Abstract

The Benioff zone geometry beneath southern Peru is determined using 32 months of arrival-time data from a local seismic network. Our data set includes 2476 located events, of which 205 are chosen to be master events; earthquakes with the most reliable locations. All the events are then relocated using sourceregion dependent station corrections derived from the station residuals of the master events. We find that the Benioff zone in the more southerly region of our study area dips at a nearly constant 30° to a depth of at least 200 km, while in the more northerly region this trend is apparent down to a depth of only 100 km, at which depth the Benioff zone becomes nearly horizontal. There are enough earthquakes in our data set in the transition zone between the regions to show conclusively that the deformation of the Benioff zone is continuous; i.e., there is no discontinuity in the seismicity that might suggest a tear in the subducting plate. These results corroborate those of Hasegawa and Sacks (1981) which used only about a third of the data now available.

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