Download The Wadati-Benioff Zone

In Class Exercise – Plate Tectonics
trench, i.e. where the
two plates meet at the
surface of the Earth.
KEY
Name: __________________________
The plot above shows a cross sectional view of earthquake hypocenters at some plate
boundary in the Earth. Answer the following questions based on this graph.
1) What type of plate boundary is this? Convergent.
How do you know? Because the earthquakes are following a curved path that mimics the shape of a subducting oceanic
plate. Other plate boundaries would simply have a vertical pattern of earthquakes below the transform or
divergent plate boundary.
2) If it is a divergent boundary, label where the ridge (spreading center) would be, if
convergent, label the trench location, or if it is a transform, label (circle the region) where
the transform fault comes to the surface of the Earth labeled above...
3) This particular plot, in general, shows a very specific tectonic feature. What is it
called? Wadati-Benioff zone. This is the idea that earthquakes map out the shape of the downgoing oceanic plate.
4) At what horizontal location in this plot is there evidence for volcanic activity? (hint:
magma movements create earthquakes) Why is there volcanic activity here?
at 500 km there is evidence for volcanic activity. There is volcanic activity here because the downgoing plate has
released its water due to increased pressure. The released water rises and lowers the melting temp of the rocks
above, causing melting. The melted rocks then rise and form volcanoes.
5) The earthquakes stop at 250 km depth, which implies that the material below 250 km is
acting in a ductile manner. What layer of the Earth is categorized by this behavior? Asthenosphere.