Cascadia Great Earthquake and Tsunami Suite
I The Great Sumatran Earthquake and
Tsunami of December 2004
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II Is the stage being set for a Great
Cascadian Earthquake and Tsunami?
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III The Search for Great Cascadian
Earthquakes and Tsunamis in the Past
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IV Impact of a Great Cascadian Earthquake
and Tsunami on one Coastal Community
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V Rupture on the Seattle Fault: A Case
Study
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Natural Hazard Case Studies
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Unit II. Is the Stage Being Set For a Great Cascadian Earthquake and Tsunami?
In this unit, students explore evidence for present-day deformations in Cascadia that may presage a future great subduction zone earthquake. The investigation explores the plate tectonic framework with an examination of the evolution of the Juan de Fuca plate as it descends beneath the North American plate.
Students then examine a table of key characteristics of the three largest earthquakes that have occurred, all where an oceanic plate is subducting a continental plate. These are the 1960 M9.6 Chilean earthquake, the 2004 M9.3 Sumatran earthquake, and the 1964 M9.2 Alaskan earthquake. The characteristics include the character of seismicity, a linear zone of active volcanoes, a very long rupture zone, and a diagnostic uplift and inland translation of the front of the upper plate. As they proceed through the unit, they will note that the Cascadian subduction zone has all characteristics in common with the other subduction zones, save one. The upper and lower plates are locked in friction in the shallow portion of the subduction zone along the length of the Cascadian margin, a length comparable to that of the other three subduction zones. Should the entire length of the locked zone slip, a magnitude 9+ earthquake could be generated. Students will discover that the upper plate is deforming and translating eastward consistent with stress build-up along the locked zone. A chain of active volcanoes is present. The Cascadian situation differs from that of the other three subduction zones only in its lack of large earthquakes.
To investigate evidence for present-day deformations in northern Cascadia, students make use of a GIS data layer for horizontal rates of the Cascadian array of GPS base stations using the UNAVCO Plate Boundary Observatory (PBO) data base. Horizontal rate vectors are in the direction of relative plate motion, and diminish in magnitude toward the continental interior. Students are able to infer the consistency of this pattern with a model of upper plate deformation above a locked portion of the subduction zone.
Students can download the PBO GPS daily north and east component data for one base station (Neah Bay, Washington), plot the data in Excel, and compute using simple trigonometry the rate of translation of the station; they can then compare the rate with the PBO-determined rate. Optionally, instructors can download finished graphs of the daily north and east component data with predetermined best-fit rates; students can then start with these and easily compute the resultant speed and direction of the displacement vector for the Neah site.
Download project files now...
ArcGIS version
MyWorld GIS version
This material is based upon work supported by the National Science Foundation under Grant Number DUE-0521936. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
In this unit, students explore evidence for present-day deformations in Cascadia that may presage a future great subduction zone earthquake. The investigation explores the plate tectonic framework with an examination of the evolution of the Juan de Fuca plate as it descends beneath the North American plate.
Students then examine a table of key characteristics of the three largest earthquakes that have occurred, all where an oceanic plate is subducting a continental plate. These are the 1960 M9.6 Chilean earthquake, the 2004 M9.3 Sumatran earthquake, and the 1964 M9.2 Alaskan earthquake. The characteristics include the character of seismicity, a linear zone of active volcanoes, a very long rupture zone, and a diagnostic uplift and inland translation of the front of the upper plate. As they proceed through the unit, they will note that the Cascadian subduction zone has all characteristics in common with the other subduction zones, save one. The upper and lower plates are locked in friction in the shallow portion of the subduction zone along the length of the Cascadian margin, a length comparable to that of the other three subduction zones. Should the entire length of the locked zone slip, a magnitude 9+ earthquake could be generated. Students will discover that the upper plate is deforming and translating eastward consistent with stress build-up along the locked zone. A chain of active volcanoes is present. The Cascadian situation differs from that of the other three subduction zones only in its lack of large earthquakes.
To investigate evidence for present-day deformations in northern Cascadia, students make use of a GIS data layer for horizontal rates of the Cascadian array of GPS base stations using the UNAVCO Plate Boundary Observatory (PBO) data base. Horizontal rate vectors are in the direction of relative plate motion, and diminish in magnitude toward the continental interior. Students are able to infer the consistency of this pattern with a model of upper plate deformation above a locked portion of the subduction zone.
Students can download the PBO GPS daily north and east component data for one base station (Neah Bay, Washington), plot the data in Excel, and compute using simple trigonometry the rate of translation of the station; they can then compare the rate with the PBO-determined rate. Optionally, instructors can download finished graphs of the daily north and east component data with predetermined best-fit rates; students can then start with these and easily compute the resultant speed and direction of the displacement vector for the Neah site.
Download project files now...
ArcGIS version
MyWorld GIS version
This material is based upon work supported by the National Science Foundation under Grant Number DUE-0521936. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.