The grounding zone (GZ) of a marine-terminating glacier, where ice transitions from grounded to floating, experiences strong mechanical changes, in particular in response to ocean tides. The spatial and temporal dynamics of these changes, however, remain poorly documented, as they require multi-scale observations capable of resolving internal ice deformation. Here we use multi-year and multi scale seismic observations to detect and locate icequakes resulting from the brittle deformation of the Astrolabe Glacier, an outlet glacier from East Antarctica (Terre Adélie). We find from automatic detection that seismicity strongly varies with tides and location of the sensors. At a multi-kilometer scale, we observe and locate large-magnitude events associated with shear margins. At smaller scale (few hundreds of meters), using a dense array of seismic nodes deployed across the GZ, we capture numerous small-magnitude events whose occurrence is controlled by the GZ geometry and dynamics. At rising tide, seismicity is dominant on the floating part of the glacier while at falling tides, it is dominant over its grounded part. These short-scale spatio-temporal variations lead us to propose a conceptual framework for the dynamics of icequake activity at the glacier GZ, accounting for its three-dimensional tidal-induced bending and its confinement in a fjord. Our findings highlight the value of dense seismic networks in capturing the high-resolution response of outlet glaciers to tidal forces at their GZ.