First images and orientation of fine structure from a 3-D seismic oceanography data set

Abstract

Abstract. We present 3-D images of ocean fine structure from a unique industry-collected 3-D multichannel seismic dataset from the Gulf of Mexico that includes expendable bathythermograph casts for both swaths. 2-D processing reveals strong laterally continuous reflections throughout the upper ∼800 m as well as a few weaker but still distinct reflections as deep as ∼1100 m. We interpret the reflections to be caused by reversible fine structure from internal wave strains. Two bright reflections are traced across the 225-mwide swath to produce reflection surface images that illustrate the 3-D nature of ocean fine structure. We show that the orientation of linear features in a reflection can be obtained by calculating the orientations of contours of reflection relief, or more robustly, by fitting a sinusoidal surface to the reflection. Preliminary 3-D processing further illustrates the potential of 3-D seismic data in interpreting images of oceanic features such as internal wave strains. This work demonstrates the viability of imaging oceanic fine structure in 3-D and shows that, beyond simply providing a way visualize oceanic fine structure, quantitative information such as the spatial orientation of features like fronts and solitons can be obtained from 3-D seismic images. We expect complete, optimized 3-D processing to improve both the signal to noise ratio and spatial resolution of our images resulting in increased options for analysis and interpretation.

Seismic reflection imaging of shallow oceanographic structures

“…This represents an improvement of two orders of magnitude compared to conventional oceanographic methods. During the last several years, SO has been extensively used for the studies of the following: (i) fine scale structures associated with thermohaline intrusions [Holbrook et al, 2003], thermohaline staircases [Biescas et al, 2010;Fer et al, 2010] and internal gravity waves [Holbrook and Fer, 2005;Krahmann et al, 2008;Holbrook et al, 2009;Blacic and Holbrook, 2010]; (ii) mesoscale structures such as current flows [Tsuji et al, 2005;Nakamura et al, 2006;Mirshak et al, 2010], and eddies and meddies [Biescas et al, 2008;Quentel et al, 2010;Ménesguen et al, 2012].…”

Temporal and spatial variations in three-dimensional seismic oceanography

“…This is not always possible for the water column because of the temporal variation. Narrow aperture 3D multiparametric stack (Bakhtiari Rad and Macelloni, 2020) or swath-by-swath common mid-point 3D stacking (Blacic and Holbrook, 2010) can both be used to create 3D seismic oceanographic images because both implement a time-dependent selection for the seismic data. However, the processing workflow for 3D seismic oceanography can be case-dependent, and we suggest to perform always an in-depth temporal analysis to avoid to sum time-inconsistent seismic data.…”

“…While it is possible to acquire a dense, high-resolution grid of 2D lines, such grids are fundamentally different from a native 3D seismic survey (Lonergan and White, 1999;Yilmaz, 2001). The close line spacing of 3D seismic and the physical illumination of the subsurface from multiple offsets and multiple azimuths remove spatial aliasing problems inherent to 2D seismic data, therefore have the potential to yield better spatial resolution, useful for 3D seismic oceanography (Blacic and Holbrook, 2010). To date, 3D seismic oceanography is not well developed, which can be due to multiple facts: the 3D seismic data are very expensive to acquire, there is an interdisciplinary gap between oceanography and geophysics, and most importantly, a fundamental understanding of capability of 3D seismic oceanography is missing.…”

Temporal and spatial variations in three-dimensional seismic oceanography

“…However, studies reveal that these reflections correspond to ocean thermohaline structures (Nandi et al, 2004;Nakamura et al, 2006) and are primarily (not completely) associated with temperature gradient (Ruddick et al, 2009). This new cross-discipline, between exploration seismology and physical oceanography, has come to be known as seismic oceanography (Holbrook et al, 2003) and has been successfully applied to imaging mesoscale and sub-mesoscale water-column structures such as ocean fronts (Gorman et al, 2018), eddies (Song et al, 2009;Tang et al, 2014a), internal waves (Holbrook et al, 2009;Tang et al, 2014b;Buffett et al, 2017), and other thermohaline fine structures (Holbrook et al, 2003). Additionally, several theoretical studies have been derived from the application of water-column seismic images including estimation of geostrophic currents (Sheen et al, 2011;Tang et al, 2014b), wave field spectra (Fortin et al, 2016), and internal wave mixing (Dickinson et al, 2017).…”