Dipole/quadrupole family modeling of paleosecular variation

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°.