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Tsunamis - Past, Present, and Future
1. Introduction

Expedition Menu

1. Introduction

2. 1964 Alaskan Tsunami

3. Indian Ocean Tsunami

4. Studying Tsunamis

5. Detecting Tsunamis

6. Japan Tsunami

7. Japan - Nova

8. Pacific Northwest

9. Evidence?

The Wave After the Undersea Earthquake

Don's Introduction

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Objectives: Students will learn about past tsunamis, and their relationship to underwater earthquakes and the potential for a major tsunami along coastal California.

Students will learn about tsunamis, in the distant and, not so distant, past along North America. Students will explore the tragedy associated with the 2004 Indian Ocean and 2011 Japan earthquakes and the ways that scientists are studying these earthquakes, and the associated tsunamis, including simulations of wave propagation in the ocean. We will also examine the methods used by scientists to detect tsunamis at sea and warn the general public about timing of impact at the coast. Lastly, we will examine the evidence for a potential tsunami striking California.

Let's return to our discussion of the 1964 Great Alaskan Earthquake, also known as the 1964 Good Friday earthquake.

We will now build on our previous expedition on undersea earthquakes and the processes along plate boundaries, for example seafloor spreading and subduction. We will now examine the effects of these earthquakes on the overlying ocean.
We see waves on the surface of the ocean, paused by the winds, the flow of ocean water due to the tides, resulting from the gravititational attraction of the moon and the sun on the ocean
Here we examine tsunamis, how they are formed, how fast they travel, and where they have been formed in the past in 1700, 1964, 2004 and 2011, and the sobering prospect of a future tsunmai striking California -- it will definitely happen again.

1964 Great Alaska Earthquake map

Wow a 9.2 Magnitude earthquake on Good Friday in 1964 - now that is big!

The yellow line marks the location of the Aleutian Trench -- the triangles mark active volcanoes -- and we have a history of very, very large magnitude earthquakes!!! Yes, it is a convergent plate boundary!

3-D Earthquake Image


Deep earthquake diagram

By taking a vertical slice through the Earth across the plate boundary in this region, as shown in the diagram above, we see that the earthquake locations in the Earth, shown by the colored dots, provide evidence of a convergent plate boundary with oceanic lithosphere of the Pacific Plate subducting (sinking) below the North American Plate.  The thick white lines outline the pieces of lithosphere is this region. 

So even the deep earthquakes, in this particular case down to 200 kilometers, which define the Benioff zone, are in the lithosphere -- in this case, the lithosphere sinking back into the Earth along convergent plate boundaries. 

At left is the earthquake distribution is shown below in three dimensions.

Contact Don Reed
Dept. of Geology
San José State University
ęCopyright 2006
Last Updated on
October 2, 2006

What type of plate boundary exists in this region of the northeast Pacific Ocean?

Plate Boundaries

 a) convergent
b) transform
c) divergent