Rapid Multi-dimensional Seismic Property Mapping of Earth Materials


   Department of Earth Sciences

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  Prof Hauke Marquardt  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Our planet’s inner dynamics and surface plate tectonics are governed by the properties of and processes in the Earth's lower mantle. A quantitative understanding of the physical and chemical properties of the lower mantle is key to modelling Earth’s dynamic evolution, including the long-term chemical interactions between mantle and atmosphere that are vital to habitability of Earth. The main approach to determining the structure, composition and dynamics of Earth’s inaccessible interior is to compare seismic interior maps of compressional Vp and shear Vs velocities, constructed from the analysis of Earthquake waves, to mineral physics predictions derived from deep Earth models. Unfortunately, this approach has led to highly ambiguous results on the state and composition of the lower mantle. The reason is that a unique interpretation of deep Earth seismic data critically relies on quantitative knowledge of the elastic (seismic) properties of Earth materials at extreme pressures and temperatures characteristic of the Earth’s deep interior. This information is largely incomplete, as existing methods for probing seismic properties are far too slow to provide the required detailed information. Seismic wave velocity measurements on mantle minerals in the diamond-anvil cell. The diamond-anvils are illuminated by the probing green laser light. The aim of this project is to develop a new experimental capability, using rapid transient grating spectroscopy (TGS) measurements to probe the elastic, i.e. seismic, properties of Earth materials in a Diamond Anvil Cell (DAC). TGS has the potential to allow measurements up to 4 orders of magnitude faster than currently-used Brillouin scattering methods. To fully exploit this speedup, automated experimental routines must be developed for TGS data collection for multiple sample orientations and changing pressures. This new capability would allow a very high resolution mapping of seismic properties as a function of pressure. By integrating a heating capability into the DAC, this could be further expanded to also allow the mapping of temperature dependence of elastic properties. This new tool will then be deployed to map out the pressure and temperature dependent properties of ferropericlase and optionally bridgmanite, the two main constituents of Earth’s lower mantle.

Geology (18)

References

Marquardt, H. and A. R. Thomson (2020).
Experimental elasticity of Earth’s deep mantle.
Nature Reviews Earth & Environment 1(9): 455-
469
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 About the Project