地中海直布罗陀海峡附近内孤立波的地球物理特征          下载免费PDF全文

孙绍箐  张锟  宋海斌 《地球物理学报》2019,62(7):2622-2632

本文主要利用地震海洋学方法研究地中海直布罗陀海峡附近内孤立波的结构特征，此处内孤立波为第一模态下沉型，为中幅度和大幅度内孤立波，垂向振幅最大可达74.5 m，振幅随深度增加呈增大趋势，传播速度随振幅增大而增大，可以确定"真"最大振幅位置位于密跃层附近.由于类多普勒效应和孤立波与测量船之间存在夹角的原因，从地震剖面上得到的为视半高宽参数，需要进行校正后才能得到比较真实的半高宽参数，校正后半高宽最高可达到1721.8 m，但是校正后的半高宽与理论结果有些差距，这可能与内孤立波的发育稳定程度有关.随着内孤立波包不断向东运动，整体波宽变大，垂向速度变小.本文将地震海洋学方法拓展应用于地中海区域内孤立波分析，进一步证明了利用地震海洋学方法研究海水运动的可行性.  相似文献   

唐山地区波速比变化特征研究     

王亚茹  宋昭  刘晓丹  郭蕾  王妍  王时  宫猛  王想 《大地测量与地球动力学》2019,39(7):686-690

选取唐山地区2008~2018年震相数据，利用单台多震和达法和多台多震和达法分别计算波速比，结合研究区内的地震活动对波速比的变化特征进行研究。结果显示，多台多震和达法得到的波速比结果较为稳定，而单台多震和达法得到的结果变化幅度大，显示更多细节；唐山地区ML≥4.5地震发生前单台波速比存在不同程度的异常，异常台站的方位与地震具有一定的对应性。  相似文献   

Temporal and spatial evolution of surface sediments characteristics in the Dagu River estuary and their dynamic response mechanism     

《China Geology》2019,2(3):325-332

Based on the 39 surface sediment samples collected in the flood season and the dry season in 2012 respectively and the measured hydrological data in October 2012, the sediment grain size characteristics has been analyzed and the response mechanism of surface sediments to estuarine hydrodynamics was revealed by calculating the range of waves and tidal currents. The results show that: (1) The grain size of the surface sediment samples decreased gradually from land to sea in the flood season. The fine sediment was redistributed under marine hydrodynamics in the dry season and the sediments showed coarser tendency ingeneral; (2) tidal current stirring sediment was very obvious in Dagu River estuary area, and wave stirring sediments mainly occurred in the tidal flat area and estuary sand bar area; (3) in the flood season, surface sediment sat the estuary were transported towards south and southeast. In the dry season, surface sediments were transported towards southwest at the north area of Jiaozhou Bay Bridge, and sediments were transported towards northeast area at the south of Jiaozhou Bay Bridge.  相似文献   

海上风电升压站平台高程确定标准的合理性研究     

潘晓春 《海洋技术学报》2019,38(6):83-88

为保证海上风电升压电站建设的经济合理与安全可靠,合理确定海上风电升压电站平台高程十分必要。文中从波浪与潮位的遭遇组合、最大波高取值与现行相关标准的比较、最大波峰高度计算的合理性等方面,全面分析了确定海上风电升压站平台高程各组成项取值标准的合理性,研究认为现行标准明显偏高。建议海上升压站平台底部高程按"100年一遇极端高水位+重现期50年波列累积频率1%的最大波峰高度+安全超高"确定。结合工程实例计算分析,按本文建议可使海上升压站平台高程明显降低,从而节省工程造价,还可减轻升压站工程对周边风机的遮蔽影响,以达到多发电量的效果。  相似文献   

Characteristics of the main inorganic nitrogen accumulation in surface water and groundwater of wetland succession zones          下载免费PDF全文

ZHOU Nian-qing  LI Tian-shui  ZHAO Shan  XIA Xue-min 《地下水科学与工程》2019,7(2):173-181

Based on the observation of a complete hydrological year from June 2014 to May 2015, the temporal and spatial variations of the main inorganic nitrogen(MIN, referring to NO_3~--N, NO_2~--N, NH_4~+-N) in surface water and groundwater of the Li River and the Yuan River wetland succession zones are analyzed. The Li River and the Yuan River are located in agricultural and non-agricultural areas, and this study focus on the influence of surface water level and groundwater depth and precipitation on nitrogen pollution. The results show that NO_3~-N in surface water accounts for 70%-90% of MIN, but it does not exceed the limit of national drinking water surface water standard. Groundwater is seriously polluted by H_4~+-N. Based on the groundwater quality standard of H_4~+-N, the groundwater quality in the Li River exceeds Class III water standard throughout the year, and the exceeding months' proportion of Yuan River reaches 58.3%. Compared with the Yuan River, MIN in groundwater of the Li River shows significant temporal and spatial variations owing to the influence of agricultural fertilization. The correlation between the concentrations of MIN and surface water level is poor, while the fitting effect of quadratic correlation between H_4~+-N concentration and groundwater depth is the best(R~2=0.9384), NO_3~-N is the next(R~2=0.5128), NO_2~--N is the worst(R~2=0.2798). The equation of meteoric water line is δD =7.83δ~(18) O+12.21, indicating that both surface water and groundwater come from atmospheric precipitation. Surface infiltration is the main cause of groundwater H_4~+-N pollution. Rainfall infiltration in non-fertilization seasons reduces groundwater nitrogen pollution, while rainfall leaching farming and fertilization aggravate groundwater nitrogen pollution.  相似文献   

Obtaining the distribution of quiescent periods directly from the power spectral densities of Sea waves     

《Applied Ocean Research》2019

There is a growing practical interest in the ability to increase the sea states at which marine operations can be safely undertaken by exploiting the quiescent periods that are well known to exist under a wide range of sea conditions. While the actual prediction of quiescent periods at sea for the control of operations is a deterministic process, the long term planning of future maritime tasks that rely on these quiescent periods is a statistical process involving the anticipated quiescence properties of the forecasted sea conditions in the geographical region of interest. It is in principle possible to obtain such data in tabular form either large scale simulation or from field data. However, such simulations are computationally intensive and libraries of appropriate field data are not common. Thus, it is clearly attractive to develop techniques that exploit standard wave spectral models for describing the quiescence statistics directly from such spectra. The present study focuses upon such techniques and is a first step towards the production of a computationally low-cost quiescence prediction tool and compares its efficacy against simulations. Two significant properties emerge for a large class of wave spectral models that encompasses the ubiquitous Neumann and Pierson Moskowitz or Bretschneider forms. Firstly, the auto-correlation function of the wave profile that are required to produce the quiescence property can be obtained analytically in terms of standard special functions. This considerably reduces the computational cost making desktop computer-based planning tools a reality. Secondly, for each class of these parametric spectra, the probability of a given number of consecutive wave heights (normalised to the significant wave heights) less than some critical value is in fact independent of absolute wave height. Thus, for a broad class of practically interesting wave spectra all that is required to obtain the statistical distribution of the quiescent periods is simple rescaling.  相似文献   

一种优化的频率域三维声波有限差分模拟方法   总被引：1，自引：1，他引：0       下载免费PDF全文

范娜  成景旺  秦雷  赵连锋  谢小碧  姚振兴 《地球物理学报》2018,61(3):1095-1108

为提高频率域有限差分（FD，finite-difference）正演模拟技术的计算精度和效率，基于旋转坐标系统的优化差分格式被广泛应用，但是只应用于正方形网格的情况.基于平均导数法（ADM）的优化差分格式，应用于正方形和长方形网格模拟.这些频率域有限差分算子，各自具有不同的差分格式和对应的优化系数求解表达式.本文基于三维声波方程发展了一种新的优化方法，只要给定FD模板形式，可直接构造频散方程，求取FD模板上各节点的优化系数.此方法的优点在于频率域FD算子的优化系数对应各个节点，可扩展优化其他格式.运用此优化方法，计算得到了不同空间采样间距比情况下27点和7点格式的优化系数.数值实验表明，优化27点格式与ADM 27点格式具有相同的精度，优化7点格式比经典的7点格式具有更小的数值频散.  相似文献   

各向异性介质的矢量波场分离与应用          下载免费PDF全文

芦俊  石瑛  杨春颖 《地球物理学报》2018,61(8):3310-3323

针对裂缝各向异性介质，本文提出一种非正交假设下的矢量波场分离方法.本文首先对多分量地震勘探中常见的波型泄漏现象进行了数学描述，提出在纵、横波波场分离的同时应该考虑恢复纵、横波的矢量振幅.为了对裂缝方位角与各向异性系数进行定量预测，本文将矢量波场分离拆分成三个步骤来实施：第一步，用Z、R两分量的仿射坐标系变换分离ZR平面内的P波投影与SV波；第二步，用ZR平面内的P波投影与T分量的仿射坐标系变换分离P波与SH波；第三步，用纯净的SV波与SH波的成像剖面分离快慢横波，并预测裂缝发育参数.模型数据与实际数据的试验结果表明，本文提出的纵、横波波场分离方法能够获得完整的矢量振幅信息，并提供裂缝预测的精度.  相似文献   

Elastic one-return boundary element method and hybrid elastic thin-slab propagator for strong-contrast media with sharp boundaries          下载免费PDF全文

Zengxi Ge  Yi Luo  Yuyan Ma  Rushan Wu 《地震科学（英文版）》2018,31(2):92-99

In this paper, we developed the theory and algorithm of an elastic one-way boundary element method(BEM) and a corresponding hybrid elastic thin-slab propagator for earth media with sharp boundaries between strong contrast media. This approach can takes the advantage of accurate boundary condition of BEM and completely overcomes the weak contrast limitation of the perturbationtheory based one-way operator approach. The one-way BEM is a smooth boundary approximation, which avoids huge matrix operations in exact full BEM. In addition, the one-way BEM can model the primary-only transmitted and reflected waves and therefore is a valuable tool in elastic imaging and inversion. Through numerical tests for some simple models,we proved the validity and efficiency of the proposed method.  相似文献   

基于背景噪声研究青藏高原东北缘瑞利波相速度和方位各向异性   总被引：2，自引：1，他引：1       下载免费PDF全文

王琼  高原 《地球物理学报》2018,61(7):2760-2775

本研究收集了甘肃、青海、宁夏等118个宽频带数字地震台站的连续波形资料，利用噪声互相关，经过计算和筛选，在5~38 s范围内，共得到5773条瑞利波相速度频散曲线.然后采用1°×1°的网格划分，反演获得青藏高原东北缘相速度和方位各向异性分布.结果表明：短周期8~12 s内，鄂尔多斯从低速异常变为高速异常；该周期范围内各向异性结果与区域断裂走向有很好的一致性.18~25 s周期内，祁连地块、松潘-甘孜地块、羌塘地块低速异常范围逐渐变大，随周期增加地壳低速异常与人工探测结果相符；鄂尔多斯表现为速度随周期增加逐渐变大，说明其中下地壳速度相对偏高，不存在低速异常；该周期范围内的各向异性特征表现为，祁连地块和松潘甘孜地块大致呈NW-SE方向，而青藏高原内部快波方向显示了顺时针旋转的形态.在30~35 s范围内面波速度主要受莫霍面深度和莫霍面附近介质速度的影响，与地壳厚度分布有非常好的吻合.综合不同方法获得的各向异性研究结果，支持印度-欧亚板块的碰撞使青藏高原东北缘地壳发生缩短和逐渐隆升的观点，认为整个岩石圈的垂直缩短变形是青藏高原东北缘的主要形成机制.  相似文献