Earth, Planets and Space

, Volume 53, Issue 1, pp 31–44 | Cite as

Shift of the mean magnetic field values: Effect of scatter due to secular variation and errors

Open Access
Article

Abstract

Paleomagnetic data are mostly given in the form of field directions (inclinations and declinations) which depend nonlinearly on the model parameters (Gauss coefficients). Because of this nonlinearity, the means of the data are affected not only by the means of the parameters but also by their fluctuations. Defining the mean directions by the Fisher method decreases this effect but does not completely eliminate it. For various mean fields, we evaluate the effect of secular variation on the means of Fisher-averaged directions by the analytical (Taylor expansion to the second order) as well as by the numerical (Monte Carlo) method. It was shown that a significant amount of offset occurs in the field values because of the fluctuation caused by secular variation. In the case of an inclination anomaly, the effect of secular variation as a function of latitude is antisymmetric about the equator, similar to that of the axial octupole term (g 3 0 ). We also show that the measurement errors do not induce biases in the mean field data, provided that they are random and isotropic.

Keywords

Secular Variation Direction Cosine Paleomagnetic Data Axial Dipole Nonlinear Data 

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Copyright information

© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2001

Authors and Affiliations

  1. 1.Department of Earth and Planetary ScienceUniversity of TokyoBunkyo-ku, TokyoJapan
  2. 2.Institute for Study of the Earth’s InteriorOkayama UniversityMisasa, TottoriJapan

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