A localized waveform inversion at teleseismic distances: An application to the D' region beneath the Cocos plate

Abstract

A localized waveform inversion technique based on hybrid modelling was developed to investigate shear wave velocity structure of the lowermost mantle. Utilizing ray theory and the Kirchhoff integral, the source wavefield from hypocentre and the receiver wavefield recorded at Earth's surface was extrapolated to the subsurface near the core--mantle boundary (CMB). Ray theory solutions are interfaced with the finite difference displacements computed in a local heterogeneous region near the CMB. The velocity structure is updated iteratively by zero-lag cross-correlation of the forward and backward wavefields in region where the finite-difference displacements were computed. As the finite difference method is applied in a small region only, the hybrid method takes much less computer memory when it is implemented to invert localized structures. We applied this method to the broadband waveform data recorded by RISTRA array from a deep south American earthquake. The resulting depth and velocity contrast across the D″ discontinuity agree reasonably well with previous observations, suggesting that the hybrid waveform inversion is a feasible and an effective technique for imaging the heterogeneous D″ region. © 2010 The Authors Journal compilation © 2010 RAS.