12. Mendocino
-- Three Plates in Contact
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
The high concentration of earthquakes at Cape Mendocino marks the boundary between three plates, the North American plate to the east, Gorda (partially enclosed by the yellow line) lying to the west of Oregon and northern California, and the Pacific plate to the west of California and to the south of the Gorda plate. The Gorda plate is considered by some people to be the southern part of the Juan de Fuca plate (mentioned in “Commotion beneath the Ocean” expedition).
A region where three plates of lithosphere come into contact in one place is called a " triple junction" (location shown with the TJ in the diagram above) -- no wonder there are so many earthquakes in this area! You see the labels with the names of the three plates and on seafloor features at each type of plate boundary in this region.
On your expediton worksheet, make a simple diagram of the geometries and types of plate boundaries in this region, and include the location of the triple junction and the names of the plates.
Given what you have learned in this course -- make two observations of the earthquake distribution that strike you as odd in this region.
Contact Don Reed
Dept. of Geology
San José State University
©Copyright 1999
Last Updated on June 21, 1999
What is
wrong with the distribution of earthquakes in the region, based on our
discussion so far?
a) there are earthquakes in the middle of Gorda plate
where there is no plate boundary
b) there are so few earthquakes along the convergent
plate boundary along the Cascadia subduction zone
c) all of the above