9. A Vertical Slice through a Convergent Plate Boundary
Expedition Menu
1.
Introduction
2. Global Distribution
3. Earthquakes & Plate Boundaries
4. The Ring of Fire
5. Convergent Boundaries
6. Atlantic Ocean
7. Atlantic Ocean II
8. Alaska Earthquake
9. Vertical Slice
10. 3-D Look
11. California Plate Boundaries
Now you see a vertical slice through the Earth along the red line on the previous web page and which crosses the plate boundary in this region.
We can see that the earthquake locations in the Earth, as 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 shallow earthquakes in the upper right corner are located near the Aleutian Trench, which marks the boundary between the North American and Pacific plates along the sea floor. The dipping region of earthquakes shown here is called the Wadati-Benioff Zone or just Benioff Zone. The thick white lines outline the pieces of lithosphere in this region.
So even the deep earthquakes, in this particular case down to 200 kilometers, are in the lithosphere -- lithosphere sinking back into the Earth along a convergent plate boundary.
We can also see earthquakes below the volcanic arc caused by the movement of molten rock or by the sinking of the crust in this region.
On the expedition worksheet, make a drawing of the earthquake distribution with an outline of the subducting Pacific Plate and the overriding North American plate.
Contact Don Reed
Dept. of Geology
San José State University
©Copyright 1999
Last Updated on June 21, 1999
Let's
see this distribution of earthquakes in three dimensions.