## Ray and finite-difference modelling
of CDP seismic sections for shallow lignite deposits

**Johana Brokesova** **,**
**Jiri Zahradnik** **&**
**Paraskevas Paraskevopoulos**
### Summary

Numerical experiment oriented to partial validation of the structural
model at Domenico lignite site is presented. The structure is 2D and
contains several lignite seams at different depths and a low-velocity
layer on the top of the model. The experiment consists in simulation
of CDP section along one 625 m long segment of the measured profile at the site.
The CDP stack was modelled by two independent calculation techniques,
based on completely different concepts:
the finite-difference method and the ray method. Due to incompletness
of the ray synthetic wave field
as well as numerical problems of finite-differences at higher
frequencies, there is a very poor agreement between the seismogram
sections obtained by the two methods for individual shot points.
On the other hand, the CDP stacked sections modelled by the ray and
finite-difference methods agree rather well. This is because the main
differences
between the wave fields computed by the two methods are due to the
presence of the low-velocity layer (ground roll, multiple reflections,
etc.). These parts of the wave field can be suppressed by a routine data
processing like f-k filtration and CDP stack for a multi-shot experiment.
This is also why the synthetic ray and finite-difference CDP stacks agree
relatively well the observed data.

### Whole paper

The paper is available in
GZIPped PostScript (1104 kB !,
colour figures, unGZIPped PostScript 99951 kB).

In: Seismic Waves in Complex 3-D Structures, Report 7,
pp. 375-397, Dep. Geophys., Charles Univ., Prague, 1998.