利用地震背景噪声互相关检测流动地震台波形时钟漂移

Detecting Seismic Wave Clock Drifts in Temporary Seismic Stations with Ambient Noise Cross-correlation

时钟精度是地震观测中最重要的参数之一,需要通过卫星授时信号来保障。当卫星信号被屏蔽或仪器守时部件出现问题时,地震计内部时钟会逐渐漂移,给后续数据处理带来极大困扰。利用地震背景噪声台站对互相关提取的经验格林函数,不仅可以用于结构成像,也可以用于检测波形时钟是否存在漂移,并获得时钟漂移幅度。使用地震背景噪声互相关方法对2017—2019年云南永胜地区4个流动观测台站的连续波形进行了时钟漂移检测,结果发现部分流动台站在不同时间段存在不同模式的时钟漂移,最大幅度可达到1.75 s。同时,利用云南宾川气枪重复震源激发的信号进行互相关计算,对上述结果进行了验证,发现两种结果具有较好的一致性。研究表明,背景噪声互相关对波形的时钟漂移有较高的灵敏度,能够有效检测出时钟问题,防止波形被误用,可为后续波形时钟校正提供参考信息。

Clock accuracy is one of the most important parameters in seismic observation,which is usually guaranteed by satellite timing signal.When the satellite signal is shielded or the time-keeping components of the instrument have problems,the internal clock of seismometer will drift gradually,which brings great affect to the data processing.The empirical Green’s function extracted from cross-correlation of seismic background noise stations can not only be used for structural imaging,but also can be used to detect whether the waveform clock has drift and how many times drifted.In this paper,the cross-correlation monitoring method of seismic background noise is used to detect the clock drift of four mobile stations in Yongsheng area of Yunnan Province from 2017 to 2019.The results show that some mobile stations have different clock drift modes in different time periods,and the maximum amplitude can reach 1.75 s.Furthermore,the above results are verified by using the repeated signals from the Fixed Airgun Signal Transmission Stations(FASTS)of Binchuan in Yunnan province.It is found that the two results have a good consistency.Our research shows that the cross correlation of background noise has a high sensitivity to the clock drift of seismic waveform,which can effectively detect the clock problem of waveform,prevent the waveform from being misused,and provide reference information for the subsequent clock correction of waveform.