A New Method for Accurate and Efficient Modeling of the Local Ocean
Induction Effects. Application to Long-Period Responses from Island
Geomagnetic Observatories
Abstract
There is significant interest in constraining mantle conductivity
beneath oceans. One data source to probe oceanic mantle conductivity is
magnetic fields measured at island observatories. From these data local
responses are estimated and then inverted in terms of conductivity.
However, island responses may be strongly distorted by the ocean
induction effect (OIE) originating from conductivity contrasts between
ocean and land. Insufficiently accurate accounting for OIE may lead to
wrong interpretation of the responses. OIE is generally modeled by
global simulations using relatively coarse grids to represent
bathymetry. We explore whether very local bathymetry influences island
responses. To address this question we developed a methodology for
efficient modeling of effects of bathymetry of any resolution. On an
example of two island observatories we demonstrate that small-scale
bathymetry dramatically influences the responses. Using new methodology
we obtain new conductivity models beneath considered islands and observe
remarkable agreement between modeled and experimental responses.