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1.
Intrinsic and attenuative dispersion characteristics of direct P-waves in and near the source area of the 1999 MW7.6 Chi-Chi,Taiwan, earthquake before and after the mainshock 
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下载免费PDF全文 Based on the measurement of the arrival time of maxima magnitude from band-pass filtering signals which were determined using a new Morlet wavelet multiple-filter method, we develop a method for measuring intrinsic and attenuative dispersion of the first cycle direct P-wave. We determine relative group delays of spectral components of direct P-waves for 984 ray paths from SML and ALS stations of the Taiwan Central Weather Bureau Seismic Network (CWBSN). Using continuous relaxation model, we deduce a new transfer function that relates intrinsic dispersion to attenuation. Based on the genetic algorithm (GA), we put forward a new inversion procedure for determining which is defined the flat part of quality factor
2.
Antoni M. Correig 《Pure and Applied Geophysics》1991,136(4):561-576
Generalizing previous studies on short-period data, it is shown that body-wave dispersion can be measured from broad-band records of earthquakes of moderate magnitude. The method is based on the direct measurement of the arrival time of the frequency components of a seismic wave, and the arrival time is defined by its expectation value. The frequency components of the signal are obtained through a narrow band-pass filtering process. Previous to any interpretation, a correction of the arrival time for instrument response and group delay of the filter is needed. In the first step, body-wave dispersion is related to an absorption band to account for intrinsic attenuation, and thereafter we generalize this interpretation by considering a cascade of filters to account for medium parameters (attenuation and a layered crust) and source parameters (source time function and finiteness of fault). An inversion scheme to obtain the filter parameters can be devised by following, in a formal way, the same procedure as for the case of surface wave dispersion. 相似文献
3.
提出了求解波动方程的四阶龙格-库塔方法的一种改进算法.首先将原四阶龙格-库塔方法合并为两级格式, 然后在第一级中引入加权参数以获得加权算法. 针对这种改进方法,研究了它的稳定性条件; 对一维问题导出了频散关系, 给出了数值频散结果,并与四阶的 Lax-Wendroff (LWC) 方法和位移-应力交错网格方法进行了对比; 对二维问题, 使用我们的改进方法、四阶LWC和交错网格三种方法进行了声波波场模拟, 并进行了计算效率分析和不同方法计算结果的比较; 最后选取两个层状介质模型进行了声波和弹性波波场模拟. 数值结果表明,本文的改进方法具有非常弱的数值频散和高的计算效率, 是一种在地震勘探领域具有巨大应用潜力的数值方法. 相似文献
4.
虽然一些时频分析方法已经被用于频散曲线提取中,但是它们自身时频窗的缺陷使的所得频散曲线信息缺失或错误.本文首次尝试利用广义S变换分析瑞利波的频散特性.以半空间模型为例确定方法的可行性,频散曲线变化准确反映地层变化情况.不同炮检距设置对频散曲线有一定影响,采用大于勘测深度,小于4倍勘测深度可以得到较稳定的结果.最后,为了得到更加光滑稳定的频散曲线,提出了一种基于多道瑞利波的改进方法.用此方法对四种典型地层模型下的多道瑞利波数据进行分析,得到频散曲线光滑稳定,且比理论频散曲线和基于单道法获得频散曲线更能准确反映地层变化情况.这就为瑞利波勘探中的反演解释提供了更可靠依据. 相似文献
5.
A central difference method with low numerical dispersion for solving the scalar wave equation 总被引：4，自引：0，他引：4
In this paper, we propose a nearly‐analytic central difference method, which is an improved version of the central difference method. The new method is fourth‐order accurate with respect to both space and time but uses only three grid points in spatial directions. The stability criteria and numerical dispersion for the new scheme are analysed in detail. We also apply the nearly‐analytic central difference method to 1D and 2D cases to compute synthetic seismograms. For comparison, the fourth‐order Lax‐Wendroff correction scheme and the fourth‐order staggered‐grid finite‐difference method are used to model acoustic wavefields. Numerical results indicate that the nearly‐analytic central difference method can be used to solve large‐scale problems because it effectively suppresses numerical dispersion caused by discretizing the scalar wave equation when too coarse grids are used. Meanwhile, numerical results show that the minimum sampling rate of the nearly‐analytic central difference method is about 2.5 points per minimal wavelength for eliminating numerical dispersion, resulting that the nearly‐analytic central difference method can save greatly both computational costs and storage space as contrasted to other high‐order finite‐difference methods such as the fourth‐order Lax‐Wendroff correction scheme and the fourth‐order staggered‐grid finite‐difference method. 相似文献
6.
流体因子是储层流体识别的重要方法,而叠前地震反演是获得流体因子的有效途径之一.本文从流体因子的构建出发,基于多孔弹性介质岩石物理模型,建立了流体因子与纵横波模量之间的直接关系,避免了流体因子计算所需的密度参数无法准确求取的问题,通过推导基于纵横波模量的Zeoppritz近似方程及弹性阻抗方程,探讨了基于弹性阻抗的纵横波模量直接反演方法,模型与实际应用表明,基于弹性阻抗的纵横波模量直接反演方法合理、可靠,减少了常规方法间接计算纵横波模量带来的累积误差,基于纵横波模量的流体因子计算方法有较好的实际应用效果. 相似文献
7.
频率-贝塞尔变换方法(Frequency-Bessel Transform method,简称F-J方法)是一种分析微动信号的新方法,由于该方法采用频率矢量波数变换处理水平层状各向同性弹性模型中时空平稳随机分布的微动信号,所以从理论上可以提取出清晰的瑞利波基阶和高阶模态频散曲线,但是目前还没有相关的野外实验对此进行研究和应用.本文首先采用该方法对上海市苏州河地区采集的城市微动信号进行处理获得了频率-相速度谱,然后提取了多模态瑞利波频散曲线,最后通过粒子群算法对频散曲线进行联合反演,得到了浅地表0~70 m深度范围的S波速度结构,并且利用钻孔数据对反演的速度结构进行了验证.另外,本文还通过对比F-J方法和传统的SPAC(SPatial AutoCorrelation method)方法分别提取的频散曲线,展示了F-J方法在处理城市微动信号方面的优势.本文研究结果表明:(1)F-J方法可以从少量台站(21个台站)短时记录(1小时)的微动信号垂直分量中提取出清晰的基阶和高阶模态瑞利波频散曲线;(2)F-J方法提取的高阶模态频散曲线比传统SPAC方法提取的更加清晰,高频部分(>13 Hz)优势更为明显;(3)联合基阶和高阶模态频散曲线反演的浅地表速度结构更加精确,可以分辨出第四系沉积层中物性相差较小的速度界面和低速异常,在城市浅地表精细结构成像方面具有较好的应用前景. 相似文献
8.
Optimal implicit staggered‐grid finite‐difference schemes based on the sampling approximation method for seismic modelling 下载免费PDF全文
下载免费PDF全文 We propose new implicit staggered‐grid finite‐difference schemes with optimal coefficients based on the sampling approximation method to improve the numerical solution accuracy for seismic modelling. We first derive the optimized implicit staggered‐grid finite‐difference coefficients of arbitrary even‐order accuracy for the first‐order spatial derivatives using the plane‐wave theory and the direct sampling approximation method. Then, the implicit staggered‐grid finite‐difference coefficients based on sampling approximation, which can widen the range of wavenumber with great accuracy, are used to solve the first‐order spatial derivatives. By comparing the numerical dispersion of the implicit staggered‐grid finite‐difference schemes based on sampling approximation, Taylor series expansion, and least squares, we find that the optimal implicit staggered‐grid finite‐difference scheme based on sampling approximation achieves greater precision than that based on Taylor series expansion over a wider range of wavenumbers, although it has similar accuracy to that based on least squares. Finally, we apply the implicit staggered‐grid finite difference based on sampling approximation to numerical modelling. The modelling results demonstrate that the new optimal method can efficiently suppress numerical dispersion and lead to greater accuracy compared with the implicit staggered‐grid finite difference based on Taylor series expansion. In addition, the results also indicate the computational cost of the implicit staggered‐grid finite difference based on sampling approximation is almost the same as the implicit staggered‐grid finite difference based on Taylor series expansion. 相似文献
9.
利用波形互相关方法识别乳山震群中的重复地震,挑选一组在时间上跨越2015年5月22日ML 5.0地震的重复地震序列（repeating earthquake sequences,RES）,利用测算单台直达P波第一个周期信号频散衰减特性的方法,估算乳山震群震源区介质品质因子,结果显示,不同路径下Qm值随时间的变化形态基本一致,即此次ML 5.0地震前Qm值升高,临震及震后Qm值下降并恢复至震前水平。同时,通过对震源区近场及远场应力状态的相关性分析,认为此次ML 5.0地震发生在远场作用下区域构造应力状态调整过程中,与区域构造的介质状态、断层分布、速度结构密切相关。 相似文献
10.
We present a summary of the available information on Rayleigh-wave dispersion data for the Italian area. The dispersion curves can be grouped into two main families according to their shape: one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec. The inversion of these data shows that there are strong lateral variation in the lithosphere system: a very rapid transition in the lithospheric thickness, from about 130 km to about 30 km, as well as in the S-wave velocity of the lithosphere and asthenosphere.Some cross-sections are described in order to have a more direct insight on the gross features of the upper mantle.An attempt is made to discuss the properties of the upper mantle taking into account the tectonic evolution of the Mediterranean. 相似文献
11.
提出一种基于直达P波信号和其它背景噪声在能量、非高斯性、非线性和偏振特性的不同而进行区域地震事件实时检测的新方法信噪综合差异特征量方法（简写为EFGLP方法）,同时对比分析了应用信号的不同统计特性来精细识别震相初至的３种有效方法,其中的TOC AIC方法是新提出的．应用山东数字地震波资料处理的结果表明:①与常规的STA/LTA地震事件触发算法相比,EFGLP方法能够有效降低地震事件的错误报警率和漏报率;②与人机交互震相识别结果相比,当信噪比比较低、震相初至比较模糊时,3种震相精细识别方法中的TOC-AIC方法识别精度最高;当信噪比比较高、震相初至比较清晰时,基于VAR-AIC 和TOC-AIC方法所测量得到的震相初至识别基本一致． 相似文献
12.
加权近似解析离散化(WNAD) 方法是近年发展的一种在粗网格步长条件下能有效压制数值频散的数值模拟技术. 在地震勘探的实际应用中, 不是所有情况都适合使用空间大网格步长. 为适应波场模拟的实际需要, 本文给出了求解波动方程的非一致网格上的WNAD算法. 这种方法在低速区、介质复杂区域使用细网格, 在其他区域采用粗网格计算. 在网格过渡区域, 根据近似解析离散化方法的特点, 采用了新的插值公式, 使用较少的网格点得到较高的插值精度. 数值算例表明, 非一致网格上的WNAD方法能够有效压制数值频散, 显著减少计算内存需求量和计算时间, 进一步提高了地震波场的数值模拟效率. 相似文献
13.
本文基于声波方程的哈密尔顿系统,构造了一种新的保辛数值格式,简称NSPRK方法.该方法在时间上采用二阶辛可分Runge-Kutta方法,空间上采用近似解析离散算子进行离散逼近.针对本文发展的新方法,我们给出了NSPRK方法在一维和二维情况下的稳定性条件、一维数值频散关系以及二维数值误差,并在计算效率方面与传统辛格式和四阶LWC方法进行了比较.最后,我们将本文方法应用于声波在三层各向同性介质和异常体模型中的波传播数值模拟.数值结果表明,本文发展的NSPRK方法能有效压制粗网格或具有强间断情况下数值方法所存在的数值频散,从而极大地提高了计算效率,节省了计算机内存. 相似文献
14.
We present maximum usable frequency (MUF) calculation results when a radiowave, radiated at a zero angle, is reflected from the ionosphere along direct and reverse paths when the latitudinal variability of the medium is significant. As an example, we consider the Novorossiysk-California path. Calculations were carried out using a “two-point” method and data of the Monthly MUF Prediction for May 1980 and May 1991. The “two-point” method is validated based on a new way of approximated representation of the Watson integral, which is an exact solution of the benchmark problem related to the point source field in a spherically layered medium. It is shown that MUFs along a reverse path are several MHz higher than MUFs along a direct path during the whole day. 相似文献
15.
根据普洱、 西双版纳地区6个地震观测台站在2008——2009年获取的5级以上的地震资料, 利用接收函数和面波衰减系数, 反演得到了研究区域的S波速度结构和Qβ结构. 基于该结构模型, 采用随机振动理论方法, 预测了2007年宁洱MS6.4地震发生后, 在震中距为10——300 km范围内引起的地面运动, 并借助获取的强震观测记录检验、 评价了该预测结果. 同时, 将地面运动预测结果与利用回归衰减公式计算得到的结果进行对比, 进而讨论该地震动预测方法在地面运动预测中的可行性． 结果表明, 该预测结果与实测结果吻合． 相似文献
16.
叠前逆时偏移是目前成像精度最高的地震偏移方法之一,其实现过程中的一个重要步骤是数值求解全波方程,所以快速有效求解全波方程的数值算法对逆时偏移至关重要. 四阶近似解析辛可分Runge-Kutta (NSPRK) 方法是近年发展的一种具有高效率、高精度的数值求解波动方程的保辛差分方法, 能在粗网格条件下有效压制数值频散, 从而提高计算效率, 节省计算机内存需求量. 本文利用四阶NSPRK方法构造的基本思想,发展了具有六阶空间精度的NSPRK方法,并对新的六阶NSPRK方法进行了详细的稳定性和数值频散分析,以及计算效率比较和波场模拟. 同时将该方法用于声波叠前逆时偏移中, 得到一种时间上保辛、空间具有六阶精度、低数值频散、可应用大步长进行波场延拓并能长时计算的叠前逆时偏移方法,对Sigsbee2B模型进行了偏移成像, 并和四阶NSPRK方法、传统的六阶差分方法、四阶Lax-Wendroff correction (LWC) 方法进行了对比. 数值结果表明, 基于六阶NSPRK方法的叠前逆时偏移能得到更好的成像结果, 是一种优于四阶NSPRK方法、传统的六阶差分方法、四阶LWC叠前逆时偏移的方法, 尤其是在粗网格情况下具有更明显的优越性. 相似文献
17.
频率-波数域方法的发展及其在台阵数据分析中的应用 总被引：1，自引：0，他引：1
频率-波数域分析(Frequency-wavenumber analysis,简称F-K analysis)是一种常用的台阵数据处理方法,在地震学等领域具有良好的应用效果。本文通过介绍F-K分析的基本原理及各种改进的F-K分析方法,并结合实例综述了其在台阵数据分析中的几种应用,包括检测微弱信号源、分析噪声特征、提取面波频散曲线、台阵设计这4方面;通过对这些研究的回顾,本文总结了该研究领域的新进展及需要注意的问题,并对F-K成像新的应用前景进行了分析和展望。 相似文献
18.
超高密度电阻率法是Australia ZZ Resistivity Imaging研发中心积近十年的研究成果提出的全新的电阻率法勘探理念,是电法勘探从手工时代向计算机时代的一次跨越式发展,采用一次布极,采集所有可能组合电极间的电位信息,信息量较常规电法在信息量上翻了40倍以上,并且避开视电阻率概念,利用处理软件直接反演获取断面真电阻率值,针对目前还没有行之有效的地面物探方法可以勘探清楚的土洞、煤窑采空区和岩溶等复杂地质问题,我们采用该方法分别对机场岩溶和土洞、煤矿运煤巷道、隐伏小煤矿采空区和复杂地质病害隧道进行了试验勘探,经钻探验证,准确率在60%以上,达到国内领先水平,取得了较好效果,对复杂地质的工程勘探具有一定参考价值. 相似文献
19.
Fracture detection and fluid identification are important tasks for a fractured reservoir characterization. Our goal is to demonstrate a direct approach to utilize azimuthal seismic data to estimate fluid bulk modulus, porosity, and dry fracture weaknesses, which decreases the uncertainty of fluid identification. Combining Gassmann’s (Vier. der Natur. Gesellschaft Zürich 96:1–23, 1951) equations and linear-slip model, we first establish new simplified expressions of stiffness parameters for a gas-bearing saturated fractured rock with low porosity and small fracture density, and then we derive a novel PP-wave reflection coefficient in terms of dry background rock properties (P-wave and S-wave moduli, and density), fracture (dry fracture weaknesses), porosity, and fluid (fluid bulk modulus). A Bayesian Markov chain Monte Carlo nonlinear inversion method is proposed to estimate fluid bulk modulus, porosity, and fracture weaknesses directly from azimuthal seismic data. The inversion method yields reasonable estimates in the case of synthetic data containing a moderate noise and stable results on real data. 相似文献
20.
数值求解波动方程是大尺度正演波场模拟、基于波动方程的地震偏移和反演成像的关键.本文针对求解二维声波方程的Runge-Kutta 间断有限元（RKDG）方法的数值频散问题,从理论推导和数值分析的角度进行了深入研究,并将其与近似解析离散化方法（Optimal Nearly Analytic Discrete Method,简称ONAD 方法）、Lax-Wendroff 修正方法、交错网格（Staggered-Grid,简称SG）方法的数值频散进行了比较研究.结果表明：RKDG方法以及近似解析离散化方法在压制数值频散方面要好于上述其他方法,特别是空间精度为3阶的RKDG方法,即使当空间步长取波长的一半,即一个波长内取2个网格点时,最大的频散误差也不超过1.67%.同时,我们也通过波场模拟对比研究了不同数值方法的数值频散问题,进一步直观地验证了数值频散的理论分析结果. 相似文献