Thickness distribution of the most recent sandy tsunami deposit in the Salmon River estuary, Oregon

Legacy core locations and descriptions collected by Wendy G. Walter in 1987 and published in Nelson and others, (2004) were georeferenced and reanalyzed to extract tsunami deposit thicknesses and the presence or absence of a buried soil horizon. Original core locations were determined through triangulation and annotated onto aerial photos. These photos were georeferenced in a geographic information system to determine the latitude and longitude for each site. Uncertainty in the 1987 core locations is unknown but assumed to be greater than the positional accuracy of GNSS-derived positions. The 1987 core descriptions note the depth of sandy layers and buried soil horizons that were originally interpreted to be from the 26 January, 1700 earthquake and tsunami.

The USGS collected cores from the Salmon River estuary in 2017 and 2018. Cores were described in the field and the presence or absence of a buried soil horizon was noted. Stratigraphy was described using the sediment classification schemes outlined in Troels-Smith (1955) and Nelson (2015). If present, depths and thicknesses of the sand layer immediately above the buried soil horizon were recorded. At the far inland extent of the sandy tsunami deposits, where the visually estimated bulk grain size of the deposit was a mixture of very fine sand and silt, only sandy lamina 1 mm or greater in thickness were identifiable as sandy deposits.