【摘要】 烈度与余震分布显示2014年云南鲁甸MW6.1(MS6.5)地震的发震构造较复杂.为深入了解鲁甸地震的发震断层与破裂特征,本文考虑了单一断层破裂和共轭断层破裂的情况,对震中距250km范围内的近震资料(宽频带资料和强震资料)和远震体波资料进行了反演,得到了鲁甸地震的破裂过程,探讨了滑动分布与余震分布之间的关系.根据反演得到的滑动分布、震源时间函数和波形拟合,认为鲁甸地震是一次在北西向主压应力与北东向主张应力的统一应力场下发生的两条共轭断层先后破裂的一次复杂地震事件.在破裂开始后0~2s,破裂主要发生在ENE—WSW向(近东西向)的断层上,随后NNW—SSE向(近南北向)断层开始破裂,释放了大部分的地震矩.由于近南北向断层南段(即震中以南)的破裂规模较大,且以左旋走滑为主,对近东西向断层的西段起到了一定程度的解锁作用,可能是震中以西无明显主震破裂但存在密集余震分布的主要原因.更多还原

【Abstract】 Both intensity and aftershock distributions have shown that the seismogenic structure of the 2014 MW6.1(MS6.5)Ludian,Yunnan,earthquake was quite complex.Especially,aftershocks distribute in a reverse L-shape on conjugated faults(i.e.,the NNW-SSE fault and the ENEWSW fault),making it difficult to determine the causative fault and rupture process.For better understanding the seismogenic structure of the Ludian earthquake,we invert local seismic(strongmotion and broadband data)as well as teleseismic data to investigate the rupture kinematics.Three cases of fault ruptures were tested.(1)Ruptures occur only on the NNW-SSE fault.(2)Ruptures occur only on the ENE-WSW fault.(3)Ruptures can propagate freely on the conjugated faults.A linear technique was used in these inversions.We have two steps in this work.First,local seismic data were inverted for rupture process to identify the rupture faults.Second,withthe determined rupture faults,the rupture model was renewed by jointly inverting local seismic and teleseismic waves.Local seismic data inversions show that data fitting of the NNW-SSE fault is better than that of the ENE-WSW fault,suggesting the NNW-SSE fault is the major rupture fault of the Ludian earthquake.Meanwhile,the best data fitting was found in inversion of conjugated faults,in which data fitting per seismic moment of the ENE-WSW fault was even slightly better than that of the NNW-SSE fault,indicating that both conjugated faults may have ruptured during the earthquake.From the joint inversion of local and teleseismic data,rupture initiated on the ENEWSW fault in the first two seconds,and after 2s,the NNW-SSE fault began to rupture.The source duration is about 17 s,but most seismic moments were released in the first 10 safter the rupture initiation.On the conjugated faults,ruptures propagated toward up-dip directions and mainly occurred in very shallow depth,which may account for the terrible earthquake damages.However,rupture extent of the NNW-SSE fault is much larger than that of the ENE-WSW fault.As a result,rupture area on the NNW-SSE fault is comparable with aftershocks along that direction,but on the ENE-WSW fault,the dimension of rupture area is much smaller than that of aftershock distribution.The above inversion results show that the Ludian earthquake is a complex conjugated ruptured earthquake.Ruptures firstly initiated on the ENE-WSW fault,and then triggered the NNW-SSE fault.Consecutive ruptures on conjugated faults constitute the complex rupture process of the earthquake.The left-lateral strike-slips in the south of the NNW-SSE fault could unlock the west part of the ENE-WSW fault,leading to aftershocks in that area where no significant ruptures were observed.更多还原