CURRENT ABSOLUTE PLATE MOTION FROM SEISMIC ANISOTROPY

The orientation of seismic anisotropy inferred from shear-wave splitting in many places may indicate the direction of the motion of the lithosphere relative to the sub-asthenospheric mantle. To estimate the absolute plate motion, Kreemer (2009) compiled a data set of 474 shear-wave splitting data, which we refer to as the SKS data set. When we invert these data in a manner similar to his, but using the MORVEL relative angular velocities, we find that the azimuth residuals of SKS-MORVEL are strongly correlated within each plate and do not have zero mean for each plate. Moreover the data for four of the eleven plates with data show no central tendency.

We adopt SKS7, a subset of the SKS data set from the seven plates evidencing a preferred orientation, and invert them while accounting for the within-plate correlated errors in the shear-wave splitting data. The resulting two global sets of angular velocities, SKS7a-MORVEL and SKS7v-MORVEL, are similar to each other. The net-rotation of the lithosphere is 0.24±0.05º/Ma [95% c.l.] of SKS7a-MORVEL, and 0.31±0.06º/Ma [95% c.l.] of SKS7v-MORVEL. These angular velocities will be compared with those estimated from the hotspot frame of reference. Implications for flow in the sublithospheric mantle will be discussed.