2024-11-16 Megan Anderson – Siletzia’s influence on the Seattle Fault
Category: Locations of Interest
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 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.2024-10-05 Harold Tobin – An Exhumed Ancient Cascadia Megathrust Fault in the Olympic Mountains
The Lecture: An Exhumed Ancient Cascadia Megathrust Fault in the Olympic Mountains
On October 5, 2024 the Quimper Geological Society will host a lecture by Harold Tobin, professor of Seismology and Geohazards at the University of Washington and Director of the Pacific Northwest Seismic Network. Harold’s research employs field mapping and geophysical techniques to investigate processes that operate in fault zones, particularly those associated with subduction zones. One of his study areas is the Olympic Mountains, where recently he and his graduate students mapped rocks in a remote area west of Mount Olympus that were covered by ice when geologists last visited the area over 50 years ago. They found intensely deformed rocks that represent a fossil megathrust fault, the type of fault responsible for great Cascadia earthquakes. Harold will discuss how integrating data from this ancient fault with seismic imaging of present-day seismic zones allow him to better understand how and why these megathrust faults slip and generate earthquakes.
This IN-PERSON ONLY lecture will start at 4 PM on Saturday, October 5, 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:
Professor Harold Tobin holds the Paros Endowed Chair in Seismology and Geohazards at the Department of Earth and Space Sciences at the University of Washington. He also serves as the Director of the Pacific Northwest Seismic Network and Washington’s State Seismologist. Despite that title, his scientific roots are in subduction zone geology and the structure of plate boundary fault zones. With a B.S. in geology and geophysics from Yale University and a PhD from University of California, Santa Cruz, Harold has held faculty positions at New Mexico Tech and the University of Wisconsin-Madison prior to moving to Seattle in 2018. His first taste of subduction geology was as an undergraduate field assistant in the Olympic Mountains in 1987, and after 30 years of offshore and onshore research in Japan, Alaska, New Zealand, Costa Rica, and California, he has come full circle to explore the core rocks of the Olympic mountains.
2024-09-14 Darrel Cowan — North to Alaska: Transport of Exotic Terranes
Saturday, September 14, 2024, 4 PM
The Lecture: Baranof Island, Alaska, and Vancouver Island were neighbors 50 million years ago
Darrel Cowan discussed the evolution of hypotheses about the large-scale coastwise displacements of tectonic elements or terranes along the western margin of North America. He presented the geologic evidence he published in 1982, which links Vancouver Island with southeast Alaska. The still-contentious Baja British Columbia hypothesis, developed in the early 1980s, was based entirely on paleomagnetic data.
This IN-PERSON ONLY lecture started at 4 PM on Saturday, September 14, 2024, at the First Baptist Church, 1202 Lawrence St, Port Townsend, WA 98368 (entrance in the back). It is was free and open to the public. The lecture was recorded and will be posted shortly after the presentation, as are all our events since 2020.
About the Speaker:
Darrel Cowan is Professor Emeritus in the Department of Earth & Space Sciences at the University of Washington. He refers to himself as a field structural geologist. Since 1974, Darrel has spent his career educating geologists in tectonics and structural geology. Darrel is a west coaster, originally from southern California. He graduated from Stanford in 1966 and finished his PhD in the Franciscan subduction complex there in early 1972. Darrel’s research projects and those of his graduate students have investigated structural and tectonic problems in the Pacific Northwest, including southwestern British Columbia and Vancouver Island, southern Alaska, Japan, and the northern Apennines and Sicily in Italy.