| 郯庐断裂带中南段及邻区基于背景噪声的瑞利波群速度层析成像 |
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| 引用本文： | 顾勤平,丁志峰,康清清,李大虎.郯庐断裂带中南段及邻区基于背景噪声的瑞利波群速度层析成像[J].地球物理学报,2020,63(4):1505-1522. |
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| 作者姓名： | 顾勤平 丁志峰 康清清 李大虎 |
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| 作者单位： | 1. 江苏省地震局, 南京 210014;2. 中国地震局地球物理研究所, 北京 100081;3. 四川省地震局, 成都 610041 |
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| 基金项目： | 中国地震局地震星火科技计划项目（XH18017Y），国家自然科学基金（41704052，41974066），我国地震重点监视防御区活动断层地震危险性评价之"栟茶河断裂活动性鉴定"项目（1530601）和江苏省地震局青年科学基金重点项目（201801）共同资助. |
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| 摘 要： | 本文收集了郯庐断裂带中南段及邻区省属和市县地震台网共261个宽频带地震台站2015年1月至2016年12月间的垂直向连续波形资料,利用长时间序列背景噪声互相关法提取台站对之间的经验格林函数,采用时频分析法提取瑞利面波混合路径频散曲线.通过质量控制和严格筛选后得到了15627条路径上的群速度频散曲线,重新构建了郯庐断裂带中南段及邻区瑞利波5～50s、分辨率为0.75°×0.75°的群速度分布图像.分析研究了6个周期的群速度分布图像和3条不同方向的纵向周期剖面,这些图像揭示了郯庐断裂带中南段及邻区地壳上地幔速度结构具有横向分块和纵向成层的非均匀性特征.结果表明,短周期(6s、10s)的群速度分布与地表地质和构造特征密切相关.拥有较厚沉积层的苏北盆地、合肥盆地及河淮盆地等显示为低速,而基岩广泛出露的鲁西隆起、大别—苏鲁造山带、扬子克拉通及华南褶皱系则呈现出大面积的高速异常.随着周期的递增(15s、20s),群速度分布受地表地质构造的影响逐渐弱化.受地壳厚度和莫霍面附近的速度差异影响,大别和苏鲁地区在较长周期(25s、30s)群速度图上表现出相对较低的速度,这可能与这些地方Moho面埋藏较深有关.纵向剖面显示,苏鲁—大别造山带及其高压、超高压变质带不仅在浅地表具有基本相同的地形地貌和构造特征,地壳内也有着极为相似的Rayleigh波群速度分布特征.壳内群速度分布总体上表现为上凸下凹状,形状似一"哑铃".上地壳具有上凸下凹的形态、相比邻区具有较高的群速度值;中地壳低速;下地壳上凸下凹且埋藏较深,反映出具有陆陆碰撞造山的残留山根特征.苏鲁及大别两地自浅地表至上地幔具有相似的Rayleigh波群速度分布不仅为二者被左旋走滑的郯庐带平移错开提供了佐证资料,同时也为郯庐带的形成与演化提供了地震学依据.
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| 关 键 词： | 郯庐断裂带中南段 噪声成像 瑞利面波 群速度 郯城地震 |
| 收稿时间： | 2019-07-02 |
Group velocity tomography of Rayleigh wave in the middle-southern segment of the Tan-Lu fault zone and adjacent regions using ambient seismic noise |
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| GU QinPing,DING ZhiFeng,KANG QingQing,LI DaHu.Group velocity tomography of Rayleigh wave in the middle-southern segment of the Tan-Lu fault zone and adjacent regions using ambient seismic noise[J].Chinese Journal of Geophysics,2020,63(4):1505-1522. |
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| Authors: | GU QinPing DING ZhiFeng KANG QingQing LI DaHu |
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| Institution: | 1. Jiangsu Earthquake Agency, Nanjing 210014, China;2. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;3. Sichuan Earthquake Agency, Chengdu 610041, China |
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| Abstract: | The middle-southern segment of the Tan-Lu fault is located at the intersection of three geological blocks. Because of its complexity and importance, it has been concerned by many geological scientists for a long time. Studying the deep structure of the crust and upper mantle, which records the dynamic evolution process, is the key to reveal the geodynamic mechanism of its generation and evolution. By collecting a whole bunch of vertical-component continuous data recorded by 261 broadband stations of the China Digital Seismic Network, provincial and municipal networks from January 2015 to December 2016, we calculate the inter-station Green's functions and measure the group velocity dispersion curves of Rayleigh wave by using the frequency-time analysis method. Through the quality control and strict screening, a total of 15,627 group velocity dispersion curves are extracted, and group velocity distribution images with the period of 5~50 s and resolution of 0.75°×0.75° are reconstructed.
We then analyze group velocity distribution images with six periods and three longitudinal profiles. These images reveal that the velocity structure of the crust and upper mantle in the middle-southern segment of the Tan-Lu fault zone and adjacent areas is characterized by inhomogeneity of transverse segmentation and longitudinal stratification. The results show that the group velocity distribution of short periods (6 s, 10 s) is closely related to surface geology and tectonic characteristics. The Subei Basin, Hefei Basin and Hehuai Basin with thicker sedimentary layers show low velocity, while the Luxi Uplift, Dabie-Sulu orogenic belt, Yangtze Craton and the South China fold system with extensive bedrock exposures, present a large area of high-speed anomalies. With the increase of the period (15 s, 20 s), the influence of surface geological structure on the group velocity is gradually weakened. Influenced by crustal thickness and the velocity contrasts across the Moho, the Dabie and Sulu regions show relatively low velocity at longer periods (25 s, 30 s), which may be related to the deeper burial Moho surface in these places. Longitudinal profiles show that the Sulu and Dabie orogenic belts and the high-pressure and ultrahigh-pressure metamorphic belts not only show the same topographic and tectonic features at the surface, but also display very similar Rayleigh wave group velocity distribution characteristics in the crust. The group velocity distribution in the crust generally shows a convex and concave pattern, and is shaped like a "dumbbell". The upper crust displays a convex and concave shape, and features with higher group velocity than in the adjacent area; the middle crust is depicted with low velocity. The lower crust also shows a convex and concave shape, which reflects the characteristics of residual mountain roots of continental collision orogeny. The similar Rayleigh wave group velocity distributions from the shallow surface to the upper mantle in the Sulu and Dabie not only provide evidences for their dislocation by the translation of the Tan-Lu fault with left-lateral strike-slip, but also provide seismological basis for the formation and evolution of the Tan-Lu fault. |
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| Keywords: | Middle-southern segment of Tan-Lu fault Ambient noise tomography Rayleigh surface wave Group velocity Tancheng earthquake |
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