My research has focused on the Woodlark Rift in southeastern Papua New Guinea. This is one of the youngest and most rapidly extending continental rifts in the world, and is an intriguing locality for investigating how continents break apart. The D'Entrecasteaux Islands, at the heart of this rift, comprise metamorphic core complexes that contain the world's youngest ultra-high pressure coesite eclogite, exhumed from 100 km depth in just 5 Ma. I have applied a variety of seismological techniques to investigate this region, using data from a temporary array of broadband seismometers installed by members of the LDEO seismology dept. that ran from 2010-2011.
My analysis of shear-wave splitting, using core-traversing teleseisms, shows strong anisotropy beneath this rift, attributed to crystallographic fabric in the shallow mantle caused by the rate and extent of continental rifting. I have related anisotropy and shear strain in the shallow convecting mantle to predict shear-wave splitting times that are very close to the splitting times I observe, bolstering our hypothesis that the anisotropy arises from mantle fabric related to rifting. My findings constrain the way in which mantle flow transitions as a rift matures from a small-scale extensional regime to a large-scale divergent boundary.
I have conducted a body-wave tomography study in the same region, using teleseismic P- and S- wave arrivals, and taking a finite-frequency approach to relate differential travel times to 3D velocity heterogeneities. My isotropic velocity model reveals a localised rift structure which persists to >200km depth, as well as an apparent slab remnant which contains the first intermediate depth seismicity observed in this region, discovered last year by members of our research group.
I have also developed a new method for conducting a joint inversion for anisotropy and velocity variations by using the results of my shear-wave splitting study to fix the geometry of the anisotropic fabric. Preliminary results indicate that shallow aligned melt pockets just south of the D’Entrecasteaux Islands are producing rift-parallel anisotropy, while the slab fragment we image is influencing the spreading-parallel fabric.
My next major project will entail a change in direction: I plan to use OBS and on-land seismic data from the Cascadia Initiative to conduct an attenuation study of the Juan de Fuca plate. We will use differential t* measurements to investigate the variation of attenuation associated with plate ageing and cooling. This work complements previous studies using surface waves and will contribute to our developing understanding of anelastic controls on seismic parameters by probing the Earth in a different frequency range.