Earth Magnetism: A Tool for Subsurface Studies (GC-04)
Most geologic exploration is restricted to surface observations except for
isolated glimpses below the surface in caves, mines and drill holes.
Because such features are widely scattered, geophysicists at the Indiana
Geological Survey must use indirect methods to study materials far below
the surface of Indiana. The earth's magnetic field at Bloomington points
almost true north and downward at an angle of about 70 degrees. If a
magnetic body lies buried within the earth, it distorts this magnetic
field very slightly. Sensitive magnetometers can detect and measure these
changed in the earth's magnetic field. Analysis of these measurements can
tell us something about the deeply buried bodies of rock or minerals that
caused them. Most variations in the earth's magnetic field in Indiana are
due to differences in the iron content and depth of basement rocks
hundreds of millions of years old.
Our Hoosier State Beneath Us: