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非饱和砂土抗拉强度的试验研究

含水合物土的抗拉强度特性对含水合物地层的稳定评估具有重要意义。以黏质粉土为赋存介质,利用四氢呋喃(THF)合成含水合物土试样,在冷冻库中利用改进后的单轴拉伸装置研究了含水合物土单轴抗拉强度特性。试验结果表明水合物饱和度、试样干密度、细粒含量对含水合物土的抗拉强度存在明显影响。随着水合物饱和度的增加,抗拉强度呈现指数函数的增长趋势。干密度和细粒含量对抗拉强度的影响在不同的水合物饱和度情况下影响不同,在低水合物饱和度情况下,干密度和细粒含量的增加会使抗拉强度增强;而在较高的水合物饱和度情况下,抗拉强度则随着干密度和细粒含量增加而降低。此外,通过分析含水合物土的波速特性,建立抗拉强度与波速之间的经验关系式。这一关系式对采用声波来估算含水合物土试样的抗拉特性具有重要的参考意义。     

中国地级以上城市土地经济密度差异的时空演化分析

以中国336个地级以上城市为研究对象,利用核密度估计和探索性空间数据分析方法,对2001~2014年中国地级以上城市土地经济密度差异的时空格局演化及影响因素进行分析和探讨。结果表明：① 中国地级以上城市土地经济密度的总体水平不断提高,平均值从2001年的4.769亿元/km²增加至2014年的15.375亿元/km²,但地区差距逐渐扩大;② 中国地级以上城市土地经济密度表现出显著的全局空间正相关性,相邻地市相互影响,呈现出“高–高”或“低–低”的空间集聚态势,且从LISA集聚图来看,城市土地经济密度通过空间聚类可以划分为“高水平均质型地域”、“塌陷型地域”、“极化型地域”和“低水平均质型地域”4种类型,不同地域类型的空间分布范围和稳定性等都存在差异;③ 中国地级以上城市土地经济密度冷、热点区域的空间分布具有相对稳定性,总体上表现出“东热西冷”的分布格局,热点区主要分布在东部的京津冀地区、长江三角洲地区和珠江三角洲地区等,广大中、西部地区则大多处于低值簇,属于城市土地经济密度的冷点区或次冷点区;④ 自然条件状况决定城市土地的供给能力和开发潜力,是导致中国地级以上城市土地经济密度差异的基础性因素,区域经济发展水平、经济发展政策、土地利用管理政策也会对城市土地经济密度差异造成一定程度的影响。     

利用JCZ-1T地震计BB通道观测数据检测地球自由振荡

采用库尔勒台JCZ-1T地震计BB通道垂直向的观测数据,利用功率谱密度估计方法,在没有对观测资料进行任何改正的情况下,获取2016-03-02印尼苏门答腊岛海域7.8级和2016-04-17厄瓜多尔7.5级大地震激发的0S7～0S60基频球型自由振荡,并与PREM模型理论值进行对比分析。结果表明,实测值与理论值相吻合,除部分振型与理论值偏差较大以外,其余振型与理论值偏差均小于0.1％。印尼苏门答腊岛海域7.8级地震所检测的球型振荡能量频谱分布及振型与厄瓜多尔7.5级地震所检测的球型振荡有一定差别,前者所能检测的振型数量相对较多。     

Quantitative geomorphological analysis of drumlins in the Peterborough drumlin field,Ontario, Canada

Drumlins are enigmatic subglacial landforms that have been interpreted to form by a number of processes, including incremental accumulation of till, erosion of previously deposited sediment, catastrophic meltwater floods, and sediment deformation. However, relatively little is known about the controls on drumlin formation, such as spatially variable glacial processes or substrate characteristics, and how these controls may be identified from variations in drumlin morphology within a single drumlin field. This paper explores a computational method that allows identification of drumlins and extraction of their morphological characteristics from existing topographic digital data for a portion of the Peterborough drumlin field in Ontario, Canada. Spatial and non‐spatial analysis of the form and distribution of drumlins across the study area identifies drumlin characteristics such as size, elongation ratio, symmetry and long axis orientation and shows that drumlins are not randomly distributed across the region and their form characteristics have distinct regional trends. Kernel density analysis is used to identify the regional trends in drumlin characteristics. Factors that appear to influence the form and distribution of drumlins in the study area include sediment thickness, length of time beneath the ice, ice velocity and direction of ice movement. The distribution of particularly well developed asymmetric and elongate drumlins coincides with the location of a broad bedrock low and is interpreted to identify the former location of a fast‐flowing ice stream.