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AAPG Bulletin

Abstract

AAPG Bulletin, V. 87, No. 2 (February 2003), P. 251-272.

Copyright ©2003. The American Association of Petroleum Geologists. All rights reserved.

Geomorphology of kilometer-scale extensional fault scarps: factors that impact seismic interpretation

Simon A. Stewart,1 Abby Reeds2

1BP plc, Chertsey Road, Sunbury on Thames, Middlesex TW16 7LN, United Kingdom; email: [email protected]
2Amerada Hess Ltd., 33 Grosvenor Place, London SW1X 7HY, United Kingdom; present address: Landmark EAME Ltd., Leatherhead, Surrey KT22 7NL, United Kingdom; email: [email protected]

AUTHORS

Simon Stewart completed a Ph.D. at Imperial College, London, on the structural geology and paleomagnetism of the Carboniferous thrust belt in north Spain. He joined Amerada Hess in 1992, working mainly on three-dimensional (3-D) seismic interpretation in the North Sea. In 2000, he joined BP as a structural geologist, working on the application of integrated drilling, geomechanical, and seismic data. His special interests include the relationship between mechanostratigraphy and structural style and development of 3-D seismic interpretation workflows for fast, accurate mapping.

Abby Reeds graduated in earth sciences from Cambridge, took a Diploma in petroleum geochemistry at the University of Newcastle-upon-Tyne, and moved in 1998 to Imperial College London, where she undertook a Ph.D., sponsored by Amerada Hess, on the tectonostratigraphy of the Moray Firth Basin. She joined Landmark Graphics in 2002, teaching geophysical interpretation applications, particularly seismic interpretation.

ACKNOWLEDGMENTS

The views expressed here are solely those of the authors and not necessarily those of Amerada Hess, BP, any partner companies, or Landmark Graphics.

ABSTRACT

The geometry of kilometer-scale extensional fault scarps appears to generally result from the interaction of three factors: initial tectonic style of the fault block, mass wasting, and setting (subareal vs. submarine). These factors are drawn together here in a matrix-style framework that highlights their interrelationships, having the intent of facilitating timely recognition of geophysical artifacts and alternative geological models during seismic interpretation. A brief review of these factors and how they could interact to affect seismic-scale fault block geometry make up this framework. This conceptual framework is then applied to a case study of seismic examples of fault blocks from the Jurassic North Sea rift. These examples span several settings from subareal to submarine exposure, with a variety of footwall lithologies. The results show that scarps that stood in deep water for as much as 50 m.y. were relatively unaffected by mass wasting, although the scarps exposed a wide variety of lithologies and structures. The principal influence on their final morphology was initial fault plane shape. However, subareally exposed scarps were strongly degraded, showing that degradation models for subareal scarps do not apply to submarine scarps. We also found that kilometer-scale posttectonic gravity collapse blocks are relatively uncommon in the study area, but where present, they can be misinterpreted as strike-slip fault zones.

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