Learning and teaching resources on Cascadia (northern California, Oregon, Washington, and southern British Columbia) earthquakes and tsunamis are provided in this section. The scientific detective story of Cascadia tsunami geology and the orphan tsunami of 1700 observed in Japan are central themes. WE also explain how Global Positioning System (GPS) data demonstrate that the Cascadia continental margin is storing elastic energy that will be released in the next great Cascadia earthquake with the resulting tsunami arriving onshore within 30 minutes. In addition to great subduction zone earthquakes, Cascadia also experiences “deep” earthquakes that occur within the subducting Juan de Fuca Plate and crustal earthquakes on faults that some times lie beneath densely-populated cities. These three kinds of Cascadia earthquakes present three distinct sets of challenges to earthquake preparedness. Finally, we the introduce learners to the newly discovered phenomenon of Episodic Tremor and Slip (ETS) and explain how motions of the Juan de Fuca and North American plates cause ETS in Cascadia.
We recommend that you start learning about Cascadia Earthquakes and Tsunamis using the TOTLE web site by viewing the Cascadia Earthquakes and Tsunamis PowerPoint Presentation. This presentation provides the basic concepts and observations as well as links to teaching resources appropriate for a middle school audience.
A PDF Guide to Cascadia Earthquakes and Tsunamis is also available. This guide is an outline of the Cascadia Earthquakes and Tsunamis topic that contains links to and a table of contents of TOTLE teaching resources on this topic.
This QuickTime animation was developed by Jenda Johnson with assistance from Bob Butler and Roger Groom. The narration is provided by Roger Groom. The animation shows how three regions of a “locked and loading” subduction zone respond as elastic energy is stored in the overriding plate. A GPS station and grid are shown for: 1. the area near the locked subduction zone boundary; 2. the area farther inland (but still outboard of the volcanic arc) that experiences episodic tremor and slip; and 3.
This QuickTime animation was developed by Jenda Johnson with assistance from Bob Butler and John Lahr. The animation shows the motion of a GPS station in the region that experiences episodic tremor and slip. The “three steps forward then one step back” pattern of motion is shown. The resulting graph of position versus time has the “sawtooth” pattern of motion that is now recognized as the signature of episodic tremor and slip. Seismic tremor vibrations are also illustrated occurring during the “back step” of the GPS station.
This QuickTime animation was developed and is narrated by Jenda Johnson. The animation shows the motion of a GPS station on the leading edge of a continent near a subduction zone during the earthquake cycle. The station is slowly pushed inland as elastic energy is stored in the overriding plate of the subduction zone then rapidly jumps seaward during a great earthquake that also generates a tsunami. This pattern of deformation has been observed during recent great subduction zone earthquakes like the February 2010 magnitude 8.8 Chile earthquake.
This QuickTime animation shows the motions of crustal blocks in the Pacific Northwest. The animation was developed by Jenda Johnson and is narrated by Bob Butler. Coastal blocks are being pushed northward by the Sierra Nevada block while the thick and strong crust of southern British Columbia acts as a back stop to this northward motion. A result of significance to earthquake risk is that much of the resulting north-south compression is accommodated by thrust faults in the Puget Lowlands such as the Seattle Fault that is capable of magnitude 7 earthquakes.
QuickTime animation of earthquakes and episodic tremor and slip (ETS) events that occurred in the Pacific Northwest from 2006 through 2009. Most of these earthquakes are shallow (less than 20 km depth) with the on-shore events occurring within the North American continental crust and the off-shore events occurring within the upper portion of the oceanic lithosphere. The ETS events are “slow slip” between the base of the North American Plate and the top of the subducting Juan de Fuca Plate in the 20 km to 40 km depth range.
QuickTime animation developed by Jenda Johnson to illustrate how sudden release of stored elastic energy (elastic rebound) in a subduction zone causes the leading edge of the over-riding plate to jump seaward and uplift while the near-shore land area subsides. The sudden displacement of the ocean floor generates a tsunami. The tsunami that arrives onshore near the subduction zone is the “local tsunami” that arrives 20 – 30 minutes after the displacement of the ocean floor by the earthqauke. The tsunami that travels into the open ocean will arrive hours later on distant shores.
This QuickTime animation was developed by Jenda Johnson. The animation shows the tsunami generated from the great Cascadia subduction zone earthquake of January 26 1700 traveling across the Pacific Ocean. The travel time to northwest Japan is about 9 hours. The arrival of this tsunami is recorded in historic documents of coastal towns in Japan. This tsunami is referred to as an “orphan tsunami” because it was not preceded by felt ground shaking in Japan cuased by a “parent” earthquake.