应用背景噪声互相关信息研究强震前后地下介质波速变化时,噪声源的方位性特征会影响互相关函数形态,从而对波速变化有效估计造成影响。本文使用2013年芦山M_S7.0地震震源区附近的天全台(TQU)2013年全年的连续波形记录,计算其垂直分量的噪声功率谱概率密度函数,分析背景噪声源能量强度特征;并通过频域极化法计算噪声源极化率以及极化方位角的概率密度函数,研究噪声源的极性特征。结果表明,研究区小于0.05Hz的长周期噪声源种类较多,且具有噪声能量强度和极化程度较高、极化方位性明显的特点;第一类地脉动(0.05～0.1Hz)极化方位角为30°和210°,噪声能量较低;第二类地脉动(0.1～0.5Hz)极化方位角分布在150°～210°,噪声能量较高,且其能量强度具有季节性变化特征;大于1Hz的高频噪声主要来自人类活动,噪声能量水平受人类活动强弱影响明显。因此,即使在远离海洋的大陆地区,在利用背景噪声监测局部波速变化时,应注意噪声强度以及噪声源方向性变化的影响。

When cross-correlation information of seismic ambient noise is used to study the seismic wave velocity changes in underground media before and after strong earthquakes,the characteristics of noise sources will affect the shape of cross-correlation function,which will affect the estimation of seismic velocity changes. Continuous waveform records from TQU station near the focal area of Lushan M_S7.0 earthquake between January 1 and December 31 of 2013 were used to calculate the power spectral density and probability density function to analyze the energy intensity characteristics of seismic ambient noise. The probability density functions of the degree of polarization and the polarization azimuth were calculated by frequency dependent polarization analysis to study the polarization characteristics of seismic ambient noise. The results indicate that there are many types of long-period seismic noise sources less than 0.05Hz in the study area,with high noise energy intensity and degree of polarization as well as obvious polarization azimuth. The single frequency microseisms(0.05～0.2Hz)has the polarization azimuth of 30° and 210°,and the noise energy is low. The polarization azimuth of double frequency microseisms(0.2～0.5Hz)ranges from 150° to 210°,and the noise energy is high,and its energy intensity has seasonal variation characteristics. The high-frequency noise greater than 1Hz mainly comes from human activities,and the noise energy level is significantly affected by the intensity of human activities. Therefore,even in continental regions far from the ocean,the influence of noise intensity and directional variation of noise sources should be noted when monitoring local seismic wave velocity changes using ambient noise.

P315

国家自然科学基金(42074103)资助