Going back to my Shaking Earth entry of March 1, note the epicenters within the box using different colored symbols.
Compare this to the figure below from the Chile earthquake poster. This shows the depth of the quakes in the box of the earlier post, projected onto the central line. The colors show the depths of the earthquake hypocenters (or foci, plural of focus): red for depths of 0-69 km, green for 70-299 km, and blue for depths of 300-700 km. (The figure below doesn't show any blue dots.) But you can see the downward dipping slab of seismicity, also known as a Benioff zone, along the Nazca plate as it subducts beneath the South American plate. There are also some shallow (red) quakes to the right,occurring in the overriding South American plate. And, you will also note the volcanoes on the South American plate, represented by the yellow triangles. These occur when the downgoing slab partially melts, and the magma rises to the surface. This cross-section view (from the side) complements the earlier map or plan view (bird's-eye view) to give a three-dimensional representation of seismicity.