The sediments in wetlands along Nehalem Bay hold evidence about prehistoric earthquakes. How large were they? When did they occur? Did they generate tsunamis?
How do we know that any given change in Nehalem sediment is a record of a great earthquake, rather than other coastal processes, such as large river floods, winter storms, or sea-level rise?
Starting back in 1987, geologists have studied stratigraphic evidence that can reveal the story of sudden changes in wetland environments around the lower part of the Nehalem River estuary. Three coastal geologists involved in the most recent of these studies, published in 2020, will describe how difficult it is to identify great earthquakes, and explain the new methods they used to estimate when they occurred, and their magnitudes.