川西理塘断裂带奔戈- 村戈段古地震事件及其非均匀性活动特征     

张克旗  吴中海  周春景  田婷婷  李跃华  李家存 《地质学报》2020,94(4):1295-1303

在对青藏高原东南缘地区的理塘左旋走滑活动断裂带野外调查研究中，在其奔戈- 村戈段开挖了两个探槽LT1301和SLT1204。在对两个探槽上所揭示出的古地震事件进行详细划分的基础上，结合所获得的10个OSL年代样品和13个14C年代样品的测试年龄，对理塘断裂带北段的古地震事件发生时代进行了厘定。结果表明2个探槽共揭示出至少4次古地震事件，其中小规模的探槽LT1301仅揭示出1次古地震，可能为发生于公元1729年的历史地震，或是可能发生于距现在950a~1. 0ka之间的一次大地震，由于关键部位年代数据不足，上述两种可能性尚无法明确。较大的探槽SLT1204揭示出包含有探槽LT1301中古地震事件在内的古地震4次，最早的古地震事件I发生于9. 9ka之前，而事件II、III和IV则发生在公元1729年~4. 8kaBP之间，复发间隔为约1. 6ka。川西理塘断裂带北段的古地震研究结果表明，该断裂的大地震复发具有非线性特征，不符合特征地震模式，其中全新世晚期的大地震活动频率明显增大，表明它正处于丛集活动阶段。  相似文献   

勉略构造带新元古代洋盆俯冲作用：来自略阳地区纸房沟岩片火山岩锆石U- Pb年龄和Lu- Hf同位素的证据     

徐通  张晓团  焦建刚  张红强  贾力 《地质学报》2020,94(12):3607-3624

纸房沟岩片位于勉略构造带略阳地区。通过细致的岩石学和地球化学研究，将纸房沟岩片内的火山岩分为拉斑玄武岩系列（Ⅰ类）和钙碱性火山岩系列（Ⅱ类）。Ⅰ类火山岩稀土配分曲线左倾，富Na贫P，整体具有N- MORB特点，形成于洋脊构造环境。相比Ⅰ类火山岩，Ⅱ类火山岩具有更高的SiO2(49.02％~61.86％)和K2O(0.32％~1.55％)含量，相对亏损Nb、Ta、P和Ti，形成于陆缘弧构造环境。Ⅱ类火山岩锆石Lu- Hf同位素测试结果显示，εHf(t)值主体为负值，介于-8.01~+0.77，表明其主要为古老地壳物质熔融成因。Ⅱ类火山岩LA- ICP- MS锆石U- Pb测年结果为854±3Ma(MSWD=0.12, n=30)、844±4Ma (MSWD=0.03, n=15)，表明纸房沟岩片火山岩结晶时代为新元古代早中期。综合前人成果认为，纸房沟岩片火山岩为新元古代勉略洋盆俯冲的产物，俯冲作用一直持续到800Ma左右，该俯冲过程很可能是对全球性Rodinia超大陆聚合事件的响应。  相似文献   

国外军事地质学热点问题     

李万伦  吕鹏  孟庆奎  王铭晗 《地质论评》2020,66(1):189-196

近年来以美国为代表的西方军事强国在军事地质学领域已取得了很大进展,尤其在应对未来战争方面作了许多准备。通过系统搜集国际军事地球科学会议(ICMG)和美国地质学会(GSA)有关军事地质学的最新专题研讨会论文与其他公开出版资料,梳理了当前国外军事地质学研究的热点问题并阐述了其新进展,其中作战领域包括地形情报研究、军事基地选址、潜在特殊战场环境调查、地下重要设施评价、非常规作战环境调查;非作战领域则包括抢险救灾、生态环境保护和环境安全评价等。最后分析了当前军事地质学研究存在的问题,并指出了其未来发展趋势。  相似文献   

Wave-forced dynamics in the nearshore river mouths,and swash zones     

Maurizio Brocchini 《地球表面变化过程与地形》2020,45(1):75-95

The role of wave forcing on the main hydro-morphological dynamics evolving in the shallow waters of the nearshore and at river mouths is analyzed. Focus is mainly on the cross-shore dynamics that evolve over mildly sloping barred, dissipative sandy beaches from the storm up to the yearly timescale, at most. Local and non-local mechanisms as well as connections across three main inter-related subsystems of the nearshore – the region of generation and evolution of nearshore bars, river mouths and the swash zone – are analyzed. The beach slope is a major controlling parameter for all nearshore dynamics. A local mechanism that must be properly described for a suitable representation of wave-forced dynamics of all such three subsystems is the proper correlation between orbital velocity and sediment concentration in the bottom boundary layer; while specific dynamics are the wave–current interaction and bar generation at river mouths and the sediment presuspension at the swash zone. Fundamental non-local mechanisms are both infragravity (IG) waves and large-scale horizontal vortices (i.e. with vertical axes), both influencing the hydrodynamics, the sediment transport and the seabed morphology across the whole nearshore. Major connections across the three subsystems are the upriver propagation of IG waves generated by breaking sea waves and swash–swash interactions, the interplay between the swash zone and along-river-flank sediment transport and the evolution of nearshore sandbars. © 2019 John Wiley & Sons, Ltd.  相似文献   

Beaver dam analogues drive heterogeneous groundwater–surface water interactions     

Jeffrey Wade  Laura Lautz  Christa Kelleher  Philippe Vidon  Julianne Davis  Julio Beltran  Casey Pearce 《水文研究》2020,34(26):5340-5353

Beaver dam analogues (BDAs) are a cost-effective stream restoration approach that leverages the recognized environmental benefits of natural beaver dams on channel stability and local hydrology. Although natural beaver dams are known to exert considerable influence on the hydrologic conditions of a stream system by mediating geomorphic processes, nutrient cycling, and groundwater–surface water interactions, the impacts of beaver-derived restoration methods on groundwater–surface water exchange are poorly characterized. To address this deficit, we monitored hyporheic exchange fluxes and streambed porewater biogeochemistry across a sequence of BDAs installed along a central Wyoming stream during the summer of 2019. Streambed fluxes were quantified by heat tracing methods and vertical hydraulic gradients. Biogeochemical activity was evaluated using major ion porewater chemistry and principal component analysis. Vertical fluxes of approximately 1.0 m/day were observed around the BDAs, as was the development of spatially heterogeneous zones of nitrate production, groundwater upwelling, and anaerobic reduction. Strong contrasts in hyporheic zone processes were observed across BDAs of differing sizes. This suggests that structures may function with size-dependent behaviour, only altering groundwater–surface water interactions after a threshold hydraulic step height is exceeded. Patterns of hyporheic exchange and biogeochemical cycling around the studied BDAs resemble those around natural beaver dams, suggesting that BDAs may provide comparable benefits to channel complexity and near-stream function over a 1-year period.  相似文献   

秦皇岛近岸海域潮间带砂质沉积物中微塑料和重金属污染特征   总被引：1，自引：0，他引：1  

陈月琴  罗维  孙聪慧  吴光红 《海洋学报》2020,42(4):113-121

基于密度分离原理，利用饱和NaCl溶液对秦皇岛近岸海域潮间带砂质沉积物中的微塑料进行了浮选和分离提取，采用显微红外光谱方法分析附着在滤膜上的微塑料颗粒形貌和材质。结合扫描电子显微镜?能谱仪(Scanning Electron Microscopy Energy Dispersive Spectrometer，SEM-EDS)对微塑料样品进行微观形貌观察及微区成分的分析。并采用地累积指数(Geo Accumulation Indexes，I_geo)和富集系数(Enrichment Factors，EF)分析砂质沉积物中重金属Hg、Cd和Pb污染水平和富集特点。分析砂质沉积物中烧失量(Loss on Ignition，LOI)、总有机碳(Total Organic Carbon，TOC)、总氮(Total Nitrogen，TN)以及碳氮的稳定同位素组成(δ13C和δ15N)，探讨有机质的可能来源。结果表明:秦皇岛近岸海域潮间带砂质沉积物中有纤维类、发泡类、薄膜类3种微塑料，以纤维类的微塑料为主。微塑料表层富集有Si、Al、Mg、Fe和Ca等元素。沉积物中Hg和Cd富集水平较高，Pb富集水平较低。沉积物TOC和TN含量较低，LOI为TOC的1.6倍，δ13C、δ15N和TOC/TN的数值范围均显示有机质以海洋浮游植物藻类等海源为主。  相似文献   

北极薄冰-煎饼冰区域中不同重力波驱动形成海流的敏感性分析     

张雪妍  戴海瑨  赵军  殷何卿 《海洋学报(英文版)》2020,39(3):123-129

A coupled ocean-ice-wave model is used to study ice-edge jet and eddy genesis during surface gravity wave dissipation in a frazil-pancake ice zone. With observational data from the Beaufort Sea, possible wave dissipation processes are evaluated using sensitivity experiments. As wave energy dissipated, energy was transferred into ice floe through radiation stress. Later, energy was in turn transferred into current through ocean-ice interfacial stress. Since most of the wave energy is dissipated at the ice edge, ice-edge jets, which contained strong horizontal shear, appeared both in the ice zone and the ocean. Meanwhile, the wave propagation direction determines the velocity partition in the along-ice-edge and cross-ice-edge directions, which in turn determines the strength of the along-ice-edge jet and cross-ice-edge velocity. The momentum applied in the along-ice-edge(cross-ice-edge)direction increased(decreased) with larger incident angle, which is favorable condition for producing stronger mesoscale eddies, vice versa. The dissipation rate increases(decreases) with larger(smaller) wavenumber, which enhances(reduces) the jet strength and the strength of the mesoscale eddy. The strong along-ice-edge jet may extend to a deep layer(> 200 m). If the water depth is too shallow(e.g., 80 m), the jet may be largely dampened by bottom drag, and no visible mesoscale eddies are found. The results suggest that the bathymetry and incident wavenumber(magnitude and propagation direction) are important for wave-driven current and mesoscale eddy genesis.  相似文献   

日照海岸带沙滩侵蚀现状及沉积物粒度特征分析     

种衍飞  郝义 《海洋地质前沿》2020,36(1):19-29

通过对日照市海岸带2个重点沙滩的现场调查和沉积物粒度计算,综合分析了沙滩的侵蚀现状和粒度参数特征。海滨国家森林公园沙滩北部和南部处于侵蚀状态,中部为缓慢淤积状态;万平口海水浴场沙滩北部、中部总体呈侵蚀趋势,南部为淤积状态。海滨国家森林公园沙滩的平均粒径总体要小于万平口海水浴场沙滩,这与两沙滩的坡度不同有关,平均粒径从滩肩到低潮线逐渐变小。海滨国家森林公园沙滩的分选性要好于万平口海水浴场沙滩,分选系数具有由陆向海、由北向南逐渐变小的趋势。沙滩的滩肩和滩面处频率曲线主要为双峰,峰态平坦,物质来源复杂,低潮线处频率曲线主要为单峰,峰态尖锐,物质来源单一。  相似文献   

复杂载荷作用下立管触地段损伤管道的动力响应     

代云云  周晶  李志刚 《中国海洋大学学报(自然科学版)》2020,(1):145-153

触地段(Touchdown zone, TDZ)是在役钢悬链线立管(Steel catenary riser, SCR)的关键部位,在复杂载荷作用下,极易形成损伤缺陷,其载荷寿命的评估是深海结构工程中的一个关键问题。本文以大型有限元软件ABAQUS为平台,运用损伤管道实体单元与土弹簧阻尼单元相互作用的模型模拟触地段损伤海底管道在复杂载荷作用下的动力响应,数值计算考虑了管-土相互作用过程中的材料非线性、几何非线性以及接触非线性。讨论了单一环向体积损伤位于触地段管道的不同位置时,触地段损伤管道在不同载荷作用下的动力特性及特征点的动力响应。结果表明,管道所受内外压力以及管道提升端的竖向位移载荷会影响结构的自振频率;体积损伤部位的动力响应较完好部位更剧烈;体积损伤的位置和动力载荷频率对管道动力放大系数的影响很大;当动力载荷的激励频率越接近结构基频时,损伤管道的动力响应及动力放大系数越大。  相似文献   

VELOCITY CHARACTRISTICS OF SHANXI AND ADJACENT AREA AND ITS TECTONIC SIGNIFICANCE          下载免费PDF全文

WANG Xia  SONG Mei-qin  ZHENG Yong  AI San-xi 《地震地质》2019,41(1):119-136

In order to acquire a better velocity structure of the crustal and uppermost mantle beneath Shanxi area, we obtain the group and phase velocities of Rayleigh wave of the periods 8s to 50s in Shanxi and adjacent area using ambient seismic noise recorded at 216 broad-band stations. All available vertical-component time series for 2014 have been cross-correlated to yield estimates of empirical Rayleigh wave Green's function. Group and phase velocity dispersion curves for Rayleigh wave are measured for each interstation path by applying frequency-time analysis. It describes finer velocity structure of the crust and upper mantle in Shanxi, which reflects the geological structure characteristics at different depths. The resolution is within 50km and the resolution of part periods can reach 40km.The Rayleigh wave group and phase speed maps at short periods(8~18s and 10~22s)show clear correlations with shallow geological structures. Mountain areas on both sides of Shanxi depression zone show apparent high-velocity anomaly, except for low-velocity anomaly in the Taiyuan Basin, Linfen-Yuncheng Basin and Weihe Basin. Especially, the areas of Youyu County-Pianguan County-Kelan County-Shuozhou City and Jingle County-Lishi District of Lüliang City in Lüliang Mountains, and Yu County-Fuping County-Yi County and Yangcheng County-Licheng County in Taihang Mountains, present higher velocity anomaly. In addition, the velocity is lowest in the Weihe Basin, and the amplitude of low velocity decreases gradually from the south to the north of the basins in Shanxi, which probably is related to the process of gradual stretching and development of the Shanxi rift zone from the southwest to the northeast. The obvious velocity difference across the latitude of 38°N exists at 18~30s period of phase and 24~35s period of group velocity maps, which is probably related to the deep and shallow Moho depth variation in the south and north of Shanxi and the suture zone of ancient blocks including "hard" southern block and "soft" northern block. At the same time, the research result of receiver function reveals that partial melting of the lower crust occurs in the northern Taihang Mountains, while the southern section remains stable(Poisson's ratio is above 0.3 in the northern Taihang Mountains and 0.25~0.26 in the southern section). The phase velocity map at 30~50s period clearly shows NW velocity gradient belt, and the low velocity anomaly in the northeast side may be related to Cenozoic volcanism. Meanwhile, the eastern border of Ordos block is the western faults of central basins in Shanxi depression zone. However, some research results indicate that the above border is Lishi Fault in the surface, inferring that the Ordos block shows a shape of wide in the upper and narrow in the lower part from the surface to deep. The Datong volcanic area at 18~45s period of phase and 24~35s period of group velocity maps shows low velocity of trumpet shape from shallow to deep, related to the upwelling of hot material from lower mantle in the Cenozoic causing a large area of intense magmatic activity. It indicates the more specific upwelling channel of Datong volcanoes simultaneously.  相似文献