The Pacific Northwest is an active continental margin The Cascadia subduction zone is where the oceanic Juan de Fuca plate subducts into the deeper mantle beneath the Pacific Northwest part of the North American plate. This region is often referred to as “Cascadia” and extends from northern CA northwards through Oregon and Washington to southern British Columbia. Figure from Bob Lillie’s book Parks and Plates: The Geology of Our National Parks, Monuments, and Seashores.

Go to viewer: Turn off Vectors Turn on Plate Boundaries—Narrate from Baja to Canada http://www.unavco.org/software/visual ization/GPS-Velocity-Viewer/GPS- Velocity-Viewer.html

Plate Motion San Andreas Fault—Describe the motion of Pacific Plate and North American Plate https://www.geolsoc.org.uk/Plate- Tectonics/Chap3-Plate- Margins/Conservative/San-Andreas- Fault

Three kinds of PNW EQs = Triple Trouble Plate boundary EQs between Juan de Fuca and North American plates. E.g. 1700 AD Great Cascadia EQ. Crustal EQs within North American continental crust. e.g. 900 AD EQ on Seattle Fault Zone. EQs within the subducting Juan de Fuca plate. e.g. Nisqually 2001. Three kinds of earthquakes in the Pacific Northwest: 1. Subduction zone earthquakes. These are plate-boundary earthquakes at the interface between the North American and Juan de Fuca plates. The last great earthquake on this boundary occurred on January 26, 1700 at about 9PM. North American geophysics, geology, and dendrochronology, in combination with Japanese written history, have shown that the most recent great earthquake on the Cascadia subduction zone occurred during the evening of 26 January 1700 and that it probably attained a magnitude of nine [Atwater, B. F., S. Musumi-Rokkaku, K. Satake, Y. Tsuji, K. Ueda, and D. K. Yamaguchi (2005), The orphan tsunami of 1700: Japanese clues to a parent earthquake in North America, U.S. Geol. Surv. Prof. Pap., 1707, 133 pp.]. These conclusions are startling, as are the geologic hazards they imply. 2. Earthquakes within the subducting Juan de Fuca plate beneath the Pacific Northwest. The most recent example is the Nisqually earthquake of 2001 that caused approximately $2 billion damage to the southern Puget Sound region. 3. Shallow earthquakes within the North American crust. These earthquakes are a major concern in the Puget Sound area Pacific Northwest and to a lesser degree also in the Portland area where these faults apparently move less frequently. Some good resources on the Seattle Fault at https://www.eeri.org/projects/earthquake-scenarios/seattle-fault-scenario/

Compression of Pacific Northwest Continental Margin Urban Corridor East of Cascades Coast CLASSROOM ACTIVITY: Motions of GPS stations at different distances from Juan de Fuca - North America plate boundary document compression of Pacific Northwest continental margin. Neah Bay Pacific Beach Tumwater Othello Kelso Tillamook Wasco La Grande CLASSROOM ACTIVITIES USING PBO DATA: Cascadia GPS 1 Gumdrop Lesson Plan This basic activity can be found at http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/LessonPlans/CASCADIA_GPS_Gumdrop__LessonPlan_TOTLE.pdf Cascadia GPS 2 "Locked and Loading" Lesson Plan This more advanced activity can be found at http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/LessonPlans/CASCADIA_GPS_Locked&Loading__LessonPlan_TOTLE.pdf VIDEO CLASSROOM DEMONSTRATIONS: Roger Groom explains how to present an introduction to GPS appropriate for a middle school Earth Science class. Parts 1 & 2: http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/Videos/GPS_Activity_VideoDemo_Part1&2.mov Parts 3 – 5: http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/Videos/GPS_Activity_VideoDemo_Part3-5.mov This activity guides students through an introduction to GPS and its application to Pacific Northwest tectonics. The goal is the provide students with an understanding of how GPS observations document the ongoing slow accumulation of compressional elastic energy within the Pacific Northwest part of the North American Plate. This storage of elastic energy is part of the earthquake cycle in which elastic energy is slowly stored as rocks near a plate boundary deform in response to plate tectonic forces. The stored elastic energy will eventually be released in an earthquake. This process of slow accumulation and rapid release of elastic energy is the “Elastic Rebound Theory” or the “Earthquake Cycle” that was developed by H. F. Reid following the 1906 San Francisco earthquake. The development of high-precision (millimeter-scale) GPS receiver technology now allows us to actually watch the year-by-year deformation of Earth’s surface during the slow accumulation phase of the earthquake cycle. Newport Corvallis

Compression of Pacific Northwest Continental Margin How does the movement of coastal stations compare to Tumwater, Kelso, and Corvallis? How are Stations east of Cascades moving? Over time what will happen to the distance between the stations on coast and stations east of the Cascades? What does this indicate about the forces acting on the Pacific NW? Neah Bay Pacific Beach Tumwater Othello Kelso Tillamook Wasco La Grande Newport Corvallis The results of GPS analysis for an array of stations across Washington and Oregon clearly shows the compressional deformation of the Pacific Northwest continental margin. The accumulating elastic energy will be released in the next great Cascadia subduction zone earthquake. For example, if all of the elastic energy accumulated over the past 310 years since the 1700 AD Cascadia earthquake were released is a great earthquake today, Pacific Beach would suddenly jump to the southwest by a distance of (310 yrs) X (17.2 mm/yr) = 5332 mm = 5.3 meters = 17.5 feet! If you were in Pacific Beach during this earthquake, that would probably ruin your whole day ;) Seriously, these are the magnitudes of sudden motion that occur during great (magnitude 9) subduction zone earthquakes. ANIMATIONS: Several animations explaining the use of GPS observations of plate tectonic and earthquake processes can be found on the IRIS Education and Public Outreach web pages. URL http://www.iris.edu/hq/programs/education_and_outreach/animations/14

Open PDF of text in Notability and look at map with Vectors Circle and underline—what new information do we have?

Animation of Cascadia subduction zone An animation showing the relative motions of plates and the resulting earthquake and volcanic activity can help learners grasp essential concepts. This animation presents the basic principles of how subduction of an oceanic plate leads to formation of a line of volcanoes (often called a “volcanic arc”) on the upper plate at a subduction zone. The magma (= melted, liquid rock) does NOT result from the melting of the rocks in the subducting oceanic lithosphere. (This is another widely-held misconception.) Water from the subducting oceanic plate induces melting of the asthenospheric mantle above the subducting plate. It is that material (not the subducting slab itself, that melts to produce magma. ANIMATION of Cascadia Subduction Zone can be found at https://media.up.edu/Physics/TOLE/CascadeVolcanoes/Animations/SubductionPacificNorthwest.mov ANIMATIONS: Numerous animations of Divergent and Convergent Plate Boundaries can be found at the IRIS Education and Public Outreach Animations web pages. URL http://www.iris.edu/hq/programs/education_and_outreach/animations/11

Animated plate motions and tsunami during a subduction zone earthquake Animation of Subduction Zone Earthquake Causes Tsunami and Ghost Forest can be found at: http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/Animations/ElasticRebound_Subduction.mov A collection of animations of subduction zone processes and earthquakes can be found at the IRIS Education and Public Outreach Animations web pages. URL http://www.iris.edu/hq/programs/education_and_outreach/animations/5

Basin and Range Extension PNW Crustal blocks SE Oregon extending. Sierra Nevada block moving north into Oregon! Coast Ranges rotating and sliding north. Seattle getting squeezed. Faults and folds within the crust are produced by these tectonic motions. Basin and Range Extension The continental crust in the Pacific Northwest is broken into crustal blocks that are moving with respect to each other. There are faults at the boundaries between these crustal blocks that are potential sources of major earthquakes. There are also faults within some crustal blocks (e.g. the Seattle Fault) that are potential sources of major earthquakes. The motions of the Pacific Northwest crustal blocks are driven primarily by northward motion of the Sierra Nevada block and extension of the Basin and Range Province that affects southeastern Oregon. PACIFIC NORTHWEST TECTONIC BLOCK MODEL: This activity features a hands-on model of crustal block motions within the Pacific Northwest active continental margin requires construction of the manipulative model developed by Philip Dinterman, Chris DuRoss, and Ray Wells of the USGS. Alternatively, you can do the classroom activity substituting the animation of the model for the actual model. PACIFIC NORTHWEST TECTONIC BLOCK MODEL CLASSROOM ACTIVITY can be found at: http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/LessonPlans/PNW_TectonicBlockModel__LessonPlan_TOTLE.pdf INSTRUCTIONS FOR BUILDING THE PACIFIC NORTHWEST TECTONIC BLOCK MODEL are available at: http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/AdditionalResources/PNW_block_model_PATTERN.pdf

Animation ANIMATION: This QuickTime animation can be found at: http://multimedia2.up.edu/Physics/TOLE/CascadiaEarthquake&Tsunamis/Animations/1.PacNW-model-8my-Narrated.mov