摘要
利用四川宜宾及周边地区布设的30个临时台站连续44天的波形记录,采用背景噪声互相关方法提取了周期为1—15 s的瑞雷面波相速度频散曲线,然后使用基于面波射线路径追踪的瑞雷面波直接成像方法得到0—10 km深度范围内三维S波速度模型,最后利用该模型作为初始模型采用相同的反演框架得到该地区的方位各向异性结构.结果表明:浅层S波波速横向分布不均匀,随着深度增加呈不均一性减弱,在2 km深度左右,筠连—高县—珙县—长宁背斜一带的S波速度呈高速分布,可能与该区域地层经历褶皱、抬升和地表风化剥蚀有关;从5 km深度起,随着深度增加狮子滩—双河场—长宁背斜区域的S波速度在西北部较东南部相对较低,而低速的分布反映出区域内介质力学性质较弱,因此可能是2019年长宁地震序列沿近北西向破裂的原因之一。方位各向异性结果表明:在孔滩背斜附近,快波方向与背斜走向近似平行,随着深度增加各向异性强度变弱,而且快波方向逐渐向北收敛向西南撒开,呈帚状分布;在区域地质构造作用、主压应力场等的共同影响下,局部区域的方位各向异性快波方向在不同深度处呈现出复杂的特征。
Based on the 44-day continuous waveform data recorded by 30 temporary stations in Yibin and its adjacent regions,Rayleigh wave phase velocity dispersion curves in the period range 1−15 s are extracted by using the ambient noise cross-correlation method.Then the direct surface wave tomographic method with period-dependent ray tracing is applied to obtain the 3-Dshear-wave velocity structure.Finally,by taking the inverted shear-wave velocity model as the initial model,we obtained the azimuthal anisotropic structure in the same inversion framework.The results show that the distribution of shallow shear-wave velocity is heterogeneous,and the degree of heterogeneity decreases with the depth.At about 2 km depth,high velocity is distri-buted beneath the Junlian-Gaoxian-Gongxian-Changning anticline,which may be related to the folding,uplift,weathering and denudation of the strata in this area.The northwest of Shizitan-Shuanghechang-Changning anticline shows relatively low velocity compared with the southeast with a depth deeper than 5 km.As we known,the medium with relatively low wave velocity are usually weaker compared with high velocity,so it may be one of the reasons for the north-westward rupture of the Changning earthquake sequence in 2019.Our results of azimuthal anisotropy show that near the Kongtan anticline,the fast wave direction is approximately paral-lel to the strike of the anticline,and the anisotropic strength becomes weaker with the increase of depth.We also found that the fast wave direction gradually converges to the north and spreads to the south,showing a brush-type structure.Under the influence of regional geological struc-ture and stress field,the fast wave directions in some local areas show complex characteristics at different depths.
作者
王金泽
李红谊
张玉婷
陈辛平
崔华伟
Wang Jinze;Li Hongyi;Zhang Yuting;Chen Xinping;Cui Huawei(School of Geophysics and Information Technology,China University of Geoscience(Beijing),Beijing 100083,China;Shandong Earthquake Agency,Ji’nan 250014,China)
出处
《地震学报》
CSCD
北大核心
2022年第2期271-285,共15页
Acta Seismologica Sinica
基金
上海佘山地球物理国家野外科学观测研究站开发基金(2020K02)资助.
关键词
背景噪声成像
面波频散直接反演
S
波速度结构
方位各向异性
ambient noise tomography
direct inversion of surface wave dispersion
shear wave velocity structure
azimuthal anisotropy
