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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,并结合由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:①50km处的气枪信号约为10nm量级,200km处的气枪信号小于1nm;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保障。
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:中央科研院所级基本业务费项目(DQJB15B09)、国家自然科学基金(41574052,41374070)和云南省陈颙院士工作站专项经费(2014IC007)共同资助
Characteristics of air­gun signals excited in the Yangtze River from analysis of permanent stations' data
Xu Yihe Wang Baoshan Wang Weitao
Key Laboratory of Seismic Observation and Geophysical Imaging,Institute of Geophysics,CEA,Beijing 100081, China
Abstract:
The Anhui Experiment of Yangtze Project,conducted in October 2015, is a large active source experiment using air-gun sources. It is the first 3 dimensional seismic survey with active sources in the Yangtze River,with exciting air guns in 20 fixed spots as the seismic source,109 permanent stations and a network formed by 11 portable survey line as the observation system. Using the data from permanent stations,we studied the seismic signals generated by air guns in the Yangtze River. The results show that the air gun signals are clearly seen in permanent stations' records,to a maximum distance of 300km. Further analysis on absolute amplitude of air gun signals shows that (1)the strength of air gun signals has scale of about 10nm at 50km away from the source,and it reduces significantly to less than 1nm at 200km; (2)an azimuthal anisotropy is observed in spatial distribution of air gun signals' strength,which may be related to the geometry of Yangtze River; (3)a low ambient noise level is essential for retrieving weak air gun signals from the records,and high quality of permanent stations network run by Chinese Earthquake Administration offers a great opportunity to retrieving air-gun signals with amplitude as small as nanometers.
Key words:  Yangtze Project  Anhui experiment  Permanent station  Large volume airgun  Ambient noise