A century of landslides in Seattle, Washington; coalescing and digitizing the city's historic landslide inventories

Landslides have impacted the built environment of the city of Seattle for over a century. We present a new historic landslide inventory for Seattle built from over 100 years of landslide records. Seattle has tracked landslide occurrence since the 1890s and has commissioned various studies to examine where and why landslides occur. During this tenure, methods for collection, display, and dissemination of landslide data have varied, resulting in a complex, non-uniform, and rich dataset. For the new database completed in 2019, multiple inventories and thousands of historic documents were combined to meet the City of Seattle's objectives of keeping landslide areas precise with respect to property boundaries. Compared with prior maps, the new map provides more information from the historical record, maps landslide extent more accurately, and tags fewer private properties with landslide features than prior maps. In addition, digitized historic documents are now attached to landslide features in the City of Seattle's public geographic information system (GIS) map. The historic inventory is complementary to a light detection and ranging (LiDAR) inventory covering the same area. This case study shows how historic data can be used to record landslides in urban areas where geomorphological signatures may be removed by development. In Seattle, access to information about historic landslides will streamline workflows for public and private engineers and geologists and will serve property owners and the general public. The map is currently available at https://www.arcgis.com/apps/webappviewer/index.html?id=f822b2c6498c41 63b0cf908e2241e9c2.