大震前地震活动迁移速率bc值的变化     

林怀存  刘希强 《华北地震科学》1998,16(2):45-52

本文给出了地震活动纤移速率ｂｃ值预测方法,利用该方法对１９７２年以来发生在中国大陆及邻区４７次Ｍ≥６级地震前区域地震活动进行了计算,其结果为：地城活动迁移率ｂｃ值在４７次大震前出现明显的低值异常。为了检验该方法是否具有实用性,文中对中国西部５个不同区域进行试算,得出在５个不同区域内发生的约３９次地震前,ｂｃ值表现不同程度的异常特点．  相似文献   

Stability Dependence of Height Scales and Effective Roughness Lengths of Momentum and Heat Transfer Over Roughness Changes   总被引：1，自引：0，他引：1  

S.M. Ma  Jianmin Daggupaty 《Boundary-Layer Meteorology》1998,88(1):145-160

It is widely accepted that the correct formulation of an effective roughness length, defined as the area average of the roughness length in heterogeneous terrain, relies upon the appropriate de-termination of a height scale. At this height a meteorological quantity is approximately in equilibrium with local surface conditions and independent of horizontal position. This research note determines explicitly the different height scales from the perturbation solutions of flow velocity and temperature, as well as the fluxes of momentum and heat, in a stratified boundary layer. These solutions are derived from the asymptotic approximation theory and shown to capture major characteristics of momentum and heat transfer over heterogeneous terrain with changes of the underlying roughness lengths. The effective roughness lengths can then be computed by use of these height scales. The dependence of height scales and effective roughness lengths upon stratification is also discussed briefly.  相似文献   

Aerodynamic Roughness of Urban Areas Derived from Wind Observations   总被引：2，自引：1，他引：1  

C.S.B. Grimmond 《Boundary-Layer Meteorology》1998,89(1):1-24

This study contributes to the sparse literature on anemometrically determined roughness parameters in cities. Data were collected using both slow and fast response anemometry in suburban areas of Chicago, Los Angeles, Miami and Vancouver. In all cases the instruments were mounted on tall towers, data were sorted by stability condition, and zero-plane displacement (zd) was taken into account. Results indicate the most reliable slow response estimates of surface roughness are based on the standard deviation of the wind speed obtained from observations at one level. For residential areas, winter roughness values (leaf-off) are 80–90% of summer (leaf-on) values. Direct comparison of fast and slow response methods at one site give very similar results. However, when compared to estimates using morphometric methods at a wider range of sites, the fast response methods tend to give larger roughness length values. A temperature variance method to determine zd from fast response sensors is found to be useful at only one of the four sites. There is no clear best choice of anemometric method to determine roughness parameters. There is a need for more high quality field observations, especially using fast response sensors in urban settings.  相似文献   

低应变动测桩频率与检测          下载免费PDF全文

陈冬贵 《探矿工程》2004,31(6):11-12

简述了低应变动测桩的频率理论，推导出了频率公式，得出了激励材质与频率、所测桩长之间的关系。  相似文献   

Effects of sunspot cycle length and CO2 on air temperature along Qinghai-Xizang railway and air temperature''s trend prediction   总被引：15，自引：0，他引：15  

Li Dongliang  GUO Hui  WANG Wen  WEI Li 《中国科学D辑(英文版)》2004,47(Z1)

There are well coherences between annual averaged air temperatures at every meteorological station along the Qinghai-Xizang railway, and its 10-year moving average correlation coefficient is 0.92. Thus, the regional averaged annual mean temperature series along the Qinghai-Xizang railway (Trw) from 1935 to 2000 are constructed. The investigation is suggested that: Trw had significant responses to the 5-year lagged sunspot cycle length (SCL) and 15-year lagged concentration of atmospheric carbon dioxide (CO2), and the correlation coefficients between them are -0.76 (SCL) and 0.88 (CO2), respectively. The future SCL is predicted by the model of average generated function constructed with its main cycles of 76a, 93a, 108a, 205a and 275a. The result shows that the SCL would be becoming longer in the first half of the 21st century, and then it could be becoming shorter in the second half of the 21st century. Based on the natural change of SCL and the effect of double CO2 concentration, Trw in the 21st century is forecasted. It could warm up about 0.50℃ in the first half of the 21st century compared with the last decade of last century. The mean maximum air temperature could be likely about 0.20℃ in July and from 0.40℃ to 1.10℃ in January. The annual air temperature difference would likely reduce 0.3-1.00℃. The probability of above predictions ranges from 0.64 to 0.73.  相似文献   

Characterizing Fracture Spatial Patterns by Using Semivariograms     

R. D. JACOBI 《《地质学报》英文版》2002,76(1):89-99

Semivariogram is applied to fracture data obtained from detailed scanline surveys of nine field sites in western New York, USA in order to investigate the spatial patterns of natural fractures. The length of the scanline is up to 36 m. How both fracture spacing and fracture length vary with distance is determined through semivariogram calculations. In this study, the authors developed a FORTRAN program to resample the fracture data from the scanline survey. By calculating experimental semivariogram, the authors found five different types of spatial patterns that can be described by linear, spherical, reversed spherical, polynomial I (for a<0) and polynomial II (for a>0) models, of which the last three are newly proposed in this study. The well-structured semivariograms of fracture spacing and length indicate that both the location of the fractures and the length distribution within their structure domains are not random. The results of this study also suggest that semivariograms can provide useful infor  相似文献   

Influence Of The Atmosphere On Earth Rotation: What New Can Be Learned From The Recent Atmospheric Angular Momentum Estimates?     

Aleksander Brzeziński  Christian Bizouard  Sergei D. Petrov 《Surveys in Geophysics》2002,23(1):33-69

The interaction between the atmosphere and the underlying solid mantle is oneof the most important sources of changes in all three components of theEarth's rotation vector on different time scales. In this paper the NCEP/NCARreanalysis time series of four times daily atmospheric effective angularmomentum (EAM) estimates is used to investigate some selected aspects of theatmospheric influence on Earth rotation. Emphasis is placed on thecontroversial features which were difficult or impossible to study using theoperational EAM data, such as excitation of the free oscillations in polarmotion, the Chandler wobble (CW) and the free core nutation (FCN), or theroles of diurnal and semidiurnal atmospheric tides and atmospheric normalmodes in the rotational dynamics of the Earth.  相似文献   

Effects of surface water storage by soil roughness on overland‐flow generation     

F. Darboux  C. Gascuel‐Odoux  P. Davy 《地球表面变化过程与地形》2002,27(3):223-233

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Geometric adjustment of pools to changes in slope and discharge: a flume experiment     

Douglas M. Thompson   《Geomorphology》2002,46(3-4)

To characterize the factors controlling pool shape, 30 different forced pools were created utilizing a 50% triangular constriction in a 0.5-m wide, 6-m long recirculating flume. Pools were scoured from an initial plane bed of sand with a d₅₀ of 0.25 mm. Pool depth and length were measured and used as dependent variables in least-squares, multiple-regression analyses. Discharge, channel-bed gradient and energy slope were the independent variables. Additional linear-regression analyses were conducted with either pool depth or length and stream power. Results indicate that both pool depth and length are primarily a function of discharge. Channel-bed and energy slopes are also significantly related to pool length but are not significantly related to pool depth. Stream power is significantly related to both pool depth and length, but R² values for pool depth versus discharge indicate stronger relations than those between pool depth and stream power. Observations on the type of geometric adjustment indicate that pools may minimize their rate of energy expenditure primarily through elongation. In contrast, pool depth appears to be more sensitive to the characteristics of the constrictions that create the forced pools. The results suggest that many field studies may suffer from cross-correlation problems. In particular, channel erodibility may exert a more dominant influence on pool geometry than hydraulic controls in many constriction-influenced channels.  相似文献   

带状区域工程测量平面坐标系统的选择     

陈永立  陈群国 《测绘与空间地理信息》2008,31(4)

叙述了工程测量对平面坐标系统的选择要求及投影长度变形的计算方法,重点讨论了在线路较长、高程变化较大的带状区域工程施工中平面坐标系统的选择方法,并用实例进行了分析.  相似文献