Deep Earth Seismology

Nature of Project

Computational and observational

Essential Background

• PHYS 3070 (Physics of the Earth)
• EMSC 8023 (Advanced Data Sciences)
• EMSC 80XX (Computational Geosciences)

Background

Deep Earth seismology focuses on the Earth’s mantle, outer core, and inner core. We study these using seismic energy from earthquakes, to determine properties such as velocity, attenuation, and anisotropy. Seismology is the only method which permits us to “see” directly into Earth’s deep interior, and hence reveal its structure and processes. These projects require data compilation, processing, and analysis, and modelling including theoretical calculations and generation of synthetic seismograms. The work will apply existing methodology, with opportunities to develop further observation and analytical techniques.
 

Possible future research avenues

  1. Revealing the hidden layer at the top of Earth’s inner core: Earth's inner core is the most extreme and dynamic environment of our planet. Approximately the size of our moon, with a temperature similar to the sun, this solid metal sphere is growing slowly as Earth cools. Its solidification has wide-ranging implications, helping to generate the geodynamo and drive mantle convection. However, due to the inner core's remote location, we know comparatively little about it. Seismologists previously discovered an east-west hemispherical asymmetry in the inner core properties. This structure has been well-documented in the upper 20-100 km of the inner core. However, the region between 0-20 km depth has not been constrained, due to several seismic waves arriving at the same time and interfering. The top region of the inner core is the location of current growth, and observations of the seismic structure may identify regions of stronger and weaker solidification, or potentially even regions of melting. Recently, we developed a technique to model the seismic phases and reveal the structures in this layer. The goal is to advance this method and apply it to new regions of the inner core, to map the anisotropic velocity structure and hemisphere boundaries, and understand the origin of the inner core hemispheres.

  2. Why does material get stuck in the mid-mantle? Exploring slab stagnation near Australia: The mantle is characterised by convecting material: hot upwelling plumes, and cold downgoing slabs. In the upper mantle, the seismic structure is dominated by discontinuities caused by mineral phase changes as pressure and temperature increase with depth. Major discontinuities are located at 410 and 660 km depth, and their depth and strength depends strongly on temperature. Some phase transitions can also impede convecting material, and downgoing slabs are observed to become stuck at the 660 km transition. Tomography reveals that both up and downwelling mantle flow is also deflected in the mid-mantle. However, there are no candidate phase changes to explain this phenomenon. Other explanations remain unconfirmed. A recent global study of the mid-mantle discontinuities shows many regional-scale reflectors from 800 to 1300 km depth. These reflectors display a strong correlation to up and downwelling material, but the relationship to both composition and deflection of flow is an unanswered problem. This work will use seismic waves which reverberate between the core-mantle boundary and the mid-mantle discontinuities. The observations will constrain detailed structures, and provide insight into how and why only some slabs stagnate, with a primary focus on those interacting with the Australian tectonic plate.

For more information about this potential research topic or activity, or to discuss any related research area, please contact the supervisor.