共查询到18条相似文献，搜索用时 364 毫秒
1.
利用基阶面波反演地壳上地幔的Qβ结构 总被引：4，自引：1，他引：3
根据中国数字化台网（ＣＤＳＮ）记录到的长周期Ｒａｙｌｅｉｇｈ面波资料,使用频变滤波技术从记录中提取基阶振型面波信号;根据与震源处于同一大圆弧上的两台记录的基附振型信号计算出台间格林函数,测定了经过中朝准地台地区周期１０－９８ｓ的基阶Ｒａｙｌｅｉｇｈ波衰减系数,在此基础上反演得到中朝准地台的地壳上地幔Ｑβ结构。所得结果表明：华北地区地壳的Ｑβ为２５０,而黄海地区地壳Ｑβ〉４５０,中朝准地台的地幔Ｑβ 相似文献
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使用适配滤波频时分析技术处理面波信号,获取滤波后的时域包络,并对具有相同群速度的各道信号包络的振幅进行叠加,取叠加所得极大值对应的走时为该频率的群延时,以此来提高群速度的测量精度对P-τ,（相慢度-时间）域的波场进行傅氏变换,然后在P-ω（相慢度-频率）平面叠加多道信号来测定相速度．利用这两种方法处理合成的短周期瑞利波地震图,结果表明：经过振型分离以后,利用基阶振型信号所求出的相速度、群速度曲线更加接近理论频散值．对地震勘探资料进行处理,取得了5-40Hz内的相速度、群速度频散,且曲线较为平滑 相似文献
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影响面波勘探精度的因素探讨 总被引：4，自引：0，他引：4
分析了影响面波勘探精度的主要因素,针对计算面波相速度的精度问题,讨论了常用测量台间以相速度方法的优缺点及其适用范围,并提出通过测量台间格林函数进行相位校正,以得到两台之间的精解相位。以合成的高频理论地震图作为记录信号,并在理论地震图上叠加了２０％的随机噪声,利用这些方法分析理论信号,数字实验表明：在相干频率范围内,格林函数方法能够精确测量台间相速度,而互相关法和窄带通滤波互相关法所得结果较为离散。 相似文献
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多重滤波方法已被证明在分析面波的频散特性时是一种有效而快速的方法。本文用单个台站的单次地震事件记录,应用MFT(Multiple Filter Technique)方法提取了内华达地区的面波频散曲线并分析了其特征,认为其具有大陆基振型瑞利波频散曲线的典型特征。还利用广义反透射系数法快速计算了瑞利面波频散曲线,尤其是基阶瑞利波相速度及群速度频散曲线;并且在由振型叠加方法合成的理论地震图的基础上,通过比较理论频散曲线和MFT方法得到的频散曲线,研究了多重滤波的可靠性。 相似文献
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在近二十年来,多道面波分析法(MASW)由于其便捷、高效等特性在浅层地震勘探领域得到了广泛的应用.本文基于多道面波勘探的采集方式,提出了一种新的面波多道分析方法——矢量波数变换法(VWTM).该方法通过对震源的近似,基于水平层状模型得到台站与震源间近似格林函数,然后进行矢量波数变换得到含有高阶模态Rayleigh波(频率-相速度)频散能量图.本研究首先利用合成地震数据到频散能量图与理论频散曲线进行叠加分析该方法的有效性和正确性;然后与相移法进行对比分析,我们发现在频散能量图中VWTM法对基阶、高阶模态成像均具有更高的分辨率和成像质量;最后我们将其应用于实际多道瞬态面波探测中,通过与相移法进行对比分析,发现VWTM法是一种方便、实用、有效的Rayleigh波频散提取方法.VWTM法提取多模态的Rayleigh波频散特征具有巨大潜力,可为基阶、高阶面波频散联合反演提供丰富的高阶模态频散信息. 相似文献
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利用Rayleigh波反演浅土层的剪切波速度结构 总被引：25，自引：7，他引：18
根据均匀半空间Rayleigh波相速度与介质剪切波速度之间的关系,对某一频率面波的影响深度内各层介质进行"均匀"化,使其等效于均匀半空间．并利用模型进行正演,以确定在这种均匀化的前提下,面波勘探深度与波长的关系．应用相匹配滤波技术从实测面波信号中分离出基阶Rayleigh波信号,对它进行多重滤波和叠加处理,精确地计算出5．0-30．0Hz之间的基阶面波相、群速度频散．使用"均匀"化的方法,从相速度频散曲线中获得反演的初始模型,利用群速度频散反演得到35m以上各土层的剪切波速度结构．结果表明,反演结果与钻孔资料较为吻合 相似文献
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从地震背景噪声、地震波直达波或者地震波尾波的相关函数中提取近似格林函数(Estimated Green's Function)已经成为地震学研究的一个热点.由近似格林函数中提取面波频散曲线,进而研究地壳和上地幔结构,已经成为地震学研究地球内部结构的一种新方法,其尺度由最初的几十千米发展到全球尺度.从原理上,只要由充分漫射波场的数据计算得到的互相关函数都可以得到近似格林函数,但在地震背景噪声数据的实际处理过程中,需要通过时间域的归一化处理压制地震信号的影响,然后利用频率域归一化压制单色噪声源影响和提高信噪比.但是时间域归一化的常用方法均为非线性,影响进一步提取噪声互相关函数(NCF)中的有效信息.我们通过对比有无时间域归一化和频率域归一化对不同数据进行计算得到了相似的NCF,发现时间域归一化处理并非必需,在此基础上频率域归一化处理也可以省略,由此得到一个简化的处理流程,直接计算长时间的地震记录的互相关函数得到近似格林函数,并且最大限度保留了原始振幅信息,可以更有效地用于研究噪声源. 相似文献
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2018年9月12日19时6分,陕西省汉中市宁强县发生5.3级地震,不同机构给出的震源深度结果相差较大。为进一步确定宁强5.3级地震的震源深度,基于区域速度模型,首先利用CAP方法反演得到该地震的震源机制解,然后采用瑞利面波振幅谱和CAP深度误差函数联合反演,进一步测定了此次地震的矩心深度。结果显示:CAP方法得到的陕西宁强5.3级地震矩心深度约为12km,瑞利面波振幅谱测定的矩心深度为13km,结合引入的误差函数联合反演,最终确定陕西宁强5.3级地震的矩心深度为13km左右,表明此次地震仍属于发生于上地壳的地震。 相似文献
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横波速度动校正后的共转换点(CCP)道集内,同时刻的各道横波信号S变换(ST)谱与其叠加道ST谱具有相似关系.因此,可基于这种相似关系设计自适应滤波器来提取多波地震数据中的横波波场.首先对共中心点(CMP)道集应用纵波速度动校正并在各道减去叠加道来去除数据中的纵波波场;然后在CCP道集应用横波速度动校正,将地震道振幅水平调整至叠加道振幅水平并做S变换,以叠加道ST谱为参考对地震道ST谱进行自适应滤波,去除数据中的残余纵波和噪声;最后,将滤波结果的振幅水平恢复至滤波前振幅水平.理论和实际数据试算表明,本文方法可有效提取多波地震数据中的横波波场,为多波多分量横波数据处理提供新思路. 相似文献
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G.-Akis Tselentis 《Pure and Applied Geophysics》1990,133(3):429-446
A new technique for calculating interstation Green's functions and attenuation coefficients for seismic surface waves is presented.The interstation Green's function is evaluated from the autocorrelation functions of the seismograms, which are obtained from a maximum entropy process.Since a data-invariant time window is not used, the evaluated Green's functions gives reliable information on both the amplitude and the phase spectra of the system.This new technique is compared with other methods by applying them to both synthetic and real data from a path in the Canadian shield. 相似文献
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选取了几种常见的小波母函数,分别提取了同一理论下的面波数据的群速度,并与理论群速度进行对比,结果表明Morlet小波提取面波群速度的效果最好.此外,将Morlet小波与常用的多重滤波提取群速度的结果进行了比较,结果表明: ① 多重滤波法非常依赖高斯滤波系数α的取值,α的取值应随面波周期的增大而减小;② 在α取值得当的前提下,在20—35 s周期范围内多重滤波法提取面波群速度的相对误差比Morlet小波小,在周期大于35 s时,两者相对误差相近; ③ 合适的α值的选取需在不同周期段耗费大量时间进行大量试验,这说明多重滤波法不具备自适应性;而采用小波变换分析短周期信号时,时间窗变窄,频率窗变长,当分析长周期信号时,时间窗变长,频率窗变窄,具有对信号的自适应性,这是小波变换相比多重滤波法的最大优点. 相似文献
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The S wave velocity structure between the hypocenter of C060394F earthquake,South Java and a series of observatory stations located in Australia and South-East Asia have been investigated through seismogram analysis in the time domain and the three Cartesian components.The synthetic seismogram is constructed from the PREMAN global earth model.Seismogram comparison between the measured and synthetic seismograms shows large discrepancies.A correction to the S wave velocity structure is needed to solve these d... 相似文献
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The method of extracting Green's function between stations from cross correlation has proven to be effective theoretically and experimentally.It has been widely applied to surface wave tomography of the crust and upmost mantle.However,there are still controversies about why this method works.Snieder employed stationary phase approximation in evaluating contribution to cross correlation function from scatterers in the whole space,and concluded that it is the constructive interference of waves emitted by the scatterers near the receiver line that leads to the emergence of Green's function.His derivation demonstrates that cross correlation function is just the convolution of noise power spectrum and the Green's function.However,his derivation ignores influence from the two stationary points at infinities,therefore it may fail when attenuation is absent.In order to obtain accurate noise-correlation function due to scatters over the whole space,we compute the total contribution with numerical integration in polar coordinates.Our numerical computation of cross correlation function indicates that the incomplete stationary phase approximation introduces remarkable errors to the cross correlation function,in both amplitude and phase,when the frequency is low with reasonable quality factor Q.Our results argue that the distance between stations has to be beyond several wavelengths in order to reduce the influence of this inaccuracy on the applications of ambient noise method,and only the station pairs whose distances are above several (5) wavelengths can be used. 相似文献
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根据欧亚大陆及西太平洋地区58个数字地震台站2861个长周期波形记录，从中挑选出符合条件的223对经过中国大陆的双台路径记录，采用相匹配滤波和频率域维纳滤波相结合的方法，计算出双台之间的混合路径衰减系数. 对中国大陆区域进行网格划分，通过网格化反演得到中国大陆区域每个网格单元的纯路径衰减系数. 根据速度和密度模型，对每个网格单元进行深度反演，得到10～350km的S波品质因子Qβ，进而得到整个中国大陆的S波品质因子分布. 结果显示：研究区域的Qβ横向和纵向变化非常显著，能够明显区分软流圈结构，各个大构造单元的Qβ结构呈现出显著的变化. 这为解释中国大陆区域地球内部介质性质和探讨地球动力学提供了丰富的信息. 相似文献
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Surface wave tomography method based on analysis of ambient noise is widely used during the last decade. It is assumed that correlated component of noise is composed of surface waves generated by sources distributed over the Earth’s surface more or less uniformly. In such a case the cross-correlation function (CCF) at two stations may be considered as the Green’s function of surface wave. This function should be symmetric relatively to zero time. However analysis of CCF at the stations located at the East-European Platform shows that as a rule CCF is characterized with a strong asymmetry. Since “purered noise cannot be extracted from seismic records due to superposition of earthquake signals, the method for calculation of CCF includes amplitude normalization for suppression of earthquakes that reduces signals from earthquakes to a noise level. The parts of records containing waves from earthquakes are neglected because of their short duration. Present study shows that this contribution turns out to be dominant at periods larger than 20–40 s. In other words, what is assumed as a “noisered in reality is a superposition of signals from earthquakes. This fact results in distortion of the Green’s function and of surface wave dispersion curve used in surface wave tomography if in the time interval used for calculation of CCF many earthquakes occur within a small area apart of an extension of the interstation path (clustering). Numerical modeling shows how clusters of sources affect CCF and dispersion curve correspondingly. Means for reducing this effect are outlined. 相似文献
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Helga Emmerich 《Physics of the Earth and Planetary Interiors》1993,80(3-4):125-134
Computing synthetic seismograms for media with localized heterogeneous regions can be performed using hybrid methods. Here, a combination of a finite-difference (FD) technique and a frequency-wavenumber (ω − k) filtering is applied to model wave reflection at different kinds of core-mantle boundary (CMB) topography. The FD method is only applied in the neighbourhood of the CMB, while the ω − k filter is used to continue the reflected wavefield to the Earth's surface. Synthetic SH-seismograms for ScS with a dominant frequency of 0.5 Hz are computed at epicentral distances from 44° to 69°. The topography varies in amplitude (maximum amplitude of 1.0–2.7 km) and in its wavenumber spectrum; it is either monochromatic (wavelengths from 55 to 270 km) or statistical (coloured noise). The seismograms for a CMB with topography are compared with those for a plane CMB. We observe that monochromatic topography with short wavelengths (less than 100 km) results in amplitude reduction and shorter travel times than in the case of a plane CMB, but no variations with epicentral distance appear, whereas greater wavelengths exhibit amplitude variations with distance as well as travel time residuals, which both correlate with the CMB topography. Statistical models show amplitude variations with epicentral distance, while the travel time residuals are very small (less than 0.1 s). All synthetics illustrate that wavefront healing occurs along the ray path from the CMB to the Earth's surface. While the seismograms at the CMB exhibit strong fluctuations, the fluctuations at the surface are smoothed and reduced. This demonstrates that it is necessary to use wave theoretical methods for computing synthetic seismograms for complicated structures at greater depth. It also follows that travel times are less sensitive to the structure than the amplitudes. 相似文献
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本文利用中国数字地震台网位于东北地区的122个宽频地震台站的18个月记录的三分量连续地震噪声数据,采用互相关方法提取了Rayleigh和Love波经验格林函数,并利用时频自动分析技术获取了相应的相速度频散曲线.通过反演频散曲线,获得了Rayleigh和Love波周期为8~35s的二维相速度分布.结果表明,东北地区相速度的分布存在横向和垂向的不均匀性.短周期的相速度分布同地表地质构造密切相关,松辽盆地及山间沉积盆地呈现低速异常,而大兴安岭、小兴安岭及东部的一些山岭显示高速异常.随着周期的增加,位于中间的松辽盆地变为高低速相间,两侧的造山带呈现低速异常.这种异常的转变,可能是受构造活动或者莫霍面深度的影响.另外,在周期为20~35s频段内,Rayleigh和Love波同一周期的相速度在松辽盆地和位于吉林地区的郯庐断裂带表现不一致,表明可能存在径向各向异性. 相似文献