Research Interests

My research focuses on better understanding the properties, structure and dynamics of the earth through the use of seismic imaging methods, namely receiver function analysis and shear wave splitting.  Below I outline some of my major research interests.   For a more detailed look, check out my blog where I discuss my published work and ongoing efforts.

Understanding the origin and evolution of stable continental interiors

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(top left) Map of stations used in study. Red lines indicate cross sections locations. (cross sections) Sp receiver functions for seismic stations. Positive (red) phase at ~30-40 km at each station is Moho. Negative (blue) phase at ~60-110 km is interpreted as either MLD (between grey dots) or LAB (beneath grey dots). From Ford et al. (2010).

The formation, evolution and longevity of continental interiors, and more specifically cratons, is an area of research in which our understanding is still evolving. Recently imaged interfaces within the mantle lithosphere (see Ford et al., 2010; Abt et al., 2010; Hopper et al., 2014) have reignited debate on how the cratons may have formed and evolved (see Selway et al., 2015). We have recently tested hypothesis that these interfaces (termed mid-lithospheric discontinuities) are the result of boundaries of deformed mantle material which express themselves as seismic anisotropy (directional dependence of seismic wave speed). Our results indicate that the continental interiors are extremely complex and record a spatially and temporal complex deformation/tectonic history (Ford et al., in review). I have recently received funding to continue research in Australia using a combination of techniques to better understand the origin of these complicated, yet intriguing, deformation fabrics and their relationship to the tectonic history of the continent.

The structure of tectonic plate boundaries

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(left) Map of LAB phase amplitudes (A) and depths (B). A statistically significant change in LAB amplitude is observed across the SAF fault system.  (above right) Cartoon interpretation of plate boundary geometry within the mantle (Ford et al., 2014).

The distribution of deformation at the base of lithospheric mantle beneath strike-slip plate boundaries is uncertain. Transform-boundary models range from diffuse shear zones hundreds of miles across to localized strike-slip shear zones that are deep extensions of individual crustal faults.

In California, an extensive dataset of scattered shear-waves (>135,000 waveform sets) was utilized to produce the first detailed three-dimensional image of the lithosphere-asthenosphere boundary (LAB) across the entire San Andreas fault system.

The results indicate that a systematic variation in LAB phase amplitude (which corresponds to a change in the physical properties and/or distribution of properties) occurs across the fault system, which requires a rapid lateral change in the vertical seismic velocity gradient that defines the seismological LAB. Importantly, these results imply that the width of the plate boundary remains relatively narrow (<50 km wide) to the base of the mantle lithosphere, in contrast to many previously published models.  For a more detailed description and summary of results, see Ford et al. (2014).

Characterizing lower mantle flow

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(above left) Map of shear wave velocities, with shear wave splitting measurements superimposed.  (above right) Cartoon of mantle flow direction that best fits the measurements shown at left.  For a complete description, see Ford et al. (2015).

The existence of two large low shear velocity provinces (LLSVPs) in the lower mantle beneath Africa and the Pacific has been well documented through the use of seismic tomography imaging. LLSVPs are thought to represent areas of chemically distinct, higher velocity material, and may act as a source for mantle plumes, however the interpretation of their origin, structure, composition, and dynamics is still poorly understood.

Utilizing observations of seismic anisotropy from analysis of shear wave splitting of SKS, SKKS and ScS phases, mantle flow along the edge of the African LLSVP in the lowermost mantle (D”) is best fit by a conceptual model in which the African LLSVP acts as a barrier to flow in the lowermost mantle, resulting in a vertical-to-oblique deflection of mantle material.

This work also supports the model that lower mantle anisotropy is due to the presence of post-perovskite.  More recently, I have utilized the same data set to evaluate previously published mantle flow models (see Ford and Long, 2015).

Other areas of active research

Current work is also being conducted on examining models of lithospheric extension in the Basin and Range, lithospheric deformation in central California, the rheology of the lithosphere-asthenosphere boundary in southern California and in the Canadian Shield.