Assessment of Geo-Hazards to Floating Offshore Wind Farms in the US Pacific Coasts

Tayebeh S Tajalli Bakhsh, RPS, Ocean Science, South Kingstown, RI, United States, Tony LaPierre, RPS Energy, Seismic Operation, Houston, TX, United States, Kent Simpson, RPS, TX, United States, Jill Rowe, RPS ASA – USA, Ocean Science, South Kingstown, RI, United States, Malcolm L Spaulding, Univ Rhode Island, Wakefield, RI, United States, Jennifer Kay Miller, Bureau of Ocean Energy Management Herndon, Herndon, VA, United States and Daniel O'Connell, BOEM, Office of Renewable Energy Programs, Camarillo, CA, United States
The BOEM Office of Renewable Energy has funded a study to assess the potential geo-hazards from seismic activities, landslides and tsunamigenic earthquakes, gas plumes, and liquefaction in the Pacific, as threats to the installation of floating wind turbines in the geologically active and hazard-prone areas, to ensure reliable development of offshore wind projects in the US.

This study reviews seismic and co-seismic sources, seabed geologic features for the coasts of California, Oregon and Hawaii, and evaluates the potential hazards on the designated potential lease sites.To help the selection of suitable sites for windfarms, after providing a comprehensive study of potential threats to the sites, we establish suitability indices for the siting in the leasing blocks based on the factors and their importance (associated weight) chosen for each region. The slope gradient is calculated from the DEMs to capture the slope stability of each region; the point data of earthquake magnitudes is used to define surface rasters over the region by using an inverse distance function; and soil type data of surficial geologic habitat mapping and seafloor geology at a regional scale are collected and ranked based on the suitability: due to the liquefaction potential, sand is assigned the minimum suitability, rock is assigned lower suitability for potential engineering constraints to suction piles and anchoring, and values increase for other soil types by decreasing grain size from cobble to mud. Next, weighted overlay functions are applied to perform site suitability analysis for all factors, after standardization into a common scale. Each of the criteria in the weighted overlay analysis is multiplied by the weights defined based on their importance in the region and then added together and suitability maps for each lease block is developed.

Comprehensive maps of geohazards and geological data in the designated lease blocks, suitability index maps, and suitability rankings for the blocks based on the hazards from earthquakes and historically-collected bathymetric and geologic data such as soil type are being generated and presented. Recommendations on further suggested studies will then be provided based on identified data gaps, to help in identifying suitable site locations and assist BOEM in making their decisions on this process.