Age–length dependence of inclined seismic zones

Abstract

HEAT flow, and hence lithospheric temperature, in the South Atlantic, North Pacific and East–Central Pacific has been shown^1,2 to decrease systematically with increasing age of the sea floor. As the oceanic lithosphere is consumed at a subducting plate margin, the limiting depth of earthquakes associated with the downgoing plate is ultimately determined by the temperature at which the lithosphere becomes too hot for brittle deformation to occur³. Isacks et al.⁴ have demonstrated that a crude correlation exists between the length of inclined seismic zones and the rate of consumption of lithosphere. However, Hyndman and Riddihough⁵ have commented that aseismicity may well result in regions where young lithosphere, at elevated temperatures, is being subducted. Here, we evaluate the latter idea and further, on the basis of a study of South American seismicity, we propose that there is a relationship between the length of inclined seismic zones and the age of the sea floor being subducted.