Environment

Decoding earthquake history: How geologists find fossilized clues in sediment

KNKX Public Radio | By Bellamy Pailthorp

Published February 26, 2021 at 5:45 PM PST

Retired USGS geologist Brian Atwater on Seattle's Duwamish River at dusk. He often explores the area at low tide looking for signs of geological activity.

Twenty years ago this Sunday, the Nisqually earthquake rattled the region. It registered 6.8 on the Richter scale and shook for 40 seconds. The damage was significant. Bricks flew. It caused cracks in the Capitol dome in Olympia and sealed the fate of Seattle’s Alaskan Way Viaduct as well as many older buildings in Pioneer Square. But it was nowhere near as drastic as some of the other possible geological scenarios that could lead to truly devastating shaking.

KNKX environment reporter Bellamy Pailthorp wanted to learn more about the geological context of that quake two decades ago … and how these scientists piece together the clues that unlock answers to some of the earth’s deepest mysteries.

Signs of prior geological activity found throughout the Duwamish River area. On the left layers of oxidized sediment representing different years of deposits on Kellogg Island. Center, fossilized plants found in the sand. Right, a sediment cake on the west side of river showing two separate deposits that help tell the story of an earthquake 1,100 years ago.

She joined retired USGS geologist Brian Atwater at a favorite spot on Seattle’s Duwamish River that he likes to explore at low tide. And she spoke with Seattle Times science writer Sandi Doughton about her book, "Full-Rip 9.0: The Next Big Earthquake in the Pacific Northwest," as well as the latest on preparedness in the region.

The Duwamish River runs through Seattle.