A hazardous fault line that runs south of downtown Seattle may have formed when the edge of the North American continent tore apart 55 million years ago, a new study suggests.
Seattle sits atop the Cascadia Subduction Zone, where the Explorer, Juan de Fuca and Gorda tectonic plates slide beneath the much larger North American Plate. This eastward movement pulled a string of volcanic islands similar to present-day Iceland toward the continent and eventually caused a collision that's still visible in the bedrock beneath the city.
