Geophonino-3D的设计与测试:应用H/V谱比法的低成本三分量地震噪声记录仪

地震效应与地震发生地的地质特性密切相关,会加强该地区的地表运动,尤其是软土地区。加强的程度与共振频率相关,可通过水平与垂直谱比法(H/V谱比法)测量地震噪声从而估算共振频率。本文设计了一种低成本用户友好型数据采集系统(Geophonino-3D),用于记录三分量地震噪声。可开发的系统由信号调节电路和安装有SD Shield(用于存储数据)的Arduino Due组成。本设备首先在实验室中对其实验灵敏度、内部噪声稳定性、通道一致性进行了测试,评估了其是否适用于H/V谱比法。随后,通过在阿利坎特省(西班牙东南部)8个土壤特性不同的场地记录地震噪声,进行了实验验证。根据比较商用地震记录仪测出的功率谱密度和H/V峰值,评估了所开发数据采集系统的性能。所得结果表明本数据采集系统适用于应用H/V谱比法记录地震噪声。Geophonino-3D采用开源和开放硬件系统,部件价格远低于其他商用设备,对于资金短缺的研究团队来说,这是明显的进步。     

一个专用地震预警网络:墨西哥地震预警系统(SASMEX)

墨西哥地震预警系统(SASMEX)于1993年开始投入使用,是首个向公众发布预警信息的系统。现今,SASMEX由97个几乎跨越整个墨西哥俯冲带的监测台站组成。系统还包括监测俯冲科科斯板块地震活动的强震仪。这些地震都发生于内陆,靠近墨西哥主要人口中心。监测台站与控制和分配中心相连,通过一个多重手段的远程通信网络接收、处理和发布警报。预警信息通过低成本的无线电接收器、付费电视和广播电台以及墨西哥城内安装在整个城区街道的市政喇叭系统进行发布。从1993~2017年,台网已记录到6 896次地震,共发布了158次地震预警。最近的地震预警成功案例是2017年9月发生于墨西哥的两次地震。在2017年9月7日特旺特佩克大地震(MW8.2)中,SASMEX在强烈震动的地震波到达墨西哥城前提供了近2min的预警时间。第二个案例是2017年9月19日莫雷洛斯地震(MW7.1)。震中距离墨西哥城约120km,较短的震中距使得在S波到达墨西哥城前仅有几秒的预警时间。     

黄河上游盆地重组所导致的快速侵蚀下切

高起伏的造山高原边缘的快速剥蚀常被用来指代区域地表隆升~(1～3)。然而,诸如岩体隆升的空间差异~4,降雨的地形效应以及冰川~5、滑坡导致的河道堵塞~(6,7)等阻碍河流下切的因素,可能会使剥蚀作用严重滞后于地表抬升~8。本文中,我们通过研究青藏高原东北缘黄河沿岸沉积盆地的地层学、年代学和地貌学特征,重建黄河上游侵蚀下切的时间、速率以及模式。我们发现河流下切的起始时间明显晚于山体开始隆升的时间(14～8Ma)~9。高原边缘的河流下切始于1.8Ma~(10),然后以大约350km/Ma的速度向上游传递~(11)。我们认为该地区在气候驱动下的湖泊扩张并溢出作用是黄河上游快速下切的主要原因,并最终导致了现代黄河地貌的形成。     

致密油岩石纵波频散及衰减特征研究:实验观测及理论模拟（英文）

非常规油气资源-致密油在中国有广泛分布,致密油储层孔隙类型多样、结构复杂。本文对12块致密油岩石样本开展了超声波实验测量,根据记录的纵波波形,利用谱比法估算了岩石在饱和不同流体时的衰减,结果显示大部分致密油样本在饱气状态下的纵波衰减强于饱水及饱油情况,并且,纵波衰减与岩石渗透率有较好的正相关性。基于扫描电镜分析结果,采用三重孔隙结构模型描述致密油岩石,正演模拟了致密油岩石的波传播特征。基于BIOT理论、BIOT-RAYLEIGH双重孔隙介质理论和三重孔隙模型对比讨论了致密油岩石的纵波速度频散和衰减规律,结果显示BIOT理论和BIOT-RAYLEIGH理论均无法解释该组致密油岩石样本的衰减特征规律,而采用三重孔隙结构模型的预测结果和实验结果能够达到很好的吻合。统计分析了致密油岩石的实验测量结果和模型参数,可推断在5-10%孔隙度范围内致密油岩石含更多的微裂隙,且在高孔隙度范围微裂隙尺寸更大。在不同孔隙度范围内,微裂隙和黏土包体体积比率相近,但微裂隙尺寸明显大于泥质尺寸,微裂隙体积模量低于泥质体积模量。     

过去2000年大气甲烷含量与气候变化的冰芯记录

温室气体与气候变化的关系是当前全球变化研究中的一个核心内容。目前关于大气温室气体含量变化只有几十年的实测资料, 而冰芯包裹气体中的CH4 不仅能反映过去大气CH4 含量随时间的变化, 而且能很好地揭示陆地CH 向大气中的释放随时间及空间的分布。近年来, 极地冰芯研究表明南极和北极过去大气层中的甲烷含 量差异很大, 北极大气层中甲烷含量远大于南极大气层。科学家们推测, 中低纬度地区是全球大气层甲烷含量变 化的驱动源。而对这一可能驱动源的甲烷含量变化, 很长时间人们一无所知。达索普冰芯记录揭示了中低纬度大 气CH4 含量与极地冰芯记录相同的变化趋势, 并明确显示工业革命以来大气CH4 含量的增长。高分辨率达索普 冰芯记录的工业革命以来大气CH4 含量变化最显著的特征是20 世纪两次世界大战期间人类活动CH4 排放的减缓 使大气CH4 含量呈负增长。中低纬度大气CH4 含量的恢复使我们有机会与极地冰芯记录进行定量对比研究。 0 ～1850A. D. 中低纬度大气CH4 的平均含量为782nmol /mol, 与格陵兰和南极大气CH4 平均含量差分别达66 nmol /mol和109nmol /mol, 并且其最大自然波动幅度超过200nmol /mol, 这是极地冰芯记录从未有过的。达索普冰芯 记录表明工业革命前中低纬度为全球大气重要的CH4 源区, 但最近1000a 来, 北半球中高纬度的排放有了显著的 加强; 过去2000a 来的自然变化时期, 气候变化的纬向差异对北半球不同纬度带CH4 排放格局有重要影响。     

Estimation of wave forces on large compliant platforms

Compliant offshore structures such as spars, tension leg platforms (TLPs) and semi-submersibles have been dramatically improved in recent years due to their capability for deep water operation. Waves are the most important environmental phenomenon affecting these offshore structures. Estimation of wave forces is vital in offshore structure design. For large compliant offshore plat-forms, Morrison's equation is not valid anymore and usually diffraction theory is used. In this research, by using the finite difference method, a detailed analysis of the first-order diffraction of monochromatic waves on a large cylinder as a structural element is per-formed to solve the radiation and diffraction potentials. The results showed that the developed model is a reliable tool to estimate the wave forces and hydrodynamic coefficients on large structure elements when wave diffraction and radiation are considered.     

Fishery resources in arid zone mangroves in gulf of Kachchh, Gujarat, northwest coast of India

The finfish and shellfish resources were assessed quantitatively and qualitatively in regard to their abundance in creek waters at three sites within a period of two years, from January 1999 to December 2000, in the western mangrove areas of Kachchh. The catch rate varied from 0.69 to 6.99 kg h⁻¹. It was low during monsoon (July to October), which could be due to the freshwater-flow-induced salinity reduction in all the sites. Among 38 species recorded, 5 were shellfish and 33 were finfish. The spawning period of fishes was found to be during summer and early monsoon period (May to August). Surface water temperatures varied from 17 °C to 37 °C. Salinity values varied from 34 to 44 and the pH ranged between 7 and 8.9. Variation in dissolved oxygen content was from 3.42 to 5.85 mL L⁻¹. The high fishery densities in these semi arid mangrove creek areas were recorded during monsoon and early winter season.     

深圳湾海域多溴联苯醚(PBDEs)生物累积及其高分辨沉积记录

深圳湾,毗邻香港,是深圳经济特区的重要经济发展和生态调节区域。为了更好地了解该湾多溴联苯醚（PBDEs）的生物累积规律及其污染历史,作者采集该海域19个鱼、2个虾、2个蟹和柱状沉积物样品,分析其中PBDE的组分与含量,以及生物体的δ^15N同位素、总脂含量和柱状沉积物的沉积年龄（^210pb）、总有机碳（TOC）。结果表明,深圳湾海域鱼类∑15 PBDEs组分的残余量为21—167ng／g lw（或0．17—4．16ng／g fw）,平均为（67±42）ng／g lw或（2．00±1．14）ng／g fw,其含量与生物体的δ^15N同位素和脂含量正相关,BDE-47、BDE-100为生物体中PBDE最优势组分且在所有生物样品中均检出,分别占46．5％、13．5％,肉食性的鱼类较植食性的鱼类PBDEs的生物累积总体上较高。柱状沉积物中∑22 PBDEs含量（0．07—4．85ng／g dw）近二十几年来有明显的上升趋势,平均沉积通量为0．25ng／（cm^2·a）,丰度最高的PBDE组分为BDE-47、BDE-49、BDE-99、BDE-183（不包括BDE-209）;PBDEs在生物体和柱状沉积物中的含量位于全球PBDEs含量的中低端范围;鱼类等生物体中PBDE的生物-沉积物累积比值（BSAF）比值（〈0．8）较小,与相应的PBDE的log Kow（辛醇／水分配比）存在一定的正相关性。     

Coupling Effect of Riser on Integrated FPS in Deepwater Area

The main challenge in predicting global responses of floating vessels in deepwater and ultra-deepwater areas comes from the system's coupled effect.In this paper,the coupled approach is used to analyze effects of riser on floating system in deepwater.The analysis results show that the coupling effects of risers will mainly affect the low frequency (LF) motions of the system.That is because risers will provide the system with a significant low frequency (LF) damping which will vary with the sea states.Under ...     

The impact of human activities on the flushing properties of a semi-enclosed lagoon: Xiaohai, Hainan, China

In this study, a Lagrangian particle tracking model driven by hydrodynamic fields was used to investigate the changes of flushing properties in Xiaohai Lagoon resulting from natural evolution and influences of human activities. Comparisons of residence times between 1936 and 2001 indicate that the flushing efficiency of the lagoon has deteriorated greatly during the past seven decades. Over this period, the average residence time of the lagoon has increased from 45 to 71 days, an increase of 59%. The Lagrangian residual velocity has decreased from 1936 to 2001 in the large portions of the lagoon, and the spatial distribution pattern of the residual current has changed significantly. The well-developed horizontal circulations in 1936 disappeared. Instead, the horizontal Lagrangian residual velocity showed uniformly seaward motion with reduced velocity in 2001. Human activities have incurred great impacts on the deterioration of flushing efficiency. The reduction of river inflow imposed the most significant impact, causing an increase of average residence time by 33%. The land reclamation in the lagoon came as the second most significant factor, causing an increase of 15%. Closure of the North Opening had posed minor impact. The model results suggest that restoring the river inflow, as well as the dredging of the tidal channel and the inner lagoon, should be the top proprieties for future water quality management.