Plate Boundaries and Their Many Motions

13 05 2008

Plate BoundariesFrom our last posts we discussed the continental drift amongst the many plates all over the Earth’s crust. We now understand that these plates have motion. Thanks to a geologist named Harry Hess, we found that the seafloor may be spreading apart from one another which he used from the theories of geologist Arthur Holmes. He believed that molten rock comes from beneath the Earth’s crust along “mid-oceanic ridges.”

Hess knew that people would then ask, “well, isn’t Earth gonna get huge?” Hess would respond with, “well, no because the seafloor will sink back into the deep ocean trenches through subduction zones.” Hess gave Wageners unexplained theory validation.

Why is this important? Because plates are moving, this causes motion and earthquakes. The discovery of the mid-oceanic ridges opened doors to not only plate motion but the age of the ocean floor! Now there are different ways in which the plates move. The different types of plate boundaries that all have relatively different motion, and characteristic geologic features.Convergent Plate

The first is a Convergent boundary, where one plate is literally going over another plate. Through a subduction zone (where one plate goes under another) this causes movement and earthquakes. Thrust faults are then created because the upper plate is being pushed into a fold or broken by thrust faults. Rock layers also scrape off the ocean floor and are then stacked into piles against the upper plate creating island and mountain chains.

Another boundary is the Divergent boundary: this is where the
pDivergentlates separate and move apart. They often form a rift zone. Most are located on the oceanic floor where new seafloor is created at the separating edges. One example is the Mid-Atlantic Ridge.

Another plate boundary is called the Strike-Slip or Transform Fault where the plates are sliding against one another without spreading apart or going over or under each other. They are also found on the ocean floor. The San Andreas fault in California is a prime example of a Transform Fault on land.

Transform Fault

Click to see an animation form of a Thrust Fault, Divergent Boundary, Transform Fault.

Why are these boundaries important to understand? How do they help geologist and seismologist understand earthquakes?

Here is a quick video interpretation of plate boundaries, I hope you find it as interesting as I did! Enjoy!