【摘要】 2013年8月28日和31日四川得荣县与云南德钦县、香格里拉县交界地区分别发生MS5.2和MS5.9地震.这两次主震连同截至2013年12月31日发生的589次M≥1.5余震,构成香格里拉—得荣震群序列.该序列的震区位于青藏高原东南隅横断山脉的三江构造带地区,地处川滇菱形块体西边界,当地有多组交错的活动断裂.为了了解这一震群序列的震源构造特征以及震区的构造动力环境,我们利用区域地震台网的数字波形资料以及中国地震台网中心的有关震相数据,建立了分区速度结构模型;使用Loc3D(川滇走时表定位软件)重新测定该震群序列中10次MS>4.0地震的位置,利用双差法对该序列中的更小地震进行重新定位;同时,采用地震矩张量的时间域反演方法获得10次MS>4.0地震震源机制的矩张量解.重新定位结果显示:香格里拉—得荣震群序列的绝大部分地震发生在NW向德钦—中甸—大具断裂中段7~15km深度的基底层,整个序列的震源分布长度约17km,横向宽度约7km;震源分布在横剖面表现为负花状构造的断裂带内,其中,NE倾向的主干活动断裂及其北东侧一条SW倾向的次级断裂分别控制该负花状构造的两个侧边.本研究反演得到的震源机制解显示:该序列所有MS>4.0地震均是德钦—中甸—大具断裂中段在近S-N向—NNE-SSW向拉张作用下的正断层作用的结果,右旋走滑作用并不明显.这与该断裂晚第四纪活动的地质地貌特征—右旋走滑为主、正断倾滑为辅—并不吻合.这种不一致可能暗示震区的现今构造运动与以往有所不同,为进一步研究青藏亚板块东南隅与缅甸亚板块以及印度板块交界地区的现今构造动力学提出了问题与线索.更多还原

【Abstract】 Two earthquakes of MS5.2 and MS5.9 occurred on August 28 and 31,2013,respectively,in the border region between Dêrong county of Sichuan province and Dêqên and Shangrila counties of Yunnan province.These two mainshocks and 589 aftershocks of M ≥1.5took place before December 31,2013,constitute the Shangrila-Dêrong earthquake swarm sequence.Situated on the Sanjiang tectonic zone of the Hengduan Mountains southeast of the Tibetan Plateau,the source region of this sequence is at the west margin of the Sichuan-Yunnan rhombic block,where there exist several groups of intersecting active faults.In order to understand the features of source structure and the tectonodynamic environments of the source region,a velocity structure model with several sub-regions is established based on the digital waveform data recorded by regional seismic networks and relevant seismic phase data collected by the China Earthquake Networks Center.Of the sequence,10 earthquakes are relocated using Loc3 D,an earthquake location program with the Sichuan-Yunnan regional 3-D travel time table,and the other smaller events of the sequence are relocated using the Double-Difference algorithm.Moreover,the seismic moment tensors and focal mechanisms of these 10 earthquakes with MS>4.0are obtained using the TDMT_INVC method.The relocation results show that most of the earthquakes in the Shangrila-Dêrong swarm sequence occurred in the middle segment of the Dêqên-Zhongdian-Daju fault at depth of 7~15km in the basement of the crust and the epicenter distribution area is 17 km long and 7km wide.The earthquake sources are distributed in a fault zone as a negative flower structure,of which the either side is controlled by the main active fault dipping to NE,and a secondary fault dipping to SW on the northeast side,respectively.The focal mechanisms obtained with the inversion method in this study show that all of the earthquakes with MS>4.0in the sequence resulted from normal faulting under tension in direction of nearly NS to NNE-SSW in the middle segment of the Dêqên-Zhongdian-Daju fault,and no significant right-lateral strike slipping is found.The focal mechanisms of the Shangrila-Dêrong earthquake swarm derived from this work are inconsistent with the geological and geomorphic features of the study area during the late Quaternary,which suggest dominant right-lateral strike slip and secondary normal dipping on the active faults.This inconsistency may imply that,to a certain extent,the modern tectonic movement is different from that of the ancient times,raising some new questions and clues for the investigation into the modern structural dynamics about the border region between the southeast part of the Qinghai-Tibet subplate,the Burma subplate and the Indian plate.更多还原