In modern subduction zones—regions around the world that have one tectonic plate sliding past another—one area can act like molasses for seismic waves. These anomalous areas are called low-velocity zones, or LVZs. In these zones, seismic waves are up to three times slower than waves that whiz through the surrounding rock. Some scientists suggest that the slowdown is because the downgoing plate maintains an undeformed top layer, whereas other researchers propose that intense deformation between the two huge plates causes LVZs.
Click here for original story, Unearthing the cause of slow seismic waves in subduction zones
Source: Phys.org