Determining the Environmental Impact of Marine Vibrator Technology

Open Access Report 2019

Final Report

Marine seismic surveys are conducted to study the geologic structure of the earth’s crust under bodies of water. These surveys are performed by projecting sound energy through the water column into the underlying geological layers, where the sound reflects and refracts off different rock and sediment types. Sound returning to the surface is measured and interpreted for a variety of purposes, including identifying potential hydrocarbon resources, detecting fault lines and earthquake risk zones, understanding plate tectonics, and siting renewable energy infrastructure on the seabed. Compressed air sources, referred to as seismic air guns, are the most commonly-used sound sources for marine geophysical surveys (Parkes and Hatton 1986); however, the geophysics industry has been interested in alternative seismic energy sources for many years. The adoption of vibroseis technology, used extensively on land, for marine environments was explored as early as the 1970s with limited success. In more recent years, concern about the potential impacts of seismic air gun sources on marine fauna and their habitats, and significant technology and geophysical data processing advancements, prompted the industry to re-invest in research and development of commercial marine vibroseis (MV) technology. In 2011, the Exploration and Production (E&P) Sound & Marine Life Joint Industry Programme commissioned an initial assessment of the potential effects of MV sources on marine fauna (LGL and MAI 2011). Since then, both the design and equipment testing of MV sources, and our understanding of the effects of underwater sounds on marine life have progressed. Although many uncertainties remain, advancements since 2011 warranted an updated analysis. This study builds on the previous assessment (LGL and MAI 2011) by evaluating current MV technology in the context of best available scientific knowledge of acoustic effects on marine life. JASCO Applied Sciences (JASCO), LGL Ecological Research Associates (LGL), and Robert Brune, LLC, conducted an extensive desktop study involving source signal, sound propagation, and animal movement and sound exposure modeling of a variety of MV and air gun array configurations in multiple operating environments. Operational scenarios were intentionally developed to enable the calculation and direct comparison of the modeled levels of the various sound signals received by animals (including acoustic particle motion in very shallow water), and distances to marine mammal, fish, sea turtle, and invertebrate effects thresholds. Several established guidelines for injury and behavioral exposure criteria were used to allow comparisons between criteria. The available injury criteria are directly applicable to the two sound sources and were used as prescribed by the authors. Behavioral exposure criteria directly applicable to low-frequency, non impulsive MV sounds were not available. Therefore, behavioral response thresholds derived for low frequency active sonar (LFAS), the most similar source for which guidelines have previously been developed, were used in this study. Using these criteria, this study employs models to quantitatively predict the relative potential exposure levels of two different seismic sources (MV versus air guns) in multiple configurations and operational environments, for a variety of marine species.

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