Dense seismic array monitoring on glaciers combined with advanced array processing may help retrieve and locate a variety of seismic sources with unprecedented resolution and spatial coverage. Here we present an array methodology that goes beyond classical localization algorithms through gathering various types of sources (impulsive or continuous) into a single scheme and sort those by their associated array phase coherence. We demonstrate that we can retrieve the spatial and temporal dynamics of active crevasses with a metric resolution using sources with high phase coherence; the presence of diffracting materials trapped in transverse crevasses using sources with moderate phase coherence; and the time evolution of two-dimensional maps of the subglacial water flow drainage system using sources with low phase coherence. With the ongoing increased use of dense seismic arrays, our study highlights the strength of using an appropriate seismological and statistical approach to image a wide range of subsurface structures.

In seismology, the rupture mechanism of an earthquake, a glacier stick-slip and a landslide is not directly observed, but inferred from surface measurements. In contrast, laboratory experiments can illuminate near field effects, which reflect the rupture mechanism but are highly attenuated in the case of real-world surface data. We directly image the elastic wave-field of a nucleating rupture non-invasively in its near-field with ultrasound speckle correlation. Our imaging yields the particle velocity of the full shear wave field at the source location and inside the 3D frictional body. We experimentally show that a strong bimaterial contrast, as encountered in environmental seismology, yields a unidirectional or linear force mechanism for pre-rupture microslips and decelerating supershear ruptures. A weak contrast, characteristic for earthquakes, generates a double-couple source mechanism for sub-Rayleigh ruptures, sometimes preceded by slow deformation at the interface. This deformation is reproduced by the near field of a unidirectional force.