The Cascadia Initiative deployed 70 seabed seismometers at 120 sites covering the entire Juan de Fuca plate to record mantle movement relative to the plate. Team members have confirmed what geophysicists expected, but one surprise is that a small appendage called the Gorda Plate moves independently of the Juan de Fuca, apparently too light to influence the mantle flow 100 miles down. This could explain earthquake segmentation at the subduction zone....