Analysis of the spatial distribution of seismicity beneath central Ecuador from a temporary network gives new insights on two main points of the Ecuadorian tectonics. Major structures in the Ecuadorian Andes are East-dipping Late Jurassic to Paleogene sutures reactivated by present-day compression. The oceanic plate is plunging continuously down to a depth of about 200 km with a dip of 25¿--35¿. We also show that the coastal plain acts as a buttress transmitting stresses to the Andes, beneath which deformation is concentrated. ¿ 2001 American Geophysical Union