Effects of redetermination of source time functions on the 3-D velocity structure inferred by waveform inversion

Abstract

As recent waveform inversion studies to determine 3-D Earth structure are increasingly using data in shorter period ranges, the sensitivity of the inversion results to source parameters, the source time function (STF) in particular, will increase. In this study we redetermine the centroid and moment tensor (CMT) solutions for 41 deep- and intermediate-earthquakes beneath South America, using only body-wave data in the same period range used in localized waveform inversion. We then redetermine the STFs of 35 of these events by stacking the displacement of P-waves. We use four slightly different methods to obtain four sets of redetermined source parameters. We find that all four sets of redetermined source parameters generally agree with the GCMT solutions, but the STF durations are systematically shorter than those for the GCMT solutions, particularly for events with moment-magnitudes larger than 6.5. We then apply the four sets of redetermined source parameters for the 35 events to localized waveform inversion for the 3-D seismic velocity structure of the D″ region beneath Central America and the Caribbean using PREM as the 1-D initial model. We improve the 3-D structure (as shown by improved variance reduction), particularly after redetermination of moment tensors and STFs. The velocity patterns of the four new 3-D structure models for the D″ region inferred by inversions using the redetermined source parameters do not differ significantly from those inferred using the GCMT source parameters. However, the amplitude of the lateral heterogeneity decreases when synthetics for the redetermined STFs are used.