Vibroseis Operations in an Urban Environment

For a period of several years, a fleet of truck-mounted vibrators (Vibroseis equipment) was used for geophysical exploration in the highly populated metropolitan centers of the Los Angeles Basin. It was planned to operate the equipment within distances as small as 10 ft from many types of buildings and other facilities. It was therefore necessary to evaluate the damage potential of surface vibrations generated by this equipment, and to predict the vibration intensities for different operating conditions and for different distances. Throughout the course of the work, the vibrators passed within a perceptible range of several million people in the area. Such a proximity of vibration sources to so many people and properties is rare. The attenuation characteristics of the vibrations were compared to those of theoretical point sources and conventional explosives sources and were seen to be characteristic of a seismic line source, of the form: ![Formula][1] In response to allegations of damage to residences near the beginning of the project, full-time vibration monitoring was instituted, criteria were developed for the prevention of actual damage, and a public relations program was put into effect in order to minimize allegations of damage. A few loose objects toppled close to the vibration sources, but there was only one instance of minor damage, consisting of aggravation of a previously existing break in an old wood beam. Strains generated in nearby structures were far less intense than those from common environmental sources. [1]: /embed/graphic-1.gif