Research

Elasto-gravitational simulations with SPECFEM

Supervised by Jeroen Tromp (Princeton University), in collaboration with Hom Nath Gharti (Queen's University)

Modelling Earth's gravitational potential field is of significant interest for both geodynamic forward and inverse problems. The fact that potential fields, unlike other fields such as displacement, are non-zero outside of a body has provided a challenge for numerical modelling as infinite space can not be meshed. This has placed limitations on numerical modelling of geodynamic processes occurring over long timescales which require consideration of gravitational forces.

SPECFEM-X, recently developed by Hom Nath Gharti and Jeroen Tromp , incorporates gravitational potential fields into SPECFEM-GLOBE using a spectral infinite-element method to solve the Laplace equation in an unbounded spatial domain (see Gharti et al 2018). This refinement enables modelling of 3D quasi-static and elastic problems involving all the features of SPECFEM-GLOBE, but with the additional capability to accurately model spatio-temporal changes to the gravitational field.

My current research involves utilising this new toolkit to simulate prompt elasto-gravitational signals (PEGS), Earth's nutations and wobbles, as well as visco-elastic modelling of sea-level change.

Our manuscript describing seismic-wave propagation incorporating self-gravitation was published recently in Geophysical Journal International, and can be found here.

Seismic scattering and wavefield diffusivity

Supervised by Tarje Nissen-Meyer (University of Exeter)

Seismic-wave scattering is observed, to variable degrees of strength, on all planetary bodies for which seismic records exist (e.g. from the InSight and Apollo missions). Global-scale imaging using scattered wavefields is a relatively juvenile topic within seismology, but it is capable of resolving structure orders-of-magnitude smaller than is possible using traditional inversion methods such as tomography. Current scattering models and analytical methods are limited to two end-member phenomena: weak single- or multiple-scattering events (ballistic), or intense scattering such that the wavefield retains no phase information (diffuse). My research explores the existence of scattering behaviour intermediate between these end-members, and the dominant properties of heterogeneous media that facilitate a transition between them. We use novel analytical techniques such as multi-scale entropy and frequency-correlation analysis. Combining these newly-developed techniques with traditional analytical methods provides a promising framework for future exploration of scattered wavefields across ballistic, transitional, and diffuse regimes. The analytical methods developed are also being used in consideration of nuclear bomb test monitoring.