This project will study the deep interior structure of the earth by fundamental and overtone modes, including body waves. They plan to perform three aspects of mantle structure study using digital data such as IDA (International Deployment of Accelerometers) and GDSN (Global Digital Seismograph Network). First they plan to invert overtone waveform data, which often appear on radial component seismograms. Preliminary study suggests that the mantle structure down to about 900 km can be resolved. But it also suggested that weighting of each datum is important to uniformly fit all seismograms, since the data consists of various size of earthquakes and various kinds of instruments. Unless weighting is done, the results of seismic velocity patterns seem to be dominated by large earthquake data. Careful analysis of inversion procedure is required in order to understand what are robust features in the solution. Secondly, they will attempt to retrieve attenuation structure from the same data set by inverting waveforms of fundamental and overtone modes in the time domain. They will use odd and even number pairs of fundamental and overtone data such as R1 and R3, G2 and G4 and X1 and X3, in order to avoid the problem of amplitude asymmetry and direct trade-off between estimated earthquake moment and attenuation measurement. Thirdly, they plan to extend the frequency range of waveform inversion to 50 mHz(20 seconds). Extending the frequency is required to obtain structure below about 1000 km, because most of the overtone data, other than the X phases used in the above study, are from minor arc body waves.
