Initiation of seismic ruptures possible in zones of slow slip events according to the PMF model of fault cores with compressible fluids

Maury, Vincent

Abstract:

Piau et al (2011)[1] proposed a model applied by Geli et al (2014)[2] that accounts for the macroscopic behaviour of geological faults saturated with potentially compressible fluids. It consists of a purely poroplastic interface of finite thickness (m) embedded in an elastic medium,. The interface’s 2D behaviour is adapted from 3D Cam-Clay model. The ellipsoidal plastic criterion account for processes related to hardening//softening regimes.

The model computes normal and tangential displacement jumps across the fault core, and the stress path acting on the fault, in response to tectonic loading, geomechanical properties of the fault core, fluid compressibility variations and sources of pressurized fluids in drained or undrained conditions. Model solutions exhibit scenarii with stable, meta-stable or unstable regimes. These regimes evolve with different time scales, stretching from tens of years for stable tectonic loading to months for meta-stable regimes, to tens of seconds for unstable/dynamic phases with seismic waves.

Scenarii including successive stable or metastable regimes induce changes in the velocity of the displacement field of the elastic medium, which could be detected by accurate GPS measurements and interpreted in some cases as slow slip events.

Also the model shows that depending upon the fluid compressibility Cfl a stable slow regime, evolving along the dilatant side of the fault failure criterion and approaching the critical state line, may either remain stable (low Cfl) or become unstable (high Cfl), initiating a seismic event (Figure).

This model allows a new look at the interplay between slow and seismic faulting behaviors in subduction zones.

[1] Maury, V., Piau, J-M. & Fitzenz, D., "Mechanical Effect of the Presence of Gas on Faults Modeled as a Sandwiched Cam-Clay Material" in Proc. of the 12th ISRM Internat. Congress on Rock Mechanics Beijing Oct. __2011_ (eds Qian, Q. & Zhou, Y.) CRC Press, 6 pages, DOI:10.13140/2.1.1077.1849 (2011)

[2] Géli, L., Piau, J.-M., Dziak, R., Maury, V., Fitzenz, D., Coutellier, Q., Henry, P. Seismic precursors linked to super-critical fluids at oceanic transform faults. Nature Geosciences 7, 757-761 (2014). Corrigendum, with Th. Driesner, M. Steele-MecInnis, D. Broseta, at press, 2015"