Preliminary Evidence For The Presence Of The Hainan Plume From Shear Wave Splitting Analyses Of A Temporary Seismic Array

We have analyzed SKS and SKKS data recorded from a temporary seismic array in Leizhou Peninsula, just to the north of the Hainan Island, to constrain anisotropic seismic structure in the upper mantle for the evidence of a Hainan mantle plume that had been suggested from global seismic tomography studies. The array consisting of 14 seismic stations is distributed over the entire Peninsula, which was mostly outcropped by Cenozoic basalt, and extended into the stable South China block. While shear-wave splitting is seen at most of the stations the fast polarization directions are divided into two different groups. At northern stations of the South China block, anisotropy with a NWW-SEE fast direction and about 0.9s delay time was observed, which is consistent with the overall movement of the South China block. However, at stations within the peninsula, anisotropy of a slightly smaller delay time of 0.7s was observed but most of the fast directions are aligned with a NE-SW direction, which is about 100 degrees from the fast direction at those northern stations. Assuming the observed anisotropy be resulted from the asthenospheric flow, the preliminary results of the difference in the fast direction between the stations within the peninsula and stations in the South China block indicate a different mantle flow pattern beneath these two regions. A possible explanation is the presence of a Hainan mantle plume beneath the Leizhou Peninsula, which could cause the mantle flow beneath the peninsula different from the mantle flow beneath the South China block, and therefore, the difference in the fast directions of the anisotropy of these two regions.