Date of Award
Doctor of Philosophy (PhD)
Anne F. Sheehan
Craig H. Jones
Megan L. Anderson
Kevin H. Mahan
In this thesis, I use passive source seismic data to image the crust and upper mantle in an effort to better understand how the lithosphere deforms. First, I examine how crustal shortening was accommodated during the Laramide orogeny in the Bighorn Mountain region of Wyoming. Second, I examine crustal and upper mantle deformation surrounding the Pacific-Australian plate boundary in the South Island of New Zealand.
Laramide basement-cored foreland arches make up many prominent ranges in the eastern Rocky Mountains (USA). While thick-skinned Laramide shortening is easily observable at the surface, how shortening was accommodated at depth remains a first order question. A diverse variety of kinematic shortening models each predict a unique, modern-day crustal geometry and are therefore testable. I use teleseismic P-wave receiver functions to image basin and Moho structure in the Bighorn Mountain region. First, I develop and test a sequential H-κ (thickness-Vp/Vs) stacking algorithm to account for error introduced by low velocity sedimentary basins. Crustal thickness observations rule out models in which a ductile lower crust undergoes pure shear thickening, forming a crustal root, and models in which faults penetrate the Moho. A mismatch between the geometry of the Bighorn Arch at the surface and that of the Moho suggest that the upper and lower crust are poorly coupled and therefore casts doubt on models in which the whole lithosphere buckles. Kinematic models that invoke a major detachment fault remain feasible and suggest a pre-Laramide origin for the modern Moho structure. I use Rayleigh phase and group velocity observations from ambient noise to construct a regional 3D shear-velocity model and find that high-velocity lower crust appears absent beneath the Bighorn Mountains.
Next, I focus on the modern day boundary between the Australian and Pacific plates on the South Island of New Zealand. I use continuous waveform data from ocean bottom seismometers to examine the anisotropic Rayleigh group velocity structure on and offshore of the South Island. Fast directions align sub-parallel to the Alpine Fault. Observations suggest distributed deformation of the lower crust and correlate well with seismic anisotropy observations of the mantle, suggesting the lower crust and mantle are well coupled.
Yeck, William Luther, "Investigation into the Deformatin of the Lithosphere Past and Present Using Passive Seismic Methods: Case Studies of the Wyoming Craton and South Island of New Zealand" (2015). Geological Sciences Graduate Theses & Dissertations. 97.