Lithospheric Structure of Greenland From Ambient Noise and Earthquake Surface Wave Tomography

We present a high-resolution shear wave velocity model of Greenland's lithosphere from regional and teleseismic Rayleigh waves recorded by the Greenland Ice Sheet Monitoring Network supplemented with observations from several temporary seismic deployments. To construct Rayleigh wave group velocity maps, we integrated signals from regional and teleseismic earthquakes with several years of ambient seismic noise and used the dispersion to constrain crustal and upper-mantle seismic shear wave velocity structure. Specifically, we used a Markov Chain Monte Carlo technique to estimate 3-D shear wave velocities beneath Greenland to a depth of 200 km. Our model reveals four prominent anomalies: a deep high-velocity feature extending from southwestern to northwestern Greenland that may be the signature of a thick cratonic keel, a corridor of relatively low upper-mantle velocity across central Greenland that could be associated with lithospheric modification from the passage of the Iceland plume beneath Greenland or interpreted as a tectonic boundary between cratonic blocks, an upper-crustal southwest-northeast trending boundary separating Greenland into two regions of contrasting tectonic and crustal properties, and a midcrustal low-velocity anomaly beneath northeastern Greenland. The nature of this midcrustal anomaly is of particular interest given that it underlies the onset of the Northeast Greenland Ice Stream and raises interesting questions regarding how deeper processes may impact the ice stream dynamics and the evolution of the Greenland Ice Sheet.