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A study of quality control of extracting dispersion curves by two-channel method of passive Rayleigh waves |
Guang-Zhou SHAO1, Liang YUE1, Yuan-Lin LI1, Hua WU2 |
1. School of Geological Engineering and Geomatics,Chang'an University,Xi'an 710054,China 2. School of Science,Chang'an University,Xi'an 710064,China |
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Abstract In recent years,the rapidly developed passive Rayleigh wave technology has the advantage of strong anti-interference capability and less limited construction conditions by using environmental noise as the source,which is more suitable for exploration in urban areas.However,the key factor affecting the imaging accuracy of the passive source method is the extracting quality of the dispersion curves.The current passive source Rayleigh wave method mainly uses the Aki formula to calculate the Rayleigh wave dispersion curve according to the relationship between spatial autocorrelation and time domain cross-correlation.This method has a good extraction effect for long-period observation data (for several months or more).Nevertheless,for practical engineering applications,it is desirable that the data observation period is as short as possible (such as one day or several hours).Under this circumstance,it will lead the zero points of the cross-correlation spectrum to increase or disappear,which will bring errors in the extraction of the dispersion curves when the Aki method is used to pick up them.Aimed at solving this problem,the authors put forward a set of quality control processes,such as using different normalization methods,selecting different window lengths for cross-correlation operations,setting Gaussian filters to filter cross-correlation functions,and selecting spectral zeros,to improve the extracting quality of dispersion curves.The authors combined certain evaluation criteria to verify the reliability of the dispersion curves and achieved the purpose of controlling the quality of the dispersion curves extraction.The passive source numerical simulation of theoretical model testing and the actual field noise data processing in Fengxiang County of Shaanxi show that the quality control method in the dispersion curve extraction is feasible and effective.This study has certain reference value and practical significance for the dispersion curve extraction of passive source Rayleigh wave method.
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Received: 28 May 2019
Published: 28 November 2019
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层序号 | 层厚度 /m | 纵波速度 /(m·s-1) | 横波速度 /(m·s-1) | 密度 /(kg·m-3) | 1 | 4 | 800 | 400 | 2000 | 2 | ∞ | 1200 | 600 | 2000 |
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Parameters of two-layer increasing velocity model
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Distribution diagram of noise source points
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Passive Rayleigh wave seismic records of two-layer increasing velocity model
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Field surveying line array
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Field measured background noise signal a—field background noise signal on line 6;b—active source seismic signal on line 6
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Flow chart of passive source Rayleigh wave data processing
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Filtering results of field measured background noise signals a—spectrum curve of original data;b—spectrum curve of filtered data
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Processing results of time domain normalization a—0~30 s seismic signal after filtering;b—filtered signal spectrum;c—seismic signal after "one-bit" method processed;d—signal spectrum after "one-bit" method processed;e—seismic signal after moving absolute average method processed;f—signal spectrum after moving absolute average method processed
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Whitening results of frequency domain normalization a—seismic signal after "one-bit" method bleached;b—signal spectrum after "one-bit" method bleached;c—seismic signal after moving absolute average method bleached;f—signal spectrum after moving absolute average method bleached
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道号 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | one-bit法 | 25.502 | 22.875 | 16.163 | 24.941 | 8.827 | 4.439 | 5.872 | 13.765 | 4.665 | 滑动绝对平均法 | 30.723 | 28.434 | 18.740 | 26.238 | 9.266 | 4.501 | 6.907 | 15.059 | 5.015 |
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SNR of cross-correlation results after whitening
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Influence of window length on cross-correlation results a—the cross-correlation result with time window length of 1 s;b—the cross-correlation result with time window length of 3 s;c—the cross-correlation result with time window length of 6 s;d—the cross-correlation result with time window length of 12 s
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时窗长度/s | 1 | 3 | 6 | 12 | 30 | 60 | 信噪比 | 5.3514 | 15.0542 | 12.002 | 9.154 | 7.5446 | 4.642 |
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SNR with different time window length
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Cross-correlation records after Gauss filtering
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Dispersion curves of geophone pairs 1~14 at different m for the theoretical model
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Dispersion curve obtained by partial processing for the theoretical model
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处理方案 | 均方误差 | 相关系数 | 只经历时间域归一化 | 15.9982 | 0.7615 | 只经历频率域归一化 | 11.6416 | 0.8852 | 时频域归一化、滤波等 | 9.2487 | 0.9948 |
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The degree of approximation between the extracted and the theoretical dispersion curve
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Dispersion curves of field measured data with different m
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Dispersion curves of Line 6
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