Effects of low-velocity layers

Abstract

Effects of low-velocity channels in the atmosphere, the ocean and the solid earth are discussed. There are two major low-velocity channels in the atmosphere, one with its axis at the tropopause, and another at a height of about 80 km. They produce “zones of silence” and permit the transmissions of waves involving the whole atmosphere. Low-velocity layers in the ocean result from the combined effects of temperature, pressure and salinity. In the earth, the sudden decrease of velocity at the boundary of the core produces a low-velocity at the boundary of the core produces a low-velocity channel for elastic waves. In the earth's crust there are two major low velocity shannels, one below theMohorovicic discontinuity, the other at a depth of about 15 Km. Misinterpretation of their effects has caused incorrect conclusions concerning the structure of the outer portion of the earth's mantle.