Mantle layering from ScS reverberations 2. The transition zone

The second paper in a four-part sequence that examines the nature of mantle layering using the ScS_n phases and internal reflections observed within the reverberative interval of SH-polarized seismograms. Mantle reflectivity profiles for 18 seismic corridors sampling portions of Indonesia, Australia, and the western and central Pacific are constructed from low-frequency (25-mHz) ScS reverberations; i.e., ScS_n-type phases reflected once from internal mantle discontinuities. Modeling the reflectivity profiles using synthetic seismograms yields precise, path-specific estimates of the travel times to the 410-km and 660-km discontinuities and their reflection coefficients. The data are consistent with an olivine-dominated model of the transition zone, marked by two major phase transitions having average apparent depths of 414 ± 2 km and 660 ± 2 km and impedance contrasts of 0.046 ± 0.010 and 0.072 ± 0.010, respectively. -from Authors