梁建宏, 孙丽, 徐志国, 刘杰. 2015: 2013年四川芦山MS7.0地震自动速报震级偏差分析及方法改进. 地震学报, 37(6): 983-996. DOI: 10.11939/jass.2015.06.009
引用本文: 梁建宏, 孙丽, 徐志国, 刘杰. 2015: 2013年四川芦山MS7.0地震自动速报震级偏差分析及方法改进. 地震学报, 37(6): 983-996. DOI: 10.11939/jass.2015.06.009
Liang J H, Sun L, Xu Z G, Liu J. 2015: Analysis on magnitude deviation of the 2013 Lushan, Sichuan, MS7.0 earthquake from Automatic Earthquake Location and Report System and its improvement. Acta Seismologica Sinica, 37(6): 983-996. DOI: 10.11939/jass.2015.06.009
Citation: Liang J H, Sun L, Xu Z G, Liu J. 2015: Analysis on magnitude deviation of the 2013 Lushan, Sichuan, MS7.0 earthquake from Automatic Earthquake Location and Report System and its improvement. Acta Seismologica Sinica, 37(6): 983-996. DOI: 10.11939/jass.2015.06.009

2013年四川芦山MS7.0地震自动速报震级偏差分析及方法改进

Analysis on magnitude deviation of the 2013 Lushan, Sichuan, MS7.0 earthquake from Automatic Earthquake Location and Report System and its improvement

  • 摘要: 使用震中距320 km范围内40个台站的波形记录, 大致还原了2013年4月20日芦山MS7.0地震的自动速报震级测定过程. 结果表明, 在中国地震局对外发布自动速报参数的时间点上, 震级还处于快速上升段, 此时测得的标准震级为M5.8, 与对外公布的标准震级M5.9比较一致, 却远小于之后人工修订的震级M7.0. 分析芦山地震自动速报震级偏差较大的原因: ① 使用限幅记录, 造成震级低估; ② 地震参数发布过于强调快而忽略了准, 参数发布时有些台站的S波(或Lg波)未到达或未完全到达, 造成计算的平均震级偏小. 通过选择合适的震中距范围, 减小限幅记录的影响并适当延时, 在震后137 s得到震级为M6.8. 另外, 应用MWP震级测定方法, 在震后77 s获得矩震级为MW6.8, 显示该方法在测定矩震级时具有快速稳定的优势. 基于上述研究结果, 本文提出改进自动测定震级的措施和方法: ① 对于M<7.0的地震, 在使用ML震级测定方法确定震级时, 需在未限幅台站占绝对优势的震中距范围内使用未限幅记录, 并延时到最远台站的S波(或Lg波)最大振幅到达后测定ML; ② 应用MWP震级测定方法测定大地震的矩震级.

     

    Abstract: The procedure of automatic determination of magnitude for the 20 April 2013, Lushan MS7.0 earthquake is roughly reproduced by using the waveforms from 40 stations within epicentral distance of 320 km in this paper. The results demonstrate that the magnitude is rising quickly when the parameters of this earthquake were issued by China Earthquake Administration (CEA). At the moment, the measured standard magnitude M5.8 is consistent well with the M5.9 announced by CEA at almost the same time, but it is much smaller than M7.0 revised by the analyst later. The magnitude determined by Automatic Earthquake Location and Report System deviates largely, and the reasons are: ① The usage of clipped records underestimated the magnitude; ② Rapidness is emphasized and the accuracy is neglected. S (or Lg) wave is absent at some stations when the earthquake parameters are issued, resulting in the magnitude smaller. Therefore, by reducing the effect of clipped records within a proper epicentral range and delaying some seconds, the magnitude will be 6.8 at 137 s after occurrence of the earthquake. Additionally, the determination method of MWP is applied and MW6.8 is available at 77 s after the earthquake, suggesting the determination method of MWP can be applied to get a stable moment magnitude rapidly. Finally, we propose the following measures for improving the method for magnitude determination by Automatic Earthquake Location and Report System. ① The determination method of ML is used for the events with magnitude less than 7.0. In this case, ML should be determined with seismograms without clipped records, selected from the stations within a proper epicentral range in an area where the number of seismograms without clipped records is absolutely predominant. Meanwhile, the determination method of ML should be delayed until the furthest station receives the maximum amplitude of S (or Lg) wave. ② The method for the MWP determination is able to be applied to determine the moment magnitude for large earthquakes.

     

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