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.