测线布设方向的不同对海底显示的影响

通过对几种典型海底沿不同方向布设测线所得到的拟合海底与原海底进行比较,发现测线布设方向的不同对海底显示的影响可归结为两种效应：平滑效应与伸缩效应。同时指出：对非线性平坦海底,沿梯度总方向布设测线、对于海底闭包按极坐标法布设测线可以很好地消除这两种效应的影响,从而达到完善海底显示的目的。实例分析结果验证了结论的正确性,该法可用于实际作业提高测深线布设对海底显示的准确度,同时直接构成海道测量智能设计系统的测深线自动布设建模。     

Upper mantle anisotropy beneath central and southwest Japan: An insight into subduction-induced mantle flow

Analysis of seismic anisotropy in the crust and mantle wedge above subduction zones gives much information about the dynamic processes inside the Earth. For this reason, we measure shear wave polarization anisotropy in the crust and upper mantle beneath central and southwestern Japan from local shallow, intermediate, and deep earthquakes occurring in the subducting Pacific slab. We analyze S phases from 198 earthquakes recorded at 42 Japanese F-net broadband seismic stations. This data set yields a total of 980 splitting parameter pairs for central and southwestern Japan. Dominant fast polarization directions of shear waves obtained at most stations in the Kanto–Izu–Tokai areas are oriented WNW–ESE, which are sub-parallel to the subduction direction of the Pacific plate. However, minor fast polarization directions are oriented in NNE–SSW directions being parallel to the strike of the Japan Trench, especially in the north of Izu Peninsula and the northern Tokai district. Generally, fast directions obtained at stations located in Kii Peninsula and the Chubu district are oriented ENE–WSW, almost parallel to the Nankai Trough, although some fast directions have NW–SE trends. The fast directions obtained at stations in northern central Honshu are oriented N–S. Delay times vary considerably and range from 0.1 to 1.25 s depending on the source depth and the degree of anisotropy along the ray path. These lateral variations in splitting character suggest that the nature of anisotropy is quite different between the studied areas. Beneath Kanto–Tokai, the observed WNW–ESE fast directions are probably caused by the olivine A-fabric induced by the corner flow. However, the slab morphology in this region is relatively complicated as the Philippine Sea slab is overriding the Pacific slab. This complex tectonic setting may induce lateral heterogeneity in the flow and stress state of the mantle wedge, and may have produced NNE–SSW orientations of fast directions. The ENE–WSW fast directions in Kii Peninsula and the Chubu district are more coherent and may be partly induced by the subduction of the Philippine Sea plate. The N–S fast directions in northern central Honshu might be produced by the trench-parallel stretching of the wedge due to the curved slab at the arc–arc junction.     

Seismic anisotropy of upper mantle in Sichuan and adjacent regions

Based on the polarization analysis of teleseismic SKS waveform data recorded at 94 broadband seis-mic stations in Sichuan and adjacent regions, the SKS fast-wave direction and the delay time between the fast and slow shear waves were determined at each station using the grid searching method of minimum transverse energy and the stacking analysis method, and the image of upper mantle anisot-ropy was acquired. The fast-wave polarization directions are mainly NW-SE in the study area, NWW-SEE to its northeast and NS to its west. The delay time falls into the interval [0.47 s, 1.68 s]. The spatial variation of the fast-wave directions is similar to the variation of GPS velocity directions. The anisotropic image indicates that the regional tectonic stress field has resulted in deformation and flow of upper mantle material, and made the alignment of upper mantle peridotite lattice parallel to the di-rection of material deformation. The crust-upper mantle deformation in Sichuan and adjacent regions accords with the mode of vertically coherent deformation. In the eastern Tibetan Plateau, the crustal material was extruded to east or southeast due to SE traction force of the upper mantle material. The extrusion might be obstructed by a rigid block under the Sichuan Basin and the crust has been de-formed. After a long-term accumulation of tectonic strain energy, the accumulative energy suddenly released in Yingxiu town of the Longmenshan region, and Wenchuan MS8.0 earthquake occurred.     

海洋水文多参数测量仪确定主波向的方法和应用

海洋水文多参数测量仪是南海海洋研究所新研制的一种可以同步测量海流、波浪、潮位、水温、电导率的仪器,利用同步观测压力和矢量流速估计海面方向谱的方法（PUV方法）可以计算得到海面方向谱,进而求得主波向。利用该仪器现场实测数据与荷兰MARKⅡ型“波浪骑士”方向浮标观测资料进行对比分析,表明两者的主波向吻合性好。     

OSMAR-S100便携式高频地波雷达海浪和海面风探测性能分析

OSMAR-S系列便携式高频地波雷达系统采用单极子/交叉环紧凑型天线阵,通过单站雷达即可实现有效探测距离约10km内海浪和海面风的单点观测。为了更好地了解OSMAR-S100雷达系统海浪和海面风的综合探测性能,于2013年1月29日至3月7日在台湾海峡西南部海域进行了雷达与浮标观测的对比试验,得到了有效波高、有效波周期、平均风速和平均风向数据。对比结果表明,OSMAR-S100便携式高频地波雷达可有效观测距雷达10km以内有效波高0.5m以上的海浪平均状况和平均风速5m/s以上的海面风,雷达反演有效波高和有效波周期的均方根误差分别为0.60m和1.60s,反演平均风速和平均风向的均方根误差为1.83m/s和16.7°。在未经区域化标定的情况下,此结果说明了该型雷达产品已初步具备了海浪和海面风的业务化观测水平。     

利用OD数据的人群活动分析

OD数据包含了城市居民活动模式,对于分析城市居民的活动、把握居民出行模式和城市空间结构具有重要意义.因此,本文提出了一种区域流动计算方法,运用区域流动倾向指数和区域主体流向来挖掘居民活动的模式.首先,根据时空粒度对区域的OD流进行统计,把OD数据映射到相应的区域内;然后,计算每个区域在不同时间段的流动倾向指数(包括流入...     

青藏高原东北缘地壳地震各向异性研究进展

青藏高原东北缘是青藏块体与华北块体的接触前缘部位,是研究青藏高原隆升扩张和深部动力学问题的重要区域。本文收集了青藏高原东北缘及其邻区由不同方法和不同资料获得的地壳地震各向异性结果,介绍了中上地壳和全地壳各向异性特征;结合区域地质构造、地表运动、构造应力和深部结构,分析了研究区域地壳各向异性的区域分布特征及其与地质构造的关系。结果表明,青藏高原东北缘地震各向异性存在明显的横向区域差异性,体现区域深部构造和地壳介质变形的复杂性;上地壳与全地壳的垂向差异性,反映出该区域可能存在各向异性分层现象。由于青藏高原隆升在其东北缘的伸展边界、物质运移及深部动力模式等尚处在探讨之中,结合多种数据并综合多种方法分析,有助于获得精细、准确的地震各向异性信息,为研究青藏高原隆升演化机制和深部动力模式提供有效的约束。     

Upper crustal anisotropy observed around the Longmenshan fault in the 2013 MS7.0 Lushan earthquake region

Based on the shear wave splitting analysis of the seismic recordings at 17 temporary stations and three permanent stations, we measured the shear wave splitting parameters (i.e., the polarization direction of fast shear wave and the time delay of slow wave) to perform a systematic analysis of the crustal seismic anisotropy around the Longmenshan fault in the 2013 M_S7.0 Lushan earthquake region. We observed apparent spatio-temporal characteristics in the shear wave splitting parameters. The spatial distribution of fast polarization directions showed a clear partitioning in the characteristics from northwest to southeast in the focal region, which changed from NW-SE to NE-SW. In the northwest of the focal region, the fast polarization direction was oriented to NW-SE, which was parallel to the maximum horizontal compressive stress direction. However, the NE-SW fast polarization direction in the southeast of the focal region was parallel to the Longmenshan fault strike. For station BAX on the Central fault in the middle of the focal region, the distribution of fast polarization directions showed a bimodal pattern, with one dominant in the NE-SW direction and the other in the NW-SE direction. With regard to the temporal variation, the time delays were large in the initial stage after the mainshock but then gradually decreased over time and tended to be stable in the later period. This indicated that stress in the focal region increased to a maximum when the main shock occurred, with the stress release caused by the mainshock and aftershock activity, and the stress gradually decreased after a period of time. The scatter of fast polarization directions was large after the main shock, but over time the scatter gradually decreased, indicating that the Lushan earthquake caused a large perturbation in the local stress field. As the stress gradually decreased and was adjusted by the aftershock activity, the perturbation gradually weakened.     

Frequency‐dependent principal component analysis of multicomponent earthquake ground motions

Stochastic ground motion simulation techniques are becoming increasingly popular because of enhanced computation power enabling direct simulation of complex response quantities. Priestley process assumption is the most general approach for stochastic modeling of earthquake ground motion. However, a framework for multicomponent ground motion simulation using the general Priestley process assumption is not available. Multicomponent motions are useful especially when the correlation structure between them significantly influences the response. The present study proposes a framework for frequency‐dependent principal component analysis (PCA), which facilitates Priestley process–based simulation of multicomponent ground motions. The study focuses only on the frequency‐dependent PCA part, and the results show high dependency of the principal components/directions on the frequency bands of the signals. The present work also advocates that the frequency‐dependent PCA should be preferred to the conventional PCA as the former can address the issues related to the frequency‐independent uniform modulation associated with the latter.     

Damping estimation of high-rise buildings considering structural modal directions

One widespread problem in damping estimation of high-rise buildings is the neglect of structural modal directions, which may induce beating in measured dynamic responses along building geometric axes and thereby induce errors in damping estimations to some extent. Based on a proposed two degrees of freedom (2-DOF) simulation model, the effects of neglecting the modal directions on damping estimate are systematically investigated. The results show that the angular differences between the modal directions and the building geometric axes, as well as the frequency difference between the involved modes, both have significant effects on the damping estimate of high-rise buildings. This paper proposes a spectral method to determine the modal directions of high-rise buildings and further validate this method by an analysis of full-scale measurements from four skyscrapers. The damping ratios estimated based on the responses along the identified modal directions are more accurate than those based on those measured along the building geometric axes. Furthermore, an empirical prediction model for damping ratio of high-rise buildings with heights over 200 m is proposed based on the field measured damping results of several buildings with consideration of the modal directions. The objective of this study is to improve the accuracy of damping estimation of high-rise buildings and therefore provide useful information for the structural design of future skyscrapers.