Page 38

2015-6

SURROUND SOUND Seismic Exploration By Dr . L a r r y Ca h o o n Seismic exploration is the first major step in identifying areas with the potential to hold oil and gas. It is important to recognize seismic techniques, which involve producing and measuring the reflection of sound waves off of layers of sediment and rock below the sea bottom, do not identify oil and gas directly. Rather, seismic exploration identifies geological formations that might hold oil and gas, based on what technical experts know about the reservoir capacity of different rocks and the likely heat and pressure condi-tions to which those rocks have been exposed. Seismic exploration techniques have evolved since the last round of exploration off North Carolina in the late 1970s. Ships tow air guns that send powerful sound waves toward the bottom and strings of hydrophones that detect the reflected sound along survey lines. The sound imagery derived from modern seismic surveys is far more sophisticated than what was possible 35 years ago. That’s partly because the hydrophones are better and partly because the data processing algorithms and capabilities are far superior. The primary concerns about seismic exploration derive from the intense sound produced by air guns and the impacts on marine fauna. Most of the energy from an air gun has a low frequency range that penetrates soil and rock well, but some energy occurs in mid-frequency ranges more important to marine mammals for hearing and communication. The intensity of the sound, especially in close proximity to the air guns, is also a concern. Oceanographic conditions can actually concentrate sound energy in what submari-ners call the layer, where mammals listening for predators and prey might lurk. One of the major issues about seismic exploration impacts is the gap between what we know and what we need to know. Industry claims there is no evidence of significant impacts on marine life by seismic exploration. But few studies have actually examined those impacts and very few properly controlled studies have ever been conducted. We do know there is evidence of harm from loud sound in some cases, and that many marine organisms, not North Atlantic right whales, photographed here by University of North Carolina Wilmington researchers in November 2009, migrate along the US East Coast during the winter. Researchers say the whales travel south to calving grounds off the coast of Georgia, South Carolina and North Carolina. Few studies have been conducted to measure how seismic testing would affect these whales — one of the most endangered in the world with only about 500 remaining — in their birthing grounds. 38 WBM june 2015 PHOTO COLLECTED BY UNIVERSITY OF NORTH CAROLINA WILMINGTON UNDER NOAA SCIENTIFIC PERMIT #948-1692-00 PHOTO COURTESY OF THE UNIVERSITY OF NORTH CAROLINA WILMINGTON MARINE MAMMAL STRANDING PROGRAM


2015-6
To see the actual publication please follow the link above