Geoacoustic Estimation of the Seafloor Sound Speed Profile in Deep Passive Margin Setting Using Standard Multichannel Seismic Data

Abstract

Seafloor geoacoustic properties are important in determining sound propagation in the marine environment, which broadly affects sub-sea activities. However, geoacoustic investigation of the deep seafloor, which is required by the recent expansion of deep-water operations, is challenging. This paper presents a methodology for estimating the seafloor sound speed, c0, and a sub-bottom velocity gradient, K, in a relatively deep-water-compacting (~1000 m) passive-margin setting, based on standard commercial 2D seismic data. Here we study the seafloor of the southeastern Mediterranean margin based on data from three commercial seismic profiles, which were acquired using a 7.2 km-long horizontal receiver array. The estimation applies a geoacoustic inversion of the wide-angle reflections and the travel times of the head waves of bending rays. Under the assumption of a constant positive K, the geoacoustic inversion converges to a unique set of parameters that best satisfy the data. The analysis of 24 measurement locations revealed an increase in the average estimates of c0 from 1537 ± 13 m s−1 to 1613 ± 12 m s−1 for seafloor depths between ~1150 m and ~1350 m. K ranged between 0.75 and 0.85 m s−1 with an average of 0.80 ± 0.035 s−1. The parameters were consistent across the different locations and seismic lines and they match the values that were obtained through depth-migration-velocity analysis and empiric relations, thereby validating our estimation methodology.

Modeling Techniques for Underwater Acoustic Scattering and Propagation (Including 3D Effects)

“…Papers of the second type are related to applications of underwater acoustics where the models of sound propagation play a significant role [8][9][10][11]. These include geoacoustic inversion [9], source-bearing estimation [8], a technique that allows one to estimate both the source position and the media properties [11], and the problem of estimating the acoustic noise levels over some water areas neighbouring the source [10].…”

“…Papers of the second type are related to applications of underwater acoustics where the models of sound propagation play a significant role [8][9][10][11]. These include geoacoustic inversion [9], source-bearing estimation [8], a technique that allows one to estimate both the source position and the media properties [11], and the problem of estimating the acoustic noise levels over some water areas neighbouring the source [10]. For example, the novel geoacoustic inversion technique from [9] requires the precise calculation of ray paths (which is performed using the BELLHOP code) that are necessary to estimate travel times of head waves.…”

“…These include geoacoustic inversion [9], source-bearing estimation [8], a technique that allows one to estimate both the source position and the media properties [11], and the problem of estimating the acoustic noise levels over some water areas neighbouring the source [10]. For example, the novel geoacoustic inversion technique from [9] requires the precise calculation of ray paths (which is performed using the BELLHOP code) that are necessary to estimate travel times of head waves. Source image methods are used in [8] to analyze the effect of horizontal refraction onto the source bearing estimation.…”