Crustal heterogeneity around active faults and volcanoes in southwestern part of Japan-Inversion analysis of coda envelopes-

尾波包层反演分析方法被应用于几个活动断裂区以及包括福井地震断裂、野岛断裂、六子断裂系统、山崎断裂系统、昂塔山、白山山和日光-什里安山在内的几个活动火山区。通过估计尾波散射体的三维分布，得到了地壳非均质性的以下特征：(1)活火山以下10-20公里处存在强散射体，可将其解释为S波反射体。(2)与通常的反射分析方法相比，得到了更详细的反射体分布。(3)在Ontake山以下0-7公里深度估计了散射体的垂直分布。(4)在0-20公里深度的活动断裂上存在强散射体。(5)福井地震断裂带附近的低震活动区对应于弱散射区。(6)在1995年兵库县南部7.2级地震断裂面以下20-30公里处估计有强散射区。该带可能与本区的下地壳相对应。(7)在上述散布带中，非均质性最强的区域位于1995年兵库县南部地震的震中附近。这项研究揭示了活动断裂和火山周围几个有意义的非均质性结构。如上文(6)和(7)所示，地壳非均质性被认为与大地震的发生密切相关，通过这种反演分析进一步研究地壳非均质性是必要的。

The inversion analysis method of coda envelopes was applied to several active fault regions and also active volcano regions that include Fukui-earthquake fault, Nojima fault, Rokko fault system, Yamasaki fault system, Mt.Ontake, Mt.Hakusan, and Mt.Nikko-Shirane. Through estimating the 3-D distribution of coda scatterers, the following characteristics of crustal heterogeneities are obtained : (1)Strong scatterers exist at 10-20 km depth below active volcanoes and the scatters are interpreted as S wave reflectors. (2)The distribution of reflectors is obtained in more detail than usual reflection analyzes. (3)A vertical distribution of scatterers is also estimated at 0-7 km depth below Mt.Ontake. (4)Strong scatterers exist along active faults at depths of 0-20 km. (5)A low seismicity area near the Fukui-earthquake fault well correlates to a weak scattering region. (6)Strong scattering zone are estimated at depths of 20-30 km just below the fault plane of the 1995 Hyogo-ken Nanbu earthquake (M7.2). This zone may correspond to the lower crust in this area. (7)The strongest heterogeneity in the above stated scattering zone is located close to the hypocenter of the 1995 Hyogo-ken Nanbu earthquake.This study has revealed several meaningful heterogeneous structures around active faults and volcanoes. Crustal heterogeneity is supposed to be strongly related to the occurrence of major earthquakes as shown in (6) and (7) above, and further investigation of crustal heterogeneities through this kind of inversion analysis will be necessary.