Dipole/quadrupole family modeling of paleosecular variation

Abstract

Contrary to previous claims that the VGP scatter and its latitude variation deduced from the present field are atypical of those for the past 5 m.y., it is shown that it is in fact typical when correctly calculated. A simple and effective model for the paleosecular variation of lavas is developed by using this important observation together with the dipole and quadrupole families from dynamo theory. The model predicts a latitudinal variation of VGP scatter, S , given by , where λ is the latitude and A and B are parameters that depend on the contribution to the scatter from the dipole family and the quadrupole family, respectively. For the present field these parameters are estimated (95% confidence limits) as A = 0.24±0.02 and B = 13.5°±0.6°, and for the past 5 m.y. as A = 0.23±0.04 and B = 12.8°±0.6°.