We compare signals recorded on hard-rock seismographic stations in Sudbury, Ontario, to those recorded in caverns below the surface stations, in the Sudbury Neutrino Observatory. Signals from shallow local events show strong apparent amplification of ground motion observed on the surface relative to those recorded at depths of 1.4–2.1 km; the amplification peaks near 2.1 Hz, where it is on average a factor of 3 to 5. The peak narrows, decreases in amplitude, and shifts toward lower frequencies (0.8–1 Hz) for regional and teleseismic events. The peak in apparent amplification for the local events is attributed to a strong Rg phase from shallow events at close distances. The frequency shift and decay of the amplitude of this peak for more distant events reflects the rapidly-diminishing influence of the higher-frequency components of this phase with distance, coupled with the increasing importance of shear-wave phases.

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