Earthquakes and Plate Tectonics

Introduction
The tectonic plates of the world are constantly moving in relation to each other. The boundaries between plates are zones of active faulting and earthquakes. There are 3 types of plate boundaries and 3 types of faults. Remember, there are two types of crust which can be involved in this faulting, oceanic crust and continental crust.

Review questions about type of crust.

  • Which type of crust floats higher?
  • Which type of crust subducts?
  • What happens when dense crust runs into buoyant crust?

    PUSH and PULL
    1) Where plates push together we call it a convergent boundary. Convergent boundaries are where subduction zones and collision zones are located. The type of faults that form along convergent boundaries are reverse faults, also called thrust faults. Convergence involving oceanic crust results in a subduction zone, where the oceanic crust dives back into the mantle. Along subduction zones, a trench forms on the ocean floor adjacent to a strato-volcano mountain range which is built on the overriding plate. When a convergent boundary involves 2 pieces of continental crust, a collision zone develops as the plates push mountains up into the sky.

    Task 1
    On a world map, identify the convergent boundaries or the zones of thrust faults. (Color the subduction zones blue and the collision zones green. Remember that you must first determine if oceanic crust is involved)
    Questions
    1a Can you name 5 countries located along 5 different convergent boundaries?

    1b. Can you locate any convergent boundaries in your space shuttle photographs?

    1c. Is the direction of motion of the portion of the convection cell in the mantle below a convergent zone UP? or DOWN?


    2) Where plates pull apart we call it a divergent boundary. Along divergent boundaries we see rifting or fracture along normal faults. Spreading centers form along ocean ridges as oceanic crust is pulled or torn apart. Under all the worlds oceans new volcanic material erupts in rift valleys in the form of pillow basalt. A shield volcano can form as the lava builds up the ocean floor above sea level. Divergent boundaries can occur under continental crust and pull pieces apart to form parallel basins and ranges. (When you pull apart a "Fig Newton" which way to the little faults form? Draw a picture).

    Task 2
    On a world map, identify the divergent boundaries or the zones of rifting and normal faults. (Color the ocean spreading centers red and rift zones orange.)
    Questions
    2a Can you name 5 places that spreading or rifting is taking place?

    2b. Can you locate any divergent boundaries on your shuttle photographs?

    2c. Is the direction of motion of the portion of the convection cell in the mantle below a divergent zone UP? or DOWN?

    3) Transform faults are associated with convergent and divergent boundaries. A transform fault moves pieces of crust past each other forming a strike-slip fault. This lateral motion can be described as either left-lateral or right-lateral. The way to determine whether a transform fault is left-lateral or right-lateral is to picture yourself standing and looking across the fault. If the land on the other side of the fault moves to your left, it's a left-lateral fault. If the land on the other side of the fault moves to your right, it's a right-lateral fault. Transform faults in continental crust can commonly involve aspects of divergence and convergence, when the fault is not straight. Where there is divergence, the land pulls apart forming a basin. Where there is convergence, the land collides, forming mountains.

    Task 3
    Circle the correct answer (You are now looking down on the Earth.)
    3a. Left-lateral or right-lateral?

    3b. Left-lateral or right-lateral?

    3c. Left-lateral or right-lateral?

    3d. Left-lateral or right-lateral?

    Draw where you would expect mountains and valleys
    3e. Left-lateral.

    3f.