[S-IT16] Deep Earth Sciences

[SIT16-P04] Hidden ultra–low-velocity zone beneath paleoslabs near the core–mantle boundary

*Justin Yen-Ting Ko¹, Don Helmberger², Jennifer Jackson² (1.Institute of Oceanography, National Taiwan University, Taipei, Taiwan, 2.Seismological Laboratory, California Institute of Technology, CA, USA)

Keywords:ultra-low-velocity zone, core-mantle boundary, paleoslab , iron-enriched accumulations

The understanding of the origin of structures in the lower mantle is crucial for comprehending Earth's system. In particular, the impact of subducted slabs on the Circum-Pacific lower mantle is complex due to a combination of phase transitions and upwelling areas. In this study, we uncover a strong ultra-low-velocity zone (ULVZ) near the core-mantle boundary (CMB) underneath a paleoslab by modeling core-diffracted shear waveforms from a deep event recorded at the South Sandwich Islands using USArray. Our 2-D model results indicate the presence of an NS-elongated, pile-like ULVZ with a diameter of approximately 300 km and a minimum height of 30 km. This ULVZ is characterized by a reduction of approximately 18% in shear wave velocity and is overlain by a high-velocity layer. Previous seismic and dynamic models have shown that ULVZs are consistent with iron-enriched accumulations that are pushed down by sinking slabs.