Seismic anisotropy beneath the Lau back-arc basin inferred from sScS-ScS splitting data

We determine upper mantle anisotropy just beneath active basins by comparin g ScS and sScS waveform splitting. We have measured sScS-ScS shear-wave spl itting with data from the SPANET and GSN seismic networks. The observed sSc S-ScS shear-wave splitting suggests that there is a large lateral variation of anisotropy beneath the Lau back-are basin. ScS- and sScS-waves which sa mple the southern part of the Lau basin show small splitting. In contrast, the northern part of the Lau basin, which is characterized to be tectonical ly active, is observed to have large seismic anisotropy with a WNW-ESE dire ction. The cause of anisotropy may be related to the mantle dynamics of the active basin.