Age dependence of oceanic intraplate seismicity and implications for lithospheric evolution.

We have determined depths for 16 oceanic intraplate earthquakes using body wave modeling. A data set composed of these and 11 other well-constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700o-800oC isotherm. The maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion. The maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics. -from Authors