摘要
2013年4月20日四川芦山地区发生了Ms 7.0级地震。利用GPS三维同震形变数据获取地表形变场,基于位错模型反演芦山地震的断层几何参数及滑动分布。首先采用多峰值颗粒群算法(multiple peak particle swarm optimization, MPSO)得到断层几何参数,其中断层走向206.47°,倾角44.11°,长度21.94 km,离地表最浅处为7.66 km,最深处为17.84 km。为了反演断层面的精细滑动分布,分析地震所在的龙门山断裂西南段破裂面具有的铲状型特征,将芦山地震破裂面确立为铲状模型,即将断层的倾角预设为上陡下缓,倾角变化范围为21°~50°。结果显示,断层破裂面在不同深度区域出现了两个滑动峰值,其中最大滑动量为0.68 m,深度位于13 km。地震释放的能量为1.47×10~(19) N·m,对应的矩震级为Mw 6.74,与地震学的研究结果一致。
On April 20 th 2013, Ms 7.0 earthquake occurred on the southern section of the Longmen Shan fault, in Sichuan Province. In this research, the three-dimensional coseismic displacement field that GPS data from 33 continuous stations are used to invert for fault geometry parameters and the slip distribution. The MPSO(multiple peak particle swarm optimization) algorithm has been successfully applied to invert for the fault model parameters.Compared with the commonly used algorithm, such as genetic algorithm, simulated annealing and the overall minimum norm optimization algorithm, MPSO algorithm has the advantages of less control parameters, high global convergence efficiency, and is very suitable for nonlinear inversion of fault parameters. The result indicates that the seismogenic fault is a thrust with a strike of 206.47°, a dip of 44.11°, and length of 21.94 km. The minimum and maximum depth is 7.66 km and 17.84 km, respectively. The fracture surface was determined as listric surface by analysis. In order to obtain the detailed slip distribution, the listric surface model is set with the default dip angle varying from 50° on the top boundary of the surface to 21° on the bottom boundary. Our inversion result shows that the rupture surface has two slip peaks at different depths. The maximum slip is 0.68 m at the depth of 13 km. The inverted geodetic moment is 1.47×10~(19) N·m and the moment magnitude Mw is 6.74, which is consistent with the result of seismology.
引文
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