| 龙门山断裂带的分段性特征——来自密集震源机制解的约束 |
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| 引用本文： | 杨宜海,张雪梅,花茜,苏利娜,丰成君,邱玉荣,梁春涛,苏金蓉,古云鹤,金昭娣,张媛媛,关昕.龙门山断裂带的分段性特征——来自密集震源机制解的约束[J].地球物理学报,2021,64(4):1181-1205. |
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| 作者姓名： | 杨宜海 张雪梅 花茜 苏利娜 丰成君 邱玉荣 梁春涛 苏金蓉 古云鹤 金昭娣 张媛媛 关昕 |
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| 作者单位： | 陕西省地震局,西安 710068;陕西西安地球深部构造野外科学观测研究站,西安 710068;中国地震台网中心,北京 100045;陕西省地震局,西安 710068;中国地质科学院地质力学研究所,北京 100081;地球勘探与信息技术教育部重点实验室(成都理工大学),成都 610059;四川省地震局,成都 610041 |
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| 基金项目： | 国家重点研发计划;中国地震局地震科技星火计划;陕西省自然科学基础研究计划;国家自然科学基金 |
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| 摘 要： | 龙门山断裂带沿倾向和走向具有明显的分带性和分段性特征,通常以4条主干断裂为界将龙门山断裂带自西向东分为5条构造带,但是对沿走向的分段性特征仍未达成共识.本文利用四川区域地震台网记录的汶川地震后近10年的波形数据,采用全波形反演获取了龙门山断裂带1495个M≥3的震源机制解.通过“滑动窗”扫描方法提取不同地震类型的数量沿龙门山断裂带走向的变化曲线,据此将龙门山断裂带的震源区划分为S1—S9段.根据反演的震源机制解,进一步采用阻尼线性反演技术求取龙门山断裂带高分辨率的构造应力场信息,从地震类型、断面结构和构造应力场等角度探讨龙门山断裂带的分段性特征.结果表明:(1)地震类型存在明显的分段性特征.其中S1的逆冲型地震比例最高,S8的走滑型地震比例最高,S9的正断型地震比例最高.汶川地震后龙门山断裂带可能存在差异性断层调整运动,且余震晚期沿断裂带走向普遍存在应力的补充和协调,芦山地震的发生可能还对S2造成了应力扰动.汶川主震附近及余震区远端经历了更长的震后调整过程,且余震区远端S9具有更复杂、强度更高的震后调整过程.(2)断面结构存在明显的分段性特征.断面结构揭示汶川主震附近和余震区远端的隐伏断裂,以及虎牙断裂南端参与了汶川余震活动.断面倾角与走滑分量具有较好的一致性,在具有明显逆冲分量的分段断面倾角主要分布在50°~70°,而在具有明显走滑分量的分段断面倾角基本在60°以上,且断面倾角增大与汶川余震带宽度收缩变窄相吻合.(3)龙门山断裂带的应力环境非常复杂.σ1方向的分段性差异导致了汶川—芦山地震空区的地壳撕裂和地幔物质上涌、汶川主震附近和余震区远端的隐伏断裂活动以及虎牙断裂南端大量的逆冲型地震.结合构造应力场与大地测量资料认为,龙门山的隆升主要是受构造应力场作用下的上地壳缩短增厚所致.
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| 关 键 词： | 龙门山断裂带 构造分段性 震源机制 构造应力场 汶川地震 |
Segmentation characteristics of the Longmenshan fault——Constrained from dense focal mechanism data |
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| YANG YiHai,ZHANG XueMei,HUA Qian,SU LiNa,FENG ChengJun,QIU Yurong,LIANG ChunTao,SU JinRong,GU YunHe,JIN ZhaoDi,ZHANG YuanYuan,GUAN Xin.Segmentation characteristics of the Longmenshan fault——Constrained from dense focal mechanism data[J].Chinese Journal of Geophysics,2021,64(4):1181-1205. |
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| Authors: | YANG YiHai ZHANG XueMei HUA Qian SU LiNa FENG ChengJun QIU Yurong LIANG ChunTao SU JinRong GU YunHe JIN ZhaoDi ZHANG YuanYuan GUAN Xin |
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| Institution: | (Shaanxi Earthquake Agency,Xi′an 710068,China;Shaanxi Xi′an Deep Earth Structure Observatory,Xi′an 710068,China;China Earthquake Networks Center,Beijing 100045,China;Institute of Geo-mechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Key Laboratory of Earth Exploration and Information Technology of Ministry of Education(Chengdu University of Technology),Chengdu 610059,China;Sichuan Earthquake Agency,Chengdu 610041,China) |
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| Abstract: | The Longmenshan fault has obvious structural zonation and segmentation characteristics.Generally,the Longmenshan fault is divided into five structural zones from west to east with four main faults as boundaries.However,there is still no consensus on the segmentation characteristics of Longmenshan fault.In this paper,seismic waveforms of the earthquakes occurred in nearly ten years following the Wenchuan earthquake were collected from Sichuan earthquake network and 1495 focal mechanism solutions with M≥3 were determined by the full waveform inversions.According to the inverted dense focal mechanism solutions,we employed the“sliding window”scanning method to calculate the variation curves of the counts of different earthquake types along the strike of Longmenshan fault.The focal areas were finally divided into 9 segments which are named S1—S9.In addition,according to the obtained focal mechanisms,we had further inverted the tectonic stress field of high resolution in the Longmenshan fault and discussed the segmentation characteristics from aspects of faulting types,fault plane structures and tectonic stress filed.Our results show:(1)The faulting types have obvious segmentation characteristics.Proportions of thrust,strike-slip and normal faulting are the highest in S1,S8 and S9,respectively.While the proportion of strike-slip faulting in the late Wenchuan aftershocks has generally increased,which is closely related to the stress supplements and adjustments along the strike of Longmenshan fault.After the occurrence of Wenchuan earthquake,the different sections of Longmenshan fault show differential adjustments.The Lushan earthquake may have caused stress disturbance in S2.In addition,the post-seismic adjustment processes near the Wenchuan mainshock and in the far end of aftershock zone are longer than that in the middle section of aftershock zone,and the S9 at the far end of the aftershock zone has more complicated and more intensive post-seismic adjustment processes.(2)The fault plane structures have obvious segmentation characteristics.The fault plane structures reveal that the buried faults near the Wenchuan mainshock and in the far end of aftershock zone as well as the south end of Huya fault participated in the post-seismic activities.The dip angles show good relationships with strike-slip components,which the dip angles range of 50°~70°in the areas with obvious thrust components and are generally larger than 60°in the areas with obvious strike-slip components.In addition,the increase of dip angles is coincided with narrowing of the width of Wenchuan aftershock zone.(3)The stress environment of Longmenshan fault is very complex.The segmentation differences ofσ1 directions lead to the crustal tearing and mantle material upwelling in the seismic gap between Wenchuan and Lushan earthquakes,the seismicities in the buried faults near the Wenchuan mainshock and in the far end of aftershock zone as well as a large number of thrust earthquakes in the south end of Huya fault.Combined the stress filed determined in this paper with previous geodetic surveys,we deduce the uplift of Longmenshan may be mainly caused by the shortening and thickening of upper crust under the tectonic stress field. |
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| Keywords: | Longmenshan fault Structural segmentation Focal mechanism Stress field Wenchuan earthquake |
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