Multistep inversion workflow for 3D long‐offset damped elastic waves in the Fourier domain

• Published in: Geophysical Prospecting 2017-09, Vol.65 (5), p.1277-1292
• Main Authors: Petrov, Petr V., Newman, Gregory A.
• Format: Article
• Language: English
• Subjects: 3D full waveform inversion; Computer memory; Damping; Data; Distributed memory; Elastic attributes; Elastic waves; Finite difference method; Forward problem; Imaging; Imaging techniques; Inversion workflow; Iterative methods; Sound waves; Three dimensional models; Wavelength; Workflow
• ISSN: 0016-8025; 1365-2478
• DOI: 10.1111/1365-2478.12487

ABSTRACT We present a new workflow for imaging damped three‐dimensional elastic wavefields in the Fourier domain. The workflow employs a multiscale imaging approach, in which offset lengths are laddered, where frequency content and damping of the data are changed cyclically. Thus, the inversion process is launched using short‐offset and low‐frequency data to recover the long spatial wavelength of the image at a shallow depth. Increasing frequency and offset length leads to the recovery of the fine‐scale features of the model at greater depths. For the fixed offset, we employ (in the imaging process) a few discrete frequencies with a set of Laplace damping parameters. The forward problem is solved with a finite‐difference frequency‐domain method based on a massively parallel iterative solver. The inversion code is based upon the solution of a least squares optimisation problem and is solved using a nonlinear gradient method. It is fully parallelised for distributed memory computational platforms. Our full‐waveform inversion workflow is applied to the 3D Marmousi‐2 and SEG/EAGE Salt models with long‐offset data. The maximum inverted frequencies are 6 Hz for the Marmousi model and 2 Hz for the SEG/EAGE Salt model. The detailed structures are imaged successfully up to the depth approximately equal to one‐third of the maximum offset length at a resolution consistent with the inverted frequencies.