利用背景噪声互相关方法研究唐山地区地震波速变化

Variations of Seismic Velocity Based on Ambient Noise Cross-correlation in Tangshan Area

本文使用唐山地区部分数字地震观测台网2013年1月~2015年12月的连续背景噪声记录,采用波形互相关方法来监测研究区地下物性介质随时间的变化特征。首先采用背景噪声互相关技术获取台站间的经验格林函数,然后通过观测台站对之间参考经验格林函数和当天格林函数中直达的瑞利波走时偏移来计算台站对之间的瑞利波速时空变化。结果显示,在2013年1月至2015年12月期间,大部分台站对的瑞利波速度未发生明显改变,预示着唐山地区中上地壳的物性介质处于相对稳定阶段。但是,部分台站对之间的瑞利波速在2015年9月14日昌黎ML4.7地震前出现上升变化,而震后随着时间的流逝又慢慢恢复到背景值附近波动。目前,虽然难以确定瑞利波速的震前上升变化跟震源区的应力积累过程有直接关系,但这种现象值得持续关注和深入研究。

We collected the long period continuous data（January 2013 to December 2015）for stations in Tangshan and adjacent areas from Earthquake Administration of Hebei Province,and monitored the feature of the underground medium changing with time by waveform cross-correlation method.Firstly,we used ambient noise cross-correlation to produce the Green＇s functions of each station-pair at the frequency range of 0.1 to 0.5 Hz.Then,we calculated the time shift between the Reference Green Function and the Current Empirical Green Function for each station-pair.The preliminary results show that most of station pairs appeared no obvious velocity changes,which revealed that underground medium of Tangshan and adjacent areas was in stable stage.However,velocity for a few station pairs increased before the Changli ML4.7 earthquake and decreased to their background value after the earthquake.At present,although we could not determine this phenomenon was related to stress accumulation around the epicenter areas,further attention and research are needed.