Slab-derived fluid storage in the crust elucidated by earthquake swarm

Abstract

Slab-derived fluids control crustal dynamics in the subduction zone. However, the slab-derived fluid budget has never been quantified beyond a geophysical and geological spatiotemporal resolution. Here, we target an intense earthquake swarm associated with the M9 Tohoku earthquake, which represented the critical dynamic behavior of slab-derived fluid. The fluid volume involved has been quantified, with a plausible range of 106−108 m3, by utilizing injection-induced seismicity insights. Comparisons with geological proxies suggest that the estimated fluid volume can be accumulated via supply from the lower crust within 102–104 y. Our study demonstrated such amount of aqueous fluid stored at the midcrustal level, which triggered consecutive swarm activity for ~2 y with the Tohoku earthquake, suggesting a possible link between earthquake swarms to M9 class earthquakes (103 y cycle) and mineral veins and deposits. This study has shed light on the quantitative understanding of the dynamic slab-derived fluid budget.