A new method to invert seismic waveforms for 3-D Earth structure

2. Summary The Earth consists of the crust, mantle (Note #1), outer core and inner core (Note #2). The D" (pronounced “Dee double prime”) layer is the name given to the lowermost several hundred km of the mantle, directly below which is the molten outer core, which is composed primarily of iron. The temperature and chemical composition within D" vary rapidly as the distance to the core-mantle boundary (CMB) decreases. Data on material and energy flux in D" can provide important information for understanding the Earth's dynamics and evolution, but the three dimensional (3-D) structure of D" was not heretofore known with sufficiently high resolution. The present study, by Kenji Kawai (a visiting researcher at the University of Tokyo and Assistant Professor at the Tokyo Institute of Technology), Robert J. Geller (Professor at the University of Tokyo), and their co-workers, has developed a new method for direct inversion of seismic waveforms for high-resolution 3-D Earth structure. The study then applied the new inversion method to a large data set of seismic waveforms recorded at seismic stations in North America for earthquakes under South America to determine seismic structure in the lowermost mantle under Central America. The study found evidence for the existence of remnants of the subducted Farallon Plate (Note #3) in D" beneath Central America. This material was carried from the Earth’s surface to D" by mantle convection. It is anticipated that the new data analysis method presented in this study can also be applied to data from many other regions to image D" on a global scale, thereby contributing to better understanding of the Earth’s dynamics and evolution.