An inverse method to derive fault slip and geometry from seismically observed vertical stratigraphic displacements using elastic dislocation theory
David Healy1, Nick Kusznir1 and Graham Yielding2
1 = Department of Earth Sciences, University of Liverpool, Liverpool L69 3GP, UK
2 = Badleys, North Beck House, Hundleby, Spilsby, Lincolnshire PE23 5NB, UK
dhealy@liverpool.ac.uk
Faults are often poorly constrained in reflection seismic datasets. This contribution describes the development of an inverse method to extract fault slip and geometry from seismic reflection datasets. Geophysical inverse theory, implemented via non-linear minimisation, is used to recover fault parameters from subsurface stratigraphic horizon data determined from seismic cross-sections. The inversion process is based on a forward model using elastic dislocation (ED) theory. The forward model component of the non-linear inversion calculates subsurface vertical displacements from fault parameters such as fault slip, dip, length and width for planar, listric or seismically observed fault geometries. Vertical subsurface displacements are measured at selected stratigraphic horizons from seismic depth sections, and these act as observations for the inversion process. A standard procedure (Powell’s method) is used to minimise an objective function (misfit parameter).
The method has been developed and tested using synthetic data generated by theoretical forward models. The inverse method can successfully recover realistic slip distributions and non-planar, including listric, fault geometries. The method has also been successfully applied to seismic reflection data. Results are consistent with direct seismic interpretations, are reproducible and geologically realistic. This inverse method provides a useful complement to subjective seismic interpretations. The retrieved fault parameters are being used in forward models using ED theory to calculate continuum displacements and strains to aid prediction of small-scale fracture patterns in faulted reservoirs.