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Abstract

AAPG Bulletin, V. 101, No. 5 (May 2017), P. 635-653.

Copyright ©2017. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/08231616065

Direct estimation of fault trajectory from structural relief

Nathan W. Eichelberger,1 Alan G. Nunns,2 Richard H. Groshong Jr.,3 and Amanda N. Hughes4

1StructureSolver, P.O. Box 335, Danville, California 94526; [email protected]
2StructureSolver, P.O. Box 335, Danville, California 94526; [email protected]
3University of Alabama, emeritus; 2504 Twain Drive, Tallahassee, Florida 32311; [email protected]
4Chevron Energy Technology Company, 1500 Louisiana Street, 28065, Houston, Texas 77002; present address: Department of Geosciences, University of Arizona, 1040 E 4th Street, Tucson, Arizona 85721; [email protected]

ABSTRACT

Confidently defining the trajectory of faults that control structural traps is a recurring challenge for seismic interpreters. In regions with fault-related folds, seismic and well data often constrain the upper fold geometry, but the location and displacement of the controlling fault are unknown. We present a generalized area–depth strain (ADS) analysis method that uses the observed depth variation in deformed horizon areas to directly estimate underlying fault depth, dip, displacement, and layer-parallel strain from a structural interpretation. Previously established ADS methods are only applicable to structures controlled by faults that sole into layer-parallel detachments. The new technique, referred to as the fault-trajectory method, generalizes ADS analysis to contractional and extensional structures controlled by fault ramps that cut across layers and displace the regional. For structures where area is conserved during deformation and shear is minimal, laterally shifting the analysis limits across the structure defines changes in fault orientation. We validate the method by applying it to numerical forward models, analog clay models, and seismically imaged structures from the San Joaquin basin in California, the Sierras Pampeanas in Argentina, and the North Sea. The fault-trajectory method is shown to be robust, because it exactly reproduces the prescribed fault trajectories and displacements used to construct the numerical and analog models. In the natural examples, the ADS-estimated fault trajectories are consistent with independent fault-location constraints such as earthquake focal mechanisms, seismic imaging, and forward modeling.

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