Seattle's massive fault may result from oceanic crust 'unzipping itself' 55 million years ago
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. New maps of this bedrock reveal the collision was extremely messy, with the northern half of the island chain riding the oceanic crust and slipping under the continent and the southern half piling onto the continent. The twist in Earth's crust where the islands switched from being subducted to obducted, or added to the top of the continent, would have been under tremendous strain and likely ripped in half. "It would have been this slow, ongoi...
