High-Resolution Analysis of Earthquake Source Processes Using 3-D Green's Functions

为了以高分辨率了解详细的震源过程，我们必须分析反映它们的高频地面运动。这意味着我们必须在一个真实的三维地下结构中使用格林函数进行分析，因为结构的细节对高频地面运动是有效的。在这项研究中，我们开发了一种利用三维格林函数对震源过程进行高分辨率分析的方法，并将其应用于日本大地震的观测记录。2003年，我们建立了三维结构模型，发展了体素有限元法。然后，我们将它们应用于1995年的神户地震进行验证。2004年，我们进一步将其应用于日本境内外最近发生的地震记录（宫城县北部地震、枥木地震、杜兹兹地震等）。我们首先使用Green函数对一维结构模型和半空间进行初步分析，然后应用三维Green函数。然而，三维模型的建立比较困难，对其中的格林函数进行数值计算耗时较长。因此，我们为观测站制作了各种一维模型，并将它们组合成一个伪三维模型。（Hikima和Koketsu， 2005）。我们使用这些伪三维格林函数对北部宫城县和中越地震序列的主震和余震进行了高分辨率分析。福冈县西部的地震发生在2005年3月20日，接近项目期限的末期。我们把所开发的方法应用到这次地震中加以验证。

In order to know detailed source processes with high resolution, we have to analyze high-frequency ground motions reflecting them. This implies that we have to carry out analyses using Green's functions calculated in a realistic 3-D underground structure, because the details of the structure are effective on high-frequency ground motions. In this study we have developed a method of high-resolution analysis of source processes with 3-D Green's functions, and applied it to observed records of large earthquakes in Japan. In 2003, we made a 3-D structure model and developed the voxel finite element method. We then applied them to the 1995 Kobe earthquake for their verification. In 2004, we further applied them to records of recent earhquakes in and outside Japan (Miyagi ken Hokubu earthquake, Tokachi-oki earthquake, Duzce earthquake, etc.). We first performed preliminary analyses using Green's functions for a 1-D structure model and a halfspace, and then applied 3-D Green's functions. However, it is difficult to construct the 3-D models and it takes a long time to numerically compute Green's functions in them. So we made various 1-D models for observation stations and combine them into a pseudo-3D model. (Hikima and Koketsu, 2005). We carried out high-resolution analyses of the mainshocks and aftershocks of the Miyagi-ken Hokubu and Chuetsu earthquake sequences using these pseudo 3D Green's functions. The west off Fukuoka prefecture earthquake occurred on March 20, 2005 near the end of the project term. We verified the method developed by applying it to this earthquake.