Deep structures of the Ecuador convergent margin and the Carnegie Ridge, possible consequence on great earthquakes recurrence interval

Geophysical Research Letters, v. 31, p. L04603, 2004. http://dx.doi.org/10.1029/2003GL018803International audienceThe deep structure of the Ecuador subduction zone and adjacent Carnegie Ridge (CR) was investigated using onshore offshore wide-angle seimics. A crustal model obtained by 2-D inversion of traveltimes reveals the overthickened (14 km) oceanic crust of the CR that underthrusts the high velocity (>6 km/s) basement of the upper plate margin wedge, interpreted as part of the accreted oceanic terranes described onshore. The plate interface dips 4°to 10°east from the trench to a depth of 15 km. Shadow zones observed on the margin OBS records are interpreted as a low velocity zone consisting of a thin layer of underthrust sediments, and the 3-km-thick CR layer 2, whose average seismic velocity of 5.1 km/s is slower than that of the margin wedge. Increased interplate coupling related to the subduction of the thick, buoyant CR may account for an apparent local increased recurrence interval between great interplate earthquakes