Determination of global-scale 3-D Earth structure and 3-D structure of subduction zones using seismic waveform inversion

这项研究的目的是确定三维地球结构（地震速度和衰减），从而获得关于地球动力学的新信息。我们一直在利用高精度和高效率的数值方法对宽频带地震波形数据进行波形反演，以计算合成地震记录及其偏导数，在本项目中，我们取得了以下成果.对于使用表面波的波形反演，我们表明了精确考虑环形-球形耦合效应的重要性（Hara和Geller，2000）。通过并行化我们的数值方案，我们能够获得CPU数量和计算效率之间的比例关系。因此，我们能够获得更详细的上地幔S波速度结构（球谐函数高达12阶，Hara和Geller，2001）。为了确认我们计算方案的准确性，我们帮助组织了COSY项目，一个国际性的 关于我们 确认计算合成地震图的方法的准确性的努力（Igel等人，2000年）。我们开发了一种用于体波数据的波形反演的算法（Takeuchi等人，2000年）。利用该算法进行了初步反演，得到了水平尺度约4000 km、垂直尺度约200 km的全地幔S波速度结构（Takeuchi and Geller，2001）.为了计算局部结构的合成地震图，我们开发了有效和准确的时域有限差分算法（Geller和Takeuchi，1998，Takeuchi和Geller，2000），使用我们的一般理论导出最佳精确算子（Geller和Takeuchi，1995）。对于具有尖锐不连续性的现实地球模型，我们表明该方案比其他方法更具成本效益（Mizutani等人，2000年）。我们导出了用于计算岩性边界与数值网格不一致的介质的合成地震图的最佳精确算子（Mizutani等人，2001年）。这应该使得有可能使用我们的方法来反演下行板的结构，或其他局部或区域尺度的结构。少

The purpose of this research is to determine 3-D Earth structure (seismic velocity and attenuation) and thereby obtain new information on the dynamics of the Earth. We have been conducting waveform inversion of broadband seismic waveform data using highly accurate and efficient numerical schemes for computing synthetic seismograms and their partial derivatives.In this project, we obtained the following results.1. For waveform inversion using surface waves, we showed the importance of accurate consideration of the effect of toroidal-spheroidal coupling (Hara and Geller, 2000).2. By parallelizing our numerical schemes, we were able to obtain a proportional relationship between the number of CPUs and the efficiency of computation. As a result, we were able to obtain a more detailed upper mantle S wave velocity structure (spherical harmonics up to degree 12, Hara and Geller, 2001).3. To confirm the accuracy of our computational schemes, we helped organize the COSY project, an international … More effort to confirm the accuracy of methods for computing synthetic seismograms (Igel et al., 2000).4. We developed an algorithm for waveform inversion of body wave data (Takeuchi et al., 2000). Using this algorithm, we carried out a preliminary inversion and obtained whole mantle S wave velocity structure on a horizontal scale of about 4000 km and a vertical scale of 200 km (Takeuchi and Geller, 2001).5. To compute synthetic seismograms for local structure, we developed efficient and accurate timedomain finite difference algorithms (Geller and Takeuchi, 1998, Takeuchi and Geller, 2000) using our general theory for deriving optimally accurate operators (Geller and Takeuchi, 1995). For realistic Earth models which have sharp discontinuities, we showed that this scheme is much more cost-effective than other methods (Mizutani et al., 2000).6. We derived optimally accurate operators for computing synthetic seismograms for the media whose lithological boundaries do not coincide with the numerical grid (Mizutani et al., 2001). This should make it possible to use our methods to invert for the structure of the downgoing slab, or for other local or regional scale structure. Less