Comparison between faults extracted from seismic and Elastic Dislocation Modelling

Most fault enhancement techniques rely on enhancing the discontinuities within the seismic signal. However, there is a large variety of phenomena that cause discontinuities in the seismic signal. Furthermore, fault heaves are lower than the Fresnel zone width thus not fully resolvable and as a result, faults are often poorly imaged and can be blurry and discontinuous. In order to overcome some of the inherent limitations of fault enhancement of small scale faults, we use Elastic Dislocation (ED) modelling to provide an independent means of assessing sub-seismic fault geometry and distribution.

ED modelling assumes that the main control on small fractures and small scale fault distribution and density is the coseismic strain perturbations that occur around large (seismically visible) faults (Dee et al., 2007). From the displacement on the large faults, and knowledge of the external stress field and rock properties, the stress distributions and thus failure characteristics can be calculated, by modelling elastic dislocations in the wall rocks enveloping a fault whose displacement distribution is known (e.g. from seismic mapping) (Dee et al., 2007). ED modelling ultimately predicts the orientation, distribution and mode (e.g. pure tensile vs. shear and hybrid fractures) of secondary fault/fractures.

Using a case study from Tunisia, we compared the small scale fault distributions predicted in the fault enhanced volume with those predicted by the ED method. Faults that can be cross validated using these two methods can be more confidently interpreted.