Project Details
Projekt
HYPO-TZ - Generation and assessment of hypothetical seismic mantle transition zone structures
Subject Area
Geophysics
Term
since 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 433009203
The mantle transition zone (TZ), typically defined as the region between about 410 to 660 km depth, marks the boundary between upper and lower mantle. It is characterized by a highly complex mineralogy and a general increase in viscosity, but no consensus has been reached yet regarding its influence on global mantle circulation. The complex behaviour of the mineral phase assemblage as a function of pressure and temperature likely impacts the vertical mass and heat flow through the TZ due to variations in buoyancy, latent heat effects as well as the potentially associated variations in rheological properties. Despite numerous studies in seismology, geodynamics and mineral physics in the last decades, no clear and consistent picture of the TZ and its influence on mantle flow has emerged yet. In this project, we aim at providing new insight into TZ structure and global mantle dynamics based on a multi-disciplinary theoretical forward-modelling approach together with comparisons of the hypothetical scenarios with seismic observations. Our study includes simulations coupling high-resolution mantle circulation models, thermodynamic models of mantle mineralogy and 3-D global seismic wave propagation as well as processing of synthetic and observed seismic data. In the first project phase, we made significant progress by linking the thermal and the seismic TZ structure of high-resolution mantle circulation models in a quantitative manner taking into account the effects of limited seismic resolution and mineralogical uncertainties. Moreover, we presented the first realizations of global TZ discontinuity topography based on geodynamically predicted 3-D temperature fields. The main objective of this follow-on project is to now provide a better quantitative understanding of the seismic signature of the TZ in the light of 3-D wavefield effects with emphasis on the seismic data processing aspects. In particular, we will predict full 3-D waveforms for our MCMs in a theoretical closed-loop experiment to investigate the ability of existing processing techniques to retrieve TZ structure from seismic observations. In addition, comparisons of the hypothetical scenarios with real seismic data will provide a better understanding on how to interpret seismic observations of TZ structure and will make it possible to identify the datasets and observables, such as PP/SS precursors or receiver functions, that are best suited to test geodynamic models and their underlying assumptions against Earth observations. Our project will provide new insight into the role of combined mineralogical and rheological effects in linking material flow in the upper and lower mantle.
DFG Programme
Research Grants
International Connection
France, Netherlands
Cooperation Partners
Professorin Dr. Arwen Deuss; Professor Dr. Benoit Tauzin
