Seismic noise in an urban environment

The results of an experiment aimed at identifying the nature of major noise sources within an urban area are described. We found the strongest noise source to be an irrigation pump located adjacent to the geophones. The noise from the pump had a narrow bandwidth centered at 75 Hz with a duration of 5 minutes every 17 and 34 minutes during the day and night, respectively. Traffic noise was mainly restricted to between 10 and 25 Hz, with its strength decreasing between 9 p.m. and 6 a.m. Passing aircraft resulted in noise between 30 and 200 Hz lasting about 1 minute. Electrical noise was observed at the supply frequency of 50 Hz, although additional noise at 45 Hz also was observed. Given these results we recommended that acquisition within the area should be restricted to late evening or early morning, receiver locations should be selected to avoid strong localized sources of electrical and/or mechanical noise, and any cables associated with the recording system should be as short as possible (although nodal systems are preferable). If nodal systems are deployed for logistical reasons, real-time noise monitoring should be deployed to identify and avoid bursts of high-amplitude, short-duration noise.