Estimation of the Magnetizations of Geologic Bodies: The Poles of Uncertainty Slides

Monday, April 22, 2002 - 9:30am - 10:30am
Keller 3-180
Robert Parker (Scripps Institute of Oceanography)
Paleomagnetists usually determine the magnetization of geological units by sampling the material. In some environments this approach may be prohibitively expensive or even impossible. Then we must resort to inferences based the external magnetic fields of the bodies. The mathematical problem of inversion of a potential field for its sources does not have a unique solution.

The ambiguity can be reduced by: (1) introducing assumptions about the sources -- but this is often overdone; (2) estimating specific properties, rather than a complete source distribution; (3) both of the preceding.

The magnetization of seamounts, which are ancient submarine volcanos, is an important geological question. Paleomagnetists are primarily concerned with the direction of the magnetization vector, and so placing bounds on the direction of the vector is a useful exercise. The solution of this optimization problem will be discussed. Another setting, the planet Mars, provides different challenges. The very large size of the observed anomalies raises the question of a the magnitude of the magnetizations, which have been reported as ten times larger than those found anywhere on Earth. We describe how a strict lower bound can be calculated on the intensity, without assumptions about magnetization direction.