A new way to find weakness in the Earth's crust

US and Australian scientists have developed a new method to estimate weakness in the Earth’s outer layers. Their work has been published in the journal Science and will help explain and predict volcanic activity and earthquakes at a much smaller scale than previously possible.

Geodynamic modelling relies on knowing the ‘viscosity’ or resistance to the changing shape of the Earth’s outer layers. As explained by study co-author Dr Derrick Hasterok, from the University of Adelaide, “Producing realistic models of these movements has been difficult because the small-scale variations in viscosity are often poorly known.”

Now, Dr Hasterok and his colleague Dr Lijun Liu, from the University of Illinois, have created a new model of the Earth’s movement in the upper crust through to upper mantle. The method uses an electromagnetic imaging technique called magnetotellurics to estimate the electrical conductivity beneath the Earth’s surface.

“The same factors which affect electrical conductivity — temperature, water content and the presence of molten material (magma) — also affect the viscosity or strength,” said Dr Liu. “The hotter, wetter or more molten, the weaker the structure.”

“In essence, we’ve developed a method to estimate small-scale (between one and 10 km) variations of viscosity within the upper 400 km of the Earth’s crust using surface-based electromagnetic imaging techniques,” said Dr Hasterok. The result is a dramatic improvement of flow models which can be used to make predictions about the forces driving tectonic plate deformation and sources of potential seismic and volcanic activity.

“This method will aid our understanding of the processes happening that cause earthquakes and volcanic activity,” said Dr Hasterok. “We’ll be able to see why earthquakes and volcanoes have occurred in the past and look for places where this might potentially happen in the future.”