2014年鲁甸M_S6.5地震前后介质波速变化特征分析

Characteristic Analysis of Seismic Velocity Changes Associated with the 2014 Ludian M_S6.5 Earthquake

本文利用研究区内13个地震台站2014年1月至12月的连续波形数据,采用背景噪声互相关方法,提取了2014年8月3日鲁甸M_S6.5地震的同震波速变化。结果表明,鲁甸地震对介质波速的影响具有明显的空间差异性,较大幅度的同震波速变化主要集中于则木河断裂—小江断裂及莲峰断裂区域。其中,莲峰断裂SW段和则木河断裂NW段区域的波速出现了较为明显的同震降低,则木河断裂和小江断裂交界处则出现了明显的波速升高。通过对比研究区内介质波速的同震变化与鲁甸地震对周边主要活动断裂应力积累的影响后发现,波速变化与应力变化在空间分布上具有较高的一致性,且两者的变化幅度也成正相关关系。由此可以看出,鲁甸地震造成的应力变化可能是地下介质波速变化的主要原因。采用相同的方法对2014年4月5日永善MS5.1地震研究后发现,永善地震后鲁甸地震震源区及其附近区域波速明显升高。

In this paper,we extracted seismic velocity changes associated with the 2014 Ludian MS6. 5 earthquake from ambient noise cross-correlation by using continuous seismic data recorded by 13 seismic stations in the research area. Base on temporal changes of seismic velocity of each seismic station pair,we got the spatial distribution of seismic velocity changes,and found that it has significant regional variation. The great changes are mainly distributed on the zones of Zemuhe fault,Xiaojiang fault and Lianfeng fault. There is a sudden post-seismic velocity drop for the region of the southwest segment of the Lianfeng fault and the northwest segment of the Zemuhe fault,and there is a sudden post-seismic velocity increase for the junctional zone of Zemuhe fault and Xiaojiang fault. We found that post-seismic velocity change and stress change have high consistency in the spatial distribution by comparing the stress accumulation of the main active faults around the Ludian earthquake. And there was a positive correlation between co-seismic velocity change and co-seismic stress change. Therefore,stress change associated with the Ludian earthquake may be the main reason of seismic velocity change. We extracted the co-seismic velocity changes associated with the MS5. 1 Yongshan earthquake of April 5,2014 by the same method.The result showed that seismic velocity increased in the source area of the Ludian earthquake after the Yongshan earthquake.