芦山地震和九寨沟地震台站实测震级差异性分析

Analysis of Difference in Magnitude Measurement for 2013 Lushan Earthquake and 2017 Jiuzhaigou Earthquake

本文选取2013年芦山地震和2017年九寨沟地震波形,重新量取垂直向振幅,计算宽频带面波震级M_(S(BB)),分析各台站实测震级出现方向性差异的原因。其中,通过572个宽频带台站实测芦山地震震级M_(S(BB))7.1,通过603个宽频带台站实测九寨沟地震震级M_(S(BB))6.9。芦山地震实测震级大于M_(S(BB))7.3的台站呈现WN-ES向分布,与断层倾向一致;实测震级小于M_(S(BB))7.0的台站呈现NE-WS向分布,与其所在断层走向一致。九寨沟地震实测震级大于M_(S(BB))7.0的台站分布呈现NE向分布,与断层倾向一致;实测震级小于M_(S(BB))6.8的台站总体分布较为离散,大体呈现NW-SE向分布,与树正断裂走向一致。实测震级偏大的台站方向性分布与多普勒效应和P波辐射花样联系不明显。对比分析芦山地震和九寨沟地震,去除场地响应和仪器自身影响,台站实测震级差异性仍然存在,因此,台站实测震级差异性是由于受到了多普勒效应、辐射花样、仪器和场地响应之外的因素影响。综合考虑地震震级涉及的影响因素,芦山地震和九寨沟地震的台站实测震级差异性可能与地震波的传播路径有关。

We selected Lushan Earthquake occurred in 2013 and Jiuzhaigou Earthquake in 2017 as case study to analyze the causes for the difference in measured magnitudes from different stations by remeasuring M_(S(BB))magnitude in vertical component.The average M_(S(BB))magnitude is 7.1 of 572 broadband seismic waveforms in Lushan earthquake,and the average is 6.9 of 603 waveforms in Jiuzhaigou earthquake meanwhile.The stations with the measured magnitude greater than M_(S(BB))7.3 in the Lushan earthquake showed a NW-SE direction distribution,consistent with the fault tendency;Less than M_(S(BB))7.0 showed a NE-SW distribution,consistent with the fault trend.The stations with the measured magnitude greater than M_(S(BB))7.0 in the Jiuzhaigou earthquake showed a NE direction distribution.M_(S(BB))6.8 or smaller ones showed a NW-SE distribution,consistent with the fault trend.The directivity distribution of stations that measured magnitude greater than the average shows no relationship with Doppler effect and the radiation pattern of the P wave.In comparing Lushan earthquake and Jiuzhaigou earthquake,after we removed the site response and the influence of instrument,the difference in the measured magnitude of the stations still exists.The difference in measured magnitude of stations influenced by other than Doppler effect,radiation pattern,instrument and site response.Considering comprehensively the influencing factors of the earthquake magnitude,the magnitudes difference between Lushan earthquake and Jiuzhaigou earthquake may be related to the propagation path of the seismic waves.