江苏省区域地表背景噪声特性的分析

Analysis on Background Seismic Noise Characteristics in Jiangsu Province

利用Welch方法,计算了江苏省"十五"数字地震台站地表背景噪声在0.01～20Hz频带范围内的功率谱值,结果显示在周期10～16s、4～8s处分别存在两个明显的峰值。对比白天和夜晚时段台站三分向地表背景噪声的功率密度谱比值发现,地表台站三分向背景噪声在高频段(≥1Hz)变化最为显著,在微震峰值频段(0.125～1Hz)几乎所有台站之间的差异都不大,低频段(≤0.125Hz)大部分台站垂直向白天时段的噪声水平比夜晚的值低,水平向则相反;但井下观测系统全频段内的比值变化都很小。此外,在2～16Hz频率范围内,沿长江的苏南—上海地区的平均噪声水平高于苏中和苏北地区,比NLNM(低噪声模型)值高约45dB左右;在0.125～1Hz频率范围内,江苏中东部的噪声水平高于其他区域,推测这可能是与区域地质构造差异有关。

In this paper, we adopted the Welch＇s method to estimate background noise velocity power spectral density （PSD） of the seismic stations in Jiangsu province at the range from 0. 01s to 20Hz. We found that there are two dominant peaks at the periods T ≈10 -16 s, T ≈4 -8 s respectively. And the day/night spectral ratios of surface seismic stations show that the strongest variation for three components is at the frequency range ≥ 1 Hz, the ratio variations at the 0. 125 - 1 Hz are not distinguished, and the day noise level of the vertical component are lower than the night time noise at the range of low frequency range （ ≤0. 125 Hz）, the horizontal components are reverse. At the same time, there is little change for day/night spectral ratios of boreholes stations at all frequency sections. In additional, we also discussed seismic noise characteristic on the terrain difference of Jiangsu, the results show that the southern Jiangsu - Shanghai region has significantly higher noise level than midnorthern at the high frequency range （2 - 16 Hz）, which is about 45 dB higher than the NLNM. At 0. 125 - 1 Hz, the mid-eastern region has higher noise than other region, these are considered to be caused by geological difference.