Waveform Modelling of High-Frequency Body-Waves in 3-D Earth Models

Abstract:

With the development of accurate purely numerical forward modeling techniques such as the Spectral Element Method (SEM; Komatitsch and Tromp, 2002a,b) it is now possible to simulate seismic wave propagation in realistic 3-D Earth models at the global scale. While up to recently the routine use of the SEM in moderate computer clusters was mostly limited to the modeling of long-period waveforms (f ~ 50 mHz), the advancement of High Performance Computing resources now allows the easy calculation of synthetic seismograms accurate up to f ~ 200 mHz. The availability of these high frequency and high accuracy waveforms pushed us to look closer at mantle body-wave phases. In particular, we are interested in studying the effects of 3-D structure on deep seismic phases such as S, Sdiff, ScS, SKS and SKKS. These phases are either transmitted, reflected or refracted in the lowermost mantle and have been extensively used to retrieve information about the D’’ layer. Despite recent studies advancing our knowledge of D’’, previous results regarding its thickness, heterogeneity and anisotropy are still not univocal. To explore the reasons of these discrepancies, we first perform a systematic analysis of the effects of the elastic, anelastic and anisotropic structure on the waveforms and secondly we compare synthetic seismograms calculated for the most recent tomographic models with real data. Our preliminary results show that the interference with other phases as well as the misinterpretation of the shape of the waveforms can lead to different models for the D’’ when these phases are used to constrain deep Earth structure. Our ultimate goal is to improve our understanding of the potentialities and limitations of these deep seismic phases for the study of the Earth’s deep interior.