中国中东部地震台站噪声互相关函数中面波前驱信号的分析研究

摘要

We calculated the cross correlation function (NCF) for each station pair using vertical component of 430 broadband stations in middle-eastern China from 2008 to 2009. Very strong precursors before Rayleigh wave are observed in most NCFs, which are persistent within two years. These signals last for about 50 s and peak from 0. 07 Hz to 0. 12 Hz in spectrum. The arrival times of these precursors are constant for same station pair but vary with different station pair, which indicates these signals may origin from a persistent localized microseism source.Triangulation location using grid search method indicates that they are generated around Kyushu island of Japan, assuming a homogeneous propagation velocity of 2. 7 km/s. This location result is further verified by comparing synthetic NCFs with observations. Special attentions should be paid to minimize possible errors caused by these precursors for studies based on ambient seismic noise. The physical mechanism of this microseism source remains to be studied.%利用中国中东部地震台网中430个宽频带台站2008和2009两年的垂直分量记录,我们计算了台站对之间的噪声互相关函数( Noise Cross-correlation Function,NCF).在相当多的NCF中,沿大圆路径传播的瑞利面波信号之前存在一个较强的前驱信号,该信号持续时间约50 s,频率范围为0.07～0.12 Hz.此信号在同一台站对的NCF中稳定存在、到时相同,而在不同台站对的NCF中到时不一致,这表明该信号可能源于一个固定的较小区域内持续存在的噪声源.基于格点搜索方法的定位结果显示该噪声源位于日本九州岛附近,其激发出的信号传播速度约2.7 km/s.假定该信号由一点产生,我们计算了合成地震图,合成地震图与观测到的前驱信号基本一致,验证了定位结果的可靠性.此噪声源会对特定路径上的面波信号产生干扰,在相关研究中需要采取一定措施避免.该噪声源的物理机制有待于进一步的研究.