What is the depth of the Nazca Plate?

Answer 1

On 9 June 1994, a magnitude-8.3 earthquake struck about 320 km northeast of La Paz, Bolivia, at a depth of 636 km
http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor5798673

Nazca Plate has a Convergent plate boundary with some subduction zones (volcanism) into the South American Plate.
Nazca plate itself (mostly oceanic) is mostly at a depth of about 100 km.
http://www.mhhe.com/earthsci/geology/mcconnell/plate_tectonics/pt.htm