### SAGA - Scientific Computing with Algebraic and Generative Abstractions

# SeisMod - Seismic simulator

The seismic simulator SeisMod was developed in close cooperation with the
Department of earth science,
University of Bergen. SeisMod is built
using the Sophus software library. This gave a
remarkable flexibility, so that 6 different versions have been developed
catering for different requirements of the geophysical model and execution
time behaviour. All the codes are available for SGI Cray and SUN Ultra
platforms. The versions are motivated by the vastly different computing
times needed for computing the models, depending on the complexity of the
rock models. Assuming isotropic rocks (seismic properties are independent
of direction) then the equations will contain many identical terms, and
the computation may be simplified accordingly. More complicated equations
are needed if we allow anisotropy. The case of transverse isotropy means
that the seismic waves will meet the corresponding property of
*spin*, so the seismic waves will not propagate with the same
velocity in the different directions of the media.
The following figures illustrate these differences. The simulation
represents a 1km by 1km uniform 2-dimensional rock model. The seismic wave was
initiated by a pulse lasting about 10ms at the center of the model.
In the transverse isotropic cases we also see a clear separation
between the faster moving p-waves, which *spin*, and
the slower moving s-waves.

Figure 1: Isotropic case, seismic wave 25ms after the pulse started.

Figure 2: Isotropic case, seismic waves 100ms after the pulse started.

Figure 3: Transverse isotropic case with vertical axis of symmetry,
seismic waves 100ms after the pulse started.

Figure 4: Transverse isotropic case with the axis of symmetry curved in
the rock, seismic waves 100ms after the pulse started.

All these different versions actually boil down to how we may
implement the tensor level of the system. Thus three versions of the
tensor module corresponds to these three cases. Furthermore, any of these
may freely be combined with a parallel implementation of the problem
grid, giving 6 versions of the program.
SeisMod also includes a poroelastic version, treating
porous rock as a two-component medium: the hard rock with oil and water. This is
implemented as a modification of the application layer in Sophus, and
it can be combined with any of the other 6 implementations, giving a
total of 12 simulation programs. Each of these versions handles a
specific combination of rock properties and sequential or parallel
execution.

SeisMod and a rock modelling tool (VelRock) are available,
also for commercial use.
Contact with a geophysical consulting company can be made on request.

These pages last updated 2010-11-15
©1999-2010 Magne Haveraaen, University of Bergen, Norway.

SAGA contact address.

Main SAGA WWW page.