| 郯庐断裂带中南段及邻区Pn波速度结构与各向异性 |
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| 引用本文： | 顾勤平,丁志峰,康清清,赵启光.郯庐断裂带中南段及邻区Pn波速度结构与各向异性[J].地球物理学报,2016,59(2):504-515. |
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| 作者姓名： | 顾勤平 丁志峰 康清清 赵启光 |
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| 作者单位： | 1. 中国地震局地球物理研究所, 北京 100081;2. 江苏省地震局, 南京 210014 |
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| 基金项目： | 江苏省地震局青年科学基金项目"江苏及邻区上地幔顶部Pn波速度及各向异性研究"(14404)和中国地震局震害防御司"栟茶河断裂活动性鉴定"项目(1530601)联合资助. |
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| 摘 要： | 郯庐断裂带是一条纵贯我国大陆东部NNE走向的巨型深断裂,其中南段及邻区(115°E—122°E,29°N—38°N)跨越了华北断块区、扬子断块区和华南褶皱系三大一级构造单元,由于其重要性和复杂性,长期以来一直是地学家们研究的热点.本文从国际地震中心(ISC)、中国地震台网及区域地震台网的地震观测报告中精心挑选出6381个Pn震相数据,用Pn波时间项层析成像法反演得到了郯庐断裂带中南段及邻区上地幔顶部Pn波速度结构和各向异性.结果显示,研究区上地幔顶部具有显著的横向非均匀性,相对于7.95km·s-1的平均速度而言,Pn波速度值在7.68~8.24km·s-1范围内变化.Pn波速度分布在郯庐断裂带中段和南段具有分段性:沿中段及周边存在一NE向低速异常带,低速可能是由于岩石圈的减薄和软流圈的高温物质沿郯庐带上涌导致;沿南段表现为一NNE向弱高波速异常带,作为高低速的边界带清晰地勾勒出了华北与扬子这两个不同块体,该边界在江苏域向华北地块NW方向凹进.Pn波速度各向异性的强弱与速度分布存在一定的相关性.总体上,如鲁西隆起及以南等低速区、茅山断裂附近的高低速过渡带,其速度各向异性较为强烈;而在具有高速异常的苏北盆地、合肥盆地等稳定区域下方其各向异性较弱.本文通过Pn波震相基本未能探测到郯庐断裂带中段的方位各向异性,推测是上地幔顶部被"冻结"下来的各向异性痕迹被软流圈热物质上涌这一强烈构造运动削弱所导致.南段具有与断裂伸展方向近乎平行的快波速方向.Pn波速度横向变化和强震活动存在一定关联.强震主要发生在Pn波低速异常区或高低速过渡带上.郯城8.5级地震震中位于中段和南段高低速过渡带,该区域也是速度横向变化最大的地方,最容易集中应力和产生应力差.
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| 关 键 词： | 郯庐断裂带 中南段 Pn波速度 各向异性 郯城地震 |
| 收稿时间： | 2015-08-01 |
Pn wave velocity and anisotropy in the middle-southern segment of the Tan-Lu fault zone and adjacent region |
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| GU Qin-Ping,DING Zhi-Feng,KANG Qing-Qing,ZHAO Qi-Guang.Pn wave velocity and anisotropy in the middle-southern segment of the Tan-Lu fault zone and adjacent region[J].Chinese Journal of Geophysics,2016,59(2):504-515. |
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| Authors: | GU Qin-Ping DING Zhi-Feng KANG Qing-Qing ZHAO Qi-Guang |
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| Institution: | 1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;2. Earthquake Administration of Jiangsu Province, Nanjing 210014, China |
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| Abstract: | The Tancheng-Lujiang fault zone is the largest deep NNE-trending fault zone in the Eastern China, which has always been focused by many geoscientists because of its importance and complexity. The middle-southern segment of the Tan-Lu fault and surrounding areas (115°E-122°E,29°N-38°N) is located in the crossing part of three Chinese geological blocks (North China block, Yangtze Craton, South China Folds).#br#We carefully selected 6381 Pn travel time picks from the earthquake bulletins of the International Seismological Center(ISC), China national seismic network and regional seismic network to invert for Pn velocity variation and anisotropy of the uppermost mantle beneath the middle-southern segment of the Tan-Lu fault and its adjacent areas by Pn wave time-term tomography method.#br#The result indicates that obvious lateral heterogeneities exist in the uppermost mantle beneath the study area and the Pn velocity varies from 7.68~8.24 km·s-1 compared to the average velocity of 7.95 km·s-1. The Pn velocity structure along Tan-Lu fault has segmentation. The middle-segment of the Tan-Lu fault zone shows obvious NE-trending low velocity zone. Low velocity may result from the strongly thinning of the lithosphere and the upwelling of the asthenosphere hot material. The southern part of the Tan-Lu fault zone has NNE-trending weak high-velocity anomaly zone, which is considered as a high low-velocity boundary of two different tectonic blocks, North China and Yangtze. We hold that Tan-Lu has the characteristics of tectonic block boundary. The boundary curve to the North China from SE to NW in Jiangsu domain. The intensity distribution of Pn velocity anisotropy is correlated with the distribution of velocity anomaly. On the whole, velocity anisotropy is strong in low-velocity anomalies like Luxi uplift and southern region or the transition zone from high to low velocities near the Maoshan fault zone. Anisotropy is relatively weak under stable block and basin like Subei basin and Hefei basin, which has high velocity anomalies. Pn velocity anisotropy is weak along Tan-Lu fault zone and cannot be detected mainly by Pn wave especially in the middle segment. Strong tectonic movement resulted from the upwelling of asthenosphere hot material along the weak tectonic belt (Tan-Lu) fault weakened the anisotropy trace, which left from early tectonic movement in the lower part of the lithosphere. The fast wave direction near southern segment of Tan-lu is consistent with the fracture extension direction. The Pn velocity lateral variation has a certain correlation with strong earthquake activity. Most of major earthquakes occured on the edges of low-velocity anomalies or the transition zone from high to low velocities. The epicenter of the Tancheng 8.5 earthquake locate on the transition zone from high to low velocities of the middle-segment and southern segment, where the lateral variation of velocity is biggest and stress most concentrate easily and produce stress difference. |
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| Keywords: | Tan-Lu fault Middle-southern segment Pn wave velocity Anisotropy Tancheng earthquake |
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