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This paper presents the first results from the monitoring of local seismicity in Severnaya Zemlya from the end of 2016 to 2023 inclusive as recorded by a single permanent seismic station installed on Bolshevik Island. A total of 73 local seismic events have been identified with P and S phases. We considered the question whether these events could be classified (earthquakes or icequakes) by comparing waveforms and spectral-temporal analysis diagrams with regional earthquakes that have occurred in the archipelago area. The spatio-temporal distribution and the rate of migration for the events show that glacial events can arise by stress release in glaciers as shallow crustal earthquakes occur within ~30 km. It is shown that, when a seismograph network is difficult to deploy, even a single permanent seismic station can furnish useful information on glacial events and crustal earthquakes. [ABSTRACT FROM AUTHOR]

Dense seismic array monitoring combined with advanced processing can help retrieve and locate a variety of seismic sources with unprecedented resolution and spatial coverage. We present a methodology that goes beyond classical localization algorithms through gathering various types of sources (impulsive or continuous) using a single scheme based on a gradient‐descent optimization and evaluating different levels of phase coherence. We apply our methodology on an Alpine glacier and demonstrate that we can retrieve the dynamics of active crevasses with a metric resolution using sources associated with high phase coherence; the presence of diffracting materials (e.g., rocks) trapped in transverse crevasses using sources with moderate phase coherence; and the two‐dimensional time evolution of the subglacial hydrology system using sources with low phase coherence. Our study highlights the strength of using an appropriate and systematic seismological approach to image a wide range of subsurface structures and phenomena in settings with complex wavefields. Plain Language Summary: Over the past two decades, the growing use of dense seismic arrays has often overcome limitations of traditional observations methods and yielded new insights on the physics of subsurface process and properties. Yet scientific and computational challenges remain to be addressed for using the appropriate array‐processing approaches and automating the techniques on large volume of data and for complex wavefields. In this paper we address such challenges in the particular case of monitoring glaciers, which host numerous and diverse sets of seismic sources that produce signals ranging from impulsive to tremor‐like. We combine a physics‐based and a statistical approach to explore with a dense seismic array the spatial coherence of the seismic wavefield generated by such a diversity of sources. We show that even a small coherence in the phase signal remains rich in statistical information on concomitant and/or low amplitudes micro‐seismic sources. This allows us to localize seismic sources with a super‐resolution (meter to decameter) and identify emerging patterns associated with a wide range of glacier features and their dynamics, ranging from active crevasses, debris in transverse passive crevasses and subglacial water flow. Such methodological and conceptual advance may enable a more efficient and complete imaging of geophysical objects. Key Points: We present an innovative array‐processing approach to image glaciers structures at high resolution by locating seismic sourcesWe investigate a large range of spatial phase coherences, from very low up to very high, over narrow frequency bands and short time windowsWe image the spatial and temporal dynamics of sources originating from active and passive crevasses as well as from subglacial hydrology [ABSTRACT FROM AUTHOR]

A subglacial groundwater system beneath Taylor Glacier, Antarctica, discharges hypersaline, iron‐rich brine episodically at the glacier surface to create Blood Falls. However, the triggering mechanism for these brine release events is not yet understood. Identifying which fracture processes are observed seismically can help us better characterize the hydrological system at Taylor Glacier, and more generally, provide us with a broader understanding of englacial hydrologic activity in cold glaciers. We document wintertime brine discharge using time‐lapse photography. Subfreezing air temperatures during the brine discharge indicate that surface melt‐induced hydrofracture is an unlikely trigger for brine release. Further, we analyze local seismic data to test a hypothesis that fracturing generates elevated surface wave energy preceding and/or coinciding with brine release events. Our results show no discernible elevated Rayleigh wave activity prior to or during Blood Falls brine release. Instead, we find a pattern of seismic events dominated by a seasonal signal, with more Rayleigh events occurring in the summer than the winter from the Blood Falls source area. We calculate that the volumetric opening of cracks that would generate Rayleigh waves at our detection limits are of similar size to myriad cracks in glacier ice, lake ice, and frozen sediment in the terminus area. We therefore propose that any fracturing coincident with brine release activity likely consists of a series of smaller opening events that are masked by other seismicity in the local environment. Plain Language Summary: Blood Falls is a reddish feature that forms at the terminus of Taylor Glacier in Antarctica when hypersaline, iron‐rich brine flows from sediment under the glacier up through the ice to emerge from cracks at the surface. We used data from a time‐lapse camera and nearby seismic sensors to document a brine release. Our images show a brine release event starting in May 2014 (austral winter), and fractures in the glacier surface observed following the event encouraged us to hypothesize that we would detect an increase in Rayleigh waves (a type of seismic wave that can be generated by surface crack opening). However, we do not observe an increase in Rayleigh wave activity prior to or during brine release. When we estimate the average size of the fractures that we detect, we find the size is similar to many types of cracks in the nearby environment (for instance, cracks in the lake ice). We conclude that any Rayleigh wave seismicity that occurred during the Blood Falls brine release must be from a series of crack openings smaller than our detection limit, and that other cracks opening in the nearby environment may mask any signal specific to the Blood Falls release. Key Points: Time‐lapse photos capture wintertime Blood Falls brine releaseBrine release occurs without evidence for enhanced Rayleigh wave seismicity near the release pointThe Blood Falls crack may open as a series of small fracture events, masked by local seismicity [ABSTRACT FROM AUTHOR]

Subglacial water flowstrongly modulates glacier basalmotion, which itself strongly influences the contributions of glaciers and ice sheets to sea level rise. However, our understanding of when and where subglacial water flow enhances or impedes glacier flow is limited due to the paucity of direct observations of subglacial drainage characteristics. Here, we demonstrate that dense seismic array observations combined with an innovative systematic seismic source location technique allows the retrieval of a two-dimensional map of a subglacial drainage system, as well as its day-to-day temporal evolution. We observe with unprecedented detail when and where subglacial water flows through a cavity-like system that enhances glacier flow versus when and where water mainly flows through a channel-like system that impedes glacier flow. Most importantly, we are able to identify regions of high hydraulic connectivity within and across the cavity and channel systems, which have been identified as having a major impact on the long-term glacier response to climate warming. Applying a similar seismicmonitoring strategy in other glacier settings, including for ice sheets, may help to diagnose the susceptibility of their dynamics to increased meltwater input due to climate warming. [ABSTRACT FROM AUTHOR]

Sliding of glacial ice over its base is typically described by a frictionless or slowly deforming bed. This view is challenged by recent seismic observations of stick‐slip motion at the ice‐bed interface. We revisit a high‐frequency (20–35 Hz) harmonic tremor recorded on Gornergletscher, Switzerland. In contrast to previous interpretation in terms of glaciohydraulic tremor, we present evidence for superimposed stick‐slip episodes as tremor sources: we locate the tremor source with matched field processing polarity optimization, which allows for azimuthal polarity patterns associated with nonisotropic moment tensors and yields a tremor source clustering near the glacier bed. Our analysis confirms an S wave radiation pattern in agreement with a double‐couple source derived from ice sliding over bedrock and explains our tremor observations in terms of glacier stick‐slip motion. Adding to observations of stick‐slip tremor beneath polar ice streams, this first report on stick‐slip tremor beneath Alpine ice favors widespread seismogenic glacier sliding. Plain Language Summary: For many years, researchers have observed cryoseismic stick‐slip tremor exclusively in Antarctica. Stick‐slip tremor is due to small repeating slip events at the glacier bed as a glacier advances downstream. This type of tremor is a telltale sign of what is happening at the ice‐bed interface and indicates frictional sliding. Here, we present first evidence for stick‐slip tremor at an Alpine glacier—Gornergletscher, Switzerland. We identify indicators in the seismic signature and apply data processing techniques that reveal that the creeping glacier sole moves under the influence of gravity and irregularly rubs over a sticky area at the bed. Key Points: We revisit a harmonic tremor recorded by a seismic array on an Alpine glacier, which was previously interpreted as hydraulic tremorApplying matched field processing that accounts for nonisotropic radiation patterns suggests a tremor source at the ice‐bedrock interfaceA focal mechanism derived from ice slip over bedrock explains our results and suggests seismogenic stick‐slip motion at the glacier's base [ABSTRACT FROM AUTHOR]

Glacial earthquakes are slow earthquakes of magnitude M~5 associated with major calving events at near-grounded marine-terminating glaciers. These globally detectable earthquakes provide information on the grounding state of outlet glaciers and the timing of large calving events. Seismic source modeling of glacial earthquakes provides information on the size and orientation of forces associated with calving events. We compare force orientations estimated using a centroid-single-force technique with the calving-front orientations of the source glaciers at or near the time of earthquake occurrence. We consider earthquakes recorded at four glaciers in Greenland – Kangerdlugssuaq Glacier, Helheim Glacier, Kong Oscar Glacier, and Jakobshavn Isbræ – between 1999 and 2010. We find that the estimated earthquake force orientations accurately represent the orientation of the calving front at the time of the earthquake, and that seismogenic calving events are produced by a preferred section of the calving front, which may change with time. We also find that estimated earthquake locations vary in a manner consistent with changes in calving-front position, though with large scatter. We conclude that changes in glacial-earthquake source parameters reflect true changes in the geometry of the source glaciers, providing a means for identifying changes in glacier geometry and dynamics that complements traditional remote-sensing techniques. [ABSTRACT FROM AUTHOR]