地震研究

水库气枪震源不同组合激发效率的对比研究^*

(1.中国地震局滇西地震预报实验场, 云南大理 671000; 2. 中国地震局地球物理研究所(地震观测与地球物理成像重点实验室), 北京 100081; 3. 南洋理工大学, 新加坡 639798)

Research on Comparison of Excitation Efficiency of Air Guns with Various Combinations in Water Reservoir

LI Xiaobin¹, YE Beng¹, YANG Jun¹, CHEN Meng^2,3, JIN Mingpei¹, WANG Baoshan²

(1.Western Yunnan Earthquake Prediction Study Area, CEA, Dali 671000, Yunnan, China)(2.Seismic Observation and Geophysical Imaging Laboratory, Institute of Geophysics, CEA, Beijing 100081, China)(3.Nanyang Technological University, Singapore 639798)

Keywords：air gun exciting; seismic signal; excitation efficiency; SNR; signal stacking

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参考文献

为研究气枪的激发特性,并为气枪发射台的堪选、建设提供参考依据,在宾川地震信号发射台进行了不同气枪组合的激发试验,并对试验数据进行了分析。结果表明:(1)单支气枪激发100多次的叠加信号可以被在150 km外的地震台记录到;(2)单支气枪激发与4支气枪同时激发的信号频率基本相同,且衰减基本一致,但4支气枪同时激发信号的均方根振幅约为单支气枪的4倍;(3)当气枪组合激发的信号的信噪比达到10 dB时,相关系数可以达到0.99以上;(4)4支气枪同时激发的激发效率是单支气枪的4倍。从分析结果可看出,宾川地震信号发射台在牺牲一定效率的情况下,单支气枪激发信号可以替代4支气枪组合的激发信号。

In order to study the excitation characteristic of the air gun, and provide the reference for the chosen site and construction of the air gun transmitting seismic station, we take the excitation test of air guns with various combinations at the Binchuan Transmitting Seismic Station(TSS). Analyzing the selected test data,we found the following results:(1)The stacked air gun signals excited by the single gun for more than 100 times can be clearly recorded at the seismic station with an epicentral distance of 150 km.(2)The frequencies of signals excited by single and four air guns are basically same,and their corresponding attenuations are basically similar, however the RMS amplitude of the signal excited by four air guns is about 4 time as much as that of single air gun.(3)When the SNR of signal exited by single gun reaches 10 dB, the correlation coefficient of it could reach above 0.99.(4)The excitation efficiency ratio of signals excited by single gun and four guns is 1:4. The analysis result shows that the signal excited by single gun can be replaced by the combination signal excited by four guns in case of losing some efficiency.

引言
1 试验情况
2 对比分析
3 讨论与结论

图1 宾川地震信号发射台及周边流动台分布情况<br/>Fig.1 Location of Binchuan Transmitting Seismic Stations(TSS)and distribution of flow seismic stations in its surrounding area

图1 宾川地震信号发射台及周边流动台分布情况
Fig.1 Location of Binchuan Transmitting Seismic Stations(TSS)and distribution of flow seismic stations in its surrounding area

图2 气枪组俯视图<br/>Fig.2 Top view of airgun array

图2 气枪组俯视图
Fig.2 Top view of airgun array

表1 试验激发参数<br/>Tab.1 The transmitting parameters in experiments

表1 试验激发参数
Tab.1 The transmitting parameters in experiments

图3 1号(a)、3号(b)、4号(c)气枪激发及4枪(d)激发时参考台信号相关系数分布<br/>Fig.3 Distribution of correlation coefficient of signals recorded by the reference station when the No.1 airgun (a), the No.3 airgun(b),the No.4 airgun(c)excited, and four airguns excited at the same time(d)

图3 1号(a)、3号(b)、4号(c)气枪激发及4枪(d)激发时参考台信号相关系数分布
Fig.3 Distribution of correlation coefficient of signals recorded by the reference station when the No.1 airgun (a), the No.3 airgun(b),the No.4 airgun(c)excited, and four airguns excited at the same time(d)

图4 单枪激发与4枪激发参考台信号波形(a)及功率谱(b); 4枪(c)、单枪(d)激发<br/>参考台信号时频分析<br/>Fig.4 Waveforms(a)and power spectrums(b)of the signal recorded by reference station when the single airgun excited and four airguns excited at the same time; time frequency analysis of the signal recorded by reference station when four airguns excited at the same time(c)and the single airgun excited(d)

图4 单枪激发与4枪激发参考台信号波形(a)及功率谱(b); 4枪(c)、单枪(d)激发
参考台信号时频分析
Fig.4 Waveforms(a)and power spectrums(b)of the signal recorded by reference station when the single airgun excited and four airguns excited at the same time; time frequency analysis of the signal recorded by reference station when four airguns excited at the same time(c)and the single airgun excited(d)

图5 单枪激发信号叠加后的剖面图
Fig.5 Profile of the stacking of signals excited by the single airgun

图6 单枪激发与4枪激发信号随距离变化的对比分析<br/>(a)单枪激发与4枪激发信号振幅随距离的变化情况;(b)单枪和4枪激发时段各台站背景噪声振幅; 单枪激发与4<br/>枪激发信号的信噪比(c)和相关系数(d)随距离的变化情况<br/>Fig.6 Comparison analysis of the signal varies with distance when the single airgun and four airguns excited (a)amplitude of signal varies with distance when the single airgun and four airguns excited;(b)amplitude of background noise of each station in the period of single airgun and four airguns excited; singnal noise

图6 单枪激发与4枪激发信号随距离变化的对比分析
(a)单枪激发与4枪激发信号振幅随距离的变化情况;(b)单枪和4枪激发时段各台站背景噪声振幅; 单枪激发与4
枪激发信号的信噪比(c)和相关系数(d)随距离的变化情况
Fig.6 Comparison analysis of the signal varies with distance when the single airgun and four airguns excited (a)amplitude of signal varies with distance when the single airgun and four airguns excited;(b)amplitude of background noise of each station in the period of single airgun and four airguns excited; singnal noise

图7 不同距离台站的信噪比与叠加次数的关系<br/>(a)ckt2;(b)53272;(c)53280;(d)53282;(e)53259; <br/>(f)53285;(g)53253;(h)53252<br/>Fig.7 Relationship between SNR of each station in different distance and stacking number

图7 不同距离台站的信噪比与叠加次数的关系
(a)ckt2;(b)53272;(c)53280;(d)53282;(e)53259;
(f)53285;(g)53253;(h)53252
Fig.7 Relationship between SNR of each station in different distance and stacking number

图8 单枪和4枪激发信号在不同距离激发效率<br/>的对比分析<br/>(a)单枪和4枪激发信号在不同距离台站的振幅比;(b)单<br/>枪激发信号不同叠加次数与4枪激发信号的信噪比对比<br/>Fig.8 Comparison analysis of the excitation efficiency of the signal in different distance when the single airgun and four airguns excited (a)amplitude ratio of signal recorded by stations in different distance when the single airgun and four airguns signals excited; (b)comparison of SNR between the single airgun in different stacking number and four airguns excited

图8 单枪和4枪激发信号在不同距离激发效率
的对比分析
(a)单枪和4枪激发信号在不同距离台站的振幅比;(b)单
枪激发信号不同叠加次数与4枪激发信号的信噪比对比
Fig.8 Comparison analysis of the excitation efficiency of the signal in different distance when the single airgun and four airguns excited (a)amplitude ratio of signal recorded by stations in different distance when the single airgun and four airguns signals excited; (b)comparison of SNR between the single airgun in different stacking number and four airguns excited