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本文选用了37个地震资料,得出昌乐地震台附近的平均地壳厚度为:H=37.3km,直达波的平均传播速度:(?)=6.20km/s,(?)=3.58km/s;反射波的传播速度 V_(p11)=6.39km/s,V_(s11)=3.74km/s;首波速度:V_(pn)=8.04km/s;该地区的平均波速比值:K=1.73,平均虚波速度:(?)=8.45km/s。根据昌乐地震台记录地震尾波衰减特点,估算了22个地震的平均 Q 值为371。并初步讨论了该区的介质状况。 相似文献
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本文第一部分选取泰安台473型地震仪1985—1990年记录的70个地震资料,通过计算,得到泰安台附近的地壳厚度为H=36.5km,直达波的平均传播速度:V_P=6.18km/s、V_s=3.55km/s;反射波的传播速度:V_(P11)=6.45km/s、V_(S11)=3.79km/s;绕射波的传播速度:V_(Pn)=7.95km/s;平均虚波速度:V_φ=8.34km/s;平均波速比K=1.74。第二部分选取了泰安台基式地震仪有SP′震相记录的地震21个,求出了泰安台附近的地壳厚度为37km,并分析了SP′震相在泰安台的记录特征,初步得到SP′震相可观测范围为25°—60°。 相似文献
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天水-礼县地区地壳速度结构 总被引：2，自引：0，他引：2
1984—1985年,利用厂坝铅锌矿工业爆破,在天水—礼县地区布设测线进行了大范围的地震测深工作。对该地区的地壳速度结构的研究结果表明,该地区沉积层平均厚度为2.5km,速度为4.0km/s(P波);地壳平均厚度为43.68km,平均速度为6.20km/s;徽县—礼县地壳速度剖面可分为5层,其中在24—29km深处有一低速层,基底深度变化较大,在礼县地壳浅部发现一断层。对天水—礼县地区还进行了P波、S波联合反演,获得了该区P波与S波速度结构,其地壳范围内的平均波速比为1.73。 相似文献
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本文选用红山地震台1986年至1987年记录到的70个SP'、28个 SP"和29个 PS_H 震相,计算了红山地震台附近的地壳结构。得到地壳内平均纵波速度 V_p=5.98±0.16km/s,地壳厚度 H=38.07±2.68km,分界面深度 H_1=20.63±1.13km,波速比 K=V_p/V_s=1.66,虚波速度 V(?)=9.04±0.22km/s.实践表明,本文的结果是比较合理的. 相似文献
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利用西藏高原及其邻区150个地震,西藏台网、四川台网、世界标准台网及在西藏布设的流动台网的 P 波和 S 波观测资料,得出了该地区的地壳和上地幔的 P 波以及 S 波的速度模型:(1)地壳平均厚度70km,可分为明显的两层.上层厚16km,P 波速度5.55km/s,S 波3.25km/s;下层厚54km,P 波速度6.52km/s,S 波3.76km/s;(2)上地幔顶层 P 波速度7.97m/s,S 波4.55km/s.140km 处出现低速层,层厚约55——62km.低速层下的正速度梯度与地幔顶部盖层相差无几. 相似文献
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基于"广义重复地震"的思路,收集整理1990—2015年海南岛及近海地震丛发区事件,利用单台单震法呈现海南台网至海南岛及近海显著地震丛发区的波速比特征,初步探讨研究区地壳介质物性信息。结果表明:(1)地震丛至单台的整体平均波速比低于理想体的1.732,2008年前后各台站的平均波速比及波速比随时间变化特征有明显差异,这可能与2007—2008年研究区地震活动较长时间平静后的应力调整以及2008年汶川地震应力传递作用有关;(2)地下介质的破碎程度及流变性影响波速比:地下岩石破碎程度高,介质流变性强可能会造成台站波速比相对高值,如QXL台、DOF台、CHM台、NAD台、SLL台等;(3)琼中南隆起区地下介质较致密、稳定,除特殊介质区的NAD台、CHM台、DOF台,其他台站波速比呈现相对低值;(4)2008年前后各地震丛发区视速度特征有差异,地震活动也存在明显不同,研究区可能处于应力调整状态;铺前—清澜断裂东西两侧呈现完全不同的视速度,主要影响来自岩性的不同以及火山地区热物质上涌等热作用过程。 相似文献
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利用青海台网记录清晰的P波震相资料,根据单层地壳模型地震走时方程,计算了P波速度和震源深度,得到直达波速度正态分布置信区间为5.96~6.09 km/s,首波波速度置信区间为7.69~8.06 km/s,震源深度置信区间为5.6~5.8 km。 相似文献
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首都圈数字地震台网覆盖京、津和河北中部,其中自2002年5月—2003年12新记录1级以上地震1186个,台站记录的纵、横波到时差约2~25 s。选取被5个以上台站所记录到的地震,震中位于网内或者网缘附近,计算其平均波速比。分析认为:(1)通过HYPODD修订震源位置,绝大多数震源深度在8~10 km,平均波速比所反映的是地壳上层的状态。(2)无论是从较长的时间尺度还是从较大的空间范围来看,平均波速比值都是非常稳定的。(3)平均波速比的可靠性有赖于较多的台站数目,以满足拟合精度的要求。少数台站的测定结果往往伴随较大的误差,单一地震的平均波速比值大幅度的涨落,不宜表征地壳介质性质的改变。 相似文献
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相速度和群速度是研究地震波传播规律和描述介质特性的重要参数,是弹性波传播理论中的核心内容,在理论研究和实际应用中有重要作用.本文根据VTI介质的刚度矩阵,利用Bond变换建立了TTI介质刚度矩阵.再利用TTI介质刚度矩阵,结合弹性动力学的本构方程、牛顿运动微分方程和几何方程,得到了三维TTI介质弹性波波动方程和Christoffel方程.通过本征值方法求解Christoffel方程,推导了三维TTI介质弹性波相速度的解析表达式.利用Berryman和Crampin推导各向异性介质群速度公式,根据三维TTI介质的相速度解析式推导了三维TTI介质群速度解析表达式.数值试例表明,随着各向异性介质参数改变,TI介质弹性波相速度变化较为平缓,群速度变化较为剧烈,qP波和SH波速度变化较为平缓,qSV波速度变化较为剧烈. 相似文献
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Einar Maeland 《Geophysical Prospecting》1997,45(4):641-651
Migration using an erroneous velocity gives a curve along which the energy is smeared. Associated with this curve is the caustic enveloped by the normal rays. It is possible to compensate for an erroneous velocity by a simple modification of the imaging principle. Formulae are derived for the general case when the velocity changes laterally, and the position of the caustic suggests how to modify the imaging principle so as to obtain an estimate of the NMO velocity. A synthetic example is used to illustrate the results of the analysis. 相似文献
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This paper studies the computation method of two-step inversion of interface and velocity in a region. The 3-D interface is
described by a segmented incomplete polynomial; while the reconstruction of 3-D velocity is accomplished by the principle
of least squares in functional space. The computation is carried out in two steps. The first step is to inverse the shape
of 3-D interface; while the second step is to do 3-D velocity inversion by distributing the remaining residual errors of travel
time in accordance with their weights. The data of seismic sounding in the Tangshan-Luanxian seismic region are processed,
from which the 3-D structural form in depth of the Tangshan seismic region and the 3-D velocity distribution in the crust
below the Tangshan-Luanxian seismic region are obtained. The result shows that the deep 3-D structure in the Tangshan seismic
region trends NE on the whole and the structure sandwiched between the NE-trending Fengtai-Yejituo fault and the NE-trending
Tangshan fault is an uplifted zone of the Moho. In the 3-D velocity structure of middle-lower crust below that region, there
is an obvious belt of low-velocity anomaly to exist along the NE-trending Tangshan fault, the position of which tallies with
that of the Tangshan seismicity belt. The larger block of low-velocity anomaly near Shaheyi corresponds to a denser earthquake
distribution. In that region, there is an NW-trending belt of high-velocity anomaly, probably a buried fault zone. The lower
crust below the epicentral region of the Tangshan M
S=7.8 earthquake is a place where the NE-trending belt of low-velocity anomaly meets the NW-trending belt of high-velocity
anomaly. The two sets of structures had played an important role in controlling the preparation and occurrence of the M
S=7.8 Tangshan earthquake.
Contribution RCEG97006, Research Center of Exploration Geophysics, China Seismological Bureau, China.
This project is supported by the Chinese Joint Seismological Science Foundation. 相似文献
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Knowledge of maximum velocity is essential for the design of structures and especially those with supplementary dampers. Although the nonlinear time history analysis leads to reliable estimation of actual velocities, it seems to be complicated for the everyday engineering practice due to the increased computational cost. This paper proposes an alternative for single‐degree‐of‐freedom (SDOF) systems to estimate the actual velocity in a straightforward and effective manner. More specifically, this study examines the inelastic velocity ratio (IVR), i.e., the ratio of the maximum inelastic to the maximum elastic velocity of an SDOF system, the knowledge of which allows the computation of maximum inelastic velocity directly from the corresponding elastic counterpart. The proposed method is general and can be applied to both conventional structures and structures with supplementary dampers. Extensive parametric studies are conducted to obtain expressions for IVR in terms of the period of vibration, viscous damping ratio, force reduction factor, and soil class. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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L.J. Srnka 《Physics of the Earth and Planetary Interiors》1977,14(3):321-329
When the relative velocity between magnetized plasma and neutral gas exceeds a critical value, the gas-plasma interaction is dominated by collective phenomena which rapidly excite and ionize the neutrals. The interaction of the solar wind with a large cloud (1024 – 1028 neutrals) vented from the moon should be of this type. Line radiation from such an interaction can yield an apparent lunar surface brightness rivaling reflected sunlight levels over small areas, if the kinetic energy flow density of the gas is sufficiently high. The aberrated solar wind flow past the moon would enhance the visibility of such interactions near the lunar sunrise terminator, supporting the statistical studies which indicate that the “Lunar Transient Phenomena” (anomalous optical phenomena on the moon) are significantly correlated with the position of the terminator on the lunar surface. 相似文献
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Migration for velocity and attenuation perturbations 总被引：1，自引：0，他引：1
Migration maps seismic data to reflectors in the Earth. Reflections are not only caused by small‐scale variations of the velocity and density but also of the quality factor that describes attenuation. We investigated scattering due to velocity and attenuation perturbations by computing the resolution function or point‐spread function in a homogeneous background model. The resolution function is the migration image of seismic reflection data generated by a point scatterer. We found that the resolution function mixes velocity and attenuation parameter perturbations to the extent that they cannot be reconstructed independently. This is true for a typical seismic setting with sources and receivers at the surface and a buried scatterer. As a result, it will be impossible to simultaneously invert for velocity and attenuation perturbations in the scattering approach, also known as the Born approximation. We proceeded to investigate other acquisition geometries that may resolve the ambiguity between velocity and attenuation perturbations. With sources and receivers on a circle around the scatterer, in 2D, the ambiguity disappears. It still shows up in a cross‐well setting, although the mixing of velocity and attenuation parameters is less severe than in the surface‐to‐surface case. We also consider illumination of the target by diving waves in a background model that has velocity increasing linearly with depth. The improvement in illumination is, however, still insufficient to remove the ambiguity. 相似文献
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Migration velocity analysis and waveform inversion 总被引：3，自引：0，他引：3
William W. Symes 《Geophysical Prospecting》2008,56(6):765-790
Least‐squares inversion of seismic reflection waveform data can reconstruct remarkably detailed models of subsurface structure and take into account essentially any physics of seismic wave propagation that can be modelled. However, the waveform inversion objective has many spurious local minima, hence convergence of descent methods (mandatory because of problem size) to useful Earth models requires accurate initial estimates of long‐scale velocity structure. Migration velocity analysis, on the other hand, is capable of correcting substantially erroneous initial estimates of velocity at long scales. Migration velocity analysis is based on prestack depth migration, which is in turn based on linearized acoustic modelling (Born or single‐scattering approximation). Two major variants of prestack depth migration, using binning of surface data and Claerbout's survey‐sinking concept respectively, are in widespread use. Each type of prestack migration produces an image volume depending on redundant parameters and supplies a condition on the image volume, which expresses consistency between data and velocity model and is hence a basis for velocity analysis. The survey‐sinking (depth‐oriented) approach to prestack migration is less subject to kinematic artefacts than is the binning‐based (surface‐oriented) approach. Because kinematic artefacts strongly violate the consistency or semblance conditions, this observation suggests that velocity analysis based on depth‐oriented prestack migration may be more appropriate in kinematically complex areas. Appropriate choice of objective (differential semblance) turns either form of migration velocity analysis into an optimization problem, for which Newton‐like methods exhibit little tendency to stagnate at nonglobal minima. The extended modelling concept links migration velocity analysis to the apparently unrelated waveform inversion approach to estimation of Earth structure: from this point of view, migration velocity analysis is a solution method for the linearized waveform inversion problem. Extended modelling also provides a basis for a nonlinear generalization of migration velocity analysis. Preliminary numerical evidence suggests a new approach to nonlinear waveform inversion, which may combine the global convergence of velocity analysis with the physical fidelity of model‐based data fitting. 相似文献
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Group velocity distribution of Rayleigh waves and crustal and upper mantle velocity structure of the Chinese mainland and its vicinity 总被引：7，自引：6，他引：1
Introduction A lot of results have been achieved on the study of crust and upper mantle structure in Chinese mainland by the surface wave dispersion. The seismometer can be classified into three types based on the development from the analog to digital instrument. FENG, et al (1981) measured the dispersion curves of group and phase velocity along 28 paths, with 19 earthquakes recorded by 15 base analog seismic stations, subdivided the Chinese mainland into 5 blocks and obtained the average c… 相似文献
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莺歌海盆地是一个有勘探潜力的盆地,尤其是莺东斜坡带附近有良好勘探前景.但是由于研究区位于莺东斜坡带附近,因此构造解释具有相当的难度,尤其是由时间解释转化为构造解释有难度,需要有一个准确的速度来进行时深转换.基于此原因,本文首先介绍了速度谱拾取过程中的一些难点及解决方法;其后是速度分析取得的成果,通过DepthTeam形成速度体,从点、面、体三个不同角度证明了速度谱拾取过程中速度的准确性以及速度体的实用性;最后对单井和地层的速度进行了统计分析,总结了本区影响速度变化的主要因素. 相似文献
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