Imaging the deep Earth: Attenuation tomography using novel observations of free oscillations

NWO Vici Grant

NWO Vici Grant
November 2016 – November 2025
Awarded to Arwen Deuss

Description

Tectonic phenomena like volcanic eruptions and earthquakes are driven by convection deep in the Earth’s mantle. Tomography has been very successful in imaging Earth’s internal variations in seismic wave velocity. However, velocity is insufficient to obtain robust estimates of temperature, water content, melt and composition and make direct links between seismic models, mantle convection and surface tectonics. Thus, it is unclear if any water or partial melt is present in the deep mantle and if lower mantle convection is driven by large-scale thermal or compositional heterogeneity. Seismic-wave attenuation (loss of energy) is key to mapping melt, water and temperature variations, and answering these questions. Unfortunately, attenuation has only been imaged using short- and intermediate-period seismic data, showing little similarity even for the upper mantle and no reliable lower mantle models exist. The aim of this project is to develop novel full-spectrum techniques, apply these to Earth’s long-period free oscillations, and then image global-scale regional variations in seismic attenuation from the lithosphere to the core-mantle boundary. The advantage of free oscillations is that they do not require approximations and have global coverage. This enables me to include scattering and focusing – problematic for shorter period techniques – using cross-coupling (resonance) between different free oscillations. My world-leading expertise in free-oscillation theory and observational techniques in combination with the increase in computer power and recent occurrence of large earthquakes, makes it now possible to unravel the small attenuation signal from free-oscillation data. We will increase the frequency dependence of attenuation to a much wider band, allowing us to distinguish between scattering (redistribution of energy) versus intrinsic attenuation. The project will deliver the first ever full-spectrum global tomographic model of 3D attenuation variations in the lower mantle, providing essential constraints on melt, water and temperature for understanding the complex dynamics of our planet.