Mapping the upper mantle: three-dimensional modeling of Earth structure by inversion of seismic waveforms.

A method is presented for the inversion of waveform data for the 3-D distribution of seismic wave velocities. The method is applied to data from the global digital networks: the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths. The moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity. A global model is constructed for shear wave velocity, expanded up to degree and order 8 in spherical harmonics, and described by a cubic polynomial in depth for the upper 670km of the Earth's mantle. The model predictions reproduce much of what is known about the dispersion of mantle waves. Since the method makes use of complete waveforms, overtone data are also included. It is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently. The model is discussed.-after Author