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Title:: Study on the Origin of the Body Wave Extracted from Ambient Seismic Noise Cross-correlation Function in Yunnan

作者:: 王伟涛¹; 杨润海²; 郑定昌²; 倪四道³; 王宝善¹; (1.中国地震局地球物理研究所,北京 100081; 2.云南省地震局,云南昆明 650224; 3.中国科学院测量与地球物理研究所动力测量重点实验室,湖北武汉 430077)

Author(s):: WANG Wei-tao¹; YANG Run-hai²; ZHENG Ding-chang²; NI Si-dao³; WANG Bao-shan¹; (1.Institute of Geophysics, China Earthquake Administration, Beijing 100081, China)(2. Earthquake Administration of Yunnan Province,Kunming 650224,Yunnan,China)(3.Key Laboratory of Dynamic Geodesy, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077,Hubei,China)

Keywords:: ambient noise; body wave signal; noise source; seasonal variation

摘要:: 利用云南地区43个宽频带地震台站记录的2008～2010年垂直分量数据,计算了台站对间的互相关函数并得到了5～40 s周期的瑞利面波信号。研究发现在5～10 s周期范围内,瑞利面波信号之前存在很强的前驱信号,该信号能量优势频段为0.1～0.2 Hz,其到时接近噪声互相关函数零点,视速度约为30 km/s。该信号到时随季节存在正负交替变化,进一步的质点分析表明该信号为出射角较小的P波信号。参考已有的研究,认为远场地脉动噪声源中的P波信号穿过地球深部到达云南地区,形成了噪声互相关函数中视速度较高的体波信号,并且相关的噪声源位置在冬季和夏季分别位于北太平洋和南印度洋,具有明显的季节性空间变化。

Abstract:: Using vertical component records observed at 43 broad-band seismic stations from 2008 to 2010 in Yunnan, we calculate the noise-cross correlation functions between each station-pair and obtain Raleigh surface wave in the period from 5s to 40s. We find that in the period from 5s to 10s, and before Rayleigh wave, there is a strong precursory wave whose dominant frequency band is between 0.1 Hz and 0.2 Hz and whose arrival time is near the zero of cross correlation functions. Moreover its negative arrival-time in Winter alternates with the positive ones in Summer. Through further analysis of particle-motion, we confirm that this wave is P-wave with smaller reflection angle whose apparent velocity is about 30km/s. Referring to the relevant research results, we conclude that originating from the ambient micro-tremor noise source at a teleseismic distance, P-wave travels through deep earth to Yunnan and reaches a higher apparent velocity. The ambient noise source, which locates in South Indian Ocean in Summer and North Pacific Ocean in Winter, varies seasonally and spatially.