Constraining outermost core velocity with SmKS waves

SmKS waves (m=2,3,4), seismic waves that travel as S‐waves in the mantle, P‐waves in the core, and reflect (m‐1) times on the underside of the core‐mantle boundary, are well‐suited for constraining outermost core V_P structure. This is due to closeness of the mantle paths and also the shallow depth range these waves travel in the outermost core. High quality digitized WWSSN and Canadian network recordings from a deep focus Java Sea event which sample the outer core beneath the northern Pacific, the Artic, and northwestern North America (roughly ⅛th of the globe), are utilized as an example to show the strength of SmKS waves to resolve outermost core structure. S3KS‐S2KS and S4KS‐S3KS differential travel times were measured and compared to those from reflectivity synthetics created from core models of past studies. Constraints and uncertainties in outer core structure using SmKS are discussed. For the event studied, the PREM core model, with possibly a small V_P decrease in the outermost 50 km of the core, provides a good fit to the data.