Using overlapping sonobuoy data from the Ross Sea to construct a 2D deep crustal velocity model

Abstract

Sonobuoys provide an alternative to using long streamers while conducting multi-channel seismic (MCS) studies, in order to provide deeper velocity control. We present analysis and modeling techniques for interpreting the sonobuoy data and illustrate the method with ten overlapping sonobuoys collected in the Ross Sea, offshore from Antarctica. We demonstrate the importance of using the MCS data to correct for ocean currents and changes in ship navigation, which is required before using standard methods for obtaining a 1D velocity profile from each sonobuoy. We verify our 1D velocity models using acoustic finite-difference (FD) modeling and by performing depth migration on the data, and demonstrate the usefulness of FD modeling for tying interval velocities to the shallow crust imaged using MCS data. Finally, we show how overlapping sonobuoys along an MCS line can be used to construct a 2D velocity model of the crust. The velocity model reveals a thin crust (5.5 ± 0.4 km) at the boundary between the Adare and Northern Basins, and implies that the crustal structure of the Northern Basin may be more similar to that of the oceanic crust in the Adare Basin than to the stretched continental crust further south in the Ross Sea.

Deep crustal structure of the Adare and Northern Basins, Ross Sea, Antarctica, from sonobuoy data

“…We confirm our 1D velocity models for each sonobuoy profile through finite difference modeling and depth migration of the data (Selvans et al, 2012). Smoothed and interpolated adjacent sonobuoy profiles along MCS Lines 13-19 allow us to also construct 2D velocity models, as do the more widely spaced sonobuoys along Transect 3 in the Adare Basin ('transects' are lines along which we analyze trends in crustal structure, even though they do not coincide with lines of MCS data, shown in black in Fig.…”

“…2). We use a Delaunay triangulation algorithm for the interpolation, with location (depth below seafloor and distance along the line) and velocity as vertices (Selvans et al, 2012).…”

“…Measuring this velocity at 5.5 ± 0.4 km below the seafloor may be due to thin crust at this location (e.g., Selvans et al, 2012), or may be due to a planar interface within the basement rock that is significantly tilted (>10 • ) up toward the Northern Basin (see Section 3.2). If the true maximum velocity detected with sonobuoy L14S1 is 7900 m/s (within measurement uncertainty), it is also possible that the interface is in fact the Moho, but is composed of serpentinized mantle such as is observed in the Svalbard continental margin (Ritzmann et al, 2004).…”

“…This is a companion paper to the analysis by Granot et al (2010) of the multi-channel seismic (MCS) reflection data from the same cruise. While MCS data are useful for determining the velocity of the shallowest rock layer, sonobuoy data allow us to directly measure layer velocities at depth (see Selvans et al, 2012).…”

Revised Eocene‐Oligocene kinematics for the West Antarctic rift system

“…These anomalies are truncated in the south by the E‐W Polar‐3 anomaly (Figure ) that has been inferred to be caused by igneous activity along a transfer fault [ Behrendt et al ., ; Davey et al ., ]. A recent seismic refraction study [ Selvans et al ., ] revealed an overall flat trend of seismic velocity contours across the shelf break suggesting a continuity of crustal type. The abnormally shallow bathymetry of the Northern Basin could be attributed, at least in part, to the seaward propagation of glacio‐marine sediment deposits [ ten Brink and Schneider , ] that have filled the basin, out over the oceanic crust, since its formation.…”