Greenlands Mantle Transition Zone and Crustal Structure Revealed by Receiver Functions

The passage of Greenland over the Iceland hotspot provides an opportunity to investigate how mantle transition zone structure recovers from hotspot interaction over time. Using data from broadband stations in Greenland and neighboring regions, including recent deployments of seismometers on the Greenland ice sheet, we analyze information from converted P-s and S-p phases to infer the characteristics of the crust and mantle transition zone below Greenland. We calculate receiver functions in a 2-100s period band using time domain deconvolution, after accurately separating the P and SV components using a free-surface transform calculated using P and S waveforms. High-quality receiver functions are identified using physically-based objective criteria, and are migrated to depth using recent 3-D tomographic models. Clear positive velocity gradients are evident at depths near 410 km and 660 km at many stations. Preliminary results suggest that measured transition zone thicknesses are typically smaller than global reference models, consistent with higher than average background temperatures, potentially a result of the passage of the Iceland hotspot. We also measure crustal thickness and Vp/Vs ratio from the receiver functions using a modified version of H/K stacking that incorporates constraints from both P-s and S-p receiver functions. On the Greenland coast, we image crustal thicknesses of 32-40 km, and Vp/Vs ratios dominated by values of approximately 1.7, consistent with relatively silica-rich continental crust. Our final models of crustal structure will guide future studies that employ glacial isostatic adjustment to infer regional mantle viscosity. As part of our interrogation of the Greenland crust, we are conducting detailed synthetic tests to explore contamination of the Moho reverberations commonly used to determine crustal structure with multiples from the base of the ice sheet. This investigation has broader implications for receiver function imaging in icy regions.