Moment tensors of acoustic emissions in shear faulting under plane-strain compression     

Fernanda C. S. Carvalho  Joseph F. Labuz   《Tectonophysics》2002,356(1-3)

The study of localized failure under controlled conditions can be accomplished within a laboratory setting with the University of Minnesota plane-strain compression apparatus. The device provides an opportunity to observe shear faulting and to compare displacements from acoustic emission (AE) sources with global measurements. A biaxial compression test on a sandstone specimen was performed with monitoring of AE. The plane-strain test showed that the shear fault was not formed until after peak load. Compaction of the shear fault was observed from the axial and lateral measurements of displacement and the orientation of the failure plane. The AE events were modeled as displacement discontinuities. The complicated deconvolution process for the transducer transfer function was eliminated by using a simplified calibration procedure. The sources of the postpeak events were characterized as being caused predominantly by slip in the direction of the global failure plane, although components of displacement associated with closing were identified. To provide an order of magnitude estimate of the slip, the field observation of a 10⁻⁴ strain drop over the seismic area was assumed. The tangential displacement from 110 AE events was estimated to be 0.01 mm. During the same period of time, the displacement along the shear fault from global measurements was 0.03 mm.  相似文献   

Three-dimensional numerical simulations of crustal deformation and subcontinental mantle convection     

L.-N. Moresi  A. Lenardic 《Earth and Planetary Science Letters》1997,150(3-4):233-243

3-D simulations of mantle convection allowing for continental crust are explored to study the effects of crustal thickening on lithosphere stability and of continents on large-scale mantle flow. Simulations begin with a crustal layer within the upper thermal boundary layer of a mantle convection roll in a 1 × 1 × 1 Cartesian domain. Convective stresses cause crust to thicken above a sheet-like mantle downwelling. For mild convective vigor an initial crustal thickness variation is required to induce 3-D lithospheric instability below the zone of crustal convergence. The amplitude of the required variation decreases with increasing convective vigor. Morphologically, instability is manifest in formation of drip-like thermals that exist within the large-scale roll associated with initial crustal thickening. A strong surface signature of the drips is their ability to cause deviations from local Airy compensation of topography. After the initial thickening phase, the crustal accumulation that forms serves as a model analog to a continent. Its presence leads to mantle flow patterns distinctly different from the steady-state roll that results in its absence. Large lateral thermal gradients are generated at its edge allowing this region to be the initiation site for continued small-scale thermal instabilities. Eventually these instabilities induce a restructuring of large-scale mantle flow, with the roll pattern being replaced by a square cell. Although preliminary and idealized, the simulations do show the fluid dynamical plausibility behind the idea that significant mantle variations can be generated along the strike of a largely 2-D mountain chain by the formation of the chain itself. The ability of a model continent to cause a change in fundamental convective planform also suggests that the effects of continental crust on mantle convection may be low-order despite the seemingly trivial volume of crust relative to mantle.  相似文献   

Gross errors in upper-mantle discontinuity topography from underside reflection data     

Filip Neele  Han de  Regt John Van  Decar 《Geophysical Journal International》1997,129(1):194-204

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On the nature of regional seismic phases–II. On the influence of structural barriers     

T. Furumura  B. L. N. Kennett 《Geophysical Journal International》1997,129(2):221-234

The blockage of the L _g wave by crustal barriers such as continental margins and graben structures has long been recognized as providing a very useful tool for mapping large-scale lateral crustal variations along the propagation path. Numerical simulation of L _g -wave propagation in complex anelastic media using the pseudospectral method provides insight into the nature of the propagation process using both snapshots of the wavefield and synthetic seismograms. A variety of 2-D structures have been investigated, including the influence of sediments, crustal thickness and attenuation.
Thick sedimentary basins covering a graben structure can have a major influence, since they remove L _g energy by generating P conversion and scattering–the principal mechanisms for strong L _g attenuation across a graben. The reduction of the L _g energy is reinforced by anelastic attenuation in the sediments as well as the influence of the gradually thinning crustal waveguide associated with an elevated Moho.
The extinction of L _g in a sequence of explosions fired across the central graben of the North Sea can be simulated by numerical calculations for the structure derived from refraction experiments.  相似文献   

Global crustal thickness from neural network inversion of surface wave data     

Ueli Meier  rew Curtis  Jeannot Trampert 《Geophysical Journal International》2007,169(2):706-722

We present a neural network approach to invert surface wave data for a global model of crustal thickness with corresponding uncertainties. We model the a posteriori probability distribution of Moho depth as a mixture of Gaussians and let the various parameters of the mixture model be given by the outputs of a conventional neural network. We show how such a network can be trained on a set of random samples to give a continuous approximation to the inverse relation in a compact and computationally efficient form. The trained networks are applied to real data consisting of fundamental mode Love and Rayleigh phase and group velocity maps. For each inversion, performed on a 2°× 2° grid globally, we obtain the a posteriori probability distribution of Moho depth. From this distribution any desired statistic such as mean and variance can be computed. The obtained results are compared with current knowledge of crustal structure. Generally our results are in good agreement with other crustal models. However in certain regions such as central Africa and the backarc of the Rocky Mountains we observe a thinner crust than the other models propose. We also see evidence for thickening of oceanic crust with increasing age. In applications, characterized by repeated inversion of similar data, the neural network approach proves to be very efficient. In particular, the speed of the individual inversions and the possibility of modelling the whole a posteriori probability distribution of the model parameters make neural networks a promising tool in seismic tomography.  相似文献   

Receiver functions in northeast China - implications for slab penetration into the lower mantle in northwest Pacific subduction zone   总被引：6，自引：0，他引：6  

Xueqing Li  Xiaohui Yuan 《Earth and Planetary Science Letters》2003,216(4):679-691

Seismic studies of the subducting lithosphere and the upper mantle discontinuities in the northwest Pacific subduction zone beneath Japan and northeast China have suggested contrary subduction scenarios. There was little consensus on the issue whether the subducting slab penetrates the upper mantle discontinuities into the lower mantle or it is deflected atop of the 660-km discontinuity over several hundred kilometers. We calculate receiver functions from a recent seismic broadband station network located in northeast China and find topographic variations of the upper mantle discontinuities. A deeper-than-normal 660-km discontinuity is observed over an area of 400 km and it coincides with the stagnant slab imaged by seismic tomography. The 660-km discontinuity is locally depressed by more than 35 km and the transition zone is thickened by more than 20 km in the east of the region where it encounters the slab. These observations provide evidence of the slab accumulating in the mantle transition zone and locally penetrating into the lower mantle.  相似文献   

三维FSM·DDM边界元法     

刘承论  秦忠诚  时洪斌 《岩土力学》2004,25(Z1):47-51

对三维FSMDDM边界元数值模拟系统进行了基础研究,开发了单一介质的三维弹性问题的FSMDDM边界元数值模拟系统和多介质三维FSMDDM边界元数值模拟系统,通过验证和实际工程应用取得了满意的效果。  相似文献   

Mapping the mantle lithosphere for diamond potential using teleseismic methods     

D.B. Snyder  S. Rondenay  M.G. Bostock  G.D. Lockhart 《Lithos》2004,77(1-4):859-872

Recent developments in seismic, magnetotelluric and geochemical analytical techniques have significantly increased our capacity to explore the mantle lithosphere to depths of several hundred kilometres, to map its structures, and through geological interpretations, to assess its potential as a diamond reservoir. Several independent teleseismic techniques provide a synergistic approach in which one technique compensates for inadequacies in another. Shear wave anisotropy and discontinuity studies using single seismic stations define vertical mantle stratigraphic columns. For example, beneath the central Slave craton seismic discontinuities at depths of 38, 110, 140 and 190 km appear to bound two distinct anisotropic layers. Tomographic (3-D) inversions of seismic wave travel-times and 2-D inversions of surface or scattered waves use arrays of stations and provide lateral coverage. In combination, and by correlation with electrical conductivity and xenolith petrology studies, these techniques provide maps of key physical properties within parts of the cratons known to host diamonds. Beneath the Slave craton, the discontinuity at 38 km is the base of the crust; the boundaries at 110 and 140 km appear to bound a layer of depleted harzburgite that is interpreted to contain graphite. To date, only some of these techniques have been applied to the Slave and Kaapvaal cratons so that the origin and geological history of the currently mapped mantle structures are not, as yet, generally agreed.  相似文献   

砾岩边坡稳定性分析与防治工程   总被引：2，自引：0，他引：2  

滕伟福  杨冬英  贾洪彪 《水文地质工程地质》2003,(Z1)

沪蓉国道主干线宜昌至恩施段高速公路,是国家“五纵七横“交通网的重要组成部分,其砾岩边坡稳定性分析与防治工程是重要的研究课题。本文以砾岩岩体结构面模拟研究,岩体力学参数估算为基础,结合砾岩特征及边坡地质环境条件,提出砾岩边坡稳定性评价的地质模型,并采用数值模拟与计算,得出砾岩边坡稳定性分析的确切结果。砾岩边坡岩土工程加固设计是关系到该高速公路安全、经济、适用的重要内容,紧密结合砾岩边坡的地质环境和砾岩岩体特征,采用信息化设计,运用生态化设计理念,充分发挥岩土工程技术优势,保护环境,提出合理的岩土工程加固设计方案。本研究成果对砾岩边坡防治工程提出了系统的研究思路,对沪蓉国道主干线宜昌至恩施段高速公路砾岩边坡的设计与施工具重要意义。  相似文献   

UK crustal structure close to the Iapetus Suture: a receiver function perspective   总被引：2，自引：0，他引：2  

J. P. Tomlinson  P. Denton  P. K. H. Maguire  J. R. Evans 《Geophysical Journal International》2003,154(3):659-665

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