On the map complete each of the following: 1. Sketch the location of all plate b

Question

On the map complete each of the following:

1. Sketch the location of all plate boundaries that can be identified on the basis of the distribution of earthquakes:

a) Show any trenches as a continuous RED line. (5 points) b) Show any oceanic ridges that you think might be present as BLACK lines. (5 points) c) Show the location of any transform faults that might be present as GREEN lines. (5 points)

2. Based on the pattern of depth of earthquakes: a) Identify where subduction is taking place on the map at the steepest angle from the horizontal (label this location “A”). (2 points) b) Identify where subduction is taking place on the map at the lowest angle from the horizontal (label this location with the letter “B”). (2 points) c) Can you recognize any location where there may be a “seismic gap”? If you think that there is one label it with the letter “C”. (2 points)

3. If you can recognize any other features that please label them with numbers and describe each feature in the space provided below the map. (2 points each total 10 points ….yes, there are 5 additional features that you should be able to find on the map).

Explanation / Answer

A divergent boundary occurs when two tectonic plates move away from each other. Along these boundaries, lava spews from long fissures and geysers spurt superheated water. Frequent earthquakes strike along the rift. Beneath the rift, magma—molten rock—rises from the mantle. It oozes up into the gap and hardens into solid rock, forming new crust on the torn edges of the plates. Magma from the mantle solidifies into basalt, a dark, dense rock that underlies the ocean floor. Thus at divergent boundaries, oceanic crust, made of basalt, is created.

When two plates come together, it is known as a convergent boundary. The impact of the two colliding plates buckles the edge of one or both plates up into a rugged mountain range, and sometimes bends the other down into a deep seafloor trench. A chain of volcanoes often forms parallel to the boundary, to the mountain range, and to the trench. Powerful earthquakes shake a wide area on both sides of the boundary.

If one of the colliding plates is topped with oceanic crust, it is forced down into the mantle where it begins to melt. Magma rises into and through the other plate, solidifying into new crust. Magma formed from melting plates solidifies into granite, a light colored, low-density rock that makes up the continents. Thus at convergent boundaries, continental crust, made of granite, is created, and oceanic crust is destroyed.

Two plates sliding past each other forms a transform plate boundary. Natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. As the plates alternately jam and jump against each other, earthquakes rattle through a wide boundary zone. In contrast to convergent and divergent boundaries, no magma is formed. Thus, crust is cracked and broken at transform margins, but is not created or destroyed.

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