Dehydration and earthquakes in the subducting slab: empirical link in intermediate and deep seismic zones

Abstract

In this study, a close link between the depth-distribution of subduction-zone earthquakes and dehydration events in the hydrated slab-peridotite is established. A phase diagram up to 27 GPa in the MgO–Al 2O 3–SiO 2–H 2O (MASH) system was constructed using a combination of thermodynamic calculation and Schreinemakers analysis on previous experimental data. At intermediate-depths (<250 km), dehydration of antigorite, talc, brucite, clinochlore, and Mg-sursassite occur. In the 200–500 km depth-range, dehydrations of Mg-sursassite and brucite+phase D are possible. Dehydration of brucite and dense hydrous Mg-silicates (phase E, D and superhydrous phase B) occurs in the mantle-transition zone. Since conditions for dehydration are dependent on slab temperature, we constructed diagrams illustrating the distribution patterns of dehydration events at several model slab-temperatures. In parallel to the mineralogical study, the depth-distribution of global subduction-zone earthquakes are compiled into a thermal parameter-depth diagram and compared with the dehydration event distributions determined previously. The distribution of dehydration events and earthquakes are comparable in terms of: (1) non-linear correlation between the maximum depth of earthquake and temperature of the slab, (2) an aseismic zone at 300–600 km depth in medium- T subduction zones, and (3) lack of deep-earthquakes in young subduction-zones. Considering those links, we propose an extended dehydration-induced earthquake (EDIE) hypothesis that considers any dehydration event has a potential to induce earthquakes in the subducting slab peridotite.