Scientists have developed a method to estimate weakness in the Earth’s outer layers that could help in understanding and even predicting volcanic activity and earthquakes.

A collaboration between researchers at the University of Illinois and the University of Adelaide has produced a new geodynamic model of the Earth’s movement in the upper crust through to the upper mantle (400 km below the surface), allowing predictions at a much smaller scale than previously possible. Geodynamic modeling relies on knowing the "viscosity" of the Earth's outer layers, or their resistance to changing shape.

Geodynamic modeling relies on knowing the "viscosity" of the Earth's outer layers, or their resistance to changing shape. Image credit: Carol M. Highsmith/Library of Congress.“Producing realistic models of these movements has been difficult because the small-scale variations in viscosity are often poorly known,” says Dr. Derrick Hasterok, of the University of Adelaide’s School of Physical Sciences. “In essence, we’ve developed a method to estimate small-scale—between 1- and 10-kilometer—variations of viscosity within the upper 400 km of the Earth’s crust using surface-based electromagnetic imaging techniques.”

The method relies on an electromagnetic imaging technique called magnetotellurics to estimate the electrical conductivity beneath the Earth's surface. The same factors that affect electrical conductivity—temperature, water content and the presence of molten material (magma)—also affect viscosity.

"The hotter, wetter or more molten, the weaker the structure,” says Dr. Lijun Liu, assistant professor of geology at the University of Illinois.

The researchers used data from a magnetotelluric survey of the western United States to demonstrate that their model works. Currently, there is a continent-wide project mapping the Australian upper mantle using the same electromagnetic technique, and the researchers believe applying this data to their new model will bring improved understanding of volcanic and earthquake activity along the southeastern and eastern coasts of Australia.