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 == Accuracy about direction of arc? == 

 This article states ""Subduction zones are arc-shaped, with the concave side oriented away from the direction of subduction because of the curvature of the Earth.""  This seems to me to indicate that that the concave side of the arc would occur on the subducting plate side, not the over riding plate side.  This doesn't seem to be correct. Consider the Aleutian Islands where the Pacific plate is sliding under the North American Plate and the arc is on the northern (over riding plate side).  In South America, the seven arcs are either straight (not concave) or are concave on the continental side.  At the very least, this needs to be reworded for clarity.   "