Project #5

Flow to friction transition and back in carbonate rocks

Main Supervisor: André Niemeijer (UU), Giulio Di Toro (UNIPD)
Co-Supervisor: Hans de Bresser (UU), Telemaco Tesei (UNIPD)

Location:Universiteit Utrecht (Netherlands) –

Duration of the PhD: 3 years

The doctoral candidate will be enrolled in a PhD program at the Universiteit Utrecht

Objectives: The rheology of carbonates during the seismic cycle, especially in the presence of pressurized fluids and at the viscous-plastic to elasto-frictional transition, remains poorly understood. In the project, we will perform experiments on both intact carbonate rocks as well as fault gouges under conditions where the transition from crystal-plastic flow to frictional behaviour might be activated.  Detailed microstructural analyses down to the nanoscale (UU & UNIPD) of the experimental products and comparison with natural fault rocks from the deep roots of fault zones exposed in the Apuane Alps (Italy) and Western Alps (Switzerland) (UNIPD) will allow us to 1) test whether the deformation mechanisms activated in the experiments occur in natural faults, 2) test and update existing calcite paleo-piezometers to estimate the state of stress at earthquake nucleation depths and beyond, 3) define the conditions under which the transition from volume-conservative crystal-plastic deformation to volume-dependent frictional deformation occurs (i.e., viscous-plastic to elasto-frictional transition). Additionally, existing flow laws for creep in fine-grained calcite aggregates that have been used to predict shear strength during seismic sliding will be tested and updated, also for their utilization in other fellow projects on the modelling of the seismic cycle proposed in TREAD.

Expected Results:

  1. Identification of the dominant deformation mechanisms across the transition from friction to flow behaviour in experimental and natural carbonate fault rocks;
  2. Updated and tested microphysical models (laws) for the full range of velocities encountered in the seismic cycle;
  3. Critical assessment of existing paleopiezometers for wet calcite rocks.

Planned secondments: UNIPD (12 months, G. Di Toro, M13-18 & M25-30, Collection of natural fault rocks and experiments at low effective normal stress).