Using ambient noise to characterize subsurface structures has revolutionized solid earth seismology. In glacial applications, this technique could provide valuable information about ice thickness and bed properties, which to date are deduced from laborious and/or expensive active source geophysics or deep drilling. Despite challenging conditions such as minimal scattering and changing sources, we show that stacks of cross‐correlation functions of several hours of ambient seismic noise can converge towards Green's functions under favorable conditions. These contain the sought‐after information about subsurface seismic velocities and ice thickness. Applying this technique to two Alpine glaciers in Switzerland, we calculate signal‐to‐noise ratios of noise correlation functions. Faster Green's functions convergence during elevated ambient noise levels suggests that increased surface melt promotes spatially homogeneous excitation of noise sources. With the help of Green's functions amplitude asymmetry as well as standard beamforming, we locate dominant noise sources. In combination with spectrograms, glacier surface velocities from GPS and proglacial water discharge measurements, we find glacier noise in the range from 2 to 8 Hz to be a combination of tremor induced by flowing water, icequakes, and anthropogenic sources. We finally calculate dispersion curves from the cross‐correlation functions to arrive at an estimate of the ice thickness. In combination with H/V spectral ratios, the method shown here allows sampling the depth and the properties of the glacier bed by deploying only two seismometers for several hours. Ambient noise correlations could therefore be a valuable ingredient for studies of glacier and ice sheet beds.

The 1960 M9.5 Valdivia and 1964 M9.2 Alaska earthquakes caused a decimeters high secondary zone of uplift a few hundred kilometers landward of the trench. We analyze GPS data from the 2010 M8.8 Maule and 2011 M9.0 Tohoku-Oki earthquakes to reveal the persistent existence of a secondary zone of uplift due to great earthquakes at the megathrust interface. This uplift varies in magnitude and location, but consistently occurs at a few hundred kilometers landward from the trench and is likely mainly coseismic in nature. This secondary zone of uplift is systematically predicted by our 2D visco-elasto-plastic seismothermo-mechanical numerical simulations, which model both geodynamic and seismic cycle timescales. Through testing hypotheses in both simple and realistic setups, we propose that a superposition of two physical mechanisms could be responsible for this phenomenon. First, a wavelength is introduced through elastic buckling of a visco-elastically layered fore-arc that is horizontally compressed in the interseismic period. The consequent secondary zone of interseismic subsidence is elastically rebound during the earthquake into a secondary zone of relative uplift. Second, absolute and broader uplift is ensured through a mass conservationdriven return flow following accelerated slab penetration due to the megathrust earthquake. The dip and width of the seismogenic zone and resulting (deep) coseismic slip seem to have the largest affect on location and amplitude of the secondary zone of uplift. These results imply that subduction and mantle flow do not occur at constant rates, but are rather modulated by earthquakes. This suggests a link between deep mantle and shallow surface displacements even at time scales of minutes.

Passive seismology allows measurement of the structure of glaciers and ice sheets. However, most techniques used so far in this context are based on horizontally homogeneous media where parameters vary only with depth (1-D approximations), which are appropriate only for a subset of glaciers. Here, we analyze seismic noise records from three different types of glaciers (plateau, valley and avalanching glacier) to characterize the influence of the glacier geometry on the seismic wavefield. Using horizontal-to-vertical spectral ratios, polarization analysis and modal analysis, we show that the plateau glacier and the valley glacier can be seen as 1-D, whereas the relatively small avalanching glacier shows 3-D effects due to its bed topography and the deep crevasses. In principle, the techniques proposed here might allow monitoring such crevasses and their depth, and thus to constrain a key parameter of avalanching and calving glacier fronts.

The 1960 M9.5 Valdivia and 1964 M9.2 Alaska earthquakes caused a decimeters-high secondary zone of uplift a few hundred kilometers landward of the trench. We analyze GPS data from the 2010 M8.8 Maule and 2011 M9.0 Tohoku-Oki earthquakes to confirm the existence of a secondary zone of uplift due to great earthquakes at the megathrust interface. This uplift varies in magnitude and location, but consistently occurs at a few hundred kilometers landward from the trench and is likely predominantly coseismic in nature. This secondary zone of uplift is systematically predicted by our 2D continuum visco-elasto-plastic seismo-thermo-mechanical (STM) numerical simulations, which physically-consistently model the dynamics at both geodynamic and seismic cycle timescales. Through testing hypotheses in both simple and realistic setups, we propose that a superposition of two physical mechanisms could be responsible for this phenomenon. First, a wavelength is introduced through elastic buckling of a visco-elastically layered fore-arc that is horizontally compressed in the interseismic period. The consequent secondary zone of subsidence is elastically rebound during the earthquake into a secondary zone of relative uplift. Second, absolute and broader uplift is ensured through a mass conservation-driven return flow following accelerated slab penetration due to a megathrust earthquake. The dip and width of the seismogenic zone and resulting (deep) coseismic slip seem to have the largest affect on location and amplitude of the secondary zone of uplift. These results imply that stick-slip modulates subduction and corner flow rates and that visco-elastic layering is important for inversion of interseismic and coseismic fault displacements.