2016年台风“尼伯特”激发微地动的频率特征分析

Analysis of Frequency Characteristics of Microseisms Excited by Typhoon Nepartak in 2016

台风可以改变海面波浪状态并激发出微地动信号,该信号可以传播至陆地并被宽频带地震仪记录到。本研究以201601号台风"尼伯特"为例,利用短时傅里叶变换,分析了7月3日12时至7月9日0时台风期间中国台湾和日本114个宽频带地震仪垂向分量信号功率谱特征。分析结果发现,在7月5日至7月7日之间,当台风距离台站1500~2000km时,中国台湾、琉球群岛及屋久岛的33个地震台站的地振动信号功率谱密度值显著增强,7月5日前后,在0.4Hz频率左右出现功率谱密度值增强的现象,之后由高频转至低频,7月7日左右功率谱密度值增强频率变化至约0.2Hz。利用全球地震背景噪声能量辐射模型模拟KGM台站所在位置(128.22°E,26.76°N)的双频微地动功率谱,结果表明7月5日至7日0.2~0.4Hz功率谱密度值增强,频率由约0.4Hz变化至0.2Hz的现象为海岸线反射效应所致。

Typhoons change the state of oceanic waves that excite microseisms propagating on land and is recorded by broadband seismometers.In this study,vertical seismic data retrieved from 114 broadband seismometers in Taiwan and Japan from 12:00:00 of July 3 to 00:00:00 of July 9 that are utilized as an example to study the power spectral characteristics of microseisms excited by#201601 typhoon Nepartak through the short-time Fourier transform.The analytical results show that the Power Spectral Density(PSD)of the vertical seismic data was significantly enhanced from July 5 to July 7.The enhancements are mainly observed at stations located in Taiwan,Ryukyu Islands and Yakushima,while the distances between the typhoon and those stations are ranged from 1500km to 2000km.The PSD increased at the frequency of 0.4Hz near on July 5.Thereafter,the enhancement of the PSD changes at the frequency from high(0.4Hz)to low and reaches to the frequency of 0.2Hz on the July 7.We used the Global Model of Seismic Noise Energy Radiation to simulate the power spectrum associated with the double frequency microseisms at the KGM station(128.22°E,26.76°N).The simulation results showed that the enhancement of the PSD changes at the frequency from high(0.4Hz)to low(0.2Hz)between July 5 and July 7,were caused by the reflection effect of the coastline.