Transmission of marine seismic survey, air gun array signals in Australian waters

Abstract

Measurements of the transmission of seismic survey signals in Australian waters are presented. The measured transmission loss showed: high variability of received signal sound exposure level at similar ranges when comparing all surveys (mean of standard deviation across ranges of 3-12 dB); high variability within a seismic survey (mean of standard deviation at any range of 2-4 dB); typical shot-shot variability of 1-3 dB (mean of standard deviation at any range) possibly produced by gun strings moving around; the importance of bathymetry profiles, seabed types and sound speed profiles in determining air gun transmission; different transmission regimes for open ocean, continental shelf and shelf-slope environments; seismic source energy transmitted at longer ranges ( < 1 km) was most commonly dominated by low frequency ( < 500 Hz) energy and only at short range ( > 1 km) was high frequency energy observed; and that a considerable amount of air gun array energy may directly excite the seabed, couple into the seabed and travel horizontally, or by way of interface waves. For locations on the shelf or shelf slope around southern and Western Australia the presence of limestone or calcarenite seabed types are critical in accurately determining seismic signal transmission.