9725601 Abers This research will test hypotheses regarding the fate of subducting slabs, by means of seismic methods to globally characterize subducted crust. At intermediate depths of 70- 300 km, subducting plates undergo a series of transformations in both compositional and mechanical properties. The transformations play a critical role in earthquake genesis, arc magmatism, plate densification, and material recycling in the mantle. Frequency-dependent behavior, or dispersion, of regional seismic body waves is generated in slabs as they interact with subducted crust and other interfaces, and so is a highly sensitive indicator of the composition of subducted crust and surrounding mantle. Previous observations show strong discrepancies in the mode of dispersion of waves through the Tonga slab compared to Japan and Alaska, suggesting remarkably different velocity structures - high frequencies arrive early in Tonga, and late in Japan and Alaska. This research will characterize that dispersion and how it varies globally between slabs. ***
