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利用固定台站分析长江激发气枪信号特征
徐逸鹤 王宝善 王伟涛
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),北京市民族大学南路5号 100081
摘要:
“地学长江计划”安徽实验是以气枪震源为核心的大型主动源探测实验。通过在长江安徽段20个固定点定点激发气枪震源,结合109个固定台站、11条流动测线组成的观测网络,首次利用主动源实现了对长江流域安徽段约6万km2面积的三维地下结构探测。本文利用固定台站对长江激发气枪信号进行了分析,结果表明,长江中气枪信号激发效果良好,固定台记录中气枪信号可识别的最远距离达300km。对气枪信号绝对振幅的研究结果表明:① 50km处的气枪信号约为10nm量级,200km处的气枪信号小于1 nm;② 气枪信号强度的空间分布存在一定的方位各向异性,可能与长江的几何形状有关;③ 台站背景噪声对于提取气枪信号至关重要,高质量的固定台网为识别nm量级气枪信号提供了可能。
关键词:  地学长江计划  安徽实验  固定台站  大容量气枪  背景噪声
DOI:
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基金项目:
Characteristics of Airgun Signals Excited in the Yangtze River from Analysis of Data from Permanent Stations
Xu Yihe, Wang Baoshan, and Wang Weitao
Key Laboratory of Seismic Observation and Geophysical Imaging, Institute of Geophysics, CEA, Beijing 100081 China
Abstract:
The Anhui Experiment, a pilot experiment of Yangtze Project conducted in October 2015, is a large active-source experiment using airgun sources. It was the first 3 - dimensional seismic survey with active sources in the Yangtze River. The sources are airguns in 20 fixed shot points, and the observation system consists mainly of 109 permanent stations and 11 wide-angle profiles. Using the data from permanent stations, we investigated the seismic signals generated by airgun sources in the Yangtze River. The results show that the airgun signals are observable in the records from permanent stations to a maximum distance of 300km. Further analysis on absolute amplitude of airgun signals shows that: (1) the strength of airgun signals is of the order of 10 nm at 50km away from the source, and then, decreases significantly to less than 1 nm at 200km; (2) an azimuthal anisotropy is observed in spatial distribution of the strength of airgun signals, which may be related to the geometry of Yangtze River; and (3 ) a low ambient noise level is essential for retrieving weak airgun signals from the records, and the high-quality China National Seismic Network and regional networks offer a great opportunity to retrieving airgun signals with amplitude as small as nanometers.
Key words:  Yangtze  Project  Anhui  Experiment  Permanent stations  Large-volume airgun  Ambient noise