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The Anhui Experiment, a pilot experiment of “Yangtze River Geoscience 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 of109 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 300 km. Further analysis on absolute amplitude of airgun signals shows that:( 1) the strength of airgun signals is of the order of10 nm at 50 km away from the source,and then,decreases significantly to less than 1nm at 200 km;( 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.
The Anhui Experiment, a pilot experiment of “Yangtze River Geoscience Project” conducted in October, 2015, is a large active-source experiment using air 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 300 km. Further analysis on absolute amplitude of airgun signals shows that :( 1) the strength of airgun signals is of the order of10 nm at 50 km away from the source, and then, decreases significantly to less than 1 nm at 200 km; (2) an azimuthal anisotropy is observed in spatial distribution of the strength of airgun signals, which may be related to the geome try 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.