Scaling of Strike Slip Faults in Jointed Granitic Rock

Sierra Field Work
Stephen J. Martel
University of Hawaii, Manoa		 Matthew A. d'Alessio
University of California, Berkeley


Introduction

Faults come in all different sizes ranging from microfaults along mineral grains to faults measured at the outcrop scale to faults that form the boundaries between plates. Previous investigators have learned great amounts from scale independent analysis but it has always been understood that the behavior of faults varies as a function of scale. Our work in the Sierra Nevada endeavors to quantify some of these differences and understand how they affect fault nucleation, growth, propagation, and slip.

Conference Presentations
  • AGU Fall Meeting, San Francisco, 1999
  • Nature and Tectonic Significance of Fault Zone Weakening, London, 2000
  • AGU Fall Meeting, San Francisco, 2001
    • Results
  • Maps and Figures
  • Photos From 1999 Field Work
  • Photos From 2000 Field Work
  • Photos From 2001 Field Work

    • An abstract from recent work

    The differences between fault terminations as a function of scale lead to valuable information on the controlling factors of fault growth.

    Small faults on the outcrop scale have trace lengths of tens of meters and accomodate tens of centimeters of slip. Opening mode fractures referred to as tail cracks mark the terminations of these small faults, but field evidence from larger faults show a more complex style of termination.

    Large fault zones observed in the Sierra Nevada, California, have trace lengths of several kilometers and accomodate several tens of meters of slip. A dense zone of small faults nearly parallel to the main fault zone is well documented near the termination of one large strike-slip fault zone. Along this fault, slip and associated intense fracturing is concentrated along a narrow zone one to three meters wide far from the end of the fault zone, but the slip is distributed to the smaller faults and spans a wider region near the fault termination.

    Numerical models show that mechanical interaction between the large fault zone and the smaller faults would dramatically impact the slip profile of the system and can produce a tapered slip profile similar to an isolated fault with a cohesive zone near its end. The mechanical interaction could be the principal physical mechanism by which large faults achieve a tapered slip profile.

    This projected is supported by funding from the Department of Energy and has been conducted with resources from the University of Hawaii at Manoa, University of California at Berkeley, and Stanford University.