We propose that the flexure of a broken elastic plate can determine the
spacing of consecutive and localized zones of shearing on a lithospheric
scale. The model provides a dynamic explanation for rift axis migration
and, as a consequence, for a `wide rift' mode of extension. Calculated
values for rift axis shifting are consistent with the available
observations and kinematic modelling results in the Tyrrhenian Basin.
The quantitative relation obtained between lithospheric fault spacing
and the effective elastic thickness (T-e) of the lithosphere can be used
in an inverse modelling approach, in which paleo T-e values are
calculated for a basin where the diachronous and spaced nature of
rifting is known.