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地球的三维结构(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的计算合成地震记录及其偏导数的数值格式对宽带地震波形数据进行波形反演。在本项目中，我们获得了以下结果。对于使用面波的波形反演，我们表明了准确考虑环面-球面耦合效应的重要性(Hara和Geller，2000)。通过对数值格式的并行化，我们能够得到CPU数量与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波的速度结构(12次球谐，Hara和Geller，2001)。为了确认我们的计算方案的准确性，我们帮助组织了COSY项目，一个国际…更加努力地确认计算合成地震图的方法的准确性(IGEL等人，2000年)。我们开发了一种体波数据的波形反转算法(Takeuchi等人，2000)。利用该算法进行了初步的反演，得到了水平尺度约4000公里、垂直尺度约200公里的全地幔S波速度结构(Takeuchi and Geller，2001)。为了计算局部结构的合成地震记录，我们发展了高效和精确的时域有限差分算法(Geller和Takeuchi，1998，Takeuchi和Geller，2000)，使用我们推导最佳精度算子的一般理论(Geller和Takeuchi，1995)。对于具有明显不连续性的真实地球模型，我们表明该方案比其他方法更具成本效益(Mizutani等人，2000)。对于岩性边界与数值网格不一致的介质，我们推导出了计算合成地震记录的最佳精确算子(Mizutani等人，2001年)。这应该使我们有可能使用我们的方法对下行板的结构或其他局部或区域尺度结构进行反演。较少

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