Scattering study and formation process of uppermost mantle at the island arc

在日本，RGES(爆炸地震学研究小组)已经进行了许多地震实验。在本研究中，我们利用RGES获得的波形建立了一个数据库。对长度大于130公里的5条测线进行了研究。大多数数据提示PMP波具有长持续时间的尾波。研究了该相的特性。考虑了几种可能的模型来解释长持续时间的尾波。对三种可靠的模型进行了检验：1)扭曲的莫霍面模型，2)反射上地幔模型，3)上地幔中存在多个散射体的模型。位于最上地幔模型中的散射体是解释长持续时间尾波的最佳模型。我们通过模拟估算了最上面的地幔和地壳的散射系数。上地幔的散射系数(0.025公里/S)略大于上地壳(0.01公里/S)和下地壳(0.02公里/S)，具有反射特征。这一研究表明，最上地幔不透明，具有散射体多的特点。日本的上地幔不透明，与大陆地区的不一致。地幔顶端的许多散射体可能与日本的岩浆活动有关。这将是了解岛弧地区单边界和上地幔形成过程的重要内容之一。

In Japan, many seismic experiments had been done by RGES (Research Group for Explosion Seismology). In this study, we made a database by the use of waveforms obtained by RGES. The five survey lines, with the length were longer than 130 km, were researched. Most of the data suggested PmP waves with long-duration coda wave. The characteristics of the phase are investigated. Several possible models are considered to explain the long duration coda-wave. Three reliable models, which are 1)distorted Moho boundary model, 2)reflective uppermost mantle model, and 3)a model in which many scatterers are located in the uppermost mantle, are examined. The scatterer located in the uppermost mantle model is the best model for explaining the long-duration coda-wave. We estimate the scattering coefficient of the uppermost mantle and crust using simulations. The scattering coefficient of the uppermost mantle (0.025km/s^<-1>) is slightly larger than those of upper crust (0.01km/s^<-1>) and lower crust (0.02km/s^<-1>) which is characterized as being reflective. This study revealed that the uppermost mantle is not transparent, and is characterized that many scatterers are located. The uppermost mantle at the Japan is nontransparent which is not consistent with that of continental area. The many scatterers in the uppermost mantle might be related to magmatism in Japan. This will be one of the important for understanding formation process of the Mono boundary and uppermost mantle at the island-arc region.