An Inverse Method to Determine Fault Slip and Geometry From Seismically Observed Subsurface Vertical Stratigraphic Displacements Using Elastic Dislocation Theory

Faults are often poorly constrained on industry seismic reflection cross-sections. This contribution describes the development of an inverse method to extract fault geometry and slip from seismic reflection datasets. We use geophysical inverse theory, implemented via non-linear minimisation, to recover fault parameters from subsurface stratigraphic horizon data determined from seismic reflection cross-sections. Our inversion process is based on a forward model using the elastic dislocation (ED) formulation of Okada (1992). 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. We measure vertical subsurface displacements at selected stratigraphic horizons from seismic reflection depth sections, and these act as observations for our inversion process. We use a standard procedure (Powell's method) to minimise an objective function, or "misfit parameter". We have developed and tested the inversion method using synthetic data generated by theoretical forward models. The inverse method can successfully recover realistic slip distributions and non-planar, including listric, fault geometries. We have successfully applied the method to observed seismic reflection data. Results are consistent with direct seismic reflection interpretations, are reproducible and geologically realistic. The inverse method provides a useful complement to subjective seismic reflection interpretations. The retrieved fault parameters from the inversion method 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.