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河南及邻区瑞利波群速度噪声层析成像
邢康, 贾漯昭
河南省地震局, 郑州 450016
摘要:
本文选取河南及邻区39个宽频带和甚宽频带地震台站记录的2014年1月~2015年12月垂直分量的连续波形资料,通过波形互相关和叠加运算得到台站间的经验格林函数,并用时频分析方法提取了498条瑞利波群速度频散曲线,进而采用噪声层析成像方法反演获得了河南及邻区8~25s的瑞利波群速度分布图像。结果表明,8s周期的群速度分布与地表构造特征密切相关,平原地区表现为低速异常,而基岩出露的山区呈现为高速异常;14s、20s周期的群速度在山区表现的高速异常与8s相似,说明中上地壳与地壳浅部结构有一定的相关性和继承性;8~20s周期的群速度在华北平原地区存在低速异常范围随周期增加而减小的现象。华北平原地区在下地壳表现出的低速异常,可能与大陆地壳减薄有关。大致以太行-武陵重力梯度带为界,下地壳表现出的西部低速、东部至研究区中部高速异常差异,体现了地壳东薄西厚的结构特征。
关键词:  河南及邻区  背景噪声  互相关  群速度频散  层析成像
DOI:
分类号:P315
基金项目:测震台网青年骨干培养专项(20170612)和中国地震局震情跟踪定向工作任务(2019010130)共同资助
Rayleigh Wave Group Velocity Tomography in Henan and Its Adjacent Areas Based on Ambient Noise
Xing Kang, Jia Luozhao
Henan Earthquake Agency, Zhengzhou 450016, China
Abstract:
We have inverted for the Rayleigh wave group velocity distribution of Henan and its adjacent areas with periods of 8~25s using ambient noise tomography. Vertical component continuous waveform data used in this study are from January 2014 to December 2015 recorded by 39 broadband seismic stations of Henan and its adjacent areas. Empirical Green's functions were extracted from waveform cross-correlation and stack of each pair of stations. Then,by using the frequency time analysis method,we got 498 group velocity dispersion curves of Rayleigh wave. The imaging results show that the group velocity distribution at period 8s shows clear correlations with the surface geological structures. The plain area is characterized by low velocity anomaly,and the mountain area is characterized by high velocity anomaly. The high velocity anomalies in the mountain area with periods of 14s and 20s are similar to those of 8s,indicating the correlation between the upper crust and the shallow crust structure. During the 8~20s periods,the range of low velocity anomalies in the North China Plain decreased with the increase of the period. Low velocity anomalies in the lower crust of the North China Plain may be related to continental crustal thinning. The velocity is high in the east and low in the west in the lower crust bounded by Taihang-Wuling gravity gradient zone. The velocity difference reflects the structural characteristics of the crust,which is thin in the east and thick in the west.
Key words:  Henan and its adjacent areas  Ambient noise  Cross correlation  Group velocity dispersion  Tomography