Free surface output

Introduction

Velocities and ground deformations can be imaged as a surface representation, in a file that can be opened in ParaView. Threads or nodes can be dedicated to write this output (see Asynchronous Output), but it is usually not necessary. The output to enabled in the Output namelist:

&Output
SurfaceOutput = 1
SurfaceOutputRefinement = 1
SurfaceOutputInterval = 0.5
/

If SurfaceOutputRefinement = 0, one triangle is outputted for each mesh cell. The unknowns are evaluated at the center of each cell. SurfaceOutputRefinement = 1 subdivides each triangle, into 4 subtriangles. Higher SurfaceOutputRefinement would further subdivide each subtriangle.

variables

v1, v2, v3: ground velocities, x y and z components

u1, u2, u3: ground displacements, x y and z components

Additionally, the writer outputs a quantity called “locationFlag”, which has the values 0 and 1 when at the elastic or acoustic side of an elastic-acoustic interface. In this way, we can distinguish between both sides of the interface even though they have the same coordinates. It has the value 2 for an ordinary free surface boundary condition and the value 3 for a free surface with gravity boundary condition. This value can be used to filter the output (which contains all these surfaces), for example using Paraview’s Threshold filter.