transition zone

1. A region within the upper mantle bordering the lower mantle, at a depth of 246-600 miles (410-1000 kilometers), characterized by a rapid increase in density of about 20% and an increase in seismic wave velocities. 2. A region within the outer core, transitional to the inner core.

Related terms:

• Low-Velocity Zone
• ultralow-velocity zone
• hyperacoustic zone
• Benioff zone
• shadow zone
• S wave
• P wave
• auroral zone blackout
• epipelagic zone
• sublittoral zone