Academic Affiliation: University of Nevada - Las Vegas
Jordan grew up in the finger-lakes region of New York State and moved to Las Vegas in high school. He currently majors in Geology after being introduced to the geosciences by a freshman studies professor, and he has an interest in crustal deformation and metamorphic petrology.
A Voyage into central Colorado crust: Linking seismic anisotropy and surface geology
Exposed igneous and metamorphic rocks contain faults, folds, and ductile fabrics that result from lithospheric deformation, but characterizing the geometry of these structures in the subsurface has remained elusive. The ability to image these subsurface structures has implications for estimating seismic hazards and understanding crustal dynamics. Analysis of crustal seismic anisotropy from passive receiver function data is a promising technique, but the successful use of receiver function data is dependent upon resolving the scale difference between km-size seismic waves and the sub-mm scale microstructures that influence seismic wave propagation. Here, we use a scaling approach that combines regional geologic map data and a worldwide compilation of crustal rock elastic tensors to compare data and scaling results with receiver function and surface wave analyses. We use the 1:100,000 Denver West quadrangle in Central Colorado as a first test of this methodology. Using a simplified lithologic map and applying best-fit elastic tensors from the compilation to surface foliation orientations, we homogenize the seismic properties across the study area. Results show 2.4% Vp anisotropy with NE-SW striking slow plane and NE plunging fast axis. We compare the modelled anisotropy with receiver function data from two stations in the area and with published regional surface wave anisotropy. Expectedly, lithologies with the strongest anisotropy control the homogenized regional anisotropy. However, averaging within the dominant lithology changes the symmetry of anisotropy, affecting interpretation of seismic results. Further analyses will be aimed at determining what fabric orientations dominantly influence anisotropy and the relationship between fabric orientations and anisotropy as a function of depth. The scaling between microstructures and seismic wavelengths allows the methodology to be applied to structurally complex crust wherever seismic and regional structural geologic data exist, with the goal of characterizing the crust from regional to continental scales.