基于分频波形拟合方法的鲁甸M_S6.5地震序列震源机制解研究

2014年鲁甸M_S6.5地震造成了极大的人员伤亡和经济损失,其孕震机理和动力学成因为国内外学者广泛关注.由于目前的反演主要采用单一的反演方法进行处理,导致结果的不确定性较大,使得该地震的发震构造及孕震机理等问题仍存在较大争议.针对目前研究存在的不足,本文基于近震波形求解震源机制解的gCAP(general Cut And Paste)方法和全波形拟合方法,分别反演了鲁甸地震主震及其9次余震的震源机制解,以此评价近震数据反演震源机制解结果的可靠性与稳定性.结果表明数据方位角覆盖对gCAP解的稳定性有较大影响.针对全波形拟合方法反演过程中,低频信号稳定、高频信号解析度高的特点,采用0.01～0.05Hz和0.01～0.2Hz分频段波形拟合思路:在低频段剔除拟合差的数据,进一步在高频段进行高解析度波形拟合,从而获得主震可靠稳定的震源机制解.研究结果表明鲁甸地震主震倾角为76°～83°、滑动角为-157°～-164°,为一次高倾角走滑型地震.两种方法获得的余震震源机制解比较一致,验证了结果的可靠性.研究结果显示,鲁甸地震的高倾角破裂特征,会导致其能量释放快速且完整,这可能是导致鲁甸地震地面破坏加重及缺乏较大震级余震的主要原因.

Focal mechanism solutions of the 2014 Ludian MS6.5 earthquake sequence derived from multiple-bandwidth waveform fitting

The 2014 Ludian M_S6.5 earthquake caused dramatic death and significant economic losses, and received much attention. Many studies have been made on the focal mechanisms of this earthquake sequence. However, due to the limitation of the inversion method and the complex structures of the seismic area, there are still some disputes on this issue, especially concerned with the dip-angle causative fault of the mainshock. In this work, we use regional seismic waveform inversion based on the gCAP method and the full waveform modeling to invert focal mechanism solutions of the mainshock and 9 aftershocks of the Ludian earthquake sequence. Results show that the azimuthal coverage has a significant effect on the reliability and stability of gCAP's inversion. To solve this problem, a two-bandwidth method is proposed in this paper, in which the bandwidths are 0.01~0.05 Hz and 0.01~0.2 Hz, respectively. With this inversion, this work determines that the dip angle and rake of the mainshock 76°~83° and 157°~-164°, respectively, implying a high-dip strike-slip rupture. The stabilities of the gCAP method and the full waveform modeling are verified by the good consistence between the derived mechanisms of the aftershocks. Our research suggests that the high-dip character of the Ludian earthquake might lead to the fast and complete energy release, which may be the main reason for the aggravating destruction and the lack of larger aftershocks.