Now that assignment 4 has already been turned in, I was just wondering, how does the Wadati-Benioff zone help us define the location of subducting plates? I understand what the Wadati-Benioff zone is but i didn't understand the second part of that question.

-- maureen kasperek (moeyy15@aol.com), December 15, 2002

Answers

All we see on earth's surface at a subduction zone is a trench on the ocean floor and a volcanic arc on the overriding plate. The volcanic activity is due to subduction, but we can't see the subducted plate, so how can we be more certain that this process is occuring? The increasing depth of earthquake foci from the trench toward the volcanic arc can be explained as the result of tremendous stress created as a plate is subducted. The earthquake foci "show" us the boundary between the subducted plate and the overriding plate and asthenosphere. Sometime the subducted plate dives steeply below the overriding plate, and we see a rapid increase in the depth to focus of earthquakes at increasing distances from the trench. In other cases, the subduction is at a gentler angle and there is a more gradual increase in depth to focus with distance from the trench.

Does that make sense to you?

-- Sharon Gabel (gabel@oswego.edu), December 16, 2002.