GeologyRocks

The asthenosphere is the region of the inner structure of the Earth between 100-200 km below the surface that is the weak or "soft" zone in the upper mantle. It lies just below the lithosphere, which is involved in plate movements and isostatic adjustments. The layer is best thought of as "plastic" in that it is solid, but deforms over time. Just above the asthenosphere is the Moho (or Mohorovičić Discontinuity). Seismic waves pass relatively slowly through the asthenosphere, the cue that originally alerted seismologists to its presence; thus it has been given the name low-velocity zone.