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 Ocean Bottom Seismometers (OBS) array recordings of ambient vibrations presents three additional challenges: (1) the localization of sensors, (2) the orientation of the OBS horizontal components, and (3) the clock error. Here, we address these challenges in an inherent preprocessing workflow to ultimately extract the Love and Scholte wave DC from small aperture OBS array measurements performed between 2018 and 2020 in Lake Lucerne (Switzerland). The arrays have a maximum aperture of 679 m and a maximum deployment water depth of 81 m. The challenges related to the OBS location on the lake floor are 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 are complemented by airgun surveys. Airgun data are first used to estimate the misorientation of the horizontal components of the OBS and second to estimate the clock error. To assess the robustness of the preprocessing workflow, 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 Scholte and Love waves for one of the OBS array sites. The results show the effectiveness of the preprocessing workflow. We observe the phase-velocity dispersion curve branches in the frequency range between 1.2 and 3.2 Hz for both array processing techniques.
Highlights
As part of the initiative to assess the hazard of earthquake-induced tsunamis at Lake Lucerne (Switzerland), an extensive Ocean Bottom Seismometer (OBS) campaign was carried out to measure seismic ambient vibrations on subaqueous slopes
For testing the robustness of the preprocessing workflow, the threecomponent High Resolution Frequency-Wavenumber (3C-HRFK; Poggi and Fah 2010) and the Interferometric Multichannel Analysis of Surface Waves (IMASW; Lontsi et al 2016) techniques are applied to the data of one OBS array site
By using a combination of the multibeam bathymetry, the backscatter map, and the differential GPS data at deployment and recovery, we can uniquely identify the position of the OBS on the lake floor with an uncertainty of 1.3 m for the NAMMU and 2.15 m for the LOBSTER
Summary
As part of the initiative to assess the hazard of earthquake-induced tsunamis at Lake Lucerne (Switzerland), an extensive Ocean Bottom Seismometer (OBS) campaign was carried out to measure seismic ambient vibrations (and earthquakes) on subaqueous slopes. With the advances in offshore seismic instrumentation, that include for example Ocean Bottom Seismometers (Webb 1998; Stahler et al 2016; Hannemann et al 2017; Shynkarenko et al 2021), high quality seismic data are emerging from the offshore environments for subsurface structure analysis These data aid us to characterize the sediments of the lake/ocean bottom and to assess the volume of sediment prone to failure. For testing the robustness of the preprocessing workflow, the threecomponent High Resolution Frequency-Wavenumber (3C-HRFK; Poggi and Fah 2010) and the Interferometric Multichannel Analysis of Surface Waves (IMASW; Lontsi et al 2016) techniques are applied to the data of one OBS array site. The dispersion curve estimation at additional OBS array sites and their inversion results are presented in Shynkarenko et al (2021)
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