STUDY ON FOCAL DEPTH OF THE MS5.4 CANGWU EARTHQUAKE IN GUANGXI

On July 31th, 2016, a magnitude 5.4 earthquake struck Cangwu Country, Guangxi Zhuang Autonomous Region, it was the largest earthquake recorded by Guangxi Seismological Network since it set up. The number of people affected by the earthquake had reached 20 000, and the direct economic losses caused by the earthquake were nearly 100 million Yuan. After the earthquake, USGS provided a global earthquake catalog showing that the focal depth of Cangwu earthquake was about 24.5km. However, the result given by the Global Centroid Moment Tensor showed the focal depth of this earthquake was 15.6km. However, the result obtained by Xu Xiaofeng et al. using CAP method was 5.1km. It was clear that the focal depths of Cangwu earthquake given by different institutions were quite different from each other. However, accurate focal depth of the earthquake has important significance for exploring the tectonic mechanism near the epicenter, so it is necessary to further determine the more accurate depth of the Cangwu earthquake. In order to further accurately determine the focal depth of Cangwu earthquake, we used the global search method for travel-time residual to calculate the focal depth of this earthquake and its error range, based on the regional velocity model, which is a one-dimensional velocity model of the Xianggui tectonic belt produced by the comprehensive geophysical profile. Then, we inverted the focal mechanism of this earthquake with the CAP method. Based on this, the focal depth of Cangwu M_S5.4 earthquake was further determined by the method of the Rayleigh surface wave amplitude spectrum and the sPL phase, respectively. Computed results reveal that the focal depth of this earthquake and its error range from the travel-time residual global search method is about(13±3)km, the focal depth inverted by CAP method is about 10km, the focal depth from sPL phase is about 10km, and the focal depth from Rayleigh surface wave amplitude spectrum is about 9~10km. Finally, we confirmed that the focal depth of Cangwu M_S5.4 earthquake is about 10km, which indicates that this earthquake still occurred in the upper crust. In the case of low network density, the sPL phase and Rayleigh wave amplitude spectrum recorded by only 1 or 2 broadband stations could be used to obtain more accurate focal depth. The focal depth's accuracy of Cangwu M_S5.4 earthquake in the USGS global earthquake catalog has yet to be improved. In the future, we should consider the error of the source parameters when using the USGS global earthquake catalog for other related research.     

Variation in the vertical zonality of erodibility and critical shear stress of rill erosion in China's Hengduan Mountains

Soil erodibility is an essential parameter used in soil erosion prediction. This study selected the Liangshan town watershed to quantify variation in the vertical zonality of rill erodibility (k_r) in China's ecologically fragile Hengduan Mountains. Soil types comprised of yellow–brown (soil A), purple (soil B), and dry-red (soil C) in a descending order of occurrence from the summit to the valley, which roughly corresponds to the vertical climate zone (i.e. cool-high mountain, warm-low mountain, and dry-hot valley sections) of the study area. With elevation, vertical soil zonality varied in both soil organic matter (SOM) content and soil particle-size fractions. A series of rill erosion-based scour experiments were conducted, using water discharge rates of 100, 200, 300, 400, 500, and 600 mL min^-1. Additionally, detachment rates (Dr) were measured under three hydrological conditions (the drainage, saturation, and seepage treatments). Results show that both Dr and flow shear stress (Ʈ) values increased as discharge increased. As elevation increased, the k_r values decreased, while the vertical zonality of critical shear stress (Ʈ_c) values showed no obvious variation. The highest k_r values were observed during the seepage treatment, followed by the saturation treatment then drainage treatment, indicating that variation in vertical hydraulic gradients could significantly alter k_r values. This study also found that land-use types could also alter k_r and Ʈ_c values. Further research, however, is necessary to better quantify the effects of subsurface hydrological conditions and land-use types on k_r under different soil zonalities in China's Hengduan Mountains. © 2018 John Wiley & Sons, Ltd.     

高墩大跨度刚构桥抗震加固有限元分析

大跨刚构桥结构桥跨较长和受力复杂。为提高抗震性能,需要对加固前后的桥梁进行抗震性能研究。以某双肢薄壁型高墩大跨度刚构桥为背景,采用ANSYS程序APDL语言,对结构进行合理的参数选取、网格划分和边界约束,结合抗震等级和桥梁规范等有关规定,研究整体结构在地震作用下的变化规律。通过沿墩高方向获取节点的方法,确定在地震作用下,各节点的最大位移从下到上逐渐增大。选取桥墩双肢相同部位各节点进行横向比较,总结得出双肢薄壁桥墩具有平分荷载和延长寿命的特点。为提高桥梁整体抗震性能,采取联结桥墩增大截面的方式进行加固,对比加固前后两模型在同一地震作用下的结构响应,得出该方法在提高结构整体刚度方面,效果显著。     

构建我国海洋能技术创新体系政策框架的思考

能源转型伴随着产业结构调整,更需要能源技术创新的支撑,能源技术进步与能源转型相互促进,正在深刻改变能源发展前景和世界能源格局。为把握海洋能技术创新方向和发展趋势,文章分析国际海洋能技术发展布局,在此基础上分析我国海洋能技术创新体系政策框架,重点研究技术创新的难点。研究结果表明：我国仍须进一步完善资源勘查、基础研究和监督管理,从而形成较成熟的海洋能产业,使海洋能技术在利基市场充分发挥优势。     

东昆仑二叠系格曲组火山岩年代学、地球化学特征及其构造意义

东昆仑古特提斯造山带经历了从洋壳俯冲到陆-陆碰撞及后碰撞伸展的造山过程,但对古特提斯洋闭合时间一直存在争议,争论的焦点集中在晚二叠世格曲组沉积盆地原型及中上二叠统之间不整合关系代表的构造事件。本文对东昆仑红石山地区格曲组火山岩开展了锆石U-Pb年代学与岩石地球化学研究,结果表明,岩石富集Rb、Th、Ba等大离子亲石元素(LILE)而亏损Nb、Ta、Ti、P等高场强元素(HFSE),具有大陆岩浆弧的地球化学特征。火山岩具有高Ba/Th比值(53.6)、Th/Ce比值(0.23)、Nb/Ta比值(18.35)及低Dy/Yb比值(1.42),表明晚二叠世火山岩由枕状玄武岩和洋底沉积物等洋壳物质俯冲至60 km左右深度时熔融所形成。锆石U-Pb定年表明,格曲组下部碎屑岩段流纹质凝灰岩和英安质沉凝灰岩206Pb/238U加权平均年龄分别为(257.5±2.5)Ma和(256.2±4.8)Ma,上部灰岩段粗安质晶屑凝灰岩206Pb/238U加权平均年龄为(251.8±2.3) Ma。结合区域上已报道的格曲组及花岗岩研究成果,认为古特提斯洋在晚二叠世开始向北俯冲消减,沉积于弧前盆地的格曲组为古特提斯...     

基于爆破荷载等效施加方法的振动波形预测与古建筑安全评估

隧道爆破开挖产生的振动对邻近的古建筑有着不容忽视的安全影响,为研究爆破振动波的传播规律以及预测地面振动效应和分析临近古建筑结构的安全性,以拉卜楞隧道为依托,采用现场实测结合数值模拟分析的方法,预测爆破荷载作用下拉卜楞寺的动力响应。结果表明：(1)随着单响总药量的增加,质点振动速度增大,衰减比也随之增大,说明高频振动衰减快,低频振动衰减慢;(2)通过理论计算将爆破荷载等效施加在弹性边界或隧道开挖轮廓面上,动力模拟结果表明在大于40 m的中远区两者振速变化规律趋于一致,故将荷载施加在开挖轮廓面上是合理的;(3)爆破地震波自由界面处体波经过反射形成沿表面传播的Rayleigh波,结合数值模拟山体内部地震波的传播规律发现,经反射叠加山体内部形成复杂的振动区;(4)当地震波到达拉卜楞寺最近点时,径向振速峰值为0.000 672 cm/s,垂向振速峰值为0.000 448 cm/s,合成振速峰值为0.000 807 cm/s,远小于古建筑安全振动控制标准。     

东太平洋CC区西区表层沉积物黏土矿物和地球化学特征

本文以太平洋CC区西区12个表层沉积物样品作为研究对象,对其粒度、化学组分和矿物成分进行分析,讨论其沉积环境和物质来源。研究区地处深海,主要以深海黏土和硅钙质黏土为主,含有少量的硅质黏土、黏土质硅质软泥和黏土质钙质软泥。黏土矿物成分主要是蒙皂石和伊利石,含有部分的高岭石和绿泥石。黏土矿物组成表明,区内沉积物主要是陆源,由高空气流携带而来,南极底流和热液活动对其物源的来源有一定影响。沉积物地球化学特征也表明,物源以陆源为主,稀土元素分布曲线和北太平洋表层海水稀土曲线类似,且表现出强的Ce亏损,表明生物活动导致的生物沉降对表层沉积物也有一定的影响。     

人工砾石海滩变化及输移率研究

在我国采用砾石海滩在某些强动力区域进行海滩养护是一种新的尝试,具有很好的适用性。以厦门天泉湾人工砾石滩为研究对象,对2015年至2016年间10条海滩剖面开展了5次周期性监测,通过综合分析,得出在人工砾石滩竣工完成后的一年时间内,滩肩外沿线、岸线及滩面底角的砂砾分界线大幅度后退,滩肩宽度变窄;滩肩外沿线明显隆起,形成滩肩脊线;滩面坡度变大,且上游侧海滩的滩面普遍比下游侧海滩的滩面陡,一年后,岸滩整体变化趋于稳定。针对砾石滩不断向西南方向运移的现状,采用Leo C.van Rijn输移率公式计算砾石滩年平均输移率,并通过测量断面法、体积变化量法对Leo C.van Rijn公式计算结果进行验证,得出砾石滩年平均输移率的范围约为1 015.66~2 392.5 m~3/a。     

Two Improvements on Numerical Simulation of 2-DOF Vortex-Induced Vibration with Low Mass Ratio

Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson''s work, the maximum amplitude of the cylinder with low mass ratio m*=2.6 can reach as large as 1.5D to be called as the “super-upper branch”, but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.     

小冰期福建海岸沙丘的沉积环境

选取福建东南沿海典型海岸沙丘——东海沙丘,运用GPR（Ground Penetrating Radar）技术探测海岸沙丘内部构造,辅助天然剖面和人工探槽观测,进行系统的年代采样与OSL（Optically Stimulated Luminescence）测年,并选择物理意义明确的粒度参数作为主要环境代用指标,获得了亚热带季风区砂质海岸带典型海岸沙丘的沉积年代和沉积结构。结果表明：（1）东海沙丘是由若干灌丛沙丘组成的横向沙丘,0～6 m主要是～0.45 ka BP以来形成的海岸风成沙丘,可以划分为～0.45 ka BP和0.22～0.12 ka BP两个阶段。（2）东海沙丘沉积过程是多因素共同作用的结果,冷干的气候环境是沙丘发育的适宜条件,入境台风频率增加可能加快了风沙的沉积过程。对比历史文献资料发现,气候异常期往往与社会动荡期、重要历史事件相对应。