Near-surface structure from ambient-noise tomography and horizontal-to-vertical spectral ratio beneath the Nankou-Sunhe fault  

作　　者：Yuting Zhang Hongyi Li Yanzhen Li Zhijie Wei Zeyu Ma Huiying Ge Tongli Wang Yafen Huang Min Liu 

机构地区：[1]School of Geophysics and Information Technology,China University of Geosciences,Beijing 100083,China [2]Shanghai Sheshan National Geophysical Observatory,Shanghai 201602,China [3]Beijing Earthquake Agency,Beijing 100080,China

出　　处：《Earthquake Science》2020年第5期232-238,共7页地震学报（英文版）

基　　金：supported by Beijing Natural Science Foundation(No.8212041);National Natural Science Foundation of China(Nos.41874063 and U1939203);Shanghai Sheshan National Geophysical Observatory(No.2020K02).

摘　　要：Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we collect continuous ambient noise data recorded by 43 temporary short-period seismograph between September 21th to October 12th 2019 to investigate the near-surface structure beneath the Nankou-Sunhe fault by using ambient noise tomography(ANT)and horizontal-to-vertical spectral ratio(HVSR)method.From ambient noise processing,fundamental-mode Rayleigh wave signals are clearly observed in the frequency band of 0.4-2.5 Hz.Then direct surface-wave inversion algorithm is applied to calculate the 3D shear-wave velocity model.Our results show that there is a sharp velocity contrast across the Nankou-Sunhe fault,with low velocities down to about 2 km on the hanging wall and high velocity on the footwall of the fault.According to the geological investigation,the low velocities are related to thicker sediments and Jurassic volcanic rock below which are the cap rock of the hydrothermal system.From the HVSR analysis,the HVSR curves of the sites near the fault shows double-peak,one less than 1 Hz and the other centered 7 Hz.After converting frequency to depth by the empirical equation,the results show that the thickness of sediments is thinned from southwest to northeast,which generally agrees well to field survey.Our results provide high-resolution near-surface structure for future study on disaster risk reduction and urban planning.

关 键 词：ambient noise tomography horizontal-to-vertical spectral ratio dense array Nankou-Sunhe fault 

分 类 号：P642.2[天文地球—工程地质学]