The parameter file in SeisSol is based on the Fortran NAMELIST format. The file is divided into different sections. Each section has a set of configuration parameters that influences the execution of SeisSol. Each configuration parameter can be one of the following:
- Integer
- Float
- Array Arrays can contain integers or floats and have a fixed size. The elements are separated by spaces (
1 2 3 4) - String
- Path A path references a file or a directory and is given as a string in the parameter file with additional restrictions. A path might be absolute or relative to the starting directory of the execution. If the path is used for an output file, the user has to make sure that the directory exists. (E.g. If the path is set to "output/wavefield", then the directory "output" must exist.)
- Path prefix Path prefixes are similar to paths. However, SeisSol will automatically append a filename extension or other suffixes (e.g. "-fault").
parameters.par
Additional, more detailed information on several sections are listed here.
The slip rate is defined as the velocity difference between the two sides of a fault, that is,
Δv = v+ − v−.
A practical issue is to define which side at an interface corresponds to "+" and which one to "-". The reference point defines which side is which and it is crucial to set it correctly.
The parameters XRef, YRef, ZRef define the coordinate vector of the reference point, which we denote with r. Furthermore, the refPointMethod has to specified, whose effect is outlined in the following.
- refPointMethod=0
In order to decide if a side of a fault is "+" or "-" we compute the vectors n, x, and y for a face of a tetrahedron, whose boundary condition indicates it to be part of the fault. The vector n is the face's normal, which always points outward with respect to the tetrahedron. The vector x is an arbitrary vertex of the face and the vector y is face's the missing vertex, that is, the vertex which belongs to the tetrahedron but not to the face.
We define
$\text{isPlus}:=\left<\mathbf{r}-\mathbf{x},\mathbf{n}\right>\cdot\left<\mathbf{y}-\mathbf{x},\mathbf{n}\right>>0$
isPlus is only true whenever r-x and y-x point in the same direction (lie in the same half-space w.r.t. n).
This method works, as long as the sign of the first dot product is the same for all faces tagged as being part of the fault.
Example: One has a planar fault with normal N and an arbitrary point z on the plane. Then a good reference point would be z+N. In this case, n=N and
$\left<\mathbf{z}+\mathbf{N}-\mathbf{x},\mathbf{n}\right>=\left<\mathbf{z}-\mathbf{x},\mathbf{N}\right>+\left<\mathbf{N},\mathbf{N}\right>=\left<\mathbf{N},\mathbf{N}\right>$
that is, the first dot product becomes independent of the face. - refPointMethod=1
Here, r should be rather be called reference direction instead of reference point.
We define, with n again being a face's normal,
$\text{isPlus}:=\left<\mathbf{r},\mathbf{n}\right>>0$
Example: One has a planar fault with normal N. Then a good reference direction would be N.
Application Example: Assume you have chosen a enu coordinate system (x=east, y=north, z=up). Your fault is in the x-z-plane with y=0 (strike-slip fault) and you set the reference point to (0,10000,0) with refPointMethod=0. Then, the faces with normal (0,+1,0) make up the "+"-side. In this case, all vertices of the "+"-tetrahedron lie in the half-space y ≥ 0.
In the fault output, a strike and dip direction is defined (see create_fault_rotationmatrix.f90). For the normal (0,-1,0), one would obtain (-1,0,0) as strike direction (west). Recalling the definition of the slip rate, a positive slip rate indicates left-lateral motion.
Read the article Left-lateral, right-lateral, normal, reverse for more information.