Physics
Scientific paper
Nov 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990pepi...64...68s&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 64, Issue 1, p. 68-86.
Physics
23
Scientific paper
Equivalent scalar magnetotelluric response functions obtained from the robust analysis of geomagnetic field daily mean values at 16 magnetic observatories have been systematically inverted. Data from these sites were found to contain sufficient one-dimensional (1-D) data consistent with required source field assumptions for meaningful interpretation, and were also found to have acceptably well-bounded response function confidence limits. Previous work is reviewed which indicates that significant lateral heterogeneity in mantle conductivity structure is required by the data, and that most of these data are adequately modeled by a series of simple two-layered Earth models with a conductivity jump at depths of 500-1000 km. Regional variations in upper mantle conductivity have previously been suggested by systematic inversion using the H+ algorithm. These features are examined in the restricted model space of conductance delta functions. The statistical significance of these variations is also investigated. New evidence is found here for the coast effect at very long periods, as well as related evidence for the presence of electrically conductive zones in the upper mantle beneath the Pacific Ocean. Semi-norm minimization inversion techniques are applied to directly place strong constraints on the sharpness of the vertical conductivity gradient in the mid-mantle. The mid-mantle conductivity jump is required to be abrupt, with values beneath this mid-mantle transition zone of O (1 S m-1) at all sites.
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