Inversion of multimode surface wave data: evidence for sub-lithospheric anisotropy     

Jean-Jacques Lévêque  Michel Cara 《Geophysical Journal International》1985,83(3):753-773

Summary. Multiparameter inversions of multimode dispersion data are performed for two large regions: the Pacific Ocean and North America. Anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry. Two fundamental questions are studied in detail: (1) how to make the inverted models consistent when using different sets of parameters, (2) what is the significance of transversely isotropic inversion for the actual Earth's structure? It is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data. The models we have obtained are discussed in the light of these investigations. Considering an olivine-rich upper mantle, we make a tentative interpretation of these models in terms of preferred orientation of the a -axis of the crystals in one fixed horizontal direction.  相似文献   

Numerical prediction of blast‐induced stress wave from large‐scale underground explosion     

Chengqing Wu  Yong Lu  Hong Hao 《国际地质力学数值与分析法杂志》2004,28(1):93-109

This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

非线性Rossby波所满足的三阶Zakharov方程与低频振荡     

罗德海 《成都信息工程学院学报》1993,(4)

本文在基本气流具有水平切变的情况下,利用摄动法导出了非线性Rossby波所满足的三阶Zakharov方程,然后,考虑了基流具有弱切变的情况,通过使用三阶Zakharov方程研究了Rossby波列的第一类不稳定性问题。结果表明:通过非线性作用,大气中的Rossby波列可产生调制不稳定。同时,本文对这种不稳定的区域,增长率和周期进行了详细的计算,并讨论了波振幅、波数、纬度和基流切变对它们的影响,指出Rossby波列的调制不稳定可以激发30～60天的低频振荡。  相似文献   

Seismic rays in an ellipsoidal earth model: theoretical analysis and estimation of deviations due to the ellipticity     

Jean-Francois Guéguen  Pho Hoang-Trong  Hilaire Legros 《Geophysical Journal International》1987,89(3):839-855

Summary. A first-order form of the Euler's equations for rays in an ellipsoidal model of the Earth is obtained. The conditions affecting the velocity law for a monotonic increase, with respect to the arc length, in the angular distance to the epicentre, and in the angle of incidence, are the same in the ellipsoidal and spherical models. It is therefore possible to trace rays and to compute travel times directly in an ellipsoidal earth as in the spherical model. Thus comparison with the rays of the same coordinates in a spherical earth provides an estimate of the various deviations of these rays due to the Earth's flattening, and the corresponding travel-time differences, for mantle P -waves and for shallow earthquakes. All these deviations are functions both of the latitude and of the epicentral distance. The difference in the distance to the Earth's centre at points with the same geocentric latitude on rays in the ellipsoidal and in the spherical model may reach several kilometres. Directly related to the deformation of the isovelocity surfaces, this difference is the only cause of significant perturbation in travel times. Other differences, such as that corresponding to the ray torsion, are of the first order in ellipticity, and may exceed 1 km. They induce only small differences in travel time, less than 0.01s. Thus, we show that the ellipticity correction obtained by Jeffreys (1935) and Bullen (1937) by a perturbational method can be recovered by a direct evaluation of the travel times in an ellipsoidal model of the Earth. Moreover, as stated by Dziewonski & Gilbert (1976), we verify the non-dependence of this correction on the choice of the velocity law.  相似文献   

密度和压缩系数的散射层析成像法   总被引：1，自引：1，他引：0  

袁晓晖  王妙月 《地球物理学报》1991,34(6):753-761

本文在速度成像的基础上研究了同时对密度和压缩系数成像的散射波层析成像法.对不同散射角度的计算可以得到一系列反演图像,拟合这些图像,从而可以有效地达到对密度和压缩系数（或速度）成像的目的.与单纯的速度成像相比,增加了反演的难度.首先是对资料的方位性要求增加;其次是对资料的利用率下降.即便如此,从对较少量的炮点和检波点资料的数值计算来看,仍取得了满意的成像结果.我们对组成字母“A”的散射体结构进行了成像计算,结果能够同时再现密度和压缩系数,成像清晰,表明了方法的可行性,并能应用于复杂结构的成像问题.  相似文献   

青藏高原及邻近区域的S波三维速度结构   总被引：25，自引：5，他引：20  

周兵  秦建业 《地球物理学报》1991,34(4):426-441,T001

本文收集了WWSSN台网和我国台网中13个地震台站的长周期地震记录,用140条10-90s瑞利波频散曲线和作者提出的Tarantola-Backus面波频散层析成象方法,作了青藏高原及邻区的速度反演,得出该地区岩石层速度结构的三维图象.结果表明,1.在10-110km深度范围内,速度结构出现与大地构造特征相关的分区性,显示出四个构造单元:青藏块体、柴达木-巴颜喀拉-三江块体、塔里木块体和印度块体.2.高原内部,深度为10-70km内速度较低,莫霍界面呈不对称盆形分布,藏北那曲附近地壳厚度超过70km,高原边缘壳厚为45-50km,90-110km为高速异常,表明高原内部存在上地幔盖层.3.高原北部的班公湖断裂和东部的三江断裂系是该区重要的分界线,是岩石层结构存在明显差异的重要接触部位,可能是冈瓦纳古陆与欧亚古陆的缝合带.4.柴达木-巴颜喀拉-三江块体内部速度分布不均匀,地壳厚度由北向南从45km加深到60km;在深度90-110km存在一低速层.5.塔里木地块内速度随深度均匀增加,从地壳到上地幔110km内没有发现低速层.地壳厚度约50km.  相似文献   

论裸眼井中的“共振纵波”和“共振横波”   总被引：3，自引：0，他引：3  

唐晓明  郑传汉 《地球物理学报》1991,34(1):125-128

一、引言 文献[1]和[2]指出,充流体裸眼井中存在频率确定、波速恒定、且沿传播方向不衰减的“共振纵波”和“共振横波”。本文的目的在于论证并指出,这两种波是不存在的。 二、论证 设一点源位于z=0的井轴上,则井轴上z处的声波频率响应为  相似文献   

Crustal structure at the easternmost termination of the Variscan belt based on CELEBRATION 2000 and ALP 2002 data     

P. Hrubcov  P. roda  CELEBRATION Working Group 《Tectonophysics》2008,460(1-4):55-75

The eastern margin of the Variscan belt in Europe comprises plate boundaries between continental blocks and terranes formed during different tectonic events. The crustal structure of that complicated area was studied using the data of the international refraction experiments CELEBRATION 2000 and ALP 2002. The seismic data were acquired along SW–NE oriented refraction and wide-angle reflection profiles CEL10 and ALP04 starting in the Eastern Alps, passing through the Moravo-Silesian zone of the Bohemian Massif and the Fore-Sudetic Monocline, and terminating in the TESZ in Poland. The data were interpreted by seismic tomographic inversion and by 2-D trial-and-error forward modelling of the P waves. Velocity models determine different types of the crust–mantle transition, reflecting variable crustal thickness and delimiting contacts of tectonic units in depth. In the Alpine area, few km thick LVZ with the Vp of 5.1 km s^− 1 dipping to the SW and outcropping at the surface represents the Molasse and Helvetic Flysch sediments overthrust by the Northern Calcareous Alps with higher velocities. In the Bohemian Massif, lower velocities in the range of 5.0–5.6 km s^− 1 down to a depth of 5 km might represent the SE termination of the Elbe Fault Zone. The Fore-Sudetic Monocline and the TESZ are covered by sediments with the velocities in the range of 3.6–5.5 km s^− 1 to the maximum depth of 15 km beneath the Mid-Polish Trough. The Moho in the Eastern Alps is dipping to the SW reaching the depth of 43–45 km. The lower crust at the eastern margin of the Bohemian Massif is characterized by elevated velocities and high Vp gradient, which seems to be a characteristic feature of the Moravo-Silesian. Slightly different properties in the Moravian and Silesian units might be attributed to varying distances of the profile from the Moldanubian Thrust front as well as a different type of contact of the Brunia with the Moldanubian and its northern root sector. The Moho beneath the Fore-Sudetic Monocline is the most pronounced and is interpreted as the first-order discontinuity at a depth of 30 km.  相似文献   

海相碳酸盐岩层系不整合量化研究及其意义——以四川盆地北部二叠系为例   总被引：2，自引：1，他引：1  

李儒峰  郭彤楼  汤良杰  陈国飞 《地质学报》2008,82(3):407-412

本文以四川盆地北部二叠系为例,将层序地层分析和沉积盆地波动过程分析相结合,提出了运用沉积波动过程分析研究沉积记录不完整性的量化方法,该方法可以相对准确地定量描述盆地形成演化过程中的升降运动,恢复无地层"记录"中的沉积-剥蚀过程,进而定量分析盆地的沉积-剥蚀过程、计算沉积间断(不整合)内的地层剥蚀量、认识其时空分布规律.同时,通过实际钻井及"人工井"的波动过程分析,结合地震剖面解释成果,可以作出主要不整合的空间分布图、各层位的剥蚀厚度图和原始厚度图、各期构造的剥蚀量分布图等重要基础图件,为盆地进一步系统分析及盆地模拟打好基础,结合沉积相研究及构造样式分析还可分析盆地沉积中心、生油层、盖层、储层等在时空中的变化规律.由于沉积盆地的升降波动过程直接影响着盆地的埋藏史、热史和生、排烃史,因此通过沉积波动过程的系统分析不仅能正确建立盆地演化的地质模型,还可以正确认识油气形成与分布规律,有效指导油气勘探.  相似文献   

Structural elements of the Makran region, Oman sea and their potential relevance to tsunamigenisis     

Mohammad Mokhtari  Iraj Abdollahie Fard  Khaled Hessami 《Natural Hazards》2008,47(2):185-199

The character of convergence along the Arabian–Iranian plate boundary changes radically eastward from the Zagros ranges to the Makran region. This appears to be due to collision of continental crust in the west, in contrast to subduction of oceanic crust in the east. The Makran subduction zone with a length of about 900 km display progressively older and highly deformed sedimentary units northward from the coast, together with an increase in elevation of the ranges. North of the Makran ranges are large subsiding basins, flanked to the north by active volcanoes. Based on 2D seismic reflection data obtained in this study, the main structural provinces and elements in the Gulf of Oman include: (i) the structural elements on the northeastern part of the Arabian Plate and, (ii) the Offshore Makran Accretionary Complex. Based on detailed analysis of these data on the northeastern part of the Arabian Plate five structural provinces and elements—the Musendam High, the Musendam Peneplain, the Musendam Slope, the Dibba Zone, and the Abyssal Plain have been identified. Further, the Offshore Makran Accretionary Complex shown is to consist Accretionary Prism and the For-Arc Basin, while the Accretionary Prism has been subdivided into the Accretionary Wedge and the Accreted/Colored Mélange. Lastly, it is important to note that the Makran subduction zone lacks the trench. The identification of these structural elements should help in better understanding the seismicity of the Makran region in general and the subduction zone in particular. The 1945 magnitude 8.1 tsunamigenic earthquake of the Makran and some other historical events are illustrative of the coastal region’s vulnerability to future tsunami in the area, and such data should be of value to the developing Indian Ocean Tsunami Warning System.  相似文献