The Lecture: What Happens When You Crash Iceland into North America? A view of Washington 50 million years ago…

The Puget Lowland of Washington State contains several potentially dangerous seismic faults, including the Seattle fault, which runs south of downtown Seattle. To accurately assess the earthquake hazard in this region, we need to understand the architecture and geologic history of the rocks that host these faults, deep below the Puget Lowland. Geologists do this by using small changes in Earth’s gravity and magnetic fields to create images of the Earth’s subsurface. These rocks formed in a subduction zone 50 million years ago when a set of volcanic islands, similar to modern-day Iceland, collided with the edge of North America. This added a mass of rock, called Siletzia, to the continent.

Megan will show that as the islands piled up, they broke and folded into mountain ranges. South of Seattle, Siletzia was pushed up and over ancient North America, whereas to the north, Siletzia was pulled down and under the continent. She will argue that a tear in Siletzia between these two zones eventually became the proto-Seattle fault, which provides a story for the Seattle fault’s origin and earliest history. Our images also provide information that can improve models of ground shaking from future earthquakes affecting the greater Seattle urban area.

This IN-PERSON ONLY lecture will start at 4 PM on Saturday, November 16, 2024. This is free and open to the public. (Donations gratefully welcome at the door.) This lecture will be recorded and posted shortly after the presentation, as are all our events since 2020.

About the Speaker:

Megan Anderson is an earthquake geophysicist at the Washington Geological Survey. Megan spent her early years in Kent, WA, during which the eruption of Mt. St. Helens spurred her fascination with geology, which was her major at Carleton College in Minnesota. She studied subduction processes and earthquakes in South America for her Ph.D. at the University of Arizona. She has studied numerous tectonic regions of the world but has always made her way back to the Pacific Northwest because there is so much left to discover. She taught for ten years at Colorado College, dragging her students and equipment across the country to do research in Washington. She is now firmly planted in Olympia as home.