An integrated multi-scale 3D seismic model of the Archaean Yilgarn Craton, Australia

The collection of a range of different seismic data types has greatly improved our understanding of the crustal architecture of Australia's Archaean Yilgarn Craton over the last few years. These seismic data include broadband seismic studies, seismic receiver functions, wide-angle recordings and mine-scale to deep seismic reflection transects. Each data set provides information on the three-dimensional (3D) tectonic model of the Yilgarn Craton from the craton scale through to the mine scale. This paper demonstrates that the integration and rationalisation of these different seismic data sets into a multi-scale 3D geological/seismic model, that can be visualised at once in a single software package, and incorporating all available data sets, significantly enhances this understanding. This enhanced understanding occurred because the integrated 3D model allowed easy and accurate comparison of one result against another, and facilitated the integrated questioning and interrogation across scales and seismic method. As a result, there are feedback questions regarding understanding of the individual seismic data sets themselves, as well as the Yilgarn Craton as a whole.The methodology used, including all the data sets in the model range, had to allow for the wide range of data sets, frequencies and seismic modes. At the craton scale, P-wave, S-wave and surface wave variations constrained the 3D lithospheric velocity model, revealing noticeable large-scale velocity variations within and across the craton. An interesting feature of the data, easily identified in 3D, is the presence of a fast S-wave velocity anomaly (> 4.8 km s^− 1) within the upper mantle. This velocity anomaly dips east and has a series of step-down offsets that coincide approximately with province and terrane boundaries of the Yilgarn Craton.One-dimensional receiver function profiles show variations in their crustal velocity across the craton. These crustal velocity variations are consistent with the larger-scale geological subdivision of the craton, and provide characteristic profiles for provinces and terranes. The receiver function results and the deep seismic reflection data both agree on the depth to the Moho, and both indicate an increase in Moho depth to the east. The 2D seismic refraction results in the south-west of the craton provide crustal thickness information, an indication of middle and lower crustal compositions, and information regarding the broad-scale architectural framework.At the province- and terrane-scale, the deep seismic reflection data and the mine-scale seismic data provide geometric constraints on crustal architecture, in particular the orientation of the region's fault systems as well as variations in the thickness of the granite–greenstone succession. Integration of the results from wide-angle seismic refraction data coincident with the deep seismic reflection data provided additional constraints on likely upper crustal lithologies.The integrated 3D seismic model implies the dominant geodynamic process involved the development of an orogenic belt that developed with a series of contractional (folding and thrusting) events, separated by equally important extensional events. The seismic reflection data in particular suggests that extensional movement on many shear zones was more common than previously thought.The seismic reflection data suggest that the dominant mineral systems involved deeply sourced fluid flowing up crustal-penetrating shear zones. These deeply sourced fluids were further focussed into sites located above fault-breached domal regions in the upper crust.     

Kinetics of the reactions of hydroxyl radicals with aliphatic ethers studied under simulated atmospheric conditions

Rate coefficients have been measured for the reactions of hydroxyl radicals with a range of aliphatic ethers by a competitive technique. Mixtures of synthetic air containing a few ppm of nitrous acid, isobutene and an ether were photolyzed in a Teflon-bag smog chamber. From the rates of depletion of the ether and of the isobutene, and based on the value of the rate coefficient k(OH+i-C₄H₈)=5.26×10^-11 cm³ molecule^-1 s^-1, the following rate coefficients were obtained for the hydroxyl radical reactions at 750 Torr and at 294±2K in units of 10^-12 cm³ molecule^-1 s^-1: diethylether = 12.0±1.1, di-n-propylether = 15.3±1.6, di-n-butylether=17.1±0.9, ethyl n-butylether = 13.5±0.4, ethyl t-butyl-ether = 5.6±0.5, and di-isobutylether = 26.1±1.6. The quoted error limits correspond to 2 standard deviations but do not include any contribution from k(OH+i-C₄H₈) for which the error limits are estimated to be about ±10%. The results are discussed in relation to the available literature data and considered in terms of the structure-activity relation for hydroxyl radical reactions with organic molecules.     

Seawall case studies and failure analysis of sloped concrete walls under static and dynamic loads

Concrete seawalls are structures in coastal facilities for shore and slope protections. Owing to several advantages of sloped or inclined walls such as minimum soil disturbance and less required earthworks, they can be considered as an appropriate alternative to vertical cantilever retaining walls. The combination of slab and strip semideep foundation instead of heel–toe slab foundations increases their capability for stability, erosion control, and storm wave energy dissipation. In this paper, three case studies from seawalls in which failure has occurred are presented and discussed. Technical performance of sloped walls against different internal and external instability factors is investigated, and comparisons are made between vertical and sloped (inclined) walls with respect to geotechnical and structural aspects through parametric study. Analysis indicates that the sloped retaining walls perform better from technical, practical, and economical standpoints. It was found that for identical static and dynamic loads, including earthquake and wave loads, inclined walls provide relatively higher safety factors against different criteria and exhibit more stable and practical performance compared with commonly used walls in practice. The case studies in this paper illustrate causes of failure in each case and gives suggestions for improving instability prevention of walls against static and dynamic loads.     

The geothermal regime of the northern Yukon and Mackenzie delta regions of northwest Canada — studies of two regional profiles

Temperature data from deep petroleum exploration wells and thermal conductivity estimates based on net rock analysis data have been used to make terrestrial heat flow estimates along two profiles across the sedimentary strata of the Mackenzie Delta, northern Yukon, and offshore Beaufort Sea regions.Both profiles exhibit low heat flow values that range from 34 mWm^–2 to 58 mWm^–2, and little change occurs over large distances in the continental part of the area. Low heat flow values (<40 mWm^–2) occur in the Beaufort-Mackenzie Basin and Rapid Depression, both of which are areas of thick successions of Cretacecus and Tertiary clastic sedimentary strata. High heat flow values of almost 80 mWm^–2 occur to the south in the Taiga Nahoni Foldbelt and values as high as 60 mWm^–2 are indicated along the Aklavik Arch Complex, northeast of Aklavik.The regional variations of effective thermal conductivity are insufficient to account for the heat flow variations along the profiles, and so these may indicate deep radiogenic or other heat sources.     

Applying historical ecology to natural resource management institutions: Lessons from two case studies of landscape fire management

Understanding the linkages between social and ecological systems is key to developing sustainable natural resource management (NRM) institutions. Frequently, however, insufficient attention is paid to the historical development of NRM institutions. Instead, discussion largely focuses on models of economic efficiency at the expense of the cultural, historical, and ecological contexts within which institutions develop. Here we use the research program of historical ecology to explore the development, maintenance, and change of two contemporary fire management institutions in northern Australia and Colorado, USA, to demonstrate how social institutions and ecological systems change and resist change over time and how institutions interact across scales to negotiate contrasting goals and motivations. We argue that these NRM institutions are not strictly speaking evolutionary or adaptive, and that historical context is critical when evaluating how and why particular institutions and institutional relationships develop. As with ecosystems, the present characteristics of the NRM institutions are dependent on what has happened before and their efficacy can only be evaluated retrospectively. Therefore, an understanding of history is essential to questions of the desirability and feasibility of institutional change where such shifts are required from an ecological, social, or economic perspective. We further propose that institutional conflict arises from the differing goals and motives of resource management institutions at different scales. Our cases reveal that larger-scale institutions can be successful at achieving narrowly defined goals but often fall short of achieving socially desirable sustainable outcomes. Our findings support the use of narratives of community history, place, and being in considering the resilience and sustainability of social-ecological systems. We offer that historical ecology is complementary with institutional and economic approaches to the analysis of NRM institutions, and possesses a particular strength in linking ecology to the values and norms of small social groups.     

石榴树包滑坡变形监测及演化趋势分析

石榴树包滑坡是长江三峡河段中大型滑坡之一黄腊石滑坡群的一个重要组成部分,它位于巴东县城东1.5km的长江北岸,下距三峡坝址66km。该滑坡体现代变形活动自20世纪70年代以来渐趋明显,特别是三峡水库蓄水以来,滑坡的变形十分显著。本文在调查分析石榴树包滑坡形态特征、结构特征及变形破坏特征的基础上,基于滑坡10多年的变形监测资料,研究了石榴树包滑坡的影响因素和变形演化特征和规律,并利用灰色GM(1,1)模型预测了滑坡的变形发展趋势,为滑坡减灾防灾实践和滑坡治理方案的设计提供了依据。     

Simulation studies on the pyrope-grossular garnet solid solution

The local structural response of Ca/Mg substitution and the energetic effects associated with dodecahedral ordering in the pyrope-grossular garnet solid solution are derived from a combination of static lattice energy calculations and Monte Carlo simulations. We start with a thorough analysis of the goodness of the empirical potential models used for the modelling of aluminosilicate garnets. The degree of polyhedral distortion was found to be a sensitive indicator for the quality of the model and, by comparison with experimental data, was used to select the best of several available empirical potentials. The Ca/Mg substitution on the dodecahedral site in garnet was found to produce strong local distortions in the surrounding tetrahedral and octahedral polyhedra. This arises from the absence of rigid unit modes (RUMS) in the garnet structure, because local rotations of otherwise rigid SiO₄ tetrahedra and AlO₆ octahedra cannot occur in order to accommodate different-sized divalent cations in the dodecahedral sites. Strain effects, therefore, mainly govern the dodecahedral substitution, and the corresponding strain field around a dodecahedral site has a minimum radius of 5?Å. Pyrope-grossular solid solution compositions were modelled using a supercell approach. For several garnet compositions many different configurations representing individual disordered arrangements were relaxed. The resulting energies were analyzed in terms of different-neighbour interactions to determine the parameters of a model Hamiltonian. The corresponding interaction energies were found to be virtually independent of composition. Surprisingly, the nearest-neighbour interaction between edge-sharing dodecahedra is of no particular significance in the garnets. Instead, the strongest interaction is only via the third-nearest neighbours, i.e. dodecahedra that are edge-shared to a common SiO₄ tetrahedron. This cannot lead to dodecahedral long-range order in garnets, but can produce significant amounts of short-range order. Monte Carlo simulations were performed on several compositions to determine the macroscopic effects such as NMR-based cluster occupancy, ordering energy and configurational entropy of the short-range ordering process. As expected, the samples tend to random disorder at high temperatures, and at low temperatures it is compositions nearer Py50Gr50 that depart most strongly from random mixing. For example, a maximum reduction of 3.5?J?mol^?1?K^?1 is predicted for Py75Gr25 and ～10?J?mol^?1?K^?1 for Py50Gr50. A comparison of NMR cluster occupancy with experimental ²⁹Si MAS NMR resonance intensity is partly successful. However, the changes in NMR cluster occupancy are relatively low (～5%) compared to changes in configurational entropy (～30%), implying that it might be difficult to estimate exact entropy data from ²⁹Si MAS NMR line intensities.     

论土体结构各层次的功能及其相互关系

土体广泛分布于地球的表层,是一个十分复杂的自然体。本文在论述了土体7个结构层次功能的基础上,从系统科学的角度阐述了各层次之间的辩证关系,包括低层次是高层次结构的基础;高层次对低层次结构的影响;层次间的协同作用;层次间交错、重叠与演变等。在与土体相关的研究工作和工程实践中,将土体作为一个系统进行合理的层次划分和分析,有助于复杂问题的简化,从而全面正确地掌握土体的工程性质及其形成机理。     

基于实时监测的河口糖厂滑坡监测系统研究

滑坡监测工作已经开展了多年,本文提出滑坡监测的内容包括基础因子、诱发因子和过程因子三部分,认为诱发因子和过程因子是滑坡监测的重点。针对降雨型滑坡监测,提出降雨-入渗-位移变形三者相结合的滑坡监测技术方法,并在河口糖厂滑坡监测工程中应用,实现了监测数据的实时自动采集、自动传输、自动入库的全自动监测系统。通过监测可知,河口糖厂滑坡降雨超过50mm达到67mm时,雨水入渗深度为7m; 10d累计降雨量达到110mm时,雨水入渗深度超过7m,但未至12m; 雨水由0m入渗至7m的入渗速率为0.53m h-1,由7m至12m的入渗速率为0.29m h-1。     

大数据与小数据结合：信息时代城市研究方法探讨

信息技术的快速发展引起了城市研究领域的“大数据”热潮,并带来了传统城市研究方法的变革。但是,其自身存在的诸多缺陷使得学者不得不重新考虑传统小数据的应用角色。但是,传统小数据并没有失去其应用价值,相反,以城市与居民行为活动关系研究为主体的信息时代的城市研究必要充分结合大数据与小数据,并探讨适宜的方法论与方法框架,从而应对日益复杂的城市问题和居民需求。提出“物质空间与活动空间结合”、“相关关系与因果关系结合”、“宏观分析与微观挖掘结合”的3个方法论,并在此基础上构建了“大样本空间发展评价+空间差异与联系发现+小样本影响因素探究”、“小样本模型构建+影响因素发现+大样本验证及挖掘”、“微观活动分析+活动空间界定+影响因素探究”3种方法框架,且分析了这些框架的具体应用,以期为未来的城市研究提供思路和方法借鉴。