What structures does the earth have deep under our feet? A new 3D model now shows the global crust and mantle in greater detail than ever before. The image of the lithosphere is based on the combination of gravitational data from an ESA satellite with geological and seismic information. The model can now contribute to a better understanding of the dynamic processes in depth. It has already provided insights into the uplift in parts of North America after the loss of the Ice Age ice sheet.
Continents migrated, mountains piled up and ocean basins opened: the face of our home planet has changed constantly over the course of millions of years and it will continue to do so. Because the outer shell of the earth is constantly in motion. Scientists have long tried to gain insight into the basics of plate tectonics, because these processes are also associated with earthquakes and volcanic eruptions. Information about the structures in the so-called lithosphere, which includes parts of the earth’s upper mantle and the earth’s crust above, is of crucial importance.
Integrated gravitational data
In order to record the characteristics of the earth’s subsurface, geologists traditionally use rock analyzes and data that arise during earthquakes: Based on the speed at which the seismic waves propagate, conclusions can be drawn about the temperature and density of the rock in the area of an earthquake. Models of the lithosphere have already been created on the basis of such data. “But they had limited resolution or were limited by the way the data was linked,” says Javier Fullea of the Complutense University in Madrid. For the development of the new model as part of the ESA project “3D-Earth”, Fullea and his international colleagues used another source of information: global gravitational data from ESA’s GOCE satellite.
For more than four years, GOCE mapped the subtle differences in the gravitational relationships of the terrestrial lithosphere with extreme detail and precision. As the researchers explain, the data from space can complement the picture of the structures in the subsurface, since the strength of the gravity signal is related to the density of the material. Another great advantage of the information source is that the satellite data cover the earth evenly and thus also areas of which there are hardly any ground measurements.
For the new 3D model of the lithosphere, the scientists have now linked the global gravitational data from the GOCE satellite with seismological observations and rock information. “This combination enabled us to describe temperature conditions and compositions in the mantle rock in a new way,” says Fullea. It is therefore a further step towards the goal of better understanding the structure and geological processes of our planet.
How a geological dent rises
“With the combination of satellite, earthquake and rock data, we can, so to speak, look with a magnifying glass on the well-known shell model of the earth’s interior and differentiate the individual layers much more precisely than before,” says Nils Holzrichter from the Christian Albrechts University in Kiel. He and his colleagues used the new model in their current study. The focus was on how the so-called “Laurentide Ice Sheet” had affected North America. This massive layer of ice covered parts of what is now Canada and the United States during the last ice age and weighed down the land masses.
Then the glaciers melted 20,000 years ago. This loss of pressure had consequences: Since then, the North American continent has been slowly rising again because the lithosphere springs back as if in slow motion. “The model made it possible to determine more precisely than before what further increase is still to be expected,” says co-author Wolfgang Szwillus. Accordingly, a further uplift of at least 200 meters is to be expected. The fact that the processes are not completed even 20,000 years after the glaciers melted shows how sluggishly the earth’s mantle reacts to the deformation. “A better understanding of how quickly the lithosphere reacts to ice mass losses is also extremely important with a view to climate change,” says Szwillus.
Finally, Roger Haagmans from ESA comments on the results of the “3D-Earth” project so far: “This work sheds new light on the structures and processes in the earth beneath our feet. Even if they happen deep down, they have an impact on the earth’s surface – from the renewal of the sea floor to earthquakes, which in turn affect us all, ”says Haagmans.
Video: European Space Agency, ESA
Source: ESA, Christian-Albrechts-Universität zu Kiel, specialist article:
Geophysical Journal International, doi: 10.1093 / gji / ggab094
Journal of Geophysical Research: Solid Earth, doi: 10.1029 / 2020JB020484