Systematic difference between first-motion and waveform-inversion solutions for shallow offshore earthquakes due to a low-angle dipping slab
Systematic difference between first-motion and waveform-inversion solutions for shallow offshore earthquakes due to a low-angle dipping slab
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小角度倾斜板片引起的浅海地震初动解和波形反演解的系统差异
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
Tatsuhiko Saito
中科院分区：
文献类型：
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作者：
S. Takemura;K. Shiomi;Takeshi Kimura;Tatsuhiko Saito
利用2016年发生在日本中部纪伊半岛东南14 km处的三重近海地震（Mw 5.8）的地震记录，检查了浅海地震初动和波形反演解之间的系统差异。观测到的地震图显示，初至波的视速度为7.2公里/秒，比地壳P波快。利用有限差分法模拟了三维菲律宾海板块，再现了初至波的视速度和偏振模式。初至波由震源向下辐射的P波组成，作为首波通过海洋莫霍面。因此，假设一维结构的初动分析会导致对震源机制和震源深度的错误估计，这些估计往往比实际的更深。我们的结果可能表明，海洋莫霍面以上的地震活动被低估，在以前的目录。
Systematic difference between first-motion and waveform-inversion solutions for shallow offshore earthquakes was examined by using the seismograms of the 2016 Off Mie (Mw 5.8) earthquake occurred at a depth of 14 km southeast off of the Kii peninsula, central Japan. Observed seismograms illustrated first arrivals with an apparent velocity of 7.2 km/s, which is faster than crustal P waves. The apparent velocity and polarization pattern of the first arrivals were reproduced by a finite-difference method simulation incorporating the three-dimensional Philippine Sea slab. The first arrivals consist of P waves radiated downward from the source, passing the oceanic Moho as head waves. Thus, a first-motion analysis, assuming a one-dimensional structure, causes incorrect estimations of the focal mechanisms and hypocenter depths, which tend to be deeper than the actual ones. Our result possibly indicates that the seismicity above the oceanic Moho was underestimated in the previous catalogs.