A Geometric Approach to Determining Sub-Seismic Fault Block Strain

Nathan M. Franklin¹, David A. Ferrill¹, Darrell W. Sims¹, Alan P. Morris², Michael P. Rigney³, Ernest A. Franke³, and Michael J. Magee³. (1) CNWRA, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, phone: 210 522 5207, nfranklin@swri.edu, (2) Department of Earth and Environmental Science, University of Texas San Antonio, San Antonio, TX 78249, (3) Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238

We have developed a method to assess the likelihood, location, and magnitude of strain within fault blocks. Our method helps overcome the resolution limits of 3D seismic data. We estimate strain by calculating fault-block elongation parallel to fault cutoff lines. Elongation can be determined using i) fault cutoff lines of rock strata, ii) the original orientation of the strata, and iii) the direction of slip along the fault surface. Here, we apply the method to results from an analog modeling experiment of an extensional fault system. At intervals during model extension, dynamic structured light (DSL) 3D imagery of the model was collected and used to construct digital terrain models (DTMs) of the surface of the model. Fault hanging wall and foot wall cutoffs are then extracted from the DTMs. The fault information is combined with stress information from the model setup and the original horizontal orientation of the model surface to calculate fault-parallel elongation for the imaged faults in the model. Fault cutoff information can be collected at different intervals during the model run, permitting the evolution of strain in the fault system to be to be studied.

Characterization and Modeling of Fractured Reservoirs (AAPG)
AAPG Annual Meeting 2004: Embrace the Future, Celebrate the Past Technical Program