A parametric analysis of two-dimensional elastic full waveform inversion of teleseismic data for lithospheric imaging

Abstract

The development of dense networks of broad-band seismographs makes teleseismic data amenable to full-waveform inversion (FWI) methods for high-resolution lithospheric imaging. Compared to scattered-field migration, FWI seeks to involve the full seismic wavefield in the inversion. We present a parametric analysis of 2-D frequency-domain FWI in the framework of lithospheric imaging from teleseismic data to identify the main factors that impact on the quality of the reconstructed compressional (P)-wave and shear (S)-wave speed models. Compared to controlled-source seismology, the main adaptation of FWI to teleseismic configuration consists of the implementation with a scattered-filed formulation of plane-wave sources that impinge on the base of the lithospheric target located below the receiver network at an arbitrary incidence angle. Seismic modelling is performed with a hp-adaptive discontinuous Galerkin method on unstructured triangular mesh. A quasi-Newton inversion algorithm provides an approximate accounting for the Hessian operator, which contributes to reduce the footprint of the coarse acquisition geometry in the imaging. A versatile algorithm to compute the gradient of the misfit function with the adjoint-state method allows for abstraction between the forward-problem operators and the meshes that are during seismic modelling and inversion, respectively. An approximate correction for obliquity is derived for future application to real teleseismic data under the two-dimension approximation. Comparisons between the characteristic scales involved in exploration geophysics and in teleseismic seismology suggest that the resolution gain provided by full waveform technologies should be of the same order of magnitude for both applications. We first show the importance of the surface-reflected wavefield to dramatically improve the resolving power of FWI by combining tomography-like and migration-like imaging through the incorporation of the forward-scattered and the backscattered wavefields in the inversion. The resolution of FWI is assessed through checkerboard tests and confirms a resolution of the order of the wavelength for both the P and S speeds, when the full wavefield is incorporated in the inversion. Secondly, we show that computationally efficient strategies, which consist of decimating the number of frequency components involved in the inversion, do not apply to teleseismic acquisitions, because the scattering-angle bandwidth sampled by plane-wave sources can be narrow and coarsely sampled, compared to that provided by dense profiles of point sources in exploration seismology. The waveform inversion is less sensitive to the band of incidence angles spanned by the plane-wave sources and to the sampling of this band. However, the deficit of vertically propagating plane waves hampers the vertical resolution of planar layers. Aliasing artefacts created by coarse arrays of receivers are illustrated. We show how taking into account the Hessian in the inversion and the suitable management of frequencies in the ...

The Pyrenean architecture as revealed by teleseismic P-to-S converted waves recorded along two dense transects

“…The main difficulty is to separate the contribution of P-to-S conversions from those of crustal multiples that will produce deep artefacts in the migrated section. While it has been demonstrated that including multiples in the imaging process improves the angular distribution of scattering, in particular in the backward direction, thus providing better images of the subsurface (Bostock et al 2001;Pageot et al 2013), because of their extra reflection beneath the free surface, those multiples are more sensitive to topography (Monteiller et al 2013) and to crustal heterogeneity than primary conversions. As a result, if receiver functions have a sufficiently broad azimuthal and incidence angle distribution, a simple stack is usually sufficient to separate the coherent contribution of primary conversions.…”

A 3‐D spectral‐element and frequency‐wave number hybrid method for high‐resolution seismic array imaging

“…unprecedented resolution based on converted or scattered teleseismic waves [e.g., Rondenay, 2009;Shang et al, 2012;Pageot et al, 2013], especially in the framework of adjoint tomography [Tong et al, 2014].…”

“…Teleseismic array imaging based on converted and scattered waves is one of the essential tools for investigating the crustal and upper mantle structures, and has contributed significantly over the past three decades to our understanding of tectonic evolution and internal geodynamic processes [e.g., Rondenay, 2009;Kind et al, 2012;Liu and Gu, 2012]. Various methods including receiver function (RF) analysis through single station stacking [e.g., Langston, 1977;Yan and Clayton, 2007], common conversion point (CCP) stacking [e.g., Revenaugh, 1995;Sheehan et al, 2000;Chen et al, 2005], inverse scattering approaches based on asymptotic methods such as generalized Radon transform [e.g., Bostock et al, 2001;Cao et al, 2010;Shang et al, 2014], teleseismic migration [e.g., Shragge et al, 2006;Shang et al, 2012], and teleseismic scattering tomography [e.g., Frederiksen and Revenaugh, 2004;Pageot et al, 2013;Burdick et al, 2014;Tong et al, 2014] have been developed for specific imaging purposes. RF analysis is a routine tool to characterize major discontinuities of the Earth's subsurface such as the Moho, 410 km and 660 km discontinuities [e.g., Rondenay, 2009;Kind et al, 2012].…”

Velocity model building from seismic reflection data by full‐waveform inversion

“…An alternative is to model the full scat-tered wavefield, to account for internal multiples with the scattered-field formulation (i.e., Pageot et al, 2013). An alternative is to model the full scat-tered wavefield, to account for internal multiples with the scattered-field formulation (i.e., Pageot et al, 2013).…”

“…In this Appendix, for the sake of simplicity, we choose to model the reflection wavefield with the single-scattering Born approximation. An alternative is to model the full scat-tered wavefield, to account for internal multiples with the scattered-field formulation (i.e., Pageot et al, 2013). This simply amounts to replacing A(m 0 ) by A(m 0 + δm) in the lefthand-side of equation (A2).…”