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Abstract

Certain travel time readings in shallow engineering seismology can be attributed to a seismic wave which has propagated through the air, but in which the energy has been transmitted into the ground before reaching the detector. Waveform evidence for this conclusion is presented, based upon the effects of altering the source conditions to delay the direct wave and of embedding the geophone in sound-absorbent material. Erroneously large depths may be computed if these air wave readings are interpreted as readings produced by direct waves through the ground. Potential difficulty exists only if velocity in the near-surface material is less than 330 meters/second (1100 feet/second).