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| -# Wavefield injection based on interface discontinuity conditions |
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| -## Definition of the wavefield injection problem |
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| -We define and discuss the wavefield injection problem in the context of linear elasticity. The wavefield is governed by the elastic wave equation |
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| - |
| 15 | +<h1> Wavefield injection based on interface discontinuity conditions</h1> |
| 16 | +<h2> Definition of the wavefield injection problem</h2> |
| 17 | +<p>We define and discuss the wavefield injection problem in the context of linear elasticity. The wavefield is governed by the elastic wave equation |
11 | 18 | $$\rho\frac{\partial^2 \mathbf{u}}{\partial t^2}-\nabla\cdot(\mathbf{C}:\nabla\mathbf{u}) = \mathbf{f}\qquad \text{in}\ \oplus,$$
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| 19 | +subject to certain boundary condition at $\partial\oplus$, where $\oplus$ denotes the entire medium of wave propagation (e.g., the whole Earth). </p> |
12 | 20 |
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| -subject to certain boundary condition at $\partial\oplus$, where $\oplus$ denotes the entire medium of wave propagation (e.g., the whole Earth). |
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| - |
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| -Now suppose that we have a *local domain* $\Omega\in\oplus$ in which structural perturbations exist and the wave propagations are of particular interest, but the source $\mathbf{f}$ is supported far away from $\Omega$, and directly solving the wavefield in $\oplus$ is too expensive. If we happen to have access to some *background wavefield* $\mathbf{u}^0$ outside $\Omega$ |
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| - |
| 21 | +<p>Now suppose that we have a <em>local domain</em> $\Omega\in\oplus$ in which structural perturbations exist and the wave propagations are of particular interest, but the source $\mathbf{f}$ is supported far away from $\Omega$, and directly solving the wavefield in $\oplus$ is too expensive. If we happen to have access to some <em>background wavefield</em> $\mathbf{u}^0$ outside $\Omega$ |
| 22 | + |
17 | 23 | $$\rho^0\frac{\partial^2 \mathbf{u}^0}{\partial t^2}-\nabla\cdot(\mathbf{C}^0:\nabla\mathbf{u}) = \mathbf{f}\qquad \text{in}\ \oplus\setminus\Omega,$$
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| 24 | + |
| 25 | +then it may be possible to reconstruct $\mathbf{u}$ using $\mathbf{u}^0$, with numerical simulations only performed in $\Omega$ (potentially in the neighbourhood of $\Omega$, but not in the entire $\oplus$).</p> |
18 | 26 |
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19 |
| -then it may be possible to reconstruct $\mathbf{u}$ using $\mathbf{u}^0$, with numerical simulations only performed in $\Omega$ (potentially in the neighbourhood of $\Omega$, but not in the entire $\oplus$). |
20 | 27 |
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| -As a more rigorous definition, if |
22 |
| -1. there is no structural perturbations in the local domain |
| 28 | +<p>As a more rigorous definition, if |
| 29 | +<ol> |
| 30 | +<li> there is no structural perturbations in the local domain |
23 | 31 |
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24 | 32 | $$\rho = \rho^0, \qquad \mathbf{C} = \mathbf{C}^0 \qquad \text{in}\ \overline{\oplus\setminus\Omega},$$
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25 | 33 |
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26 |
| -2. the source term is supported outside the local domain |
| 34 | +<li> the source term is supported outside the local domain |
27 | 35 |
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28 | 36 | $$\mathbf{f} = 0 \qquad \text{in}\ \overline{\Omega},$$
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| 37 | +</ol> |
29 | 38 |
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30 |
| -then reconstructing $\mathbf{u}$ using $\mathbf{u}^0$ is called the *wavefield injection problem*. |
| 39 | +then reconstructing $\mathbf{u}$ using $\mathbf{u}^0$ is called the <em>wavefield injection problem</em>.</p> |
31 | 40 |
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32 |
| -## The equivalence between the wavefield injection problem and the interface discontinuity condition problem |
33 |
| -If we define wavefield |
| 41 | +<h2> The equivalence between the wavefield injection problem and the interface discontinuity condition problem</h2> |
| 42 | +<p>If we define wavefield |
34 | 43 |
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35 |
| -$$\mathbf{w}:=\left\\{\begin{array}{ll} |
| 44 | +$$\mathbf{w}:=\left\{\begin{array}{ll} |
36 | 45 | \mathbf{u} & \qquad \text{in}\ \Omega, \\
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37 | 46 | \mathbf{u}-\mathbf{u}^0 & \qquad \text{in}\ \oplus\setminus\Omega,
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38 | 47 | \end{array}\right.$$
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41 | 50 |
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42 | 51 | $$\rho\frac{\partial^2 \mathbf{w}}{\partial t^2}-\nabla\cdot(\mathbf{C}:\nabla\mathbf{w}) = 0\qquad \text{in}\ \oplus,$$
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43 | 52 |
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44 |
| -but $\mathbf{w}$ is discontinuous in its displacement and traction across the interface between $\Omega$ and $\oplus\setminus\Omega$ |
| 53 | +but $\mathbf{w}$ is discontinuous in its displacement and traction across the interface between $\Omega$ and $\oplus\setminus\Omega$: |
45 | 54 |
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46 |
| -$$\mathbf{w}\Big|\_{\Gamma+}^{\Gamma-} = \mathbf{u}^0\Big|\_{\Gamma},$$ |
| 55 | +$$\mathbf{w}\Big|_{\Gamma+}^{\Gamma-} = \mathbf{u}^0\Big|_{\Gamma},$$ |
47 | 56 |
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| -$$\hat{\mathbf{n}}\cdot(\mathbf{C}:\nabla\mathbf{w})\Big|\_{\Gamma+}^{\Gamma-} = \hat{\mathbf{n}}\cdot(\mathbf{C}:\nabla\mathbf{u}^0)\Big|\_{\Gamma}.$$ |
| 57 | +$$\hat{\mathbf{n}}\cdot(\mathbf{C}:\nabla\mathbf{w})\Big|_{\Gamma+}^{\Gamma-} = \hat{\mathbf{n}}\cdot(\mathbf{C}:\nabla\mathbf{u}^0)\Big|_{\Gamma}.$$</p> |
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