Abstract

What causes instraslab earthquakes in subduction zones? The Hellenic subduction system provides a natural laboratory for exploring this question owing to its complex structure straddling two subduction regimes. I will discuss key results from data collected across western Greece, primarily from the MEDUSA dense teleseismic array (2006-2009). This work has provided important new insight both into the subduction dynamics of the Western Hellenic Subduction Zone and into fluid processes operating in subduction zones globally. High-resolution seismic images show that subduction in western Greece transitions from rapidly retreating oceanic slab subduction in the south to slow-converging continental slab subduction in the north. Intraslab seismicity stops exactly at the transition from oceanic to continental subduction, pointing to fluids as playing a key role in the generation of these earthquakes. Closer inspection of the earthquakes reveals the existence of localized seismicity clusters at the plate interface and in the mantle wedge. These patterns of seismicity, also detected in other subduction zones worldwide, suggest that earthquakes in cold subduction zones track the migration of fluids from their source in the slab to their sink in the mantle wedge.