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161.
The infinitesimal and finite stages of folding in nonlinear viscous material with a layer-parallel anisotropy were investigated using numerical and analytical methods. Anisotropy was found to have a first-order effect on growth rate and wavelength selection, and these effects are already important for anisotropy values (normal viscosity/shear viscosity) < 10. The effect of anisotropy must therefore be considered when deducing viscosity contrasts from wavelength to thickness ratios of natural folds. Growth rates of single layer folds were found to increase and subsequently decrease during progressive deformation. This is due to interference between the single layer folds and chevron folds that form in the matrix as a result of instability caused by the anisotropic material behaviour. The wavelength of the chevron folds in the matrix is determined by the wavelength of the folded single layer, which can explain the high wavelength to thickness ratios that are sometimes found in multilayer sequences. Numerical models including anisotropic material properties allow the behaviour of multilayer sequences to be investigated without the need for resolution on the scale of individual layers. This is particularly important for large-scale models of layered lithosphere. 相似文献
162.
163.
This paper presents a case study of mesoscale convective band (MCB) development along a quasi-stationary front over the Seout metropolitan area.The MCB,which initiated on 1500 UTC 20 September 2010 and ended on 1400 UTC 21 September 2010,produced a total precipitation amount of 259.5 mm.The MCB development occurred during a period of tropopause folding in the upper level and moisture advection with a low-level jet.The analyses show that the evolution of the MCB can be classified into five periods:(1) the cell-forming period,when convection initiated; (2) the frontogenetic period,when the stationary front formed over the Korean peninsula; (3) the quasi-stationary period,when the convective band remained over Seoul for 3 h; (4) the mature period,when the cloud cover was largest and the precipitation rate was greater than 90 mm h-1; and (5) the dissipating period,when the MCB diminished and disappeared.The synoptic,thermodynamic,and dynamic analyses show that the MCB maintained its longevity by a tilted updraft,which headed towards a positive PV anomaly.Precipitation was concentrated under this area,where a tilted ascending southwesterly converged with a tilted ascending northeasterly,at the axis of cyclonic rotation.The formation of the convective cell was attributed in part by tropopause folding,which enhanced the cyclonic vorticity at the surface,and by the low-level convergence of warm moist air and upperlevel divergence.The southwesterly flow ascended in a region with high moisture content and strong relative vorticity that maintained the development of an MCB along the quasi-stationary front. 相似文献
164.
松辽盆地反转构造运动学特征 总被引:20,自引:4,他引:16
摘要:松辽盆地是我国东北部一大型的中新生代板内裂谷盆地,嫩江期末至明水期末的构造反转作用是盆地发育的重要阶段。拉张—挤压构造作用的交替,使构造通过先存正断层逆向再活动和褶皱两种方式实现构造缩短。本文从定性和定量两方面论述了松辽盆地反转构造形成的运动学特征 相似文献