Poisson’s ratio structure and three-dimensional P wave velocity structure beneath the profile across the Gakkel ridge 85°E axis

During active-source 2D marine ocean bottom seismic exploration, significant deviations of shot lines from the designed survey lines can introduce errors in 2D structural models, particularly in areas with rough bathymetry, such as mid-ocean ridges. By employing 3D tomography, it is possible to construct a three-dimensional model of the survey area that incorporates the actual shot locations and Ocean Bottom Seismometer (OBS) positions, leading to more accurate velocity structure models.

In 2021, the Joint Arctic Scientific Mid-Ocean Ridge Insight Expedition (JASMInE) acquired high-quality OBS data from the Gakkel Ridge in the Arctic Ocean. However, due to the presence of dense floating ice, significant offsets occurred between the shot lines and the OBS station profiles. Consequently, applying a 3D tomography-based modeling approach is essential for imaging the velocity structure in this region.

This study utilized the JIVE3D software to develop a 3D P-wave velocity model along a profile perpendicular to the 85°E spreading axis of the Gakkel Ridge, based on high-resolution multibeam bathymetry data. Compared to the velocity structure derived from 2D modeling, the P-wave velocities beneath the spreading axis are found to be lower in the 3D model, while lateral velocity variations in the upper oceanic crust are more pronounced away from the spreading axis. Despite these differences, the overall velocity structure and crustal thickness trends are consistent, indirectly validating the reliability of the 2D structural model.

Based on this 2D P-wave model, with data of 1257 S-wave arrival times picked from 9 OBS stations along the profile perpendicular to the mid-ocean ridge, using a forward modeling trial-and-error approach, a preliminary Poisson’s ratio structure beneath the profile was obtained. The Poisson’s ratio in Layer 2 of the oceanic crust ranges from 0.36 to 0.40, with relatively lower values beneath the spreading axis. In Layer 3, the Poisson’s ratio varies from 0.28 to 0.38. The relatively higher Poisson’s ratio values may indicate the presence of abundant fractures or fluids within the oceanic crust in this region.