# Point source (older implementation)

Using Type = 50 is the old and non-optimal way to include a point source in SeisSol. It might nevertheless still be useful for modeling a non double-couple point source (not currently possible with the nrf source description).

&SourceType
Type = 50
FileName = 'source.dat'
/


Where source.dat has the following format

header line (e.g. 'Seismic Moment Tensor')
M11 M12 M13
M21 M22 M23
M31 M32 M33
header line (optional, but has to contain 'velocity' to be recognized)
d1 d2 d3    (optional)
header line (e.g. 'Number of subfaults')
nsubfaults
header line (e.g. 'x y z strike dip rake area Onset time')
x y z strike dip rake area Onset time(1)
x y z strike dip rake area Onset time(2)
....
x y z strike dip rake area Onset time(nsubfaults)
header line (e.g. 'source time function')
dt ndt
STF(1,1)
STF(1,1)
...
STF(1,ndt)
STF(2,1)
...
STF(nsubfaults,1)
...
STF(nsubfault,ndt)


Using this implementation one can specify point sources in the following form:

\begin{split}\begin{aligned} \frac{\partial}{\partial t}\sigma_{xx} - (\lambda + 2\mu) \frac{\partial}{\partial x} u - \lambda \frac{\partial}{\partial y} v - \lambda \frac{\partial}{\partial z} w &= M_{xx} \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \frac{\partial}{\partial t}\sigma_{yy} - \lambda \frac{\partial}{\partial x} u - (\lambda+2\mu) \frac{\partial}{\partial y} v - \lambda \frac{\partial}{\partial z} w &= M_{yy} \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \frac{\partial}{\partial t}\sigma_{zz} - \lambda \frac{\partial}{\partial x} u - \lambda \frac{\partial}{\partial y} v - (\lambda + 2\mu) \frac{\partial}{\partial z} w &= M_{zz} \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \frac{\partial}{\partial t}\sigma_{xy} - \mu \frac{\partial}{\partial x} v - \mu \frac{\partial}{\partial y} u &= M_{xy} \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \frac{\partial}{\partial t}\sigma_{yz} - \mu \frac{\partial}{\partial z} v - \mu \frac{\partial}{\partial y} w &= M_{yz} \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \frac{\partial}{\partial t}\sigma_{xz} - \mu \frac{\partial}{\partial z} u - \mu \frac{\partial}{\partial x} w &= M_{xz} \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \rho \frac{\partial}{\partial t} u - \frac{\partial}{\partial x} \sigma_{xx} - \frac{\partial}{\partial y} \sigma_{xy} - \frac{\partial}{\partial z} \sigma_{xz} &= d_x \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \rho \frac{\partial}{\partial t} v - \frac{\partial}{\partial x} \sigma_{xy} - \frac{\partial}{\partial y} \sigma_{yy} - \frac{\partial}{\partial z} \sigma_{yz} &= d_y \cdot S_k(t)\cdot \delta(x - \xi_k) \\ \rho \frac{\partial}{\partial t} w - \frac{\partial}{\partial x} \sigma_{xz} - \frac{\partial}{\partial y} \sigma_{yz} - \frac{\partial}{\partial z} \sigma_{zz} &= d_z \cdot S_k(t)\cdot \delta(x - \xi_k). \\ \end{aligned}\end{split}

For details about the source term read section 3.3 of An arbitrary high-order discontinuous Galerkin method for elastic waves on unstructured meshes – I. The two-dimensional isotropic case with external source terms

Mij and di are defined in a fault local coordinate system defined by strike, dip and rake, see for instance here: https://github.com/SeisSol/SeisSol/blob/master/src/SourceTerm/PointSource.cpp#L48

The above equations also hold for viscoelastic or anisotropic materials. In the viscoelastic case, the equations are extended by the memory variables. In the anisotropic case, $$\lambda$$ and $$\mu$$ are replaced by the entries of the Hooke tensor $$c_{ij}$$.

For poroelastic materials, we add the possibility to consider forces in the fluid or pressure sources. To do so, add these two lines before Number of subfaults:

header line (optional, but has to contain 'pressure' to be recognized)
p
header line (optional, but has to contain 'fluid' to be recognized)
f1 f2 f3


In the case of a poroelastic material, the equations of motion differ from above equations. For the velocities in $$x$$ direction, they read:

\begin{split}\begin{aligned} \frac{\partial}{\partial t} u - \frac{1}{\rho^{(1)}} \frac{\partial}{\partial x} \sigma_{xx} - \frac{1}{\rho^{(1)}} \frac{\partial}{\partial y} \sigma_{xy} - \frac{1}{\rho^{(1)}} \frac{\partial}{\partial z} \sigma_{xz} - \frac{1}{\rho^{(1)}} \frac{\rho_f}{m}\frac{\nu}{\kappa} u_f &= d_x \cdot S_k(t) \delta(x - \xi_k) \\ \frac{\partial}{\partial t} u_f - \frac{1}{\rho^{(2)}} \frac{\partial}{\partial x} \sigma_{xx} - \frac{1}{\rho^{(2)}} \frac{\partial}{\partial y} \sigma_{xy} - \frac{1}{\rho^{(2)}} \frac{\partial}{\partial z} \sigma_{xz} - \frac{1}{\rho^{(2)}} \frac{\rho}{\rho_f}\frac{\nu}{\kappa} u_f &= f_x \cdot S_k(t) \delta(x - \xi_k) \\ \end{aligned}\end{split}

with

$\begin{split}\rho^{(1)} &= \left(\rho - \frac{\rho_f^2}{m}\right), \quad \rho^{(2)} &= \left(\rho_f - \frac{m \rho}{\rho_f} \right).\\\end{split}$

In particular, the terms $$d_x$$ and $$f_x$$ are not divided by $$\rho^{(1)}$$ or $$\rho^{(2)}$$, respectively.