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安徽气枪实验固定台层析成像初步结果
张云鹏 王宝善 王伟涛 徐逸鹤
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:
为探索气枪震源在探测区域性地壳结构中的应用,2015年10月10~20日在长江马鞍山-安庆段开展了气枪流动激发实验(安徽实验),在20个固定点激发2973炮,中间流动激发1872炮,由周边109个固定台、700个流动台(包括11条测线)进行接收。为获取郯庐断裂带南端较为精细的地壳速度结构,本文利用安徽气枪实验中采集到的固定台数据进行初至P波震相拾取,对20个气枪源、52个台站、335个震相进行体波层析成像,验证了利用气枪震源激发进行体波层析成像的可行性,并得到了P波速度结构的初步研究结果:①利用大容量气枪震源激发可进行三维体波层析成像;②15km深度的成像结果显示出大区域高、低速异常区的清晰轮廓,即从研究区中心向外整体呈现出低-超低-低-高的分布特征,该特征与地质构造背景相关,具有显著的横向不均匀性;③秦岭-大别造山带显示出高速异常,与其深部超高压变质岩相对应,而长江中下游地区整体呈现低速异常,与其特殊的成矿背景相对应。
关键词:  郯庐断裂带南端 大容量气枪 震相拾取 体波层析成像
DOI:
分类号:
基金项目:国家自然科学基金(41374070、41574052)、云南省陈颙院士工作站专项经费(2014IC007)联合资助
Preliminary result of tomography from permanent stations in the Anhui air­gun experiment
Zhang Yunpeng Wang Baoshan Wang Weitao Xu Yihe
Key Laboratory of Seismic Observation and Geophysical Imaging,Institute of Geophysics,CEA,Beijing 100081, China
Abstract:
The Air-gun source has many advantages:economical and environmental protection and excellent repetition. The method has been used to study changes of the subsurface structure in recent years,and there are a lot of achievements. In order to explore the ability on imaging crust structure using active air-gun source,we conducted an experiment along the Yangzte River from Ma'anshan to Anqing segment using offshore air-gun source(the Anhui experiment). 2973 shots and 1872air-gun shots were excited at twenty fixed points and were received by 109 permanent stations and 700 mobile stations(11 lines). Air-gun source can form motivating and observational network densely with the accurate origin time and position. Compare with explosive source,air-gun has a very clear S phase. Thus,air-gun source can reduce the source location error in tomography,and can take full advantage of direct and later phases. To get the crust velocity structure in the southern tip of Tan-Lu fault,we used the data received by permanent stations in the Anhui air-gun experiment to pick P phase,and make tomography by 20air-gun sources,52 permanent stations,and 335 phases. We got a very good preliminary result of P wave velocity and verified the possibility to make tomography using air-gun source: (1)The use of high-capacity air-gun can make 3D body wave tomography. (2)Image of 15km depth shows the clear velocity anomaly outline,which is related to the geological tectonic background with prominent heterogeneity in transverse. (3)The Qinling-Dabie orogenic belt shows high velocity,which is associated with the ultrahigh-pressure metamorphic rocks in depth region,while the Yangtze River region presents low velocity anomaly,corresponding to the special background of mineralization.
Key words:  Southern tip of Tan­Lu fault  Large volume air­gun  Phase picking  Body­wave tomography