Triple junction
While most places have trenches where two large tectonic plates meet, Chile is one of the few places where three major plates meet. In other words, it is a triple junction.
The Nazca Plate, borders the South American Plate for most part of the continent. But towards the tip of the continent and bordering Chile is the Antarctic Plate.
The Nazca Plate is subducting beneath the South American Plate at a rate of 80 mm a year; the Antarctic Plate is subducting beneath the South American Plate at a rate of 20 mm per year.
What makes Chile suffer from very powerful quakes is the fact that the angle of subduction (diving) by the Nazca Plate below the South American Plate is very shallow — 5 to 15 degrees.
The place where one plate subducts beneath another is called a trench. The place where new ocean crust is formed is called a ridge. It can be seen as the recycling of the ocean crust — new ocean crust is formed at the mid-oceanic ridges and is consumed (destroyed) at the subduction zones (trenches).
Chile: where three tectonic plate boundaries meet | Science Chronicle (journosdiary.com)
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