1.5D inversion of lateral variation of Scholte-wave dispersion

Reliable models of in-situ shear-wave velocities of shallow-water marine sediments are important for geotechnical applications, lithological sediment characterization, and seismic exploration studies. We infer the 2D shear-wave velocity structure of shallow-water marine sediments from the lateral variation of Scholte-wave dispersion. Scholte waves are recorded in a common receiver gather generated by an air gun towed behind a ship away from a single stationary ocean-bottom seismometer. An offset window moves along the common receiver gather to pick up a local wavefield. A slant stack produces a slowness-frequency spectrum of the local wavefield, which contains all modes excited by the air gun. Amplitude maxima (dispersion curves) in the local spectrum are picked and inverted for the shear-wave velocity depth profile located at the center of the window. As the window continuously moves along the common receiver gather, a 2D shear-wave velocity section is generated. In a synthetic example the smooth lateral variation of surficial shear-wave velocity is well reconstructed. The method is applied to two orthogonal common receiver gathers acquired in the Baltic Sea (northern Germany). The inverted 2D models show a strong vertical gradient of shear-wave velocity at the sea floor. Along one profile significant lateral variation near the sea floor is observed.