Multiscale brittle-ductile coupling and genesis of slow earthquakes

Klaus Regenauer-Lieb, D. A. Yuen

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


We present the first attempt to explain slow earthquakes as cascading thermal-mechanical instabilities. To attain this goal we investigate brittle-ductile coupled thermal-mechanical simulation on vastly different time scales. The largest scale model consists of a cross section of a randomly perturbed elasto-visco-plastic continental lithosphere on the order of 100 × 100 km scale with no other initial structures. The smallest scale model investigates a km-scale subsection of the large model and has a local resolution of 40 × 40 m. The model is subject to a constant extension velocity applied on either side. We assume a free top surface and with a zero tangential stress along the other boundaries. Extension is driven by velocity boundary conditions of 1 cm/a applied on either side of the model. This is the simplest boundary condition, and makes it an ideal starting point for understanding the behavior of a natural system with multiscale brittle-ductile coupling. Localization feedback is observed as faulting in the brittle upper crust and ductile shearing in an elasto-viscoplastic lower crust. In this process brittle faulting may rupture at seismogenic rates, e.g., at 102-103 ms-1, whereas viscous shear zones propagate at much slower rates, up to 3 × 10-9 ms-1. This sharp contrast in the strain rates leads to complex short-time-scale interactions at the brittle-ductile transition. We exploit the multiscale capabilities from our new simulations for understanding the underlying thermo-mechanics, spanning vastly different, time- and length-scales.

Original languageEnglish (US)
Pages (from-to)523-543
Number of pages21
JournalPure and Applied Geophysics
Issue number3-4
StatePublished - Apr 2008

Bibliographical note

Funding Information:
We are grateful for discussions with Bruce Hobbs and Charley Kameyama. This research has been supported by NSF’s ITR and Math-Geo programs and the Western Australian Premiers Fellowship program, the University of Western Australia and the CSIRO Exploration and Mining Division.


  • Brittle-ductile transition
  • Fast instabilities
  • Numerical modelling
  • Rheology
  • Slow earthquakes


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