Unified explanation of envelope broadening and maximum‐amplitude decay of high‐frequency seismograms based on the envelope simulation using the Markov approximation: Forearc side of the volcanic front in northeastern Honshu, Japan
Unified explanation of envelope broadening and maximum‐amplitude decay of high‐frequency seismograms based on the envelope simulation using the Markov approximation: Forearc side of the volcanic front in northeastern Honshu, Japan
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DOI：
10.1029/2004jb003225
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发表时间：
2005
影响因子：
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通讯作者：
Tatsuhiko Saito;H. Sato;M. Ohtake;K. Obara
中科院分区：
文献类型：
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作者：
Tatsuhiko Saito;H. Sato;M. Ohtake;K. Obara
[1]S波在非均匀岩石圈中传播时，脉冲源辐射的持续时间随传播距离的增加而增大，最大振幅随传播距离的增大而减小。我们将这些现象分别称为“包络展宽”和“最大幅度衰减”。本文首次尝试对随机介质中基于波散射的包络展宽和最大幅度衰减做出统一的解释。在日本本州岛东北部火山前缘弧侧观测到的S波包络在2~16赫兹的频率范围内具有如下特征：包络持续时间与距离的1.7~1.8成正比，最大幅度与与−3~−2的距离成正比。这些观测是通过考虑波速随机波动且随频率衰减的介质中沿向前方向的小角度波散射来模拟的。包络持续时间和最大幅度联合分析在估计介质非均质性和衰减方面优于单独分析包络持续时间或最大幅度。在von Karman型随机介质的假设下，我们估计了S波速起伏的功率谱密度函数为P(M)≈0.004m−5.0-0.01m−4.0km~3，范围在0.5<；m<；50 km−1之间，其中m是不均匀的波数。由估计的随机不均匀和衰减计算的理论包络成功地给出了日本本州东北部包络展宽和最大幅度衰减的统一解释。
[1] During propagation through heterogeneous lithosphere, S waves impulsively radiated from a source increase in duration and decrease in maximum amplitude with increasing travel distance. We term these phenomena “envelope broadening” and “maximum-amplitude decay,” respectively. The present study is the first attempt to make a unified explanation of the envelope broadening and the maximum-amplitude decay based on wave scattering in random media. S wave envelopes observed at the forearc side of the volcanic front in northeastern Honshu, Japan, have the following characteristics in the frequency range from 2 to 16 Hz in the distance range from 75 to 410 km: Envelope duration increases with increasing travel distance in proportion to the distance to the power 1.7 to 1.8, and maximum amplitude decreases with increasing travel distance in proportion to the distance to the power −3 to −2. These observations are modeled by considering small-angle wave scattering around the forward direction in the media having randomly fluctuating wave velocity with frequency-dependent attenuation. The joint analysis of envelope duration and maximum amplitude is superior in estimating medium inhomogeneity and attenuation over the analysis of envelope duration or maximum amplitude alone. Assuming the von Karman–type random media, we estimate the power spectral density function of S wave velocity fluctuation as P(m) ≈ 0.004m−5.0–0.01m−4.0 km3 in the range between 0.5 < m < 50 km−1, where m is the wave number of the inhomogeneity. The theoretical envelope calculated from the estimated random inhomogeneity and attenuation successfully gives a unified explanation of the envelope broadening and the maximum-amplitude decay in northeastern Honshu, Japan.