INITIAL RESULTS FROM THE ICEMELT EXPERIMENT - BODY-WAVE DELAY TIMES AND SHEAR-WAVE SPLITTING ACROSS ICELAND (VOL 23, PG 459, 1996)

We present results from the first stage of the ICEMELT broadband seism ometer experiment designed to determine upper mantle structure beneath Iceland, a hotspot located on the Mid-Atlantic Ridge. Relative delays of teleseismic body waves across Iceland are in excess of 1 s for P w aves and as large as 3 s for S waves. The patterns of P and S wave del ays suggest a low-velocity anomaly in the upper few hundred kilometers (100-350 km) beneath central Iceland, consistent with the signature o f mantle upwelling beneath a hotspot. Shear-wave splitting measurement s of the fast polarization direction phi and the delay time delta t be tween the fast and slow shear waves have been obtained at several netw ork stations. Splitting times range from 0.7 to 1.7 s, and fast direct ions are generally between N20 degrees W and N45 degrees W. While spli tting times of this magnitude must be primarily signatures of the anis otropy of the Icelandic upper mantle, the directions of fast polarizat ion are inconsistent with simple models of horizontally diverging flow either in the plate spreading direction or radially from the center o f the hotspot. A hypothesis consistent with splitting data obtained to date is that the dominant contribution to upper mantle anisotropy is from the large-scale mantle flow field of the North Atlantic.