Geophysical Mapping
Geophysical mapping allows scientists to understand the composition and structures of rock beneath the Earth’s surface.
Although scientists cannot see rock that is deep beneath the Earth’s surface, they can still measure some important properties of these rocks that provide clues about what kinds of minerals they might contain, and how they are arranged beneath the Earth’s surface.
High-quality geophysical surveys are one of our best modern tools for identifying mineral, energy and groundwater resources, and natural hazards like buried seismic faults that cause earthquakes.
We are rapidly accelerating the collection of high-quality geophysical data across the Nation. We conduct three kinds of geophysical mapping:
Magnetic geophysical mapping
Rocks below the surface contain different amounts of magnetic minerals and therefore produce magnetic signatures that can be detected at the surface. Airborne magnetic surveys image geology just below the surface down to tens of miles into the crust. Data are collected by airplanes or helicopters flying roughly 300 ft above the surface equipped with an elongated sensor mounted to the underside of the aircraft. Magnetic data can be used to identify ancient faults, different rock types, and other geologic features including the signatures of potential mineral deposits.
Radiometric geophysical mapping
Rocks can also contain unstable atoms that produce radiation. These rocks typically aren’t radioactive enough to be harmful to humans, but the amount of radiation they produce can be useful for predicting what kinds of rocks lie below the surface of the Earth. For instance, rocks that are rich in uranium, thorium, and potassium are associated with radiometric hot spots.
By flying a plane equipped with special sensors, scientists can map the radiometric properties of large swaths of land. Most Earth MRI surveys collect magnetic and radiometric data at the same time using the same aircraft.
Electromagnetic geophysical mapping
This kind of geophysical mapping provides information about the electromagnetic characteristics of rocks up to a few hundred meters below the Earth’s surface. The data are typically collected by a low-flying helicopter or plane carrying a large circle of wire carrying an electric current that is capable of picking up nuanced contrasts in the conductivity of materials below the Earth’s surface.
Electromagnetic surveys are particularly helpful for identifying conductive minerals such as graphite and pyrrhotite. These data are also powerful for understanding the quantity and quality of groundwater resources.