The complete ordered ray expansion—II. Multiphase body wave tomography

In a companion paper (Clarke 1993) we described a method for the calculation of body wave synthetic seismograms, referred to as the ‘Complete Ordered Ray Expansion’. Here we present a new method for the inversion of body wave seismograms, based on the CORE algorithm. This multiphase waveform tomography allows us to incorporate many body wave arrivals from each seismogram in an inversion, vastly increasing the amount of structural information that may be extracted from a set of observed traces. We present an example of a synthetic inversion for a low-velocity anomaly representing a mantle plume, and show that our method allows us to retrieve the major features of the perturbation very successfully. Our computational scheme does not demand excessive storage, but the amount required does grow in proportion to the number of events and stations. We thus investigate the effect of partitioning the procedure, by initially performing trace by trace inversions, and combining the information in a final step. The fact that small amplitude phases are less well constrained in the preliminary inversions leads to a somewhat degraded final image. Nevertheless this technique is useful in situations where a single, full inversion is impractical, or where data become available over an extended period of time.