郯庐断裂带中南段及邻区Pn波速度结构与各向异性

发布时间：2018-06-21 19:56

本文选题：郯庐断裂带 + 中南段　；参考：《地球物理学报》2016年02期

【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.
[Abstract]:The Tanlu fault zone is a giant deep fault which runs through the NNE direction of the eastern part of the mainland of China. The southern and adjacent areas (115 E - 122 degree E, 29 N 38 degree N) span the North China fault block area, the Yangtze fault block area and the Southern China fold system three large and one level tectonic units. Because of their importance and complexity, this paper has long been the hot spot of geoscientists. 6381 Pn seismic phase data were carefully selected from the International Seismological Center (ISC), China seismic network and regional seismic network. The Pn wave velocity structure and anisotropy of the upper mantle in the middle and south parts of the Tanlu fault zone were obtained by Pn wave time term tomography. The results showed that the top of the upper mantle of the study area was on the top of the study area. Significant lateral inhomogeneity, compared with the average velocity of 7.95km s-1, the Pn wave velocity varies in the middle and southern segments of the Tan Lu fault zone in the range of 7.68~8.24km. S-1, and there is a low velocity anomaly belt along the middle section and the periphery, and the low velocity may be due to the thinning of the lithosphere and the high temperature of the asthenosphere. Along the Tanlu belt upwelling, along the south section, it shows a NNE direction weak high wave velocity anomaly zone. As a high and low velocity boundary zone, it clearly outlines the two different blocks of North China and Yangtze. The boundary has a certain correlation with the intensity and velocity distribution of the.Pn wave anisotropy in the NW direction of the North China block from the Jiangsu region to the North China block. The velocity anisotropy of the high and low velocity transition zone near the Maoshan fault is relatively strong, while the anisotropy of the high velocity transition zone near the Maoshan fault is strong, but the anisotropy is weak under the stable region of the Subei Basin and the Hefei basin, which has high velocity anomalies. The anisotropic trace of the top of the mantle is "frozen", which is caused by the weakening of the strong tectonic movement of the hot material in the asthenosphere. There is a certain correlation between the transverse change of the.Pn wave velocity in the direction of the fast wave velocity which is near parallel to the direction of the fracture extension and the strong earthquake activity. The strong earthquakes mainly occur in the low velocity anomaly area of the Pn wave or the high and low velocity transition. The epicenter of the Tancheng earthquake of magnitude 8.5 is located in the middle and south segment of the high and low speed transition zone, which is also the largest lateral variation in velocity, which is the most likely to concentrate stress and stress difference.
【作者单位】：中国地震局地球物理研究所;江苏省地震局;
【基金】：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) 中国地震局震害防御司“h茶河断裂活动性鉴定”项目(1530601)联合资助
【分类号】：P315.2

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