エネルギー輸送理論に基づく高周波数地震波形エンベロープの研究

局地地震的高频地震记录是由地球上分布的随机非相干散射波组成的。我们可以从地震记录包络的特征定量地测量随机非均质性。对于高频能量传播的研究，辐射传递理论是非常有用的；然而，这个理论过于简单，无法分析复杂的地震记录。1997年，为了采用描述实际震源的非球形源辐射，我们发展了辐射传递理论。将该理论应用于1994年远东三陆地震的强震记录，估计了地震断层高频能量辐射的空间分布。高频辐射在断裂结束时最强，这与最大断层滑动的位置不同。1998年，我们发展了辐射传递理论，采用了随深度增加的实际速度结构。将发展的理论应用于1995年神户地震，在断裂面上发现了几个强辐射点。因此，我们提出了辐射传递理论在源辐射过程反演中的有用性。此外，我们在东北地区的托诺和三陆地区安装了两套小型地震阵列，以分析地球介质速度结构的频谱。首席研究员出版了一本教科书，介绍了高频地震波在非均质地球介质中的散射和传播。

High-frequency seismograms of local earthquakes are composed of incoherent scattered waves from distributed random heterogeneities in the Earth. We can quantitatively measure the random heterogeneity from the characteristics of seismogram envelopes, For the study of high-frequency energy propagation, the radiative transfer theory is know to be very useful ; however, this theory was too simple to analyze complex seismograms. In 1997, we have developed the radiative transfer theory in order to adopt nonspherical source radiation, which describes realistic seismic source. Applying this theory to strong motion records of the 1994 far-east off-Sanriku earthquake, we estimated the spatial distribution of high-frequency energy radiation from the earthquake fault. The high-frequency radiation was found to be the strongest at the end of rupture, which is different from the location of the largest fault-slip. In 1998, we have developed the radiative transfer theory to adopt realistic velocity structure, which increases with depth. Applying the developed theory to the 1995 Hyogo-ken Nanbu (Kobe) earthquake, we found a few strong-radiation spots on the fault plane. Thus, we have presented the usefulness of the radiative transfer theory in the inversion for the source radiation process. In addition, we have installed two sets of small seismic arrays at Tono and Sanriku in the Tohoku district in order to analyze the spectra of the velocity structure of the earth medium. The head investigator published a textbook which introduces scattering and propagation of high-frequency seismic waves in the heterogeneous Earth medium.