losses in riparian land and property. The braided reach of the Lower Yellow River underwent continuous channel aggradation during the period from 1986 to 1999, and then remarkable channel degradation in 1999–2015 owing to the state of operation of the Xiaolangdi Reservoir in 1999. Here we quantify associated thalweg migration changes and identify the key influencing factor in the braided reach. Thalweg‐migration distances and intensities at section‐ and reach‐scales were calculated during the past 30 years from 1986 to 2015, in order to investigate the characteristics of thalweg migration in the reach. There was a 47% reduction in the reach‐scale thalweg‐migration distance and a 35% reduction in the corresponding migration intensity after the reservoir operation. It is also revealed that fluvial erosion intensity is a dominant factor in controlling the thalweg migration, based on the investigation into various influencing factors in the study reach. The thalweg‐migration intensity of the braided reach can be expressed as a power function of the previous four‐year average fluvial erosion intensity. The calculated thalweg‐migration intensities in 1986–2015 using the proposed relation generally agree with the observed data. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A NEW FINDING OF SURFACE RUPTURE ZONES ASSOCIATED WITH THE 1936 LINGSHAN M6(3/4) EARTHQUAKE,GUANGXI, CHINA          下载免费PDF全文

LI Xi-guang  LI Bing-su  PAN Li-li  NIE Guan-jun  WU Jiao-bing  LU Jun-hong  YAN Xiao-min  LI Zhi-yong 《地震地质》2017,39(4):689-698

On April 1, 1936, an M6(3/4) earthquake occurred on the Fangcheng-lingshan Fault. This event is the biggest historical earthquake on the coastal seismic zone, South China ever. But so far, no any findings about the surface rupture of this event have been reported. This paper is the first to find several intact surface rupture zones associated with the 1936 Lingshan seismic event, in the areas of Gaotang, Jiaogengping etc. on the northeast segment of the Fangcheng-Lingshan Fault. According to the field work, the surface rupture stretches to 10km and distributes along NE direction in front of Luoyang Mountain, represented by earthquake scarp, extensional fracture, dextrally faulted gully and river system etc. The characteristics of surface ruptures and faulted landforms indicate that the surface rupture is of normal-dextral strike slip faulting. The trenching on this fault exposed that at least three seismic events have been recorded, including two historical earthquake events and the latest one is the 1936 Lingshan M6(3/4) earthquake. These surface rupture zones are the key to the detection of seismogenic structure and the re-estimate of magnitude of this event. The new finding of these surface rupture zones would be particularly significant for the detection of the seismogenic structure of Lingshan M6(3/4) earthquake.  相似文献   

基于经验模态分解的分数维地震随机噪声衰减方法          下载免费PDF全文

颜中辉  栾锡武  王赟  潘军  方刚  施剑 《地球物理学报》2017,60(7):2845-2857

经验模态分解算法(EMD)是一种基于有效波和噪声尺度差异进行波场分离的随机噪声压制方法,但由于实际地震数据波场复杂,导致模态混叠较严重,仅凭该方法进行去噪很难达到理想效果.本文基于EMD算法对信号多尺度的分解特性,结合Hausdorff维数约束条件,提出一种用于地震随机噪声衰减的新方法.首先对地震数据进行EMD自适应分解,得到一系列具有不同尺度的、分形自相似性的固有模态分量(IMF);在此基础上,基于有效信号和随机噪声的Hausdorff维数差异,识别混有随机噪声的IMF分量,对该分量进行相关的阈值滤波处理,从而实现有效信号和随机噪声的有效分离.文中从仿真信号试验出发,到模型地震数据和实际地震数据的测试处理,同时与传统的EMD处理结果相对比.结果表明,本文方法对地震随机噪声的衰减有更佳的压制效果.  相似文献   

鲁科一井上白垩统沉积岩岩石磁学和天然剩磁分析:兼论利用剩磁方向恢复钻孔岩芯原始方位的可行性          下载免费PDF全文

韩非  秦华峰  季强  孙靖鹏  邓成龙  潘永信 《地球物理学报》2017,60(12):4730-4740

本文对"鲁科一井"(CCSD-LK-Ⅰ)768.9~1112.3m之间的上白垩统沉积岩样品进行了岩石磁学、磁化率各向异性(AMS)以及天然剩磁组分的研究.在此基础上,分析了利用特征剩磁(ChRM)和黏滞剩磁(VRM)方向恢复岩芯原始方位的可行性.三轴等温剩磁热退磁曲线、磁滞回线、反向场退磁曲线、一阶反转曲线等岩石磁学测量结果表明,沉积岩的主要载磁矿物为磁铁矿和赤铁矿.335块样品的AMS测量结果表明磁化率椭球主轴的最大轴K1和中间轴K2与水平面夹角较小,最小轴K3接近垂直于水平面分布,说明沉积岩保留了原始沉积磁组构特征.系统热退磁实验表明,多数样品在25~350℃和500~690℃温度段分别获得VRM和ChRM分量.利用ChRM偏角方向,并考虑构造旋转量校正,对VRM偏角方向进行恢复,Fisher统计得到DVRM=-1.3°,IVRM=59.6°,与当地现代地磁场方向(D=-6.7°,I=53.9°)基本一致.用ChRM偏角方向对磁化率主轴K1偏角方向进行校正,校正的结果为:D_(ch_K1)=349.2°,I_(ch_K1)=-0.7°.本文研究结果对于地质勘探中利用古地磁学方法恢复钻孔岩芯原始方位具有一定参考意义.  相似文献   

汶川8.0级地震环境剪应力特征研究   总被引：1，自引：0，他引：1       下载免费PDF全文

田秀丰  尹志文  张璇  潘章容  张卫东 《地震工程学报》2017,39(3):527-533

基于甘肃强震固定台和流动观测记录的汶川8.0级地震主震及余震加速度资料,选用三分向记录均完整的87次地震(震级范围为3.0~8.0级),根据用位错理论二维断裂模式推导的震源峰值加速度与环境剪应力关系式计算汶川地震序列的环境剪应力值,探讨其环境剪应力场特征。结果表明,环境剪应力和矩震级有较好的相关性,3~5级地震对应的应力值多在3~6 MPa,5~6级多在6~9 MPa,6~7级多在9MPa以上,且环境剪应力对震源深度也有较强的依赖性。  相似文献   

南天山西段地震尾波Q值研究     

尼鲁帕尔&#;买买吐孙  夏爱国  海仁妮莎 《中国地震》2017,33(3):432-441

基于新疆地震台网的数字地震波形资料,采用Aki的地震尾波单次散射模型,选取了南天山西段10个台站周围60km范围内M_S≥2.0的397次地震事件计算并得到了不同台站的尾波Qc值。结果显示,南天山西段尾波Q_0值平均值在140~390之间,其中喀什台和乌恰台Q_0值最低;频率相关系数η的平均值在0.62~1.00之间,拟合平均Q值与对应频率之间的关系结果为Q=261.2±110.8f~(0.80±0.28),表明该地区是以低Q_0高η值为特征的构造活跃区。  相似文献   

杭州湾枯季水沙若干特征分析     

葛灿  潘存鸿  张沈阳 《海洋工程》2021,39(2):70-79

根据2014年1月及2017年2月杭州湾大、小潮水沙资料,计算了流速、含沙量、单宽潮量、单宽输沙量,进而分析了潮周期断面净潮量、净输沙量和区域冲淤分布。研究发现杭州湾涨、落潮平均流速比值整体较20世纪八九十年代增大,绝大部分区域大于1.0,涨潮流相对增强,澉浦南岸和金山北岸尤为显著。含沙量平面上分布澉浦、杭州湾南岸两个高值区(大潮大于3 kg/m³,小潮大于1.3 kg/m³)以及北岸湾口至乍浦之间的低值区(大潮小于2 kg/m³,小潮小于0.9 kg/m³),随潮汛变化显著,最大含沙量浓度通常滞后于急流时刻。各测站涨、落潮量和输沙量呈现“大涨大落”和“大进大出”的特征,造成杭州湾短时间尺度内的“大冲大淤”。大潮两涨两落金山与乍浦、乍浦与澉浦之间区域净输沙量可达几千万吨,净冲淤则在几百万吨。  相似文献   

滇池水体中微囊藻毒素含量变化与环境因子的相关性研究   总被引：24，自引：1，他引：23  

潘晓洁  常锋毅  沈银武  刘永定  李敦海  李根保  肖邦定 《湖泊科学》2006,18(6):572-577

本文对2003年4-12月滇池马村湾、海东湾微囊藻毒素和总磷、总氮、溶解氧、透明度、光照强度、叶绿素a、pH值、水温及微囊藻种群优势度进行了分析,讨论了以上指标在滇池马村湾和海东湾的分布和月变化情况以及与微囊藻毒素含量之间的关系．相关性分析表明马村湾、海东湾微囊藻毒素在水体中分布与总氮和氮磷比之间呈现非常显著的负相关性(P<0．01);与透明度、光照强度和微囊藻种群优势度存在显著的正相关性(P<0．05)．在影响微囊藻毒素的各因素中,运用多因素逐步回归分析得知马村湾、海东湾微囊藻毒素浓度主要南水体的总氮、总磷、叶绿素a和溶解氧以及透明度决定(R2=0．560,P<0．017)．  相似文献   

Influence of land use on the persistence effect of riverine phosphorus          下载免费PDF全文

Dingjiang Chen  Fang Xia  Xu Shang  YuanYuan Liu  Randy A. Dahlgren  Kun Mei 《水文研究》2018,32(1):118-125

The persistence effect contribution of legacy nutrients is often cited as a reason for little or no improvement in water quality following extensive implementation of watershed nutrient mitigation actions, yet there is limited knowledge concerning factors influencing this response, often called the “persistence effect.” Here, we adopted detrended fluctuation analysis and Spearman analysis methods to assess the influence of land use on the watershed phosphorus (P) persistence effect, using monthly water quality records during 2010–2016 in 13 catchments within a drinking water reservoir watershed in eastern China. Detrended fluctuation analysis was used to calculate the Hurst exponent α to assess watershed legacy P characteristics (α  ≈ 0.5, α  > 0.5, and α  < 0.5 indicate white noise, persistence, and anti‐persistence, respectively). Results showed weak to strong P persistence (0.60–0.81) in the time series of riverine P in the 13 catchments. The Hurst exponent α had negative relationships with agricultural land (R = ?.47, p = .11) and developed land (R = ?.67, p = .01) and a positive relationship with forest land cover (R = .48, p = .10). The persistence effect of riverine P was mainly determined by retention ability (biogeochemical legacy) and migration efficiency (hydrological legacy). A catchment with strong retention capacity (e.g., biomass uptake/storage and soil PO₄ sorption) and low migration efficiency results in a stronger persistence effect for riverine P. In practice, source control is more effective in catchments with weak persistence, whereas sink control (e.g., riparian buffers and wetlands) is preferred in catchments with strong persistence effects.  相似文献   

基于新《电力设施抗震设计规范》的地震动随机模型参数研究          下载免费PDF全文

田利  高国栋  盖霞 《地震工程学报》2018,40(6):1206-1210

根据新《电力设施抗震设计规范》(GB50260-2013)对随机地震动功率谱参数的取值进行分析。介绍新《电力设施抗震设计规范》中设计反应谱,推导设计谱到功率谱的转换过程。选取常用的Clough-Penzien修正过滤白噪声模型作为拟合函数,通过功率谱参数拟合,得到不同场地类别、不同抗震设防烈度下的地震动模型参数。该研究成果可为电力工程抗震设计分析提供参考。  相似文献