About the Talk
Earthquakes and Tsunamis from the Cascadia Subduction Zone
The Port Townsend Marine Science Center will sponsor what should be a very popular pair of presentations on earthquake and tsunami hazards of the Port Townsend region. Our invited speakers are Brian Atwater, a geologist with the U.S. Geological Survey in Seattle and Ron Tognazzini, a retired civil engineer from Sequim. Interestingly, this early talk from out Geology Group Lecture Series drew a record crowd—225 persons—largely as a result of excellent and free publicity. On March 11, 2011, two weeks prior to the lecture, the Tōhoku Earthquake struck Japan and a very large tsunami took out the Fukushima Nuclear generating plant. Over 17,00 fatalities resulted from this disastrous event.
Dr. Atwater’s specialty is paleoseismology—the study of prehistoric earthquakes. Brian will begin with detective stories of Pacific Northwest earthquakes and tsunamis. Then he’ll turn to eyewitness accounts of tsunamis in Indonesia, and of the public-safety lessons they provide. If you have a business or residence near the coast, this presentation will show you what might happen during the run-up from a large tsunami.
About the co-Speaker
Ron is a civil engineer by practice but has considerable experience in natural disaster preparedness and emergency response. Ron will present recent award-winning research by Marley Iredale, a Sequim high-school student that he mentored in 2009. Marley’s research records 2,500 years of recurring tsunamis at Discovery Bay, near the Snug Harbor Restaurant. This record applies equally well to the Port Townsend region, where no tsunami studies have been conducted so far. In the adjacent photo, Ron is holding a latex peel of marsh and tsunami sand deposits.
Ancient buried forests—Indicators of catastrophic geologic events
Patrick Pringle, Associate Professor of Earth Science at Centralia College, returns to the Port Townsend Marine Science Center to present an intriguing lecture titled “Ancient buried forests—Indicators of catastrophic geologic events.” These fossil and old forests are associated with tsunamis, debris flows, and landslides, some as close as Crescent Lake, southwest of Port Angeles.
About the Speaker
Dr. Pringle is a highly regarded geologist who has studied throughout western Washington and is the author of roadside geology guides to Mount Rainier and Mount St. Helens.
Read more about Pat’s publications etc…
About the Talk
Ray Wells of the U.S. Geological Survey presented a lecture on the Revoluntary Tectonics in the Pacific Northwest.
Rotational History of the Pacific Northwest
Crustal deformation and paleomag-netic rotations over the past 50 million years indicate that the Cascadia forearc is moving northward along the west coast and breaking up into large rotating blocks. Deformation occurs mostly around the margins of a large, relatively non-seismic Oregon coastal block composed of thick oceanic crust. This 400 km-long block is moving slowly clockwise with respect to North America about a rotation pole in eastern Oregon, thus increasing convergence along its leading edge near Cape Blanco and creating an extensional volcanic arc on its trailing edge. Northward movement of the block breaks western Washington into smaller, seismically active blocks and compresses them against the Canadian Coast Mountains. Movement of these blocks may be up to 9 mm/yr, sufficient to produce damaging earthquakes in a broad deformation zone along block margins.
Recent GPS data show that clockwise rotation of Oregon continues today, and rotation rates from GPS studies are similar to older paleomagnetic rates. Northward moving Oregon is currently squeezing Washington against slower moving Canada: this constriction has produced the Yakima fold and thrust belt and its analogs, like the Seattle fault, in the forearc. Locally, right lateral shear in the forearc is apparent in the GPS data, consistent with recently discovered right-lateral faults in the Portland area that may be seismically active. In a broad sense, the smaller, clockwise rotating blocks of the Pacific Northwest appear to be caught like a giant ball bearing between the much larger Pacific and North American plates.
About the Speaker
Dr. Wells has been a research geologist for almost 30 years, concentrating on the use of field geology, magnetic rock properties (paleomagnetism), and GPS to solve large-scale problems in the Earth’s on-going structural evolution. Ray has produced a simple, hands-on block model of the Pacific Northwest, which he will demonstrate at the talk. Today, 165 of the models are used in classrooms around the Pacific Northwest.