comprehensive study on the changing process of focal mechanisms of the 2014 huoshan ms4.3 earthquake sequence

doi:10.3969/j.issn.0253-4967.2015.04.006

Abstract

Abstract:

In this paper, the focal mechanisms of Huoshan M_S4.3 earthquake sequence since October 2013 are calculated with the method developed recently by Snoke, which combines the use of first motion of P, SV and SH waves and their amplitude ratios(referred to as Snoke method). We estimate the difference(also referred to consistency parameter θ)between the stress axis direction of focal mechanism solution and the mean stress tensor on one hand, and get the relative changes of focal mechanisms rather than the focal mechanisms themselves on the other hand, by using methods of correlation coefficient of body-wave spectral amplitudes, first motions and amplitude ratios of vertical P wave of single station, as limited by the network layout and density of observation points, focal mechanism solutions of small earthquakes are not easy to obtain. We studied the changing process of focal mechanisms of Huoshan M_S4.3 earthquake sequence since October 2013 with many methods such as consistency parameter, correlation coefficient of body-wave spectral amplitudes, first motion and amplitude ratio of vertical P wave of single station, to determine the type of the sequence. The result shows that: before Huoshan M_S4.3 earthquake of April 20, 2014, the consistency parameter of the earthquake sequence was lower than the mean for a long period, correlation coefficient of body-wave spectral amplitudes was always at high values(about 0.9), odds ratio of first motions of vertical P wave of single station near the epicenter, defined as the ratio of predominant number to contrast number of first motions, was up to 13.8 at station SJH, 3.8 at BZY and 3.6 at LNA, respectively; first motions of vertical P wave of single station showed an obvious predominant distribution as a whole, and the amplitude ratios of vertical P were consistent, which suggests that before Huoshan M_S4.3 earthquake, focal mechanisms were consistent, so the earthquake sequence before Huoshan M_S4.3 earthquake is the foreshock sequence. After Huoshan M_S4.3 earthquake, correlation coefficient of body-wave spectral amplitudes was lower(about 0.6), first motions and amplitude ratios of vertical P wave of single station were in disorder, which suggest that the focal mechanisms are inconsistent after the Huoshan M_S4.3 earthquake, so the earthquake sequence after Huoshan M_S4.3 earthquake is the aftershock sequence, and subsequent larger earthquakes are not likely to occur. The focal mechanisms in Huoshan region during the period of Huoshan M_S4.3 earthquake experienced a process from scattering to convergency and to scattering again.

Key words: consistency of focal mechanisms, parameter correlation coefficient of body-wave spectral amplitudes, initial motion, amplitude ratio, Huoshan M_S4.3 earthquake

摘要：

综合利用震源一致性参数、体波谱振幅相关系数、单台的P波初动和振幅比方法研究2013年10月以来霍山M_S4.3地震序列震源机制的变化过程, 进而科学判定该序列的类型, 探索震后地震趋势的判别方法。结果表明, 2014年4月20日霍山M_S4.3地震前, 霍山地震序列的震源一致性参数低于多年均值, 体波谱振幅相关系数在0.9附近波动、持续处于高值状态, 单台的P波初动总体优势分布明显、振幅比较为一致, 均显示霍山M_S4.3地震前序列的震源机制较为一致, 为前震序列; 霍山M_S4.3地震后, 序列的体波谱振幅相关系数较低, 在0.6附近波动, 单台的P波初动、振幅比较为紊乱, 表明霍山M_S4.3地震后序列的震源机制较为紊乱, 为余震序列, 后续发生更大地震的可能性不大。因此, 霍山M_S4.3地震前后震源区的震源机制经历了散乱—一致—散乱的过程。

关键词: 震源一致性参数, 体波谱振幅相关系数, 初动, 振幅比, 霍山M_S4.3地震

CLC Number:

P315.3⁺3

NI Hong-yu, LIU Ze-min, HONG De-quan, WANG Xiao-li, ZHAO Peng. comprehensive study on the changing process of focal mechanisms of the 2014 huoshan m_s4.3 earthquake sequence[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(4): 1004-1019.

倪红玉, 刘泽民, 洪德全, 汪小厉, 赵朋. 综合研究2014年霍山M_S4.3地震序列的震源机制变化过程[J]. 地震地质, 2015, 37(4): 1004-1019.

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