The Chilean Mantle Wedge seismicity as a marker for serpentinization.

The mantle wedge seismicity of the Atacama segment of the Northern Chilean subduction, a region with complex slab geometry, has recently been mapped in a high-density seismicity catalog. In order to better constrain the underlying mechanisms responsible for its occurrence, we investigate the spatio-temporal evolution of the seismicity along the plate interface and within the overriding (upper) plate. We find that the b-value of the mantle wedge seismicity is consistently greater than 1, averaging around 1.5, and that for earthquakes of similar magnitude, there are few, if any, aftershocks in the mantle wedge compared to the interface seismicity. We also estimate the seismic wave velocities Vp and Vs according to the amount of serpentinization and compare to the results of recent high quality tomography images. We estimate that the region of active seismicity, located mainly between 450-550°C isotherms, corresponds to a partially serpentinized part of the mantle wedge while the corner of the cold nose, which corresponds to a fully serpentinized zone, is deprived from earthquakes.