坡地地形对竖向地震动反应谱特性的影响分析     

李英民  王丽萍  赵耀 《地震工程与工程振动》2010,30(5)

为分析坡地地形对竖向地震动反应谱特性的影响规律,采用有限元数值分析方法,对黏弹性岩质坡地在白噪声输入下的响应进行计算。分析了坡地地形对场地竖向反应谱及谱比的影响,研究了随着坡高及坡角的增加,坡地斜坡段及平台段竖向反应谱及谱比的变化规律,给出了坡地斜坡段及平台段设计竖向地震动放大系数,有关的研究结论可为坡地上工程结构的抗震设计提供参考。  相似文献   

Ionospheric Tomography Network of Egypt: A New Receiver Network in Support of the International Heliophysical Year     

T. W. Garner  T. L. Gaussiran II  J. A. York  D. M. Munton  C. M. Slack III  A. M. Mahrous 《Earth, Moon, and Planets》2009,104(1-4):227-235

The International Heliophysical Year (IHY) 2007 is an international scientific program designed to coordinate observations of the heliosphere, the region of space from the solar surface through the solar wind and various planetary magnetospheres to the planetary upper atmospheres. A particular emphasis is given to the development of long-term international collaborations that will study the external drivers to the space environment and climate. The Ionospheric Tomography Network of Egypt (ITNE) is one such collaboration. It is a new chain of ionospheric tomography receivers that will be deployed to investigate the equatorial regions of the Earth’s ionosphere. The distribution of plasma density within 20° of the magnetic equator is highly sensitive to forcing from the solar wind through a process known as the equatorial fountain. ITNE will provide new observations of the density structures associated with the equatorial fountain.  相似文献   

Accommodation of lithospheric shortening on Mercury from altimetric profiles of ridges and lobate scarps measured during MESSENGER flybys 1 and 2     

Maria T. Zuber  Laurent G.J. Montési  Steven A. Hauck II  Roger J. Phillips  David E. Smith  James W. Head III  Thomas R. Watters 《Icarus》2010,209(1):247-255

The Mercury Laser Altimeter on the NASA MESSENGER mission has ranged to several ridges and lobate scarps during two equatorial flybys of the planet Mercury. The tectonic features sampled, like others documented by spacecraft imaging and Earth-based radar, are spatially isolated and have vertical relief in excess of 1 km. The profiles also indicate that the faulting associated with their formation penetrated to tens of kilometers depth into the lithosphere and accommodated substantial shortening. To gain insight into the mechanism(s) of strain accommodation across these structures, we perform analytical and numerical modeling of representative dynamic localization mechanisms. We find that ductile localization due to shear heating is not favored, given our current understanding of thermal gradients and shallow thermal structure of Mercury at the time of ridge and scarp formation, and is likely to be of secondary importance at best. Brittle localization, associated with loss of resistance during fault development or with velocity weakening during sliding on mature faults, is weakly localizing but permits slip to accumulate over geological time scales. The range of shallow thermal gradients that produce isolated faults rather than distributed fault sets under the assumption of modest fault weakening is consistent with previous models for Mercury’s early global thermal history. To be consistent with strain rates predicted from thermal history models and the amount of shortening required to account for the underlying large-offset faults, ridges and scarps on Mercury likely developed over geologically substantial time spans.  相似文献   

Defining hydroclimatic regions using daily rainfall characteristics in the southern Appalachian Mountains     

Johnathan W. Sugg  Charles E. Konrad II 《International Journal of Digital Earth》2020,13(7):785-802

ABSTRACT

This paper addresses warm season hydroclimatic variability in the southern Appalachian region of the southeastern U.S., where precipitation can vary as much as 127?mm or more, with maximum seasonal totals exceeding 736?mm in extreme cases. Despite the occurrence of droughts, floods, and their socioecological impacts, hydroclimate variability is still poorly understood. This study characterizes the regional scale variations in the hydroclimate by examining the daily distribution of precipitation patterns in different topographic environments. Parameter-elevation relationships on independent slopes model (PRISM) gridded precipitation estimates are used to identify the location and frequency of different types of rainfall events. Several types of clustering algorithms are used as a regionalization approach to define areas where the precipitation regime exhibits similarities in its frequency of occurrence. The results are compared with internal validation statistics and a visualization is used to assess how well the resulting hydroclimatic regions align with different topographic environments. This study reveals the intricate spatial footprint of dry and wet regimes and demonstrates how clustering applications can be used with gridded climate data to determine where extremes are most likely to develop across mountain catchments.  相似文献   

Direct evaluation of effectiveness of prefabricated vertical drains in liquefiable sand     

Wen-Jong Chang  Ellen M. Rathje  Kenneth H. Stokoe  II  Brady R. Cox 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):723

A dynamic full scale testing program was performed to quantitatively assess the effectiveness of prefabricated vertical drains as a liquefaction countermeasure. The testing program involved a new in situ liquefaction testing technique, which uses a large hydraulic vibrator to generate waves propagating through an embedded instrumentation area to measure the coupled soil-pore water response. The effectiveness of prefabricated vertical drains is assessed experimentally by comparing the pore pressure generation, pore pressure dissipation, and settlement from two reconstituted soil specimens; one without a drain in place and the other with a single drain installed. Because the prefabricated drain was installed during the specimen preparation process, no accompanying densification during installation occurred. Therefore, the effect of drainage alone was evaluated. The testing results show that the drainage provided by prefabricated drains can significantly reduce pore pressure generation, accelerate post-shaking pore pressure dissipation, and limit associated settlement. The outcome also shows that the new developed in situ liquefaction testing technique can be an alternative to quantitatively evaluate the effects of various liquefaction remediation techniques.  相似文献   

Chowdhury and Stedinger's approximate confidence intervals for design floods for a single site     

R. Whitley  T. V. Hromadka II 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(1):51-63

A basic problem in hydrology is computing confidence levels for the value of the T-year flood when it is obtained from a Log Pearson III distribution in terms of estimated mean, estimated standard deviation, and estimated skew. In an important paper Chowdhury and Stedinger [1991] suggest a possible formula for approximate confidence levels, involving two functions previously used by Stedinger [1983] and a third function, λ, for which asymptotic estimates are given. This formula is tested [Chowdhury and Stedinger, 1991] by means of simulations, but these simulations assume a distribution for the sample skew which is not, for a single site, the distribution which the sample skew is forced to have by the basic hypothesis which underlies all of the analysis, namely that the maximum discharges have a Log Pearson III distribution. Here we test these approximate formulas for the case of data from a single site by means of simulations in which the sample skew has the distribution which arises when sampling from a Log Pearson III distribution. The formulas are found to be accurate for zero skew but increasingly inaccurate for larger common values of skew. Work in progress indicates that a better choice of λ can improve the accuracy of the formula.  相似文献   

The Pitman Canyon paleoseismic record: A re-evaluation of southern San Andreas Fault segmentation   总被引：2，自引：0，他引：2  

Gordon Seitz  Ray Weldon  II  Glenn P. Biasi 《Journal of Geodynamics》1997,24(1-4)

Correlation of three well-resolved paleoseismic records, including the Pitman Canyon site with its emerging record, presents a new possibility to understand fault segmentation. To be a useful concept, fault segment boundaries must be relatively stationary over multiple seismic cycles and must appear frequently in limiting the rupture extent of earthquakes; thus, sites on the same segment should share more paleoseismic events than those on different segments. A conclusive event correlation between sites is difficult or impossible due to dating uncertainties. However, often the data are adequate to preclude correlation and thus provide firm limits on rupture extent for those events. Thus clear non-correlations provide more information about segmentation than do unprovable potential correlations.The southern end of the most recent rupture in 1857, between Wrightwood and Pitman Canyon, is often used to define a segment boundary. However, there is an absence of significant non-correlation between the previous five Pitman Canyon events and the Wrightwood events. While both Pallett Creek and Wrightwood ruptured in 1857, only two of the previous five Wrightwood events can correlate with Pallett Creek events, which may or may not indicate that they actually do. These paleoseismic records do not support the existence of a segment boundary between Wrightwood and Pitman Canyon as defined by the 1857 rupture extent, suggesting a reevaluation of southern San Andreas Fault segmentation, and using historic ruptures to define segments in general.  相似文献   

Scale Dependency of Hydraulic Conductivity Measurements   总被引：8，自引：0，他引：8  

Charles W. Rovey II  Douglas S. Cherkauer 《Ground water》1995,33(5):769-780

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Confidence intervals for flood control design     

R. J. Whitley  T. V. Hromadka II 《Stochastic Environmental Research and Risk Assessment (SERRA)》1988,2(2):151-155

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Modeling land use and cover as part of global environmental change   总被引：9，自引：0，他引：9  

William E. Riebsame  William B. Meyer  B. L. Turner II 《Climatic change》1994,28(1-2):45-64

Land use and cover changes are important elements of the larger problem of global environmental change. Landuse patterns result in landcover changes that cumulatively affect the global biosphere and climate. We describe efforts to analyze the driving forces behind land transformations and to create land use models that can be linked to other types of global change models. Two efforts to model land use in the U.S. are reviewed. One projects aggregate agricultural, forest, and range land, and the other attempts to model forest land use change at the parcel scale in two mountain landscapes. We conclude with suggestions for new approaches that could clarify the role of land use/cover change in global change and in natural resources management.  相似文献