Abstract
Quantitative imaging of subsurface earth properties in elastic media is performed from distributed acoustic sensing data. A new misfit functional based upon the reciprocity gap is designed, taking crosscorrelations of displacement and strain, and these products further associate an observation with a simulation. In comparison with other misfit functionals, this functional has the advantage of only requiring little a priori information on the exciting sources. In particular, the misfit criterion enables the use of data from regional earthquakes (teleseismic events can be included as well), followed by exploration data to perform a multiresolution reconstruction. The data from regional earthquakes contain the low-frequency content that is missing in the exploration data, allowing for the recovery of the long spatial wavelength, even with very few sources. These data are used to build prior models for the subsequent reconstruction from the higher frequency exploration data. This results in the elastic full reciprocity-gap waveform inversion method, and we illustrate its performance with a pilot experiment for elastic isotropic reconstruction.
Highlights
Adjoint tomography and full waveform inversion in global and exploration seismology have, over the past two decades, dramatically improved our capabilities to estimate material properties and structure of Earth’s interior, e.g., Tarantola (1984); Gauthier et al (1986); Pratt et al (1998); Ravaut et al (2004); Tromp et al (2005); Fichtner et al (2006a,b); Tape et al (2007); Liu and Tromp (2008); Fichtner et al (2008); Luo et al (2009); Virieux and Operto (2009); Brossier et al (2009); Fichtner (2010); Komatitsch et al (2016) and Modrak and Tromp (2016)
The key feature of our underlying Full Reciprocity-gap Waveform Inversion (FRgWI) method is that the misfit functional we introduce does not require knowledge of the passive and active sources
Contrary to conventional teleseismic inversion which needs distant earthquake to work with plane wave illumination, FRgWI allows for any type of passive sources, enabling the use of data from local events
Summary
Adjoint tomography and full waveform inversion in global and exploration seismology have, over the past two decades, dramatically improved our capabilities to estimate material properties and structure of Earth’s interior, e.g., Tarantola (1984); Gauthier et al (1986); Pratt et al (1998); Ravaut et al (2004); Tromp et al (2005); Fichtner et al (2006a,b); Tape et al (2007); Liu and Tromp (2008); Fichtner et al (2008); Luo et al (2009); Virieux and Operto (2009); Brossier et al (2009); Fichtner (2010); Komatitsch et al (2016) and Modrak and Tromp (2016). In adjoint tomography and full waveform inversion, here collectively referred to as FWI, the identification of Earth’s parameters can be conducted via a minimization problem, where one optimizes a misfit criterion between observed data and simulations It was first developed for the wave equation by Bamberger et al (1977, 1979); Lailly (1983) and Tarantola (1984), while the time-harmonic formulation was proposed by Pratt et al (1996; 1998; 1999). The main difficulty comes from the local minima in the misfit functional, which are due to the inaccurate background velocity information that causes phase shifts between observed and computed signals This issue of cycle-skipping has motivated several studies aiming at mitigating their occurrences, e.g., Gauthier et al (1986); Luo and Schuster (1991); Bunks et al (1995); Clement et al (2001); Fichtner et al (2008); Virieux and Operto (2009) and Faucher et al (2020b). If “true” Earth models are restricted to be piecewise smooth, there is a precise way to recover these through scattering control, avoiding optimization (Caday et al, 2019)
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