July 13, 2009 The Earth's mantle, situated under the Earth's crust, is very much the spot for studying interesting geological processes. Although we do not realise it, right under our feet there is a sultry world of circulating Earth layers. We only come into contact with these hot Earth layers in the event of earthquakes and volcanic eruptions. It is therefore important to learn more about the characteristics of the Earth's mantle.
These characteristics can be portrayed using seismic waves. However, the techniques used for this purpose still have various shortcomings. Dutch-sponsored research Ebru Bozdag demonstrated this during her doctoral research.
Seismic waves are frequently used to image the Earth's mantle. They are generated by earthquakes and registered with measuring equipment. Subsequently the characteristics of the seismic waves are converted into an image of the geological structure of the layer. Bozdag used 3D-simulations of seismic waves to test the reliability of these images. She specifically focused on tomographic images. These are the images where the mantle is portrayed in a 3D cross-section. The mantle tomography techniques currently used are still far from perfect.
As measurements of the mantle are influenced by the Earth's crust above, the data are corrected for this. However, Bozdag's research revealed that due to inaccuracies this correction can still lead to erroneous data and consequently an incorrect interpretation of the measurements. The outcome is a wrong representation of the mantle. The imperfections demonstrated for the crust layer are shocking. Characteristics previously attributed to the mantle now appear to be merely the result of these wrong corrections. Thanks to new computer facilities, Bozdag is the first to have demonstrated these problems using simulations.
The problems can be alleviated by no longer correcting for the crust but by measuring both the mantle and the crust and by using 3D wave simulations as a control tool. These techniques are not only suitable for studying the Earth's mantle but can also be used on a smaller scale. Obtaining an accurate picture of the Earth's structure is vitally important. Besides providing insights into the geological evolution of the Earth, it also provides more information about the development of earthquakes.
Bozdag's research took place within the SPICE project of the European Union and the NWO Vici project 'Quantitative Seismology: Toward a New Understanding of Earth's Deep Interior'.
Bozdag shall continue this line of research during a postdoc at Princeton University, where she wants to focus on on the Marmara region in Turkey, a risk area for earthquakes.
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The above story is based on materials provided by NWO (Netherlands Organization for Scientific Research).
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