Asthenosphere
The ductile, mechanically weak, deformable upper mantle layer located directly beneath the rigid lithosphere.
Governing formula
Seismic Low-Velocity Zone (LVZ): Depth ~ 100–250 km
SI unit
Pa·s (Mantle Viscosity ~10¹⁹–10²¹ Pa·s)
In depth
High temperatures and pressures near silicate melting points cause solid asthenosphere rock to deform plastically via slow creep, allowing lithospheric plates to slide across it.
Examples in the real world
Seismic P and S waves slowing down in the asthenospheric Low-Velocity Zone due to partial melting.