[S-CG66] [EE] Shallow and intermediate depth intraslab earthquakes: seismogenesis and rheology of the slab

[SCG66-02] Is serpentine dehydration a viable mechanism for intermediate-depth earthquakes?

*Bruno Reynard¹ (1.CNRS Ecole Normale Superieure de Lyon 69364 Lyon cedex 07 France)

Serpentines and magnesian chlorites are major components of ultramafic rocks that interacted with aqueous fluids released at depths in convergent margins. They play an especially important role at subduction interface where the presence of thin layers with high seismic anisotropy suggests intense deformation. Their rheology suggests that they play a role in the brittle to ductile transition by allowing plastic deformation at low temperatures where anhydrous rocks are brittle. When they decompose, the release of aqueous fluids may trigger brittle failure, and coincidence of the lower seismicity plane in double Wadati-Benioff zones with the dehydration temperature of serpentine is taken as good evidence for the validity of this mechanism (Peacock, 2001). I discuss here geophysical evidence in contradiction with this conclusion and potential geophysical observations necessary to resolve this issue.

Peacock, S.M. (2001) Are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle? Geology 29, 299-302.