Intermediate‐wavelength magnetic anomalies over the central Pacific

Abstract

We have extracted the intermediate‐wavelength magnetic anomaly field from the marine survey data of the central Pacific in the band pass of 4000–400 km (spherical harmonic degree 10–100). Our technique minimizes the effects of external field sources, secular variation, and strike aliasing. The objective of this paper is to demonstrate this capability, compare the derived sea surface field to the equivalent MAGSAT data set, and demonstrate that anomalies observed in both fields are correctable to geologic features within the oceanic lithosphere. As expected, the sea surface field exhibits a strong spatial correlation to and a better resolution than the MAGSAT field. However, the MAGSAT field also displays a diminished resolution for wavelengths less than 1900 km when compared to the upward continued sea surface data. Two reasons are likely for this diminished resolution: (1) differences in the resolution of the spherical harmonic reference fields and (2) an increased noise level in the MAGSAT data at the shorter wavelengths. Other sources of error are also considered. We also demonstrate that the remanent magnetization of the central Pacific seamounts produces negative magnetic anomalies which are observed at satellite altitude. Other sources including the thickened crust of the oceanic plateaus and regional petrologic variations can be associated with intermediate‐wavelength anomalies observed in both the MAGSAT and the sea surface fields.