安宁河-则木河断裂带及周边地区Rayleigh波群速度背景噪声成像研究
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摘要
安宁河-则木河断裂带位于川滇地块、巴颜喀拉地块和华南地块的交接部位,是川滇菱形块体的东部重要边界。利用布设在安宁河-则木河断裂带周边区域的西昌台阵和川西台阵均历时两年、共187个宽频带地震台站的垂直分量的背景噪声数据,采用噪声层析成像方法获得了这一区域4~20s的Rayleigh波群速度分布图像。与前人研究相比,本文结果的横向分辨率有明显改进,在安宁河-则木河断裂带可达20km左右,在其它区域可以达到20~40km。成像结果表明,安宁河-则木河断裂地区上地壳的速度结构存在明显横向不均匀性,速度分布特征与地表地质构造基本一致,不同周期的速度分布变化较小。盐源盆地、西昌盆地和四川盆地西南缘表现为低速异常。九龙附近和南部的德昌-盐边-巧家附近表现为高速异常,分别与出露的花岗岩体和峨眉山玄武岩有关。在安宁河断裂南段和则木河断裂北段能观测到断裂两侧的速度存在明显差异,其余断裂带两侧的速度对比不明显。贡嘎山附近的中上地壳表现为明显的低速异常,其东侧和西南侧高速体的阻挡,以及鲜水河-安宁河断裂带走向的变化,在贡嘎山区形成一个挤压弯曲段,使得川滇菱形块体的东南向水平运动转换为垂直于断裂的挤压作用和垂直隆升,导致了贡嘎山的快速隆起。
The Anninghe-Zemuhe fault zone is located at the junction of the Sichuan-Yunnan block,the Bayan Har block and the Southern China block,and is an important eastern boundary of the Sichuan-Yunnan block. The Rayleigh wave group velocity maps of 4 ~ 20 s in this area are obtained with ambient noise tomography method,using two years vertical component ambient noise data recorded by 187 broadband seismic stations around the Anninghe-Zemuhe fault zone.Compared with previous studies,the lateral resolution has been improved greatly in this paper. The resolution is about 20 km in the central Anninghe-Zemuhe fault zone,and 20 ~ 40 km in other regions. The imaging results show that the velocity structure of the middle-upper crust in the Anninghe-Zemuhe fault area has obvious lateral inhomogeneity. The velocity structure is basically consistent with the surface geological structure,and the velocity maps differ little at different periods. The Yanyuan Basin,the Xichang Basin and the southwest margin of the Sichuan Basin are characterized by low velocity anomalies. The high speed anomalies near Dechang-Yanbian-Qiaojia,near the southern part of Jiulong are related to the exposed granite bodies and the Emeishan basalt.In the southern segment of Anninghe fault and the northern segment of the Zemuhe fault zone,there are obvious velocity contrasts between the two sides of the fault. The middle and upper crust in the vicinity of the Gongga Mountain is characterized by obvious low velocity anomalies. The obstruction of the high speed bodies in the east and the southwest sides of the Gongga Mountain,and the changes in the strike of the Xianshuihe fault and Anninghe fault,form a compression bending section in this area,making the south-east horizontal movement of the Chuandian block transfer to compress effect perpendicular to the fracture and vertical deformation,resulting in rapid vertical uplift of the Gongga Mountain.
The Anninghe-Zemuhe fault zone is located at the junction of the Sichuan-Yunnan block,the Bayan Har block and the Southern China block,and is an important eastern boundary of the Sichuan-Yunnan block. The Rayleigh wave group velocity maps of 4 ~ 20 s in this area are obtained with ambient noise tomography method,using two years vertical component ambient noise data recorded by 187 broadband seismic stations around the Anninghe-Zemuhe fault zone.Compared with previous studies,the lateral resolution has been improved greatly in this paper. The resolution is about 20 km in the central Anninghe-Zemuhe fault zone,and 20 ~ 40 km in other regions. The imaging results show that the velocity structure of the middle-upper crust in the Anninghe-Zemuhe fault area has obvious lateral inhomogeneity. The velocity structure is basically consistent with the surface geological structure,and the velocity maps differ little at different periods. The Yanyuan Basin,the Xichang Basin and the southwest margin of the Sichuan Basin are characterized by low velocity anomalies. The high speed anomalies near Dechang-Yanbian-Qiaojia,near the southern part of Jiulong are related to the exposed granite bodies and the Emeishan basalt.In the southern segment of Anninghe fault and the northern segment of the Zemuhe fault zone,there are obvious velocity contrasts between the two sides of the fault. The middle and upper crust in the vicinity of the Gongga Mountain is characterized by obvious low velocity anomalies. The obstruction of the high speed bodies in the east and the southwest sides of the Gongga Mountain,and the changes in the strike of the Xianshuihe fault and Anninghe fault,form a compression bending section in this area,making the south-east horizontal movement of the Chuandian block transfer to compress effect perpendicular to the fracture and vertical deformation,resulting in rapid vertical uplift of the Gongga Mountain.
引文
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王运生、李云岗,1996,西昌盆地的形成与演化,成都理工学院学报,23(1),85~90.
闻学泽、范军、易桂喜等,2008,川西安宁河断裂上的地震空区,中国科学:D辑,38(7),797~807.
徐锡伟、闻学泽、郑荣章等,2003,川滇地区活动块体最新构造变动样式及其动力来源,中国科学:D辑,33(增刊Ⅰ),151~162.
杨卓欣、王夫运、段永红等,2011,川滇活动地块东南边界基底结构——盐源-西昌-昭觉-马湖深地震测深剖面结果,地震学报,33(4),431~442.
姚华建、徐果明、肖翔等,2004,基于图像分析的双台面波相速度频散曲线快速提取方法,地震地磁观测与研究,25(1),1~8.
易桂喜、闻学泽、范军等,2004,由地震活动参数分析安宁河-则木河断裂带的现今活动习性及地震危险性,地震学报,26(3),294~303.
袁静、肖龙、万传辉等,2011,松潘-甘孜南部放马坪-三岩龙花岗岩的成因及其构造意义,地质学报,85(2),195~206.
张建岭、吴德超、王道永,2011,四川九龙地区八窝龙-玉农希断裂构造变形特征及活动性,四川地质学报,31(4),395~398.
张友南、孙君秀,1998,华北地壳岩石波速类型及其地质意义,地震地质,20(1),73~81.
张岳桥、李海龙,2016,青藏高原东部晚新生代重大构造事件与挤出造山构造体系,中国地质,243(6),1829~1852.
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郑晨、丁志峰、宋晓东,2016,利用面波频散与接收函数联合反演青藏高原东南缘地壳上地幔速度结构,地球物理学报,59(9),3223~3236.
郑定昌、王俊,2017,基于背景噪声的川滇地区勒夫波层析成像,地震学报,39(5),633~647.
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