洪灾风险评价与区划研究进展

洪灾风险评价是洪灾风险管理的首要步骤。洪灾风险区划是在洪灾风险评价基础上的宏 观分区, 有助于更清晰的把握洪灾风险的空间格局与内在规律。文章首先对洪灾风险相关概念进 行了阐述, 试图达到理清和规范的目的。然后对洪灾风险评价常用方法和洪灾风险区划研究进行 了评述。目前主要的洪灾风险评价方法有地貌学方法、水文水力学模型与系统仿真模拟方法、基 于历史灾情数据的方法、基于水灾史料和古洪水调查的方法、遥感与GIS 方法、基于洪灾形成机 制的系统分析方法等。最后对洪灾风险评价与洪灾风险区划研究进行了小结, 并指出了未来在洪 灾风险评价与区划的数据基础、洪灾风险评价的时空尺度、洪灾风险区划的理论与方法、洪灾风 险评价与区划的技术手段等方面的可能发展前景。     

地裂缝场地建筑结构动力响应特征及抗震设防研究

为研究地震作用下地裂缝场地建筑结构的动力响应特征,以西安地裂缝场地为研究背景,分别考虑独立基础、片筏基础、桩基础和桩筏基础上的框架结构,对结构峰值加速度、层间位移等动力响应特征及其影响因素和影响规律进行系统研究。研究结果表明：(1)地裂缝附近场地上的结构加速度响应和层间位移响应具有明显的放大效应,动力响应峰值随着距地裂缝距离的增大逐渐减小,最终趋于稳定,放大效应的影响范围约为24 m,此范围内的结构需提高抗震设防水平;(2)结构的峰值加速度随层高的增大而增大,整体呈现出“S”形,层间位移角随层高的增大先增大后减小,二者均表现出明显的“上盘效应”,即上盘结构响应强于下盘,且随着输入地震动强度的增大,上、下盘结构动力响应差异进一步扩大,上盘效应愈发显著;(3)片筏基础、桩基础和桩筏基础结构的加速度响应接近,而独立基础结构的加速度与前三者差异明显,但随着楼层的增大,基础形式对结构层间位移角的影响逐渐减弱;(4)上、下盘结构的峰值加速度、峰值位移大小及峰值出现的时间等存在一定差异,这是由于地震波经过地裂缝时发生复杂的反射和折射,结构受到非一致性激励造成的。     

A Nonlinear Representation of Model Uncertainty in a Convective-Scale Ensemble Prediction System

How to accurately address model uncertainties with consideration of the rapid nonlinear error growth characteristics in a convection-allowing system is a crucial issue for performing convection-scale ensemble forecasts. In this study, a new nonlinear model perturbation technique for convective-scale ensemble forecasts is developed to consider a nonlinear representation of model errors in the Global and Regional Assimilation and Prediction Enhanced System(GRAPES)Convection-Allowing Ensemble Predi...     

开孔率对明基床上开孔沉箱波浪反射系数影响的数值研究

开孔率是开孔沉箱波浪反射系数的重要影响因素,迄今为止关于开孔沉箱的物模试验研究成果(包括《防波堤设计与施工规范》)中,开孔率μ通常以线性关系反映在开孔沉箱波浪反射系数的计算关系式中,适用范围为0.2~0.4。但当μ0.2或μ0.4时,开孔率μ对波浪反射系数Kr的影响规律尚需进一步的研究探讨。现借助二维数值波浪水槽,在扩大了的开孔率取值范围内,模拟不规则波与可渗明基床上开孔沉箱的相互作用。结果表明:在0.2≤μ≤0.4的范围内,用线性关系描述开孔率μ对波浪反射系数Kr的影响是合适的;在μ0.4时,数模值和物模试验拟合的经验关系式的趋势是一致的;在μ0.2时,开孔沉箱反射系数K_r随开孔率μ的减小而增大,用物模试验拟合的经验关系式及《防波堤设计与施工规范》中计算公式的线性关系来描述开孔率μ对反射系数K_r的影响是不恰当的。研究成果对开孔沉箱消浪机理的深入认识和开孔沉箱结构的优化设计具有重要意义。     

海岸破波带内悬沙空间分布试验研究和解析表达式

关于海岸破波带内悬沙浓度水平和垂向分布的研究对于计算海岸输沙率和地形演变具有重要意义。本研究进行了规则波、波群和不规则波三种波浪情况破波带内悬沙浓度的水平和垂向分布的试验测量。试验在大尺度波浪水槽进行,接近实际海岸波况尺度。给出了破波带内多断面悬沙垂向分布的细致测量结果,并以此为基础给出了预报实际海岸破波带内悬沙浓度水平和垂向分布解析表达式,讨论了形成这些分布的物理原因和不同波况、不同破波带区域对分布的影响。     

The REM Adjoint System and Its 4DVar Data Assimilation Experiments

The Regional Eta-coordinate Model(REM) has performed well in forecasting heavy rainfalls in China in recent years.A four-dimensional variational assimilation system(4DVar) is developed to improve the forecast skill of the REM.The tangent linear model and adjoint model codes are written according to thecode to coderule,and the establishment of the REM adjoint modeling system is introduced in detail in this paper.The tangent linear and adjoint models of the REM are validated against the observational data,...     

The response of vegetation at the end of the last glacial period (MIS 3 and MIS 2) in littoral areas of NW Iberia

This paper describes and discusses the palaeobotanical data obtained from organic levels of two exposed deposits on the Atlantic shore of the northwestern Iberian Peninsula. Radiocarbon dating assigns these levels to a period of marine regression at the end of MIS 3 and the beginning of the Last Glacial Maximum. The pollen record shows an initial predominance of tree taxa (mainly deciduous, including the presence of Fagus far from its current limit), followed by an episode of partial forest retraction related to the end of MIS 3 and the beginning of the Last Glacial Maximum. However, the presence of numerous tree taxa in the record, even during the cold intervals associated with Heinrich events, points to the existence of sheltered refugia for these species during this period, in keeping with the conclusions of recent reviews of the vegetation dynamics of this region for the Lateglacial and the Holocene.     

Mantle dynamics of the Paleoproterozoic North China Craton: A perspective based on seismic tomography

We investigate the mantle dynamics beneath the North China Craton (NCC) and surrounding regions based on a synthesis of recent P-wave mantle tomographic data down to depths of 600–800 km and their correlation with the surface geological features, with particular reference to the Paleoproterozoic tectonic events associated with the incorporation of the NCC within the Columbia supercontinent amalgam. From the tomographic images, we identify a hot corridor in the mantle transition zone beneath the central region of the Western Block of the NCC sandwiched between two cold corridors. This scenario is similar to the donut-shaped high-velocity anomaly surrounding a region of low-velocity anomaly in the lowermost mantle under the Pacific and suggests that the cold regions might represent slab graveyards which provide the fuel for the plumes rising from the center. A tomographic transect along the collisional suture of the NCC with the Columbia supercontinent, covering the Yinshan-Ordos Blocks in the Western Block through the Central Orogenic Belt and into the Eastern Block of the NCC reveals a ca. 250 km thick lithospheric keel below the Ordos Block defined by a prominent high-velocity anomaly. We identify slab break-off and asthenospheric upwelling in this region and suggest that this process probably initiated the thermal and material erosion of the tectosphere beneath the Eastern Block from the Paleoproterozoic, which was further intensified during the Mesozoic when a substantial part of the sub-continental mantle lithosphere was lost. We visualize heat input from asthenosphere and interaction between asthenosphere and overlying carbonated tectosphere releasing CO₂-rich fluids for the preservation of ultra-high temperature (ca. 1000 °C) metamorphic rocks enriched in CO₂ as well as high-pressure mafic granulites as a paired suite in this region. We also identify a hot swell of the asthenosphere rooted to more than 200 km depth and reaching up to the shallow mantle in the tomographic section along 35°N latitude at a depth of 800 km. This zone represents a cross-section through the southern part of the NCC. The surface distribution of Paleoproterozoic Xiong’er lavas and mafic dykes in this region would indicate that this region might have evidenced similar upwellings in the past. Our study has important implications in understanding the evolution of the NCC and suggests that the extensive modification of the mantle architecture and lithospheric structure beneath one of the fundamental Precambrian nuclei of Asia had a prolonged history probably dating from the Paleoproterozoic suturing of the NCC within the Columbia supercontinent amalgam.     

The Characteristics of Migration of Ore Solutions in No.6 East Tin Deposit of the Songshujiao Orefield, Gejiu

No. 6 East tin deposit in the Songshujiao orefield, Gejiu, is characterized by one-stage hydrothermal activity and monotonous country rocks. The authors selected this deposit and used the multivariate statistical analysis to study the types of association of main ore-forming elements at different temperatures and pressures and their distribution in the deposit. On that basis combined with the structural analysis of the deposit, the recto-geochemical features of No.6 East tin deposit have been revealed and the direction and channel of migration of the ore solutions in faults and the deposit have been deduced. This research can appropriately elucidate the control of faults on the migration of ore solutions and the sites where ore solutions are dispersed and accumulated, thus providing the theoretical basis for the prediction of hydrothermal deposits in question.     

黔南桂西早中三叠世碳酸盐台地边缘和斜坡沉积模式及其演化

黔南桂西地区(东经105°-107°,北纬24°20＇-26°40＇)地跨扬子准地台和加里东褶皱带(华南褶皱带)两个一级大地构造单元。属于南盘江沉积盆地的北部或西北边缘。区内早、中三叠世碳酸盐地层出露良好、层序完整,为台地边缘和斜坡沉积。详细研究该区碳酸盐台地边缘和斜坡沉积,对了解台地边缘特征和演化、海平面变化以及边缘的构造作用等有着重要的理论意义,为确定三叠糸南盘江沉积盆地的西北或北部边缘的构造性质提供可靠的沉积学依据。