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Title:: Determining Focal Mechanism Solution of the 2000 Yao'an M_S6.5 Earthquake Sequence Using the First Motion and Amplitude Ratio of P and S wave

Author(s):: LIU Li-fang; MAO Hui-ling; SU You-jin; QIN Jia-zheng; (Earthquake Administration of Yunnan Province,Kunming 650224,Yunnan,China)

Keywords:: first motion; amplitude ratio; focal mechanism solution; Yao'an earthquake

摘要:: 利用P波、SV波和SH波的初动和振幅比计算了2000年姚安6.5级地震序列中14次M≥3.0地震的震源机制解。结果表明,姚安6.5级地震的主要发震断裂走向为北西,高倾角,在北北西向近水平主压应力作用下,呈现出以右旋走滑为主的断层错动性质; 姚安地震序列以走滑型为主,个别地震为斜滑型,是在北北西向水平或近水平的主压应力作用下的构造运动方式; 主震发生后1～3天断层错动以走滑型为主,个别为斜滑型,主震发生后3～30天断层错动为走滑型; P轴和T轴的方位总在按与构造应力场走向由一致到不一致再到一致的规律反复变化; 在强余震明显活动期间,地震以水平或近水平向主压应力作用下的断层错动方式为主,有一定的斜向作用,然后为水平或近水平的主压应力作用方式,主震后应力场有明显的调整变化过程。

Abstract:: We calculate the focal mechanisms of 14 earthquakes with M≥3.0 of the 2000 Yao'an M_S6.5 earthquake sequence using the first motions of P,SV and SH waves and their amplitude ratios.The main seismogenic fault of the Yao'an earthquake trends in NW and has high dip angle,showing the feature of right lateral strike-slip under nearly horizontal main pressure stress.The focal faults of the Yao'an earthquake sequence mainly move by strike-slip with sporadic oblique-slip faulting under horizontal or nearly horizontal main pressure stress,and in 1-3 days after the mainshock,the fault slips by the way above mentioned,but in 3-30 days after the mainshock by the way of strike-slip.The azimuth of P-axis and T-axis changes with the direction of structural stress field regularly from consistently to inconsistently again to consistently.During the activity of strong aftershocks,the faults move mainly under horizontal or nearly horizontal main pressure stress,with certain oblique.The stress field shows obvious adjustment process after the mainshock.