The amplitude of ambient earth noise is investigated as a function of depth for several models. The noise radiating in the layers is described hypothetically by combinations of Rayleigh-wave modes with a prescribed form of energy partition.The anomalously low shear velocity of alluvium or weathered zones at the earth's surface tends to produce larger amplitudes (+6 db) at the free surface, and smaller amplitudes (as much as -20 db) at the base, as compared to an arbitrarily defined 'continental' structure consisting only of the more competent rocks. Results further indicate that the low-velocity layers must reach a critical thickness before large attenuations at depth can be expected.

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