Characterizing the upper mantle Low-velocity-layer atop the 410km discontinuity beneath Southern Peru from S-to-P conversions

A low-velocity-layer (LVL) atop the 410 km discontinuity has been widely detected and often attributed to dehydration melting by water release from the mantle transition zone (a major water reservoir in the deep Earth), which is thus thought to be a ubiquitous signature; however, such a LVL has not been frequently observed in South America. In this study, we find evidence for the existence of a LVL beneath Southern Peru from source-side S-to-P converted phases, which were generated from two intermediate depth earthquakes in this area and recorded by the USArray. The S-to-P phases behavior as prominent later arrivals after the direct P, and their slowness is slightly lower than that of P. By constraining the relative traveltimes, slownesses and amplitudes, our analyses conclude that the LVL is characterized with approximately 10% velocity reduction occurring at its top interfaces around 340- and 380-km depths beneath two locations, respectively. Our observations thus not only play a role in complementing those of other seismic results, including receiver functions from previous studies, but also demonstrate that searching for source-side conversion phases can be used to other places, in particular beneath subduction zones where have not been studied by seismic experiments.