华南地区在中强震发生前有4级左右地震频繁活动和小震群频发的特点。
Before the moderately strong earthquakes in the region there are frequent seismic activity with magnitude of 4 or so and small earthquake swarms.
初步认为荣成震群是一次频发性震群，不是前兆震群。
It is suggested that the swarm might occur frequently and was not a precursory one.
本文研究海洋环境噪声与舰船噪声的频间相关与群延迟特性。
The characteristics of frequency correlation and group time delay of ambient noise and ship radiated noise in the sea are studied.
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