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Solid Earth An interactive open-access journal of the European Geosciences Union
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Volume 5, issue 2
Solid Earth, 5, 1151–1168, 2014
https://doi.org/10.5194/se-5-1151-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Solid Earth, 5, 1151–1168, 2014
https://doi.org/10.5194/se-5-1151-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Method article 26 Nov 2014

Method article | 26 Nov 2014

Wave-equation-based travel-time seismic tomography – Part 1: Method

P. Tong1, D. Zhao2, D. Yang3, X. Yang4, J. Chen4, and Q. Liu1 P. Tong et al.
  • 1Department of Physics, University of Toronto, Toronto, M5S 1A7, Ontario, Canada
  • 2Department of Geophysics, Tohoku University, Sendai, Japan
  • 3Department of Mathematical Sciences, Tsinghua University, Beijing, China
  • 4Department of Mathematics, University of California, Santa Barbara, California, USA

Abstract. In this paper, we propose a wave-equation-based travel-time seismic tomography method with a detailed description of its step-by-step process. First, a linear relationship between the travel-time residual Δt = Tobs–Tsyn and the relative velocity perturbation δ c(x)/c(x) connected by a finite-frequency travel-time sensitivity kernel K(x) is theoretically derived using the adjoint method. To accurately calculate the travel-time residual Δt, two automatic arrival-time picking techniques including the envelop energy ratio method and the combined ray and cross-correlation method are then developed to compute the arrival times Tsyn for synthetic seismograms. The arrival times Tobs of observed seismograms are usually determined by manual hand picking in real applications. Travel-time sensitivity kernel K(x) is constructed by convolving a~forward wavefield u(t,x) with an adjoint wavefield q(t,x). The calculations of synthetic seismograms and sensitivity kernels rely on forward modeling. To make it computationally feasible for tomographic problems involving a large number of seismic records, the forward problem is solved in the two-dimensional (2-D) vertical plane passing through the source and the receiver by a high-order central difference method. The final model is parameterized on 3-D regular grid (inversion) nodes with variable spacings, while model values on each 2-D forward modeling node are linearly interpolated by the values at its eight surrounding 3-D inversion grid nodes. Finally, the tomographic inverse problem is formulated as a regularized optimization problem, which can be iteratively solved by either the LSQR solver or a~nonlinear conjugate-gradient method. To provide some insights into future 3-D tomographic inversions, Fréchet kernels for different seismic phases are also demonstrated in this study.

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A wave-equation-based travel-time seismic tomography method is developed including a detailed description of its step-by-step process. The forward problem is solved in the two-dimensional (2-D) vertical plane passing through the source and the receiver, and the final model is parameterized on 3-D inversion grid nodes. This 2-D--3D tomography method takes into account finite-frequency effects, accurately simulates seismic wave propagation in complex media, and has great computational efficiency.
A wave-equation-based travel-time seismic tomography method is developed including a detailed...
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