CONSTRAINTS ON PRESENT-DAY SHORTENING RATE ACROSS THE CENTRAL EASTERNANDES FROM GPS DATA

Two years of continuous GPS data from several sites in South America i ndicate that Arequipa in the southern Peruvian Andes has a velocity of 13+/-3 mm/yr (two standard errors) to the northeast with respect to s table South America. We interpret these data as reflecting a combinati on of elastic strain accumulation associated with a locked Nazca-South America subduction zone and a small amount of crustal shortening acro ss the fold and thrust belt on the eastern margin of the Andes. Models of elastic strain accumulation for fully locked and partly locked sub duction zones constrain shortening in the eastern Andes to 0-3 mm/yr ( fully locked) and 0-12 mm/yr (partly locked), slower than some geologi c estimates averaged over millions of years.