Acoustic and seismic ambient noise measurements in urban and rural areas

Abstract

Using portable sound level meters, simultaneous one-third octave spectral measurements of acoustic and seismic ambient noise as a function of frequency were conducted in different urban terrains and at two rural locations. The acoustic measurement frequency band of 6Hz–20kHz includes frequencies lower than are commonly measured in acoustic surveys, while the seismic band of 6Hz–1kHz extends to higher frequencies than most past seismic measurements. The urban acoustic measurements are dominated by traffic noise. The seismic signatures also are heavily influenced by traffic noise but exhibit more variation with respect to urban location due to the influence of subsurface conditions. For most urban measurement sites, the acoustic peak frequency was usually around 60Hz, while the peak seismic frequencies were usually less than 25Hz. The measured urban seismic spectra also tended to have more structure and variation in spectral shape from one location to another compared to the acoustic spectra, and a more rapid decline with increasing frequency, usually decreasing by about 30dB from 30Hz to 600Hz.