嫩江断裂带北段的第四纪活动特征初步研究

嫩江断裂带是松辽盆地的西边界断裂,但受第四系强覆盖等研究条件的限制,前人对该断裂第四纪构造活动的研究较少。本文针对该断裂带北段开展了野外地质调查,并综合大地电磁测深和纵波速度结构等结果,初步研究了嫩江断裂带北段的第四纪活动特征。调查发现,该断裂北段主要发育地貌陡坎、基岩滑坡、地层揉皱变形、近垂直擦痕、基岩崩塌与线性断塞塘等特征。探槽古地震研究揭示断裂带北段在（80.9±4.6）—（62.9±2.3）ka BP曾发生1次古地震事件,运动方式为正断,垂直位移量约1.5m,震级约为M_S 7.1—7.3,断裂在晚更新世曾发生过强烈活动。研究结果有助于认识了解该断裂和松辽盆地的第四纪构造变形过程,并为评价该断裂及邻区的地震活动潜势提供参考。     

2018年9月8日云南墨江5.9级地震预测回顾与资料论证

通过分析墨江5.9级地震前预测意见和预测资料,认为云南地区M≥5.5地震平静异常突出,M≥5.0地震连续间隔时间达200天以上,通海2次5.0级地震震级偏小是震前地震活动异常的显著特征;通海地震的指示意义、前兆异常M≥5.7地震中期和M≥5.0地震短临综合预测指标是判断地震短期可能性的主要依据;1900年以来,通海50km范围内M≥5.0地震后云南地区发生M≥5.0地震优势对应关系和GNSS表征的区域面应变变化特征为地点判定提供了线索。墨江5.9级地震的预测经验及资料的论证丰富了对地震孕育复杂性的认识,为震例积累了新的资料。     

Numerical modeling of lock-exchange gravity/turbidity currents by a high-order upwinding combined compact difference scheme

This study presents two-dimensional direct numerical simulations for sediment-laden current with higher density propagating forward through a lighter ambient water.The incompressible NavierStokes equations including the buoyancy force for the density difference between the light and heavy fluids are solved by a finite difference scheme based on a structured mesh.The concentration transport equations are used to explore such rich transport phenomena as gravity and turbidity currents.Within the framework of an Upwinding Combined Compact finite Difference(UCCD)scheme,rigorous determination of weighting coefficients underlies the modified equation analysis and the minimization of the numerical modified wavenumber.This sixth-order UCCD scheme is implemented in a four-point grid stencil to approximate advection and diffusion terms in the concentration transport equations and the first-order derivative terms in the Navier-Stokes equations,which can greatly enhance convective stability and increase dispersive accuracy at the same time.The initial discontinuous concentration field is smoothed by solving a newly proposed Heaviside function to prevent numerical instabilities and unreasonable concentration values.A two-step projection method is then applied to obtain the velocity field.The numerical algorithm shows a satisfying ability to capture the generation,development,and dissipation of the Kelvin-Helmholz instabilities and turbulent billows at the interface between the current and the ambient fluid.The simulation results also are compared with the data in published literatures and good agreements are found to prove that the present numerical model can well reproduce the propagation,particle deposition,and mixing processes of lock-exchange gravity and turbidity currents.     

2017年3月27日漾濞5.1级地震前后气枪震源观测走时数据的变化

以2017年3月27日漾濞5.1级地震为例,根据区域特性和信噪比要求,选取数据较为完整的6个台站记录的2017年1月1日～6月6日期间的宾川地震信号发射台气枪震源波形资料,采用互相关检测技术提取6个台站各自稳定震相的走时数据,并对漾濞5.1级地震前后走时数据的变化情况进行分析。结果表明,漾濞5.1级地震前后6个台站各自稳定震相存在较为明显的走时变化,且短期内走时变化具有较好的同步性,相关台站异常幅度大小和异常出现时间存在细小差异。地震发生前,6个台站走时低值异常过程明显,以YUL台最为显著。地震发生前后走时变化形态特征为双“V”型,漾濞5.1级地震发生在第1个“V”型末端。地震发生后,不同方位相关台站受地震的影响程度不同,走时波动大小存在差异。     

Evolution of permafrost in China during the last 20 ka

The formation and evolution of permafrost in China during the last 20 ka were reconstructed on the basis of large amount of paleo-permafrost remains and paleo-periglacial evidence, as well as paleo-glacial landforms, paleo-flora and paleofauna records. The results indicate that, during the local Last Glacial Maximum(LLGM) or local Last Permafrost Maximum(LLPMax), the extent of permafrost of China reached 5.3×106-5.4×106 km2, or thrice that of today, but permafrost shrank to only0.80×106-0.85×106 km2, or 50% that of present, during the local Holocene Megathermal Period(LHMP), or the local Last Permafrost Minimum(LLPMin). On the basis of the dating of periglacial remains and their distributive features, the extent of permafrost in China was delineated for the two periods of LLGM(LLPMax) and LHMP(LLPMin), and the evolution of permafrost in China was divided into seven periods as follows:(1) LLGM in Late Pleistocene(ca. 20000 to 13000-10800 a BP)with extensive evidence for the presence of intensive ice-wedge expansion for outlining its LLPMax extent;(2) A period of dramatically changing climate during the early Holocene(10800 to 8500-7000 a BP) when permafrost remained relatively stable but with a general trend of shrinking areal extent;(3) The LHMP in the Mid-Holocene(8500-7000 to 4000-3000 a BP)when permafrost degraded intensively and extensively, and shrank to the LLPMin;(4) Neoglaciation during the late Holocene(4000-3000 to 1000 a BP, when permafrost again expanded;(5) Medieval Warming Period(MWP) in the late Holocene(1000-500 a BP) when permafrost was in a relative decline;(6) Little Ice Age(LIA) in the late Holocene(500-100 a BP), when permafrost relatively expanded, and;(7) Recent warming(during the 20 th century), when permafrost continuously degraded and still is degrading. The paleo-climate, geography and paleopermafrost extents and other features were reconstructed for each of these seven periods.     

Characteristics of Vegetation Carbon,Nitrogen, and C/N Ratio in a Tamarix chinensis Coastal Wetland of China

Variations in carbon (C) and nitrogen (N) of the vegetation in a Tamarix chinensis coastal wetland located in Laizhou Bay, China, are analyzed. It is found that T. chinensis accumulates more C and N than the surrounding herbs, and it allocates more C and N in the aboveground parts but less in the roots. Branches store more C, whereas leaves and flowers accumulate more N than other tissues. The C and N contents in the aboveground parts of T. chinensis are mainly influenced by pH, electrical conductivity (EC), water content, and clay content in the top 100 cm of soil as well as the distance from the sea. For the herbs, their C contents vary little in the supratidal zone, but they are higher than those in the intertidal zone. However, N contents in the herbs are higher in the aboveground parts and varied among different communities. The contents of C and N in the herbs are affected by EC, water content as well as the contents of organic C and total nitrogen (TN) in the top 10 cm of soil. The findings confirm that increasing the biomass of T. chinensis is an effective way to increase C sequestration in temperate coastal wetland.     

豫北地区视应力时空变化特征

利用2008年以来豫北地区49次M_L 2.5以上地震资料,通过Brune模型,结合遗传算法,反演计算得到豫北地区地震视应力范围为0.029 9 MPa—0.642 MPa,平均视应力为0.174 8 MPa,分析该区视应力时空变化特征,讨论震级和能量的关系,结果表明,豫北地区目前处于应力积累阶段,应力高值集中在聊兰断裂濮阳—鄄城段范县地区。     

百度地图位置解析技术在地震应急基础数据库的应用

分析百度地图位置解析技术功能及特点,提出使用地址解析及坐标转换功能,对地震应急基础属性数据进行解析,实现基础属性数据空间化,设计地理坐标纠偏算法,提高地震应急基础数据的可用性,为地震应急工作提供数据保障。该算法操作简单,运行快捷,解决了地震应急基础数据库中属性数据及时更新的关键技术问题。     

Constraining the characters of the upper mantle discontinuities beneath the NE margin of the Tibetan Plateau with a dense broadband seismic array

Based on observations from a dense broadband seismic array located along the northeastern (NE) margin of the Tibetan Plateau in southeastern Gansu Province,we use receiver functions (RFs) to pick the arrival times of P-to-S converted waves and bin the traces in different grids according to the piercing points of the 410 and 660 km discontinuities in the upper mantle.The depths of the two discontinuities are estimated by the ray tracing method with the IASP91 velocity model and a 3-D tomography model.The results indicate the following:(1) The arrival times of the P410s and P660s converted phases are delayed by approximately 1 s than those predicted by the IASP91 model.The mantle transition zone (MTZ) is thicker than that in the global model.(2) The synchronous lags in the P410s and P660s arrival times are consistent with low-velocity anomalies in the upper mantle,which are believed to result mainly from the eastward migration of materials beneath the NE margin of the Tibetan Plateau.(3) Combined with previous tomography results,the depression of the'660'discontinuity and the thickened MTZ are somewhat consistent with the big mantle wedge (BMW) model.However,due to data limitations,more studies are required to explore the BMW in the future.     

A three-dimensional variational data assimilation system for a size-resolved aerosol model: Implementation and application for particulate matter and gaseous pollutant forecasts across China

A three-dimensional variational(3DVAR) data assimilation(DA) system is presented here based on a size-resolved sectional aerosol model, the Model for Simulating Aerosol Interactions and Chemistry(MOSAIC) within the Weather Research and Forecasting model coupled to Chemistry(WRF-Chem) model. The use of this approach means that both gaseous pollutants such as SO_2, NO_2, CO, and O_3 as well as particulate matter(PM_(2.5), PM_(10)) observational data can be assimilated simultaneously.Two one-month parallel simulation experiments were conducted, one with the assimilation of surface hourly concentration observations of the above six pollutants released by the China National Environmental Monitoring Centre(CNEMC) and one without assimilation in order to verify the impact of assimilation on initial chemical fields and subsequent forecasts. Results show that, in the first place, use of the DA system can provide a more accurate model initial field. The root-mean-square error of PM_(2.5), PM_(10), SO_2, NO_2, CO, and O_3 mass concentrations in analysis field fell by 29.27 μg m~(-3)(53.5%), 34.5 μg m~(-3)(50.9%),30.36 μg m~(-3)(64.2%), 8.91 μg m~(-3)(39.5%), 0.46 mg m~(-3)(47.4%), and 15.11 μg m~(-3)(51.0%), respectively, compared to a background field without assimilation. At the same time, mean fraction error was reduced by 42.6%, 53.1%, 45.2%, 43.1%,69.9%, and 48.8%, respectively, while the correlation coefficient increased by 0.51, 0.55, 0.48, 0.38, 0.47, 0.65, respectively.Secondly, the results of this analysis reveal variable benefits from assimilation on different pollutants. DA significantly improves PM_(2.5), PM_(10), and CO forecasts leading to positive effects that last more than 48 h. The positive effects of DA on SO_2 and O_3 forecasts last up to 8 h but that remains relatively poor for NO_2 forecasts. Thirdly, the influence of assimilation varies in different areas. It is possible that the positive effects of DA on PM_(2.5) and PM_(10) forecasts can last more than 48 h across most regions of China. Indeed, DA significantly improves SO_2 forecasts within 48 h over north China, and much longer CO assimilation benefits(48 h) are found in most regions apart from north and east China and across the Sichuan Basin. DA is able to improve O_3 forecasts within 48 h across China with the exception of southwest and northwest regions and the O_3 DA benefits in southern China are more evident, while from a spatial distribution perspective, NO_2 DA benefits remain relatively poor.