Gutenberg Discontinuity

(seismic wave guide), the stratum in which seismic waves move at decreased velocities in the upper mantle of the earth. It is named after B. Gutenberg, who discovered the existence of the stratum. The upper boundary of the Gutenberg discontinuity is 80–100 km beneath the continents and about 50 km beneath the oceans. The lower boundary seems to be at a depth of about 400 km. In certain places the Gutenberg discontinuity is absent or only the velocities of transverse seismic waves are decreased. It is conjectured that the cause of the slower passage of seismic waves is a large geothermal gradient, or a temperature close to the melting point. This gives reason to equate the Gutenberg discontinuity with the asthenosphere.