Workflow for robust Scholte and Love waves phase-velocity estimation from small aperture Ocean Bottom Seismometer arrays in Lake Lucerne: deployment, location, orientation, and clock error correction

Abstract The phase-velocity dispersion curve (DC) is an important characteristic of the propagation of surface waves in sedimentary environments. Although the procedure for DC estimation in onshore environments using ambient vibration recordings is well established, the DC estimation in offshore environments using arrays of Ocean Bottom Seismometers (OBS) presents three main challenges. These are the localization, the orientation of the OBS horizontal components, and the clock error. Here, we concentrate on the workflow for a robust estimation of the phase-velocity dispersion curves from small aperture OBS array measurements in Lake Lucerne (Switzerland). OBS array campaigns were performed between 2018 and 2020 using arrays with a maximum aperture of 679 m at a maximum water depth of 81 m. The challenges related to the OBS location on the lake floor were addressed by combining the multibeam bathymetry map and the backscatter image for the investigated site with the differential GPS coordinates of the OBS at recovery. The OBS measurements were complemented by airgun surveys. Airgun data were first used to estimate the misorientation of the horizontal components of the OBS and second to estimate the clock error. Finally, we use two array processing methods, namely the three-component high-resolution frequency-wavenumber and the interferometric multichannel analysis of surface waves, to estimate the dispersion characteristics of the propagating surface waves for one of the array sites. We clearly observe the phase-velocity dispersion curve branches for Scholte and Love waves in the frequency range between 1.2 and 3.2 Hz for both array processing techniques.