Dynamic Site Characterization of Soft Ground in Seattle: Workflow, Analysis and Results

Seattle is a city that underwent significant regrading as it expanded in the 1900s, resulting in fill materials with depths ranging from a few feet to over 200 feet. Many of the locations of fill material present the largest seismic hazards in the Seattle area; however, some areas are not well characterized. This project consists of a field campaign at a soft ground site near the University of Washington, Montlake Playfield Park, where site frequency was found at 43 stations across the park using the Horizontal-to-Vertical Spectral Ratio (HVSR) Method with broadband seismometers. The project examines aspects of HVSR workflow and analysis to inform future best/standard practices for future research. The H/V data in this project can be reused in multiple ways, including: (1) to compare the site frequency in other stiff soil sites to examine basin resonance, (2) to compare other processing sensitivities of HVSR applications (Geopsy, HVSRpy, etc.) and settings (3) to inform hazard mapping in the University District area, etc. This project is intended for those interested in non-invasive site characterization methods and Seattle geologic hazards.