Seismic on floating ice on shallow water: Observations and modeling of guided wave modes

Abstract

Seismic mapping of the shallow, coastal areas of the Arctic is best facilitated in periods when the sea is covered with solid, floating ice. Data from three seismic acquisition campaigns on sea ice floating on shallow water reveal how coherent noise related to guided waves is differently exposed for various source and receiver systems placed on and below the ice. The main coherent noise is due to interference of ice flexural and Scholte waves. The experimental data were overall successfully modeled using a wavenumber integration technique. A seismic source at or near the ice generates high-amplitude, slowly propagating, and highly dispersive flexural waves. Their amplitudes are severely reduced when recorded at hydrophones deployed 5 m or more below the sea ice. The extent of flexural waves generated using an air gun below the ice similarly reduces as the depth of the air gun increases, but then the amplitudes of the seabed Scholte waves increase. Our experiments indicate that an inline line source of detonating cord on the ice combined with hydrophones deployed at the appropriate depth below the ice constitute an efficient setup for reducing the imprints of the ice flexural and Scholte waves on seismic data.

Characterization of seabed properties from Scholte waves acquired on floating ice on shallow water

“…Often V Sc = 0.9 V s is a good approximation for the Scholte‐wave velocity (Johansen et al . ). When sediment properties and correspondingly seismic velocities vary with depth the Scholte waves become dispersive and several wave modes occur.…”

“…Further details about the seismic experiments and the recording equipment can be found in Johansen et al . (2019a,b). The instrument responses were all similar to that of analogue geophones, but with a natural frequency, which varied between the different types of sensors.…”

“…Its usage for modelling guided wave modes is reported in Johansen et al . (2019a). Figure shows the synthetic seismograms, and we see that the main characteristics of the Scholte wave are reproduced.…”

“…Results from experiments on floating ice conducted by Johansen, Ruud and Hope (,b) show that guided waves along the seabed referred to as Scholte waves can be generated either using an explosive source at the surface of the ice or using an air gun below when the water depth is relative shallow.…”