Variations in crustal thickness and seismic anisotropy in the northeastern United States from receiver function analyses

The northeastern region of the United States has a long and complex geologic history, which has influenced and is recorded in its crustal composition and structure. Constraining the thickness and layering of the crust using seismic waves can yield information on crustal composition and history of deformation. Conversions of P to S waves across impedance contrasts provide information on layering beneath a seismometer, and can be analyzed using the receiver function method. We analyzed Ps receiver functions from 35 stations in the northeast US to better constrain the crustal structure. We focused on structural and crustal thickness variations across a region centered around the Chester gneiss dome in Vermont. The depth to Moho varies from 29 to 42 km, and is thicker in the northwest. We used harmonic decomposition of receiver functions from each station to constrain dipping layers as well as the presence of crustal seismic anisotropy - the dependence of seismic wavespeed on polarization and propagation direction. Observations of seismic anisotropy can help constrain the structure and composition of the middle and lower crust by complementing the information coming from isotropic Vp and Vs. Because seismic anisotropy can be affected by several factors such as oriented cracks and mineral preferred orientations, it is important to investigate the relationship between these factors and the behavior of seismic anisotropy. To do so, we carry out forward modeling of the observed Ps receiver function harmonic decompositions using the Raysum code (Fredricksen and Bostock, 1999), and present a model of crustal anisotropy in the northeastern United States.