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排序方式: 共有72条查询结果,搜索用时 319 毫秒
61.
采用法向矢量单位圆描述结构面剖面线粗糙度,从各微分段的角度关系阐述粗糙度,进而将二维问题转化为一维问题处理并提出"角度粗糙度"的概念.考虑到各微分段的实际长度对粗糙度的贡献,采用加权均值与加权方差定量描述角度粗糙度;角度粗糙度越大表明该剖面越粗糙.对规则剖面线与不规则剖面线采用"角度粗糙度"进行描述,所得结果跟已有的剖... 相似文献
62.
Coastal communities in the western United States face risks of inundation by distant tsunamis that propagate across the Pacific Ocean as well as local tsunamis produced by great (Mw?>?8) earthquakes on the Cascadia subduction zone. In 1964, the Mw 9.2 Alaska earthquake launched a Pacific-wide tsunami that flooded Cannon Beach, a small community (population 1640) in northwestern Oregon, causing over $230,000 in damages. However, since the giant 2004 Indian Ocean tsunami, the 2010 Chile tsunami and the recent 2011 Tohoku-Oki tsunami, renewed concern over potential impacts of a Cascadia tsunami on the western US has motivated closer examination of the local hazard. This study applies a simple sediment transport model to reconstruct the flow speed of the most recent Cascadia tsunami that flooded the region in 1700 using the thickness and grain size of sand layers deposited by the waves. Sedimentary properties of sand from the 1700 tsunami deposit provide model inputs. The sediment transport model calculates tsunami flow speed from the shear velocity required to suspend the quantity and grain size distribution of the observed sand layers. The model assumes a steady, spatially uniform tsunami flow and that sand settles out of suspension forming a deposit when the flow velocity decreases to zero. Using flow depths constrained by numerical tsunami simulations for Cannon Beach, the sediment transport model calculated flow speeds of 6.5?C7.6?m/s for sites within 0.6?km of the beach and higher flow speeds (~8.8?m/s) for sites 0.8?C1.2?km inland. Flow speed calculated for sites within 0.6?km of the beach compare well with maximum velocities estimated for the largest tsunami simulation. The higher flow speeds calculated for the two sites furthest landward contrast with much lower maximum velocities (<3.8?m/s) predicted by numerical simulations. Grain size distributions of sand layers from the most distal sites are inconsistent with deposition from sediment falling out of suspension. We infer that rapid deceleration in tsunami flow and convergences in sediment transport formed unusually thick deposits. Consequently, higher flow speeds calculated by the sediment model probably overestimate the actual wave speed at sites furthest inland. 相似文献
63.
George R. Priest Chris Goldfinger Kelin Wang Robert C. Witter Yinglong Zhang António M. Baptista 《Natural Hazards》2010,54(1):27-73
To explore the local tsunami hazard from the Cascadia subduction zone we (1) evaluate geologically reasonable variability
of the earthquake rupture process, (2) specify 25 deterministic earthquake sources, and (3) use resulting vertical coseismic
deformations for simulation of tsunami inundation at Cannon Beach, Oregon. Maximum runup was 9–30 m (NAVD88) from earthquakes
with slip of ~8–38 m and M
w ~8.3–9.4. Minimum subduction zone slip consistent with three tsunami deposits was 14–15 m. By assigning variable weights
to the source scenarios using a logic tree, we derived percentile inundation lines that express the confidence level (percentage)
that a Cascadia tsunami will not exceed the line. Ninety-nine percent of Cascadia tsunami variation is covered by runup ≤30 m and 90% ≤16 m with a “preferred”
(highest weight) value of ~10 m. A hypothetical maximum-considered distant tsunami had runup of ~11 m, while the historical
maximum was ~6.5 m. 相似文献
64.
近年来,大型空间信息系统用户交互数据、业务监测数据、遥感影像数据等不断增长。高效的海量空间数据存储管理、迅速准确的检索、简便可靠快速的扩展已成为地学信息科学和水利业务应用领域日益关注的热点问题。本文结合NoSQL和全文检索技术,在江西省水利数据共享平台建设实践中基于MongoDB和Lucene开源软件库设计实现了OGC Web地图服务瓦片数据的存储管理、海量空间矢量数据和元数据的全文检索。平台建设完成后大幅提升了数据库管理和检索的效率,达到了100万条记录模糊检索毫秒级响应的目标,较好地实现了海量水利数据的管理,具有良好联通性和互动性、地理数据丰富的空间分析能力,期望能以此为基础带动江西省水利信息的交流融合,促进江西省水利现代化建设。 相似文献
65.
Local and remote response of the North Sea dynamics to morphodynamic changes in the Wadden Sea 总被引:1,自引:1,他引:0
The response of the tidal system in the southern North Sea to morphodynamic changes was investigated in a modelling study using fine resolution bathymetric observations available for 1982–2011. The Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) was set up for the different sets of bathymetries. One set of bathymetry was compiled from a large number of bathymetric measurements over many years, while the other two reflected bathymetry state in the area of Wadden Sea during 2000 and 2011, respectively. The temporal and spatial evolution of bathymetry was dominated by migration of tidal channels. The M4 tide showed larger sensitivity to bathymetric change in the Wadden Sea than the M2 tide, whereas the structure of the latter remained rather robust. The largest change of the tidal wave due to the differences in bathymetries was located off the North Frisian Wadden Sea. Traces of changes were also found far away from the regions of their origin because the tidal waves in the North Sea propagate the local disturbances basin-wide. This illustrated an efficient physical mechanism of teleconnectivity, i.e. effecting the local responses to the larger-scale or remote change of ocean bottom caused by erosion and deposition. The tidal distortion resulting from the relatively small bathymetric changes was substantial, particularly in the coastal zone. This is a manifestation of the nonlinear tidal transformation in shallow oceans and is crucial for the sediment transport and the morphodynamic feedback, because of the altered tidal asymmetry. 相似文献
66.
深水动力定位(DP)石油钻井平台依赖于高精度的位置参考基准,精密单点定位(PPP)技术是提供海上高精度位置服务的首选方式。目前海上石油钻井平台DP系统所需的高精度位置参考基准以GPS为主。随着我国北斗卫星导航系统(BDS)的全球组网,BDS实时PPP必将为全海域作业提供自主高精度的位置参考基准。本文就自主研制的BDS实时PPP产品开展实船应用研究,并接入南海作业的某DP系统。结果表明,相比于国外同类产品,收敛后的三维位置差异性小于50 cm,接入DP系统后BDS与GPS信息所占的权值一致,验证了BDS单系统实时PPP在海洋石油钻井平台DP系统应用的可行性。 相似文献
67.
George R. Priest Yinglong Zhang Robert C. Witter Kelin Wang Chris Goldfinger Laura Stimely 《Natural Hazards》2014,72(2):849-870
This paper explores the size and arrival of tsunamis in Oregon and Washington from the most likely partial ruptures of the Cascadia subduction zone (CSZ) in order to determine (1) how quickly tsunami height declines away from sources, (2) evacuation time before significant inundation, and (3) extent of felt shaking that would trigger evacuation. According to interpretations of offshore turbidite deposits, the most frequent partial ruptures are of the southern CSZ. Combined recurrence of ruptures extending ~490 km from Cape Mendocino, California, to Waldport, Oregon (segment C) and ~320 km from Cape Mendocino to Cape Blanco, Oregon (segment D), is ~530 years. This recurrence is similar to frequency of full-margin ruptures on the CSZ inferred from paleoseismic data and to frequency of the largest distant tsunami sources threatening Washington and Oregon, ~M w 9.2 earthquakes from the Gulf of Alaska. Simulated segment C and D ruptures produce relatively low-amplitude tsunamis north of source areas, even for extreme (20 m) peak slip on segment C. More than ~70 km north of segments C and D, the first tsunami arrival at the 10-m water depth has an amplitude of <1.9 m. The largest waves are trapped edge waves with amplitude ≤4.2 m that arrive ≥2 h after the earthquake. MM V–VI shaking could trigger evacuation of educated populaces as far north as Newport, Oregon for segment D events and Grays Harbor, Washington for segment C events. The NOAA and local warning systems will be the only warning at greater distances from sources. 相似文献
68.
69.
1109号超强台风“梅花”预报误差分析及思考 总被引:5,自引:2,他引:5
针对2011年第9号超强台风"梅花"的预报服务,中央气象台在其路径、强度和降雨预报方面均出现了一定偏差,在一定程度上造成了预报服务的被动。本文利用常规及非常规气象资料、业务数值预报模式、NCEP再分析资料(1°×1°)以及国家气象中心海气耦合模式对"梅花"的预报偏差进行了初步分析,结果发现:(1)"梅花"路径预报偏差的主要原因是乐观地估计了日本附近副热带高压向黄海的西进,而西风槽和双台风对"梅花"北上具有重要影响,"梅花"东侧的1110号台风"苗柏"东北行则对副热带高压南落具有一定指示意义;(2)当数值预报存在较大分歧时,如何更好地发挥集合/集成预报的作用,是进一步提高台风路径预报准确率的关键;(3)"梅花"强度预报偏差的主要原因是仅片面考虑了海温的影响,而忽视了干空气卷入和环境风垂直切变对台风强度变化的影响;(4)"梅花"降雨预报的偏差除了受"梅花"路径和强度预报的偏差影响外,还与业务预报中对"梅花"干台风特征的估计不足以及中低纬系统相互作用弱有关。 相似文献
70.
乌鲁木齐市某蔬菜基地富硒土壤地球化学特征及生物效应研究 总被引:1,自引:0,他引:1
对乌鲁木齐市某蔬菜基地富硒土壤地球化学特征及生物效应分析可知,以硒含量大于等于0.4 mg/kg标准圈定富硒土壤面积约52.89 km^2,硒含量均值为0.78 mg/kg;富硒土壤中重金属元素含量较低,养分元素含量适量丰富,农作物富硒效应较好,安全性较高。通过对土壤中硒元素赋存状态分析,发现区内土壤中存在大量土壤缓效硒,潜在供硒能力较强,且对植物吸收有利的有效硒占比达4.02%;土壤中硒的有效性不仅取决于总硒的含量,还与土壤pH、有机质等有一定关系;农作物中硒的含量水平可能受土壤中有效硒、总硒、有机质、pH等多个因素综合影响。 相似文献