Page 12 - 2016Winter

Robert C. Gisiner
Postal:
International Association of Geophysical Contractors 1225 North Loop West, Suite 220 Houston, Texas 77008 USA
Email:
bob.gisiner@iagc.org
Sound and Marine Seismic Surveys
Underwater sound has been used for over 50 years in marine geological research and exploration.
Introduction
Sound has been used as a tool for imaging geological structure on land and in wa- ter for more than 50 yrs (Figure 1). Compressed air sources, referred to as airguns, have been the dominant marine sound source since the 1960s (Parkes and Hatton, 1986). Whether on land or in the water, the basic principle is that the acoustic energy from the sound source is reflected and refracted by the rock layers beneath the surface back to the receivers, thereby enabling geophysicists to reconstruct an “image” of the underlying geology, in a way that is analogous to medical ultrasonic imaging (Figure 2).
On land, the acoustic energy comes from buried explosives or vibratory sources that are in contact with the ground, returned vibrations are received by geophones (Sheriff and Geldart, 1995). Little or no energy is transmitted to the air to be per- ceived as sound.
Figure 1. A synoptic view of six decades of offshore seismic survey activity in Australia, color- coded by decade, to illustrate the extensive use of seismic surveys in oil- and gas-producing regions of the world. Box on bottom right suggests less activity, but it only covers the first four years of the current decade. From Knuckey et al. (2016), with permission from the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) and Fisheries Research and Development Corporation (FRDC).
10 | Acoustics Today | Winter 2016 | volume 12, issue 4 ©2016 Acoustical Society of America. All rights reserved.