Time-distance maps demonstrating the transverse motion. Slits used to construct time-distance maps are shown by white dashed lines (left column). Numbers denote the number of each slit. Time-distance maps were constructed from the slits taken across the spine (middle column) to show the evidence of the movement in the transverse direction. The third column shows a zoomed-in view with the points fitted to the propagating pulse. The zoomed-in view is indicated by a blue rectangle in each figure in the middle column.