Estimating the elastic parameters of anisotropic media using a joint inversion of P-wave and SV-wave traveltime error     

R.J. Ferguson  M.K. Sen 《Geophysical Prospecting》2004,52(6):547-557

A method is presented to estimate the elastic parameters and thickness of media that are locally laterally homogeneous using P‐wave and vertically polarized shear‐wave (SV‐wave) data. This method is a ‘layer‐stripping’ technique, and it uses many aspects of common focal point (CFP) technology. For each layer, a focusing operator is computed using a model of the elastic parameters with which a CFP gather can be constructed using the seismic data. Assuming local homogeneity, the resulting differential time shifts (DTSs) represent error in the model due to anisotropy and error in thickness. In the (τ?p) domain, DTSs are traveltimes Δτ that connect error in layer thickness z, vertical slowness q, and ray parameter p. Series expansion is used to linearize Δτ with respect to error in the elastic parameters and thickness, and least‐squares inversion is used to update the model. For stability, joint inversion of P and SV data is employed and, as pure SV data are relatively rare, the use of mode‐converted (PSV) data to represent SV in the joint inversion is proposed. Analytic and synthetic examples are used to demonstrate the utility and practicality of this inversion.  相似文献   

Structure and tectonics of convergent plate margins     

Aleš Špi?ák  Ond?ej ?adek  E.Robert Engdahl 《Physics of the Earth and Planetary Interiors》2004,141(4):241

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Influence of the zone of weakness on dip angle and shear heating of subducted slabs     

Martin Kuka?ka  Ctirad Matyska 《Physics of the Earth and Planetary Interiors》2004,141(4):243-252

We study the importance of the zones of weakness and the pattern of downgoing flow in steady-state models of subducting lithosphere, which interacts mechanically and thermally with the ambient mantle. The non-linear system of governing equations consists of (i) the momentum equation in stream function formulation and (ii) the steady-state heat transfer equation including conduction and advection of heat and dissipation. A finite element method has been applied to this system. We consider the viscosity to be a non-linear function of both the temperature and the stream function. In steady-state two-dimensional (2D) flow, the stream function isolines follow material trajectories. They are used to follow the top of the subducting slab, which because of its possible increase in water content, is assumed to have a lower viscosity. The zone of weakness has been thus obtained in the self-consistent fashion since the stream function as well as the temperature are the output from our modeling and no a priori assumptions about the shape of the bending lithosphere are taken into account. It was shown that several orders decrease of viscosity in the zone of weakness is required to obtain the dip angle of about 45°. If the decrease of viscosity is not sufficient enough, the subducted slab either sinks almost vertically or does not exhibit a plate-like behavior. We have also demonstrated that shear heating can unrealistically increase at the zone of weakness for fast subductions if decrease of viscosity is underestimated.  相似文献   

一次强风暴的垂直环境特征数值模拟分析   总被引：4，自引：2，他引：4  

陈力强  周小珊  杨森 《气象》2004,30(9):3-8

应用MM 5模式对东北冷涡诱发的 2 0 0 2年 7月 1 2日强风暴进行了数值模拟 ,较成功地模拟出中尺度强对流风暴。发现冷涡后部中层干冷空气绝热下沉是东北冷涡 70 0hPa附近干暖盖形成和维持的重要机制 ,而低层暖湿气流爬升及干暖盖的抑制作用是东北冷涡强对流不稳定能量积累的重要机制。风暴发生前持续的低层西南风到中层西北风的风垂直切变产生的差动平流 ,加剧了层结不稳定 ,而风暴临近风垂直切变方向的快速逆转使热成风不平衡 ,必须通过激发垂直环流以适应其变化 ,对风暴发展有重要作用。  相似文献   

沈阳近百年的温度变化特征及其环流形势分析   总被引：7，自引：1，他引：7       下载免费PDF全文

周小珊  李辑  杨森  周广胜 《气象科学》2004,24(4):424-431

沈阳地处全球温度变化的敏感带，在近百年的温度观测记录中，沈阳的温度变化呈逐渐上升之势，近百年增高约1．7℃，这种上升趋势在冬季远比夏季明显。沈阳的年平均温度变化有一个12a的周期，各周期温度基本呈阶梯状上升，20世纪末的周期冬季平均温度比世纪初的周期升温2．8℃左右。从近50a的极端温度的变化趋势来看，极端最低温度明显升高，而极端最高温度并没有上升，变化趋势甚至略下降，以致冬、夏两季温差缩小。从沈阳的最低平均温度和最高平均温度变化来看，两者均随时间逐渐升高，说明沈阳市的增温不仅是最低温度升高造成的，最高温度的增温作用亦十分重要。从冬季环流形势分析来看，东亚大槽及其后弱脊和地面蒙古高压在上世纪80年代、90年代明显减弱，使得冷空气向南侵袭的径向气流减弱，是导致位于冷空气通道中的沈阳冬季增温明显的原因之一。  相似文献   

A Modeling Study of the Effects of Anomalous Snow Cover over the Tibetan Plateau upon the South Asian Summer Monsoon   总被引：1，自引：0，他引：1  

刘华强  孙照渤王举 闵锦忠 《大气科学进展》2004,21(6):964-975

The effect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SNINIR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo effect, which is compensated by weaker upward sensible heat flux associated with colder surface temperature, whereas the effects of snow melting and evaporation are relatively smaller.The anomalies of surface heat fluxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May.The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this influence is only obvious in early summer and almost disappears in later stages.  相似文献   

Tetrahedral Plots of the Phase Relations for Basalts     

Sven Maal?e  Richard N. Abbott Jr. 《Mathematical Geology》2005,37(8):869-893

The phase relations of quaternary systems are generally represented by projections onto ternary compositional planes. Such projections often obscure relationships that would only be evident in a three-dimensional tetrahedral plot. The tetrahedral plot requires that compositions of the minerals and melts be transformed into Cartesian coordinates. It is shown here how this transformation is carried out. The application is demonstrated by tetrahedral plots of experimental melt compositions of partially molten lherzolite. Furthermore, the plot can be used to evaluate whether or not a particular basaltic composition represents a primary melt. The methods are applicable to any four-component system.  相似文献   

Geochemistry of Rohtas Limestone from Vindhyan Supergroup,Central India: Evidences of detrital input from felsic source   总被引：1，自引：0，他引：1  

Shinjana Sen  Meenal Mishra 《Geochemistry International》2015,53(12):1107-1122

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Spatially controlled Fe and Si isotope variations: an alternative view on the formation of the Torres del Paine pluton     

Norbert?A.?GajosEmail author  Craig?C.?Lundstrom  Alexander?H.?Taylor 《Contributions to Mineralogy and Petrology》2016,171(11):93

We present new Fe and Si isotope ratio data for the Torres del Paine igneous complex in southern Chile. The multi-composition pluton consists of an approximately 1 km vertical exposure of homogenous granite overlying a contemporaneous 250-m-thick mafic gabbro suite. This first-of-its-kind spatially dependent Fe and Si isotope investigation of a convergent margin-related pluton aims to understand the nature of granite and silicic igneous rock formation. Results collected by MC-ICP-MS show a trend of increasing δ⁵⁶Fe and δ³⁰Si with increasing silica content as well as a systematic increase in δ⁵⁶Fe away from the mafic base of the pluton. The marginal Torres del Paine granites have heavier Fe isotope signatures (δ⁵⁶Fe = +0.25 ± 0.02 2se) compared to granites found in the interior pluton (δ⁵⁶Fe = +0.17 ± 0.02 2se). Cerro Toro country rock values are isotopically light in both Fe and Si isotopic systems (δ⁵⁶Fe = +0.05 ± 0.02 ‰; δ³⁰Si = ?0.38 ± 0.07 ‰). The variations in the Fe and Si isotopic data cannot be accounted for by local assimilation of the wall rocks, in situ fractional crystallization, late-stage fluid exsolution or some combination of these processes. Instead, we conclude that thermal diffusion or source magma variation is the most likely process producing Fe isotope ratio variations in the Torres del Paine pluton.  相似文献   

Shallow lithosphere-asthenosphere boundary beneath Cambay Rift Zone of India: Inferred presence of carbonated partial melt     

Prakash Kumar  Gautam Sen  Prantik Mandal  Mrinal K. Sen 《Journal of the Geological Society of India》2016,87(4):401-410

A vast area between Phalodi in Jodhpur and Pokaran in Jaisalmer district of western Rajasthan, is occupied distinctly by rocky, shallow gravelly surfaces and occasional hills. These surfaces exhibit quartz and quartzite pebbles, angular, sub-angular and few rounded sandstone gravels, have slightly convex outline and can be best described as desert pavements. Such land features assume significance because of their extent and variability under a dominantly dry aeolian environment. Morphology and distributional pattern of such formations indicate that sediments are either of in situ origin or may have been transported to a short distance. The present study is based on field level assessment of such surfaces in the above two desert districts. Over much of the area, the profile shows a surficial concentration of gravels followed by thick sand and silt mixed with gravels and then the parent material. There are also occasional rock outcrops of very low relief exhibiting vertical, horizontal and conchoidal pattern of fractures over these surfaces near Pokaran and north of Jaisalmer which indicate disintegration of rocks under extreme diurnal fluctuation of temperature. Such manifestations in the morphology indicate impact of both thermal as well as aeolian processes. In the east of Jaisalmer town near Basanpir and Bhojka, the pavement surfaces are found covered with abundant sub-rounded to rounded pebbles and cobbles. This type of condition would indicate a profound action by fluvial activities followed by wind sorting. Our study found significant spatial variability in the distribution of pavement surfaces, which carried imprints of climatic fluctuations and environment of deposition during Holocene.  相似文献