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Abstract

(Begin page 221)

AAPG Bulletin, V. 85, No. 2 (February 2001), P. 221-232.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Effects of subsidiary faults on the geometric construction of listric normal fault systems (Geologic Note)

Tingguang Song,1 Peter A. Cawood2

1Tectonic Special Research Centre, School of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, Western Australia, 6845; email: [email protected]
2Tectonic Special Research Centre, School of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, Western Australia, 6845; email: [email protected]

AUTHORS

Tingguang Song completed his M.S. degree in petroleum geology at China University of Geosciences (Wuhan) in 1986., He then worked as a lecturer at that university and was involved in research on extension and compression basins in eastern and western China. His main interests include seismic interpretation, basin analysis, faulting and its control on petroleum accumulation, and basin inversion. Currently he is completing a Ph.D. on the geometry and kinematics of the Perth Basin, Western Australia.

Peter A. Cawood heads the Curtin University node of the Tectonics Special Research Centre. His research is concerned with the integration of field and laboratory studies of orogenic belts and associated sedimentary basins with the development of tectonic models. He has worked in a variety of Archean to Mesozoic orogenic systems in Australia, New Zealand, China, eastern North America, and the Middle East and in their modern analogs from the southwest Pacific.

ACKNOWLEDGMENTS

We thank Premier Oil Australasia for providing seismic data for the Perth Basin. Careful and constructive reviews by John H. Shaw and N. White resulted in substantial improvements to the original manuscript. In addition, this article benefited from constructive comments by AAPG editor Neil Hurley and Mike Middleton. We also acknowledge Norm Uren and Murry Hill for their support of the Landmark Systems facilities for seismic interpretation in the Department of Geophysics at Curtin University. This article is Tectonic Special Research Centre Publication 109.

ABSTRACT

Listric normal fault systems are one of the most important sites for petroleum exploration in extension basins. The geometry of these systems at depth is commonly uncertain because of poor seismic data. Thus several techniques have been developed to construct the shape and position of the master fault at depth using one or more shallower horizons. Antithetic and synthetic faults commonly disrupt the continuity of bedding in the deformed hanging wall and contribute to the overall extension. Current models either neglect or do not adequately account for the effect of these faults in estimating the geometry of the master fault. We suggest that the extension of individual subsidiary faults should be added to the amount of extension on the master fault during the bed-fault construction. The extension on subsidiary faults is supposed to be transferred into the main fault, along the inclination of shear, although the linking mechanism between the small and main faults is unclear. The inclined shear angle can be estimated by orientation of the antithetic faults. Occurrence of synthetic faults may slightly distort the particle motion trajectories (inclined shear) relative to a hanging-wall reference frame but does not change the overall relative motion pattern. Application of our modification of the inclined shear model to unpublished and published seismic data, as well as an analog experiment model, agrees well with observed fault geometry. Negating the amount of heave on subsidiary faults results in an overestimation of depth to detachment.

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