|Budget Amount *help
¥2,900,000 (Direct Cost: ¥2,900,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1998: ¥1,300,000 (Direct Cost: ¥1,300,000)
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
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