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An analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress

Fletcher, John M. and Teran, Orlando J. and Rockwell, Thomas K. and Oskin, Michael E. and Hudnut, Kenneth W. and Spelz, Ronald M. and Lacan, Pierre and Dorsey, Matthew T. and Ostermeijer, Giles and Mitchell, Thomas M. and Akciz, Sinan O. and Hernandez-Flores, Ana Paula and Hinojosa-Corona, Alejandro and Peña-Villa, Ivan and Lynch, David K. (2020) An analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress. Geological Society of America Bulletin . ISSN 0016-7606. (In Press)

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The moment magnitude 7.2 El Mayor−Cucapah (EMC) earthquake of 2010 in northern Baja California, Mexico produced a cascading rupture that propagated through a geometrically diverse network of intersecting faults. These faults have been exhumed from depths of 6−10 km since the late Miocene based on low-temperature thermochronology, synkinematic alteration, and deformational fabrics. Coseismic slip of 1−6 m of the EMC event was accommodated by fault zones that displayed the full spectrum of architectural styles, from simple narrow fault zones (<100 m in width) that have a single high-strain core, to complex wide fault zones (>100 m in width) that have multiple anastomosing high-strain cores. As fault zone complexity and width increase the full spectrum of observed widths (20−200 m), coseismic slip becomes more broadly distributed on a greater number of scarps that form wider arrays. Thus, the infinitesimal slip of the surface rupture of a single earthquake strongly replicates many of the fabric elements that were developed during the long-term history of slip on the faults at deeper levels of the seismogenic crust. We find that factors such as protolith, normal stress, and displacement, which control gouge production in laboratory experiments, also affect the architectural complexity of natural faults. Fault zones developed in phyllosilicate-rich metasedimentary gneiss are generally wider and more complex than those developed in quartzo-feldspathic granitoid rocks. We hypothesize that the overall weakness and low strength contrast of faults developed in phyllosilicate rich host rocks leads to strain hardening and formation of broad, multi-stranded fault zones. Fault orientation also strongly affects fault zone complexity, which we find to increase with decreasing fault dip. We attribute this to the higher resolved normal stresses on gently dipping faults assuming a uniform stress field compatible with this extensional tectonic setting. The conditions that permit slip on misoriented surfaces with high normal stress should also produce failure of more optimally oriented slip systems in the fault zone, promoting complex branching and development of multiple high-strain cores. Overall, we find that fault zone architecture need not be strongly affected by differences in the amount of cumulative slip and instead is more strongly controlled by protolith and relative normal stress.

Item Type:Article
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Oskin, Michael E.0000-0002-6631-5326
Hudnut, Kenneth W.0000-0002-3168-4797
Additional Information:© 2020 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Manuscript Received 30 March 2019; Revised Manuscript Received 6 December 2019; Manuscript Accepted 22 December 2019. This work was financed by Consejo Nacional de Ciencia y Tecnología, Mexico City, Mexico (CB-2014-239818) and the Southern California Earthquake Center (SCEC), Los Angeles, California, USA (EAR-1033462 and U.S. Geological Survey G12AC20038, SCEC paper 10004). The paper was greatly improved by reviews from Victoria Langenheim, Deven McPhillips, Jaime Delano, Michael Taylor, and An Yin. We are grateful for technical support provided by Jose Mojarro and Luis Gradilla. We also thank Jaime Delano and other reviewers for their suggestions and comments that greatly improved the paper.
Funding AgencyGrant Number
Consejo Nacional de Ciencia y Tecnología (CONACYT)CB-2014-239818
Southern California Earthquake Center (SCEC)UNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center10004
Record Number:CaltechAUTHORS:20200506-133335627
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Official Citation:John M. Fletcher, Orlando J. Teran, Thomas K. Rockwell, Michael E. Oskin, Kenneth W. Hudnut, Ronald M. Spelz, Pierre Lacan, Matthew T. Dorsey, Giles Ostermeijer, Thomas M. Mitchell, Sinan O. Akciz, Ana Paula Hernandez-Flores, Alejandro Hinojosa-Corona, Ivan Peña-Villa, David K. Lynch; An analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress. GSA Bulletin doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103042
Deposited By: Tony Diaz
Deposited On:06 May 2020 21:19
Last Modified:07 Jul 2020 19:29

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