Food Deserts in the Prairies? Supermarket Accessibility and Neighborhood Need in Edmonton,Canada*

The U.S. and U.K. literatures have discussed “food deserts,” reflecting populated, typically urban, low‐income areas with limited access to full‐service supermarkets. Less is known about supermarket accessibility within Canadian cities. This article uses the minimum distance and coverage methods to determine supermarket accessibility within the city of Edmonton, Canada, with a focus on high‐need and inner‐city neighborhoods. The results show that for 1999 both of these areas generally had higher accessibility than the remainder of the city, but six high‐need neighborhoods had poor supermarket accessibility. We conclude by examining potential reasons for differences in supermarket accessibility between Canadian, U.S., and U.K. cities.     

新一代天气雷达在泥石流灾害中的应用探讨

天气雷达的发展大致经历了4个阶段，其主要用于监测强对流天气、定量估计降水，是气象部门的重要探测和监测手段之一。新一代天气雷达观测的实时回波强度（Z）、径向风速（V）、速度谱宽（W）的回波图像中，提供了丰富的有关强对流天气的信息，综合使用Z、V、W的图像分析，有利于较准确和及时地监测灾害性天气。云南滑坡泥石流灾害高发区与云南暴雨中心有很好的对应关系，云南滑坡泥石流灾害空间分布与暴雨空间分布的空间相关系数为0．19，通过了0．05的显著性水平检验，也进一步说明云南暴雨在滑坡泥石流灾害发生中起着重要作用。以2004年7月5日德宏州特大山洪泥石流灾害为例子，探讨了新一代天气雷达在泥石流灾害的临阵预警中的应用。     

Seismic Subduction of the Nazca Ridge as Shown by the 1996–97 Peru Earthquakes

—By rupturing more than half of the shallow subduction interface of the Nazca Ridge, the great November 12, 1996 Peruvian earthquake contradicts the hypothesis that oceanic ridges subduct aseismically. The mainshock’s rupture has a length of about 200 km and has an average slip of about 1.4 m. Its moment is 1.5 × 10²⁸ dyne-cm and the corresponding M _w is 8.0. The mainshock registered three major episodes of moment release as shown by a finite fault inversion of teleseismically recorded broadband body waves. About 55% of the mainshock’s total moment release occurred south of the Nazca Ridge, and the remaining moment release occurred at the southern half of the subduction interface of the Nazca Ridge. The rupture south of the Nazca Ridge was elongated parallel to the ridge axis and extended from a shallow depth to about 65 km depth. Because the axis of the Nazca Ridge is at a high angle to the plate convergence direction, the subducting Nazca Ridge has a large southwards component of motion, 5 cm/yr parallel to the coast. The 900–1200 m relief of the southwards sweeping Nazca Ridge is interpreted to act as a "rigid indenter," causing the greatest coupling south of the ridge’s leading edge and leading to the large observed slip. The mainshock and aftershock hypocenters were relocated using a new procedure that simultaneously inverts local and teleseismic data. Most aftershocks were within the outline of the Nazca Ridge. A three-month delayed aftershock cluster occurred at the northern part of the subducting Nazca Ridge. Aftershocks were notably lacking at the zone of greatest moment release, to the south of the Nazca Ridge. However, a lone foreshock at the southern end of this zone, some 140 km downstrike of the mainshock’s epicenter, implies that conditions existed for rupture into that zone. The 1996 earthquake ruptured much of the inferred source zone of the M _w 7.9–8.2 earthquake of 1942, although the latter was a slightly larger earthquake. The rupture zone of the 1996 earthquake is immediately north of the seismic gap left by the great earthquakes (M _w ～8.8–9.1) of 1868 and 1877. The M _w 8.0 Antofagasta earthquake of 1995 occurred at the southern end of this great seismic gap. The M _w 8.2 deep-focus Bolivian earthquake of 1994 occurred directly downdip of the 1868 portion of that gap. The recent occurrence of three significant earthquakes on the periphery of the great seismic gap of the 1868 and 1877 events, among other factors, may signal an increased seismic potential for that zone.     

Saving lives in earthquakes: successes and failures in seismic protection since 1960

This paper will look at what we have and have not achieved in reducing the risks to human life from earthquakes in the last 50 years. It will review how success has been achieved in a few parts of the world, and consider what needs to be done by the scientific and engineering community globally to assist in the future task of bringing earthquake risks under control. The first part of the talk will re-examine what we know about the casualties from earthquakes in the last 50 years. Almost 80% of about 1 million deaths turn out to have been caused by just ten great earthquakes, together affecting a tiny proportion of the territory at risk from heavy ground shaking. The disparity between richer and poorer countries is also evident, not only in fatality rates, but also in their rates of change. But the existing casualty database turns out to be a very poor basis for observing such differences, not only because of the small number of lethal events, but also because of the very limited data on causes of death, types and causes of injury. These have been examined in detail in only a few, recent events. All that can be said with certainty is that a few wealthier earthquake-prone countries or regions have made impressive progress in reducing the risk of death from earthquakes, while most of the rest of the world has achieved comparatively little, and in some areas the problem has become much worse. The second part of the paper looks in more detail at what has been achieved country-by-country. Based on a new expert-group survey of key individuals involved in earthquake risk mitigation, it will examine what are perceived to be the successes and failures of risk mitigation in each country or group of countries. This survey will be used to highlight the achievements of those countries which have successfully tackled their earthquake risk; it will examine the processes of earthquake risk mitigation, from campaigning to retrofitting, and it will consider to what extent the achievement is the result of affluence, scientific and technical activity, political advocacy, public awareness, or the experience of destructive events. It will ask to what extent the approaches pioneered by the global leaders can be adopted by the rest. The final section of the talk will argue that it can be useful to view earthquake protection activity as a public health matter to be advanced in a manner similar to globally successful disease-control measures: it will be argued that the key components of such programmes—building in protection; harnessing new technology and creating a safety culture—must be the key components of earthquake protection strategies also. It will consider the contribution which the scientific and engineering community can make to bringing down today’s unacceptably high global earthquake risk. It will be suggested that this role is wider than commonly understood and needs to include: Building-in protection

戈壁风沙流结构特性及其意义

通过砾质戈壁风沙流野外实测数据的分析以及风洞模拟实验研究发现：戈壁风沙流结构具有与沙漠风沙流完全不同的风沙流特征,戈壁风沙地表的粗糙度随风速的增大而增加,其表面风沙流输沙量高度分布表现出独特的"象鼻"效应,在一定高度处呈现最大值,并随风速的增加而增高。该"象鼻"效应导致戈壁风沙流结构特征值λ远大于 1,不论风速多大,风沙流都处于未饱和状态的非堆积搬运状态。这种特殊性质比较清楚地解释了敦煌莫高窟千年来不被沙山埋没的谜底。并且在风沙防治工程实践中,采用砾石压沙措施,构造类似与砾质戈壁的下垫面,人工促使风沙流结构呈现"象鼻"形状,可使防沙工程达到理想的输导作用。     

The role of rock and clast fabric in the physical performance of crushed-rock aggregate

Crushed rock aggregate responds in a rational and predictable manner to the two tests designed by British Standards for assessing aggregate strength, i.e., Aggregate Impact (IV) and Crushing Values (ACV). The values obtained in both tests are influenced by intrinsic geological factors namely, petrology, petrography, rock and clast fabric. The Impact Value is affected further by procedural variables which have been identified and evaluated. When the effects of all these variables are known it is possible to understand the meaning of variation in test values within and between rock groups.Two new indices Impact and Aggregate Crushing Value Residues were introduced to probe more deeply the effects of cataclasis during testing. These have proved to be sensitive indicators of the geological variables like petrology and clast shape.In view of the rational behaviour of aggregate in the predictive tests it is possible to erect a new and more utilitarian classification of roadstone materials based on mechanical factors rather than the mineralogical-chemical basis of existing classifications. An outline of such a classification is presented.