Preliminary study on community structures of meiofauna in the middle and eastern Chukchi Sea

Sediment core samples were collected from 17 stations in the middle and eastern Chukchi Sea during the sixth Chinese National Arctic Research Expedition(CHINARE-Arctic) in summer 2014.The samples were analyzed for composition,abundance,biomass,vertical distribution,size spectra,and ecological indexes of meiofauna.A total of 14 meiofauna taxa were detected,and the free-living marine nematodes comprised the most dominant taxon,accounting for 97.21% of the average abundance.The abundance and biomass of meiofauna were within ranges of(218.12±85.83)-(7 239.38±1 557.15) ind./(10 cm~2) and(130.28±52.17)-(3 309.56±1 751.80) μg/(10 cm~2),with average values of(2 391.90±1 966.19) ind./(10 cm~2) and(1 549.73±2 042.85) μg/(10 cm~2)(according to dry weight)respectively.Furthermore,91.26% of the individuals were distributed in the top layer of 0-5 cm of surface sediment,and 90.84% had sizes of 32-250 μm.Group diversity index of meiofauna in the survey area was low,and the variation of abundance was the main difference in meiofauna communities among all stations.Abundance and biomass of meiofauna were not significantly correlated with environmental factors except concentration of nutrient Si in bottom seawater.Abundance of meiofauna in shallow water of marginal seas in the Pacific sector of the Arctic Ocean is likely at a same level and higher than that in most of China sea areas,suggesting that the shallow water of the summer Chukchi Sea is a continental shelf area with rich resources of meiofauna.The Chukchi Sea is important for studying the ecosystem of the Arctic Ocean and environmental responses.However,studies on meiofauna in the Chukchi Sea are still not enough,and in the future,natural and human disturbances may increase due to global warming,the Arctic channel opening,and other factors.Thus,more studies on meiofauna should be required,in order to know more about how the Arctic benthic community would alter.     

基于三参量威布尔分布的潜在震源区强震危险性估计

本文提出了一种基于三参量威布尔分布模型估计潜在震源区强震危险性的方法。选择日本东海-南海地震带为潜在震源区,分别基于强震发震时间间隔服从二参量和三参量的威布尔分布,估计该区强震危险性,结果表明三参量威布尔分布的拟合效果优于二参量威布尔分布。选择马尼拉海沟俯冲带为潜在震源区,基于三参量威布尔分布估计该区强震危险性,结果显示未来10、30和50年该区强震（M≧7.5）复发概率分别为62%、82%和89%,最短发震时间间隔估计为1.70年。     

基于三轴试验的软土震陷简化计算方法研究

本文通过对天津滨海新区典型软土的静、动力学试验,分析了软土残余应变的变化规律,提出了结合地区震陷经验系数的软土震陷简化计算方法,并利用1976年唐山7.8级地震中天津塘沽地区软土震陷观测资料对计算方法进行了验证。结果表明,本方法用于估算自由地表震陷量是可行的,对中小工程中软土震陷量的估算具有一定的参考价值。     

Cross double‐difference inversion for simultaneous velocity model update and microseismic event location

Microseismic monitoring is an approach for mapping hydraulic fracturing. Detecting the accurate locations of microseismic events relies on an accurate velocity model. The one‐dimensional layered velocity model is generally obtained by model calibration from inverting perforation data. However, perforation shots may only illuminate the layers between the perforation shots and the recording receivers with limited raypath coverage in a downhole monitoring problem. Some of the microseismic events may occur outside of the depth range of these layers. To derive an accurate velocity model covering all of the microseismic events and locating events at the same time, we apply the cross double‐difference method for the simultaneous inversion of a velocity model and event locations using both perforation shots and microseismic data. The cross double‐difference method could provide accurate locations in both the relative and absolute sense, utilizing cross traveltime differences between P and S phases over different events. At the downhole monitoring scale, the number of cross traveltime differences is sufficiently large to constrain events locations and velocity model as well. In this study, we assume that the layer thickness is known, and velocities of P‐ and S‐wave are inverted. Different simultaneous inversion methods based on the Geiger's, double‐difference, and cross double‐difference algorithms have been compared with the same input data. Synthetic and field data experiments suggest that combining both perforation shots and microseismic data for the simultaneous cross double‐difference inversion of the velocity model and event locations is available for overcoming the trade‐offs in solutions and producing reliable results.     

Decadal morphological evolution of the mouth zone of the Yangtze Estuary in response to human interventions

The morphology of the Yangtze Estuary has changed substantially at decadal time scales in response to natural processes, local human interference and reduced sediment supply. Due to its high sediment load, the morphodynamic response time of the estuary is short, providing a valuable semi-natural system to evaluate large-scale estuarine morphodynamic responses to interference. Previous studies primarily addressed local morphologic changes within the estuary, but since an overall sediment balance is missing, it remains unclear whether the estuary as a whole has shifted from sedimentation to erosion in response to reduced riverine sediment supply (e.g. resulting from construction of the Three Gorges Dam). In this paper we examine the morphological changes of two large shoals in the mouth zone (i.e. the Hengsha flat and the Jiuduan shoal) using bathymetric data collected between 1953 and 2016 and a series of satellite images. We observe that the two shoals accreted at different rates before 2010 but reverted to erosion thereafter. Human activities such as dredging and dumping contribute to erosion, masking the impacts of sediment source reduction. The effects of local human intervention (such as the construction of a navigation channel) are instantaneous and are likely to have already resulted in new dynamic equilibrium conditions. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be >30 years (starting from the mid-1980s). Accounting for the different adaptation time scales of various human activities is essential when interpreting morphodynamic changes in large-scale estuaries and deltas. © 2019 John Wiley & Sons, Ltd.     

江苏盐城盐纺井地球化学异常信息提取及机理分析

依据江苏省盐城市纺织厂井Ca²⁺和Cl^-月均值浓度,利用从属函数和自适应阈值法对该井进行了地球化学异常信息提取与分析;结合波速比和地磁谐波振幅比数据,利用膨胀扩容模式开展了映震机理讨论。结果表明,2008～2016年Ca²⁺浓度出现6次从属函数异常和5次自适应阈值异常,Cl^-浓度出现4次从属函数异常和5次自适应阈值异常,较好地对应了台站200km范围内M_L≥4.0的地震。此外,根据波速比、地磁谐波振幅比和该井地下水地球化学成因等分析结果,判断Ca²⁺、Cl^-浓度在震前的快速上升与深部流体上涌有关。     

Merging multi-source precipitation products or merging their simulated hydrological flows to improve streamflow simulation

Satellite and reanalysis precipitation products are widely utilized for streamflow simulation, which is one critical hydrological application, especially for ungauged regions. Possible ways to improve streamflow simulation are investigated in this study by merging multi-source precipitation products, or directly merging streamflow simulated with different precipitation products. Two satellite-based precipitation products, Tropical Rainfall Measuring Mission (3B42 Version 7) and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR), and one reanalysis precipitation product, National Centers for Environment Prediction-Climate Forecast System Reanalysis (NCEP-CFSR) are selected. Bayesian model averaging (BMA) is used to merge multi-source precipitation estimates and streamflow simulations. The results show that merging multi-source precipitation products made little difference to improve streamflow simulation. Merging multi-source streamflow simulations using the BMA generally achieved better performance on streamflow simulation, indicating that this approach is more efficient than merging multi-source precipitation products.     

秦王川盆地西缘断裂活动性综合研究及盆地成因分析

秦王川盆地西缘断裂发育于陇中盆地地震构造区内部,本文对其进行了综合研究。浅层人工地震探测表明,该断裂在最小埋深130m处有显示,联合钻探结果表明该深度处为新近纪湖相沉积地层,泥岩层顶面向盆地方向呈斜坡状,槽探未揭露出断层。综合研究表明该断裂发育在新近纪地层内部,并未上穿第四纪沉积物,属于前第四纪隐伏断层。秦王川盆地在古近纪—新近纪山间泛湖盆的基础上,由于区域构造应力不均匀挤压抬升,形成山间负向地形,成为第四纪多变环境下河流堆积的拗陷盆地。秦王川盆地西缘断裂不具有控制中强地震空间分布的作用和形成地表破裂的能力,对盆地的构造稳定性不构成影响,亦不影响兰州新区的规划发展。     

Major advances in studies of the physical geography and living environment of China during the past 70 years and future prospects

The natural environment provides material essentials for human survival and development. The characteristics,processes, regional differentiation and forcing mechanisms of the elements of the natural environment(e.g. geomorphology,climate, hydrology, soil, etc.) are the main objects of research in physical geography. China has a complex natural environment and huge regional differentiation and therefore it provides outstanding reserach opportunities in physical geography. This review summarizes the most important developments and the main contributions of research in the physical geography and human living environment in China during the past 70 years. The major topics addressed are the uplift of the Tibetan Plateau and the evolution of its cryosphere, the development of fluvial systems, the acidification of the vast arid region of the Asian interior, variations in the monsoon and westerly climate systems on multiple timescales, the development of lakes and wetlands, the watershed system model, soil erosion, past human-environment interactions, biogeography, and physical geographic zonality. After briefly introducing international research developments, we review the history of research in physical geography in China, focusing on the major achievements and major academic debates, and finally we summarize the status of current research and the future prospects. We propose that in the context of the national demand for the construction of an ecological civilization, we should make full use of the research findings of physical geography, and determine the patterns and mechanisms of natural environmental processes in order to continue to promote the continued contribution of physical geography to national development strategies, and to further contribute to the theory of physical geography from a global perspective.     

The Research of the Activity of the Piedmont Fault on the Tangshankou Segment of the Yuguang Basin Southern Marginal Fault

The Yuguang basin is a half-graben basin in the basin-range tectonic zone in northwest Beijing, located at the northern end of the Shanxi graben system, and the Yuguang basin southern marginal fault (YBSMF) controls the formation of this basin. A linear fault escarpment has formed in the proluvial fan on the piedmont fault zone of the Tangshankou segment of YBSMF. A trench across this escarpment reveals three paleo-earthquake events on two active faults. One fault ruptured at about 9ka for the first time, and then faulted again at about 7.3ka, causing the formation and synchronous activity of another fault. Finally, they faulted for the third time, but we cannot determine the faulting time due to the lack of relevant surface deposition. The accumulative vertical displacement of these three events is about 8.1m. We estimate that the average recurrence period of the piedmont fault is about 1.7ka, and the average slip rate of the piedmont fault is about 1.6mm/a. We also estimate the reference magnitude of each event according to the empirical formula.