Full Waveform Seismic Tomography for geophysical velocity model in Canterbury region based on the Adjoint-Wavefield method

Trung Dung Nguyen, Robin L. Lee, Alan Juarez, & Brendon A. Bradley

Submitted July 25, 2019, SCEC Contribution #9266, 2019 SCEC Annual Meeting Poster #310 (PDF)

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In this paper we apply Full Waveform Tomography (FWT) based on the Adjoint-Wavefield (AW) method to iteratively invert a 3-D geophysical velocity model for the Canterbury region (Lee, 2017). The seismic wavefields was generated using numerical solution of the 3-D visco- elastodynamic equations (EMOD3D was adopted (Graves, 1996)), and through the AW method, gradients of model parameters (compressional and shear wave velocity) were computed by implementing the cross-adjoint of forward and backward wavefields. The Waveform Perturbation Kernels (WPK) constructed from Generalized Seismic Data Functional Analysis (GSDF) (Gee, 1992) were utilized as the adjoint sources. For inversion, we also account for the near source/ station effects, gradient precondition, smoothening and optimal step length.

Simulation-to-observation misfit measurements based on 148 sources at 78 seismic stations in the Canterbury region (Figure 1) were used into our inversion. The inversion process includes multiple frequency bands, starting from 0.05-0.1Hz, and advancing to higher frequency band (0.05-0.2Hz). Each frequency band was used for up to 10 iterations or no optimal step length found.

After 2 FWT inversion runs, the simulated seismograms computed using our final velocity model show a good matching with the observed seismograms at frequencies from 0 - 0.2 Hz and the normalized least-squared misfit error has been significantly reduced. Over all, the synthetic study of FWT shows a good application to improve the crustal velocity models from the existed geological models and the seismic data of the different earthquake events happened in the Canterbury region.

Key Words
Full waveform tomography, velocity model, GSDF, Adjoint-wavefield method

Citation
Nguyen, T., Lee, R. L., Juarez, A., & Bradley, B. A. (2019, 07). Full Waveform Seismic Tomography for geophysical velocity model in Canterbury region based on the Adjoint-Wavefield method. Poster Presentation at 2019 SCEC Annual Meeting.


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SCEC Community Models (CXM)