Simultaneous waveform inversion for three-dimensional Earth structure and earthquake source parameters considering a wide range of modal coupling

Abstract

We perform iterative inversion of long-period seismic waveform data to determine simultaneously the 3-D structure of the upper and uppermost lower mantle and earthquake source parameters. We perform direct inversion of the observed data using the methods of Geller and Hara (1993) and Hara (1997), thus intermediate parameters such as 'splitting functions' are not used. We analyse data in the period bands 178-185, 282-299 and 347-376 s using the Direct Solution Method (DSM) to compute synthetic seismograms and their partial derivatives. A wide range of modal coupling is considered in these computations. We conduct numerical experiments that show that neglecting toroidal-spheroidal coupling can significantly bias estimates of 3-D Earth structure for the period band 282-299 s; note that previous studies for this band generally did not consider such coupling. A numerical experiment for the period band 347-376 s suggests that our inversion approach can extract more information on odd angular order structure for the period band 347-376 s than previous techniques.