Seismic behavior of breakwaters on complex ground by numerical tests: Liquefaction and post liquefaction ground settlements

A large number of breakwaters have been constructed along coasts to protect humans and infrastructures from tsunamis.There is a risk that foundation soils of these structures may liquefy,or partially liquefy during the earthquake preceding a tsunami,which would greatly reduce the structures’capacity to resist the tsunami.It is necessary to consider not only the soil’s liquefaction behavior due to earthquake motions but also its post-liquefaction behavior because this behavior will affect the breakwater’s capacity to resist an incoming tsunami.In this study,numerical tests based on a sophisticated constitutive model and a soil-water coupled finite element method are used to predict the mechanical behavior of breakwaters and the surrounding soils.Two real breakwaters subjected to two different seismic excitations are examined through numerical simulation.The simulation results show that,earthquakes affect not only the immediate behavior of breakwaters and the surrounding soils but also their long-term settlements due to post-earthquake consolidation.A soil profile with thick clayey layers beneath liquefied soil is more vulnerable to tsunami than a soil profile with only sandy layers.Therefore,quantitatively evaluating the seismic behavior of breakwaters and surrounding soils is important for the design of breakwater structures to resist tsunamis.     

2016年门源6.4级地震地磁谐波振幅比异常特征分析

2016年门源6.4级地震为甘—青地区孤立地震事件,且震中附近地磁台站分布均匀,分析总结此次地震前后地磁谐波振幅比变化特征。结果显示：①地震发生前后,震中附近台站地磁谐波振幅比下降—转折—恢复的异常变化过程,持续时间约1—2年;②震中距较小的台站记录显示,地震基本发生在谐波振幅比曲线转折恢复的变化后期阶段,且异常持续时间长;震中距较大的台站记录显示,地震一般发生在曲线趋势性下降—转折阶段,且异常持续时间稍短;③地震发生后,距震中较近的台站1年内Y_ZHx（NS）和Y_ZHy（WE）方向所有或大部分周期基本趋于恢复状态,且同步变化;距震中较远的台站1年内Y_ZHx（NS）和Y_ZHy（WE）方向大部分周期未达到恢复状态,且不同步变化显著。     

用CAP方法研究重庆荣昌2014年2月23日M_L3.8地震震源机制

利用CAP(cut-and-paste)法反演2014年2月23日重庆荣昌ML3.8地震震源机制,得到MW震级为3.04,节面Ⅰ走向46°、倾角44°、滑动角74°,节面Ⅱ走向247°、倾角48°、滑动角104°,P轴方位147.25°、仰角-2.09°,T轴方位46°、仰角-78.76°,表明该地震是带走滑分量的逆冲型地震。CAP测定的这次ML3.8地震的震源深度为3km,在油气的储层内,震源机制解中节面Ⅱ走向、倾角与震中附近的一条深度为1700m以下走向为SW230°倾向NW,倾角约45°的"腹底"逆断层基本一致。震中位于荣昌天然气田,附近有几口废水回注深井,曾发生大量的注水诱发地震。本次地震亦有可能是在区域主应力场的作用下,注水后岩石的孔隙压发生变化触发了盆地盖层内"腹底"断层活动的结果。     

The sources and seasonal fluxes of particulate organic carbon in the Yellow River

The Yellow River transports a large amount of sediment and particulate organic carbon (POC), which is thought to mainly derive from erosion of the Chinese Loess Plateau (CLP). However, the compositions, sources and erosional fluxes of POC in the Yellow River remain poorly constrained. Here we combined measurements of mineralogy, total organic carbon content (OC_total), stable organic carbon isotopes (δ¹³C_org), radiocarbon (¹⁴C) activity of organic matter in bulk suspended sediments collected seasonally from the upper and middle Yellow River, to quantify the compositions and fluxes of the POC and to assess its sources (biospheric and petrogenic POC, i.e. POC_bio and POC_petro, respectively). The results showed that the POC loading of sediments was controlled by mineralogy, grain size and specific surface area of loess particles. The F_mod of POC (0.71 to 0.31) can be explained by mixing of POC_petro with modern and aged POC_bio. A binary mixing model based on the hyperbolic relationship of the F_mod and OC_total revealed a wide range of ages of POC_bio from 1300 to 11100 ¹⁴C years. Relative to the upstream station, the annual POC_bio and POC_petro fluxes in the Yellow River are more than doubled after it flows crossing the CLP within 35% drainage area gain, resulting in POC_bio and POC_petro yields of the CLP at 3.50 ± 0.59 and 0.48 ± 0.49 tC/km²/yr, respectively. POC flux seasonal variation revealed that monsoon rainfall exerts a first-order control on the export of both POC_bio and POC_petro from the CLP to the Yellow River, resulting in more than 90% of the annual POC exported during the monsoon season. Around one third of annual POC erosional flux was transported during a storm event period, highlighting the important role of extreme events in POC export in this large river. © 2020 John Wiley & Sons, Ltd.     

中文权威核心期刊学术论文价值综合评价体系的构建与实践:以地理学科为例

深入解读中国科研评价中存在的3个现象,即过度重视SCI(Science Citation Index)/SSCI(Social Sciences Citation Index)、“唯高影响因子”和“唯发表成果为王”。其中,过度重视SCI/SSCI直接或间接造成了“唯高影响因子”和“唯发表成果为王”现象的出现,成为中国学术界当前亟待解决的重要问题。“科研评价和学术地位认定政策”“学术成果影响力”和“学术影响力评价”是影响中文权威核心期刊学术论文价值认可度的3大公因子。结合对中国地理学领域为主的近千位科研人员的感知调查,构建了包括期刊影响因子、论文被引频次、论文下载量、论文社会价值以及论文创新性5个指标的新的学术论文价值综合评价模型。最后从国家、部委、学会、期刊和学者层面分别提出改革过度推崇SCI/SSCI的学术评定政策、树立科研成果服务国民经济主战场的导向;强化政策执行力与构建服务于学术本质的考核标准;发挥桥梁和纽带作用及制定和完善评价体系;提升文化自信、凸显特色化和差异化、强化市场化和增值多元化;增强母语成果自信和提升在中文权威核心期刊建立学术地位的动力等实践建议。     

Internal Tide Generation and Dissipation by Small Periodic Topography in Deep Ocean

Internal tides generated by a rough sea floor are an important source of mixing in the abyssal ocean. Two linear models are employed to evaluate the conversion rate from barotropic tides to internal tides and the energy distribution in each mode. Considering the periodicity of internal tides, the topography is represented by periodically distributed knife edges and sinusoidal ridges within one wavelength of mode-1 internal tides. The knife edges generate greater internal tides than the sinusoidal ridges due to their sharp shape, which approximates an extremely supercritical condition. Energy flux concentrates in modes whose numbers are multiples of the knife edge or ridge number. Then, a fully nonlinear model that integrates viscosity and diffusion is implemented, and its results are compared with those of the linear model. Internal wave rays generated in the nonlinear model show a distribution similar to the linear models' prediction. High dissipation rates coincide with the rays, suggesting that nonlinear wave-wave interaction is a dominant mechanism for internal tide dissipation in the abyssal ocean.     

An Assessment of Snow Cover Duration Variability Among Three Basins of Songhua River in Northeast China Using Binary Decision Tree

The dynamics of snow cover differs greatly from basin to basin in the Songhua River of Northeast China, which is attributable to the differences in the topographic shift as well as changes in the vegetation and climate since the hydrological year (HY) 2003. Daily and flexible multi-day combinations from the HY 2003 to 2014 were produced using Moderate Resolution Imaging Spectroradiometer (MODIS) from Terra and Aqua remote sensing satellites for the snow cover products in the three basins including the Nenjiang River Basin (NJ), Downstream Songhua River Basin (SD) and Upstream Songhua River Basin (SU). Snow cover duration (SCD) was derived from flexible multiday combination each year. The results showed that SCD was significantly associated with elevation, and higher SCD values were found out in the mountainous areas. Further, the average SCDs of NJ, SU and SD basins were 69.43, 98.14 and 88.84 d with an annual growth of 1.36, 2.04 and 2.71 d, respectively. Binary decision tree was used to analyze the nonlinear relationships between SCD and six impact factors, which were successfully applied to simulate the spatial distribution of depth and water equivalent of snow. The impact factors included three topographic factors (elevation, aspect and slope), two climatic factors (precipitation and air temperature) and one vegetation index (Normalized Difference Vegetation Index, NDVI). By treating yearly SCD values as dependent variables and six climatic factors as independent variables, six binary decision trees were built through the combination classification and regression tree (CART) with and without the consideration of climate effect. The results from the model show that elevation, precipitation and air temperature are the three most influential factors, among which air temperature is the most important and ranks first in two of the three studied basins. It is suggested that SCD in the mountainous areas might be more sensitive to climate warming, since precipitation and air temperature are the major factors controlling the persistence of snow cover in the mountainous areas.     

Implications for Cultural Landscape in a Chinese Context: Geo-analysis of Spatial Distribution of Historic Sites

The protection of historic sites, especially their relationship with urban development, has become a worldwide issue, both in developed and developing countries. In the context of rapid urbanization in China, the realistic compatibility between urban construction and the protection of historic sites is always a key research topic. In this study, first, to comprehend their spatial distribution patterns, 828 historic sites throughout the country are selected based on certain criteria. Then, we conduct quantitative research using GIS software, adopting indicators that include Nearest Neighbor Index, Gini Coefficient, and Geographic Concentration Index to analyze the spatial characteristics of historic sites on the three levels of city, province and nation. The results indicate that the spatial distribution of the different types of historic sites is an agglomeration on the nationwide scale, most of which is located in the regions of the Pearl (Zhujiang) River Delta, Yangtze (Changjiang) River Delta and Beijing-Tianjin Region. Because the majority of historic sites are located within approximately 10 km of the downtown area, a certain pattern has emerged, showing that the larger cities own more historic areas, which are in a more incomplete state of preservation, indicating the fragmentation of heritage spaces. The formation mechanism of the historic sites’ distribution pattern is based on the conditions of the cities/towns as well as the bid-rent theory.     

"亚太六号"卫星发射日气象保障及数值模拟分析

2005年4月11～12日西昌发射场遭遇了一次寒潮天气过程,而这正值"亚太六号"卫星预定的发射日.针对这一情况,发射中心气象部门利用多种探测手段,综合分析各类气象信息,采取逐步逼近的方式,在复杂条件下抓住了有利战机,准确预报出了此次寒潮过程及对场区的影响程度,圆满完成了气象保障任务.此外,利用相关资料对发射日资料进行了数值模拟,结果表明,MM5模式较好地模拟了本次天气过程中的降水、降温和增压过程.     

基于GF-1卫星遥感的冰川边界识别

高分一号（GF-1）卫星的成功发射开启了国产高分辨率对地观测的新时代, 为探讨国产高分卫星在冰川边界识别中的有效性, 在缺少短波红外和热红外波段的情况下, 将GF-1影像、 建立的波段比值Band1/Band4, 数字高程模型和坡度相结合, 采用面向对象的分析方法, 经过反复试验, 确定影像分割和合并尺度, 进而确定冰川边界的知识规则, 最终实现冰川边界的识别。以研究区第二次冰川编目数据集作为参考数据, 采用混淆矩阵的方法对识别结果进行验证, 总体精度和Kappa系数为90.05%和0.79。同时将识别结果与人工修订冰川边界进行对比, 可以发现除少量冰舌末端冰川外, 该方法可以有效地对冰川进行识别。建立的知识规则显示仅仅利用蓝色波段和DEM就可以有效地提取裸冰区, 波段比值、 坡度和纹理特征更有助于冰舌的提取。该研究表明GF-1卫星数据可以有效识别冰川范围, 为冰川研究提供可靠的数据和研究基础。