[S-CG20] Intermediate-depth and deep earthquakes: their origins and material properties of subducting slabs

[SCG20-11] Dehydration-driven stress transfer as a mechanism for lower Wadati-Benioff earthquakes

*Ferrand Pascal Thomas¹, Nadège Hilairet², Sarah Incel¹, Damien Deldicque¹, Julien Gasc^3,4, Loïc Labrousse⁵, Joerg Renner⁶, Yanbin Wang⁴, Alexandre Schubnel¹ (1.Ecole Normale Supérieure, UMR 8538, PSL Research University, Paris, 75005, France, 2.Unité Matériaux et Transformations, UMR 8207, Villeneuve d'Ascq, 59655, France, 3.Géosciences Montpellier, 34090, France, 4.GeoSoilEnviroCARS, University of Chicago, Argonne, IL 60439, USA, 5.Institut des Sciences de la Terre de Paris, Univeristé Pierre et Marie Curie, Paris, 75005, France, 6.Institut für Geologie, Mineralogie und Geophysik, Ruhr Universität Bochum, 44780, Germany)

Keywords:Antigorite, Olivine, Earthquakes, Mantle, Lower Wadati-Benioff Plane, Pseudotachylyte

Although extensively documented, intermediate-depth earthquakes (40-400 km) within subducting oceanic slabs remain enigmatic. Here we reconcile more than a decade of apparently contradictory experimental studies on the possible link between these earthquakes and serpentine dehydration. We show that for realistic compositions, antigorite dehydration triggers dynamic embrittlement of sintered olivine-antigorite aggregates deformed at confining pressure and temperature conditions representative of intermediate-depth seismicity (1 to 3.5 GPa, 500 to 800°C). At 1.1 GPa pressure, dehydration of antigorite in volume proportion as low as 5% triggers dynamic shear failure of the olivine load-bearing network. For higher contents, deformation remains silent and distributed. At 3.5 GPa pressure, acoustic emissions are observed for mixtures with up to 50% antigorite. In both cases, dehydration of antigorite proportion as low as 5% is sufficient to trigger analogs of lower Wadati-Benioff earthquakes in the laboratory. Intermediate-depth seismicity could therefore ultimately be seen as an indicator for the degree of hydration in subducting lithospheric mantle.