The USGS has produced a new series of earthquake hazard maps for the City of Seattle.
These ‘urban seismic hazard’ maps provide a much higher-resolution view of the potential for strong earthquake shaking than previously available. This new view is particularly important for Seattle, which sits atop a sedimentary basin that strongly affects the patterns of earthquake ground shaking and therefore, of potential damage.
These hazard maps for Seattle depict the hazard for ground shaking at frequencies of about 1 cycle per second. Generally speaking, buildings of 10 stories in height are most sensitive to ground shaking at this frequency, so these maps show the hazard to medium-sized buildings. Since single-family houses are most sensitive to ground-shaking frequencies higher than 1 cycle per second, these maps may not always be a good indicator of the hazard to single-family houses. However, areas of artificial fill and young alluvium (soft soils), as indicated by the locations with highest hazard in these maps, have elevated levels of hazard for a variety of building types, including single-family houses. We are currently conducting research to assess the vulnerability of single-family houses to basin surface waves with frequencies around 1 cycle per second. We expect that many earthquake sources will produce such surface waves in the Seattle basin.
Source: USGS