Although the inner core is solid (unlike the liquid outer core) and denser than the lower mantle, seismological models (e.g., PREM) show it has anomalously low shear rigidity and seismic wave velocities compared to the lower mantle, because metallic iron-nickel alloy under core conditions has an intrinsically lower shear modulus relative to its density compared to silicate mantle rock.
Standard Earth models (e.g., Preliminary Reference Earth Model) show that despite being solid and very dense, the inner core has notably lower P- and S-wave...
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