Analogue (plaster) modelling and synthetic seismic representation of hangingwall fault

The complex structuring associated with ramp-flat-ramp extensional master faults, as well as the strain pattern in the hanging-wall fault block of such faults, have been analysed with the help of analogue Plaster of Paris models. This analysis shows that the shallow-dipping master fault commonly develops several fault branches due to either asperity bifurcation or hanging-wall and footwall splaying, and that the deeper parts of steeper early generation faults are sometimes cut by younger faults. This generates a very complex fault pattern in the deeper part of the hanging-wall fault block. Based on the analogue models, the possibility of generating synthetic reflection seismograms by the use of simple modelling techniques (ray tracing and finite-difference models) has been investigated. It is concluded that the two methods produce significantly different results in terms of resolution and noise. The ray-tracing method resulted in a highly idealized image that can be viewed as the end product after an idealized processing sequence in that no noise, no multiples or other artefacts are incorporated. Furthermore, all reflections are in the correct position and are displayed with the correct amplitude in each case. Although the result can be used as a good reference for what can be obtained by simple seismic modelling, the weak aspect of this method is obviously the over-simplified and unrealistically ‘clean’ image presented. A more ‘realistic’ reflection seismic image is obtained in cases where the synthetic seismogram is generated by the finite-difference method. However, the structural features stand out with less clarity, and it is less likely that the interpreter of this section would be able to identify the two master fault planes or to distinguish the complex structural pattern in the deep part of the hanging-wall fault block.