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Zusammenfassung:
Seismic body waves from distant earthquakes travel steeply to a seismic station and carry rich information about subsurface structures. In an ice sheet environment, the sharp seismic discontinuity at the ice-bedrock interface effectively reflects the energy that is bounced from the free surface. Thus, the ice sheet acts as a waveguide to trap a large portion of incident seismic energy, resulting in repetitive ground motions recorded by over-ice seismometers. The weak self-similar signals can be amplified by cross-correlating the earthquake seismograms with themselves (i.e., autocorrelation) before stacking over multiple events. Here, we apply this autocorrelation technique to the records of P-wave arrivals and following reverberations (i.e., the P-wave coda) of stations deployed over the central region of the Greenland ice sheet (GrIS), the second-largest ice sheet on Earth. Firstly, we estimate the thickness and P- over S- wave speed ratio of the ice sheet beneath several recording sites and find good agreement with independent estimates primarily based on airborne radio-echo-sounding data.
Furthermore, we observe seasonal fluctuation in amplitudes of P-wave coda autocorrelograms, with stronger reflection peaks in summers and weaker in winters. We use numerical experiments to decipher the mechanism underlying temporal variation. Our findings could shed light on the working mechanisms of the GrIS and similar environments, including future missions to icy planets and satellites.
