- Past, Present, and Future
The Wave After the Undersea Earthquake
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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.
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
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.
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!
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
type of plate boundary exists in this region of the northeast Pacific