An alternative explanation for intermediate‐wavelength magnetic anomalies

Abstract

Harrison and Carle [this issue] and others have examined very long profiles of the magnetic field and have calculated one‐dimensional power spectra. In these they expect to see, but do not find, a minimum in power at intermediate wavelengths, between 65 and 150 km. Conventional one‐dimensional models of the field predict very little power in this band, which lies between the spectral peaks arising from sources in the crust and the core. Mantle sources or high‐intensity, long‐wavelength magnetizations have been proposed to account for the observations. An alternative, more plausible explanation is that one‐dimensional spectra of two‐dimensional fields contain contributions from wavenumbers in the perpendicular (i.e., nonsampled) direction. Unless the seafloor spreading anomalies are perfectly lineated at right angles to the profile, some low‐wavenumber energy must be attributed to this effect; we propose that such directional aliasing is a major factor in the power spectra. To support this idea, we discuss theoretical models and analyze a large‐scale marine survey.