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S变换是一种用于分析非平稳信号的时频变换方法, 可以很好地刻画地震信号的时频特性. 本文将S变换用于地震面波数据的噪声去除中, 首先介绍了S变换的理论基础, 然后设计了时频滤波和阈值滤波两种方法, 分别对天然地震面波数据和背景噪声数据进行去噪处理, 并与相位匹配滤波进行了比较． 结果表明, 面波数据经S变换去噪后, 群速度频散曲线的短周期部分得到改善, 能够连续追踪至6 s左右, 但长周期部分出现了缺失; S变换去噪的效果优于相位匹配滤波, 两者相结合会得到更加理想的结果． 相似文献
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选取2019年1月—2021年12月灌云地震台远震事件记录，将灌云地震台测算的面波震级与中国地震台网中心统一正式报目录震级进行对比，计算二者面波震级偏差平均值，并分析震级偏差与震级、震中距、震中方位之间的关系。结果表明：灌云地震台面波震级与中国地震台网中心统一正式报目录震级平均偏差为-0.08，总体偏差较小，表明该台地震记录精度较高。 相似文献
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DK1地震仪的面波震级起算函数研究di 总被引：4，自引：0，他引：4
使用1987～1993年DK1地震仪的地震记录，以国际地震中心(ISC)MS震级为标准震级，根据误差理论用最小二乘法拟合导出DK1地震仪面波震级起算函数．又从起算函数物理意义出发，根据成层介质中面波传播理论，考虑到地震波的频散、介质的吸收、地球介质与DK1地震仪所组成的线性滤波器对面波振幅和周期的影响，并假定面波最大振幅对应于Airy相，导出了DK1地震仪测定面波震级的起算函数．
使用本文导出的起算函数，不附加任何校正值．通过315个地震，对36个速报台的单台DK1面波震级和DK1速报台网的面波震级测定误差检验，结果表明，DK1面波震级MS(DK1)与国际地震中心(ISC)相应地震面波震级MS(ISC)之间在统计上无系统误差，平均误差接近于零． 相似文献
4.
地震震级是地震三要素之一,如何准确测定震级对于地震速报与应急工作至关重要。选取赤峰中心地震台2016年1月1日到2019年5月31日测定的674个地震事件的面波震级进行分析,并与中国地震台网中心发布的正式目录进行比较,并根据不同的震中距和方位角,给出面波震级偏差及校正值。结果表明:随着震级和震中距增大,震级偏差增大;赤峰中心地震台以北地区的不同方位角范围内,地震面波震级偏差分别为0.15、-0.13,以南地区的不同方位角范围内,地震面波震级偏差分别为0.22、0.16;根据参考校正值重新计算震级,通过震级对比结果表明校正效果较好。 相似文献
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利用1995年至2009年中国东北及邻近地区11个宽频带台站记录到的77个地震事件、3个化学爆炸和2次朝鲜核爆的区域地震资料,标定该区域台网的Rayleigh波震级.通过对8~25 s 周期的垂直分量Rayleigh波形进行分析,获取基于最大振幅的面波震级.计算82个区域事件不同周期的台基响应,经过台基校正后取最大振幅的面波震级为事件震级.2006年和2009年两次朝鲜核爆的面波震级分别为2.93±0.19和3.62±0.21.将地震和核爆事件的面波震级Ms与体波震级mb(Lg)进行比较,发现根据该区域台网的数据利用Ms-mb识别方法无法鉴别朝鲜地区的核爆与地震.朝鲜核爆的面波震级相对较大,使Ms-mb识别方法失效,其原因可能是源区介质的不均匀性、由核爆炸冲击引发的深部的拉伸破坏被抑制,或者是近爆源区存在张性的构造预应力.假定核爆可能的埋藏深度范围是0.01~1.0 km,用Rayleigh波震级估计朝鲜核爆的当量,对2006年和2009年核爆当量的估值范围分别为0.42~3.17 kt和2.06~15.53 kt. 相似文献
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本文基于瑞利面波的激发和传播理论,导出了零级地震的理论面波谱表达式;并以零级地震为参考地震,以零级地震所相应的面波谱和地震矩作为地幔波震级规范化标定的参照依据,进而提出了测定地幔波震级的新方案。利用CDSN-LPZ信道中的面波资料测定了1987-1990年间全球54次浅源大地震的地幔波震级Mm,并对Okal和Talandier（1989）用GEO-SCOPE-VLPZ及PAS-VLPZ信道中的基阶瑞利波所测1970-1987年间88次地震的结果作了校正。综合这两部分观测结果,得到Mm=1.00 1gM0-12.13,由此测定的地幔波震级与中小地震的面波震级Ms趋势相一致,为解决面波震级饱和问题提供了一种可行的途径。 相似文献
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地幔波震级的规范化标定与观测 总被引：1，自引：0，他引：1
本文基于瑞利面波的激发和传播理论,导出了零级地震的理论面波谱表达式;并以零级地震为参考地震,以零级地震所相应的面波谱和地震矩作为地幔波震级规范化标定的参照依据,进而提出了测定地幔波震级的新方案。利用CDSN-LPZ信道中的面波资料测定了1987—1990年间全球54次浅源大地震的地幔波震级M_m,并对Okal和Talandier(1989)用GEO-SCOPE-VLPZ及PAS-VLPZ信道中的基阶瑞利波所测1970—1987年间88次地震的结果作了校正。综合这两部分观测结果,得到M_m=1.00 1gM_0—12.13,由此测定的地幔波震级与中小地震的面波震级M_s趋势相一致,为解决面波震级饱和问题提供了一种可行的途径。 相似文献
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本文介绍了全球主要地震机构对2008年5月12日汶川地震参数的速报和修订情况，分析了美国地质调查局国家地震信息中心测定的面波震级。通过对比198个全球地震台站测定的面波震级和面波周期，得出如下结论:测定面波震级偏大的台站主要分布在震中的东北方向，测定面波震级偏小的台站主要分布在震中的西南和东南方向，面波周期偏小的台站主要分布在震中东北方向。由于此次地震破裂方向是以北东向单侧破裂为主，且地震多普勒效应导致震中东北方向振动加强，因此该方向上的面波震级偏大，地震烈度衰减慢；而震中西南方向的振动减弱，此方向面波震级偏小，地震烈度衰减快。从而造成地震烈度沿中央断裂带的北东方向衰减慢，而南西方向衰减快的特征分布。 相似文献
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v--vOur goal is to develop and test an effective method to detect, identify, extract, and quantify surface wave signals for weak events observed at regional stations. We describe an automated surface wave detector and extractor designed to work on weak surface wave signals across Eurasia at intermediate periods (8 s-40 s). The method is based on phase-matched filters defined by the Rayleigh wave group travel-time predictions from the broadband group velocity maps presented by Ritzwoller and Levshin (1998) and Ritzwoller et al. (1998) and proceeds in three steps: Signal compression, signal extraction or cleaning, and measurement. First, the dispersed surface wave signals are compressed in time by applying an anti-dispersion or phase-matched filter defined from the group velocity maps. We refer to this as the `compressed signal.' Second, the surface wave is then extracted by filtering `noise' temporally isolated from the time-compressed signal. This filtered signal is then redispersed by applying the inverse of the phase-matched filter. Finally, we adaptively estimate spectral amplitude as well as group and phase velocity on the filtered signal. The method is naturally used as a detector by allowing origin time to slide along the time axis. We describe preliminary results of the application of this method to a set of nuclear explosions and earthquakes that occurred on or near the Chinese Lop Nor test site from 1992 through 1996 and one explosion on the Indian Rajasthan test site that occurred in May of 1998. 相似文献
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—?We present results from a large-scale study of surface-wave group velocity dispersion across the Middle East, North Africa, southern Eurasia and the Mediterranean. Our database for the region is populated with seismic data from regional events recorded at permanent and portable broadband, three-component digital stations. We have measured the group velocity using a multiple narrow-band filter on deconvolved displacement data. Overall, we have examined more than 13,500 seismograms and made good quality dispersion measurements for 6817 Rayleigh- and 3806 Love-wave paths. We use a conjugate gradient method to perform a group-velocity tomography. Our current results include both Love- and Rayleigh-wave inversions across the region for periods from 10 to 60 seconds. Our findings indicate that short-period structure is sensitive to slow velocities associated with large sedimentary features such as the Mediterranean Sea and Persian Gulf. We find our long-period Rayleigh-wave inversion is sensitive to crustal thickness, such as fast velocities under the oceans and slow along the relatively thick Zagros Mts. and Turkish-Iranian Plateau. We also find slow upper mantle velocities along known rift systems. Accurate group velocity maps can be used to construct phase-matched filters along any given path. The filters can improve weak surface wave signals by compressing the dispersed signal. The signals can then be used to calculate regionally determined M S measurements, which we hope can be used to extend the threshold of m b :M S discriminants down to lower magnitude levels. Other applications include using the group velocities in the creation of a suitable background model for forming station calibration maps, and using the group velocities to model the velocity structure of the crust and upper mantle. 相似文献
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Jing Liu Youcai Tang Kai Tao Chunquan Yu Jie Chen Jieyuan Ning Yongshun John Chen Yongge Feng 《地震科学（英文版）》2010,23(6):627-636
We have developed a new stacking technique in ambient noise tomography to obtain high-quality dispersion curves of Rayleigh waves.This technique is used to stack the vertical components of the Estimated Green Functions(EGFs) obtained respectively from cross correlation of the ambient noise data recorded by a remote seismic station and one of the short distance seismic stations of a seismic array.It is based on a phase-matched filter and is implemented by a four-step iterative process:signal compression,stacking,signal extraction and signal decompression.The iterative process ends and gives the dispersion curve of Rayleigh wave when the predicted one and the processing result converge.We have tested the method using the vertical components of synthetic Rayleigh wave records.Results show that this new stacking method is stable and it can improve the quality of dispersion curves.In addition,we have applied this method to real data.We see that the results given by our new technique are obviously better than the ones employing the traditional method which is a three-step process:signal compression,signal extraction and signal decompression.In conclusion,the new method proposed in this paper can improve the signal to noise ratio of EGFs,and can therefore potentially improve the resolution of ambient noise tomography. 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 theory of statistical communication provides an invaluable framework within which it is possible to formulate design criteria and actually obtain solutions for digital filters. These are then applicable in a wide range of geophysical problems. The basic model for the filtering process considered here consists of an input signal, a desired output signal, and an actual output signal. If one minimizes the energy or power existing in the difference between desired and actual filter outputs, it becomes possible to solve for the so-called optimum, or least squares filter, commonly known as the “Wiener” filter. In this paper we derive from basic principles the theory leading to such filters. The analysis is carried out in the time domain in discrete form. We propose a model of a seismic trace in terms of a statistical communication system. This model trace is the sum of a signal time series plus a noise time series. If we assume that estimates of the signal shape and of the noise autocorrelation are available, we may calculate Wiener filters which will attenuate the noise and sharpen the signal. The net result of these operations can then in general be expected to increase seismic resolution. We show a few numerical examples to illustrate the model's applicability to situations one might find in practice. 相似文献
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One of the main objectives of seismic digital processing is the improvement of the signal-to-noise ratio in the recorded data. Wiener filters have been successfully applied in this capacity, but alternate filtering devices also merit our attention. Two such systems are the matched filter and the output energy filter. The former is better known to geophysicists as the crosscorrelation filter, and has seen widespread use for the processing of vibratory source data, while the latter is. much less familiar in seismic work. The matched filter is designed such that ideally the presence of a given signal is indicated by a single large deflection in the output. The output energy filter ideally reveals the presence of such a signal by producing a longer burst of energy in the time interval where the signal occurs. The received seismic trace is assumed to be an additive mixture of signal and noise. The shape of the signal must be known in order to design the matched filter, but only the autocorrelation function of this signal need be known to obtain the output energy filter. The derivation of these filters differs according to whether the noise is white or colored. In the former case the noise autocorrelation function consists of only a single spike at lag zero, while in the latter the shape of this noise autocorrelation function is arbitrary. We propose a novel version of the matched filter. Its memory function is given by the minimum-delay wavelet whose autocorrelation function is computed from selected gates of an actual seismic trace. For this reason explicit knowledge of the signal shape is not required for its design; nevertheless, its performance level is not much below that achievable with ordinary matched filters. We call this new filter the “mini-matched” filter. With digital computation in mind, the design criteria are formulated and optimized with time as a discrete variable. We illustrate the techniques with simple numerical examples, and discuss many of the interesting properties that these filters exhibit. 相似文献
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A. J. BERKHOUT 《Geophysical Prospecting》1974,22(4):683-709
In this paper properties of the discrete zero-phase time function are derived and compared with related properties of the discrete minimum-phase time function. The two-sided minimum-length signal is introduced and it is derived that, for any given amplitude spectrum, the two-sided minimum-length signal and the signal with zero-phase spectrum are identical signals. A comparison is made between the one-sided minimum-length signal (minimum-phase signal) and the two-sided minimum-length signal (zero-phase signal). A computational scheme is discussed which determines the zero-phase correspondent of a given signal. A method is proposed to compute zero-phase least-square inverse filters. The efficiency of minimum-phase and zero-phase least-square inverse filters is shown on signals with different phase properties. A criterion is derived which determines whether a symmetric time function has the zero-phase property. The close relationship with the minimum-phase criterion is discussed. Finally the relationship between signal length and resolving power is illustrated on numerical examples. 相似文献
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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
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A filter method is presented which allows a qualitative and quantitative identification of wave modes observed with plasma experiments on satellites. Hitherto existing mode filters are based on the MHD theory and thus they are restricted to low frequencies well below the ion cyclotron frequency. The present method is generalized to cover wave modes up to the characteristic ion frequencies. The spectral density matrix determined by the observations is decomposed using the eigenvectors of the linearized Hall-MHD equations. As the wave modes are dispersive in this formalism, a precise determination of the κ-vectors requires the use of multi-point measurements. Therefore the method is particularly relevant to multi-satellite missions. The method is tested using simulated plasma data. The Hall-MHD filter is able to identify the modes excited in the model plasma and to assign the correct energetic contributions. By comparison with the former method it is shown that the simple MHD filter leads to large errors if the frequency is not well below the ion cyclotron frequency. Further the range of validity of the linear theory is examined rising the simulated wave amplitudes. 相似文献