Lower Mantle Seismic structures investigated with unusual seismic phases

• Applicant: Professorin Dr. Christine Thomas
• Subject Area: Geophysics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 505078268

Understanding structures in the Earth lower mantle provides information about mineralogy and dynamics within the mantle. Especially the lowermost mantle has been shown to contain a number of different structures on several length scales including reflectors at different depth and large regions of reduced velocity (LLSVPs) as well as scattering regions. While it is possible to test many regions in the Earth, a better coverage is often limited by i) the available source-receiver combinations and ii) distance ranges needed to study a particular seismic wave and hence a particular region in the Earth's mantle. In this study, we aim to use unusual seismic arrivals in the wavefield, understand and validate their origin using modelling of scattering layers, anisotropy or seismic discontinuities to mention only a few. This proposal is in part exploratory and in the first funding period we have studies unusual arrivals that can be explained with a scattering layer in the mid mantle. We have also modelled anisotropy using geodynamic constraints and mineral physics results, to explain arrivals in the wavefield. And additionally, we explored the mantle transition zone and upper mantle in the Arctic, finding that some arrivals indicate the presence of MORB beneath a subducted slab. Following the first funding period, a number of studies are necessary to verify our current interpretation, to test how other waves in the wavefield are affected by the structure we propose to cause the unusual seismic arrivals, and to test whether these affected waves corroborate our interpretation. To successfully finish this study, and in order to be able to study large datasets, we will also develop and employ a machine learning approach. The mantle regions we propose to study include the mid mantle (scattering layer, anisotropy and discontinuities) and the lowermost mantle with similar structures. The synthesis of the different tasks will help to distinguish different structures, and verify structures with other seismic arrivals. And since we will use all available information, including amplitudes, polarities, waveforms, arrival times and frequency dependence and the proposed seismic modelling results can we achieve to gain detailed knowledge on seismic structures in the mid and lower mantle.

• DFG Programme: Research Grants
• International Connection: China
• Cooperation Partner: Professor Dr. Daoyuan Sun