Pure and Applied Geophysics

, Volume 168, Issue 12, pp 2427–2449 | Cite as

Earthquake Rupture at Focal Depth, Part II: Mechanics of the 2004 M2.2 Earthquake Along the Pretorius Fault, TauTona Mine, South Africa

  • V. Heesakkers
  • S. Murphy
  • D. A. Lockner
  • Z. RechesEmail author


We analyze here the rupture mechanics of the 2004, M2.2 earthquake based on our observations and measurements at focal depth (Part I). This event ruptured the Archean Pretorius fault that has been inactive for at least 2 Ga, and was reactivated due to mining operations down to a depth of 3.6 km depth. Thus, it was expected that the Pretorius fault zone will fail similarly to an intact rock body independently of its ancient healed structure. Our analysis reveals a few puzzling features of the M2.2 rupture-zone: (1) the earthquake ruptured four, non-parallel, cataclasite bearing segments of the ancient Pretorius fault-zone; (2) slip occurred almost exclusively along the cataclasite-host rock contacts of the slipping segments; (3) the local in-situ stress field is not favorable to slip along any of these four segments; and (4) the Archean cataclasite is pervasively sintered and cemented to become brittle and strong. To resolve these observations, we conducted rock mechanics experiments on the fault-rocks and host-rocks and found a strong mechanical contrast between the quartzitic cataclasite zones, with elastic-brittle rheology, and the host quartzites, with damage, elastic–plastic rheology. The finite-element modeling of a heterogeneous fault-zone with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite-bearing segments, as observed, due to the strong mechanical contrast between the cataclasite and the host quartzitic rock.


Deformation Modulus Witwatersrand Basin Axial Fracture South African Minis Gouge Zone 
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We are in debt to many people and organizations. Foremost to Gerrie van Aswegen of ISS International who guided and advised us throughout this entire study. This work was not possible without the invaluable help and support by Hannes Moller, Pieter van Zyl, Rob Burnet, and many other workers in TauTona mine and ISSI. We greatly appreciate the help in underground work by Tom Dewers, Amir Allam, Kate Moore, and Matthew Zechmeister of University of Oklahoma, Reginald Domoney, Selwyn Adams, and Curnell Campher, of the University of Western Cape, South Africa, Amie Lucier of Stanford University, and Malcolm Johnston, US Geological Survey. This work could not be completed without the important advice, suggestions and encouragement by the NELSAM team of Tom Jordan, Malcolm Johnston, Mark Zoback, TC Onstott, as well as Hiroshi Ogasawara, Ritsumeikan University, Japan, and Uli Harms, GFZ, Germany. Many thanks to AngloGoldAshanti for the permission to work in the TauTona mine and the generous logistic support. The thoughtful comments of two anonymous reviewers significantly improved the manuscript. This work was supported by the National Science Foundation under Grant no. 0409605 (NELSAM project), and the drilling grant by ICDP (DAFSAM project). Other sponsors of this work include US Geological survey, AngloGoldAshanti, ISS International, and National Research Foundation (NRF).


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Copyright information

© AOCS (outside the USA) 2011

Authors and Affiliations

  • V. Heesakkers
    • 1
    • 2
  • S. Murphy
    • 3
  • D. A. Lockner
    • 4
  • Z. Reches
    • 1
    Email author
  1. 1.School of Geology and Geophysics, University of OklahomaNormanUSA
  2. 2.Chevron ETCHoustonUSA
  3. 3.AngloGold AshantiCarletonvilleSouth Africa
  4. 4.US Geological SurveyMenlo ParkUSA

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