- Wed Feb 03, 2021 10:31 pm
In the second paragraph, the author tells us about a theory by scientists who are trying to explain why there are some areas with high levels of subduction that nevertheless relatively free of earthquakes. The scientists propose that the difference has to do with the direction the plates are moving in. In the areas with lots of earthquakes, the plates move in opposite directions; in the earthquake free zones, the plates move in the same direction.
Why does the direction that the plates are moving in impact the likelihood of earthquakes? The paragraph goes on to state that when the plates are moving in the same direction (relatively few earthquakes) "the overtaking plate in this type of collision reduces the amount of contact between the two plates, and the earthquake-producing friction is thereby reduced as well." But when the plates are moving in opposite directions (areas with lots of earthquakes), "the subducted plate receives relatively little resistance from the mantle, and so its angle of descent is correspondingly shallow, allowing for a much larger plane of contact between the two plates." So the reason that the directions the plates are moving in affects earthquake likelihood has to do with how large the plane of contact is between the two plates.
All of this suggests that it's the large plane of contact between plates during subduction that makes it more likely for earthquakes to occur.
Hope this helps!