Seismic Mapping of Subglacial Hydrology Reveals Previously Undetected Pressurization Event

Labedz, C. R.; Bartholomaus, T. C.; Amundson, J. M.; Gimbert, Florent; Karplus, M. S.; Tsai, Victor C.; Veitch, S. A.

doi:10.1029/2021jf006406

Cited by 6 publications

(7 citation statements)

References 53 publications

(114 reference statements)

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“…The main difference between the data from Greenland and the data from Gornergletscher is that in Figure 9 the low frequency window (i.e., 14-30 Hz) is consistently higher than the other two frequency windows. An explanation for this could be that the SG-box in Greenland was located close to a sub-glacial or englacial water channel or moulin that would dominate on-ice noise in this frequencies range (Bartholomaus et al, 2015;Röösli et al, 2016b;Köpfli et al, 2022;Labedz et al, 2022). The hydrological system on the Greenland icesheet is of a different scale than at an Alpine glacier, such as Gornergletscher.…”

Section: Discussionmentioning

confidence: 99%

“…Generally, seismic energy caused by glaciohydraulic processes and surface meltwater flow is concentrated at frequencies below 35 Hz (Bartholomaus et al, 2015;Podolskiy and Walter, 2016;Röösli et al, 2016b;Labedz et al, 2022) and is therefore not likely to explain the periods of high frequency noise (>100 Hz) during pe-riods with low wind speeds and high air temperature such as at the start and end of the test period. We also have to consider that the weather data originates from a weather station next to the Monte Rosa Hut, which is 850 m from the deployment and at 450 m higher elevation.…”

Section: Background Noise Wind and Air Temperaturementioning

confidence: 99%

“…These processes include microseismic stick-slip events and stick-slip tremor at the bed enabling us to study basal sliding which is difficult to monitor with other methods (Helmstetter et al, 2015;Röösli et al, 2016a;Guerin et al, 2021). Moreover, fracture icequakes as a result of crevasse formation provide information on stresses at and below the surface (Mikesell et al, 2012;Lind-ner et al, 2019), changing seismic velocities can be diagnostic for englacial damage (Walter et al, 2015;Sergeant et al, 2020;Chmiel et al, 2021) and glaciohydraulic tremors allow us to study subglacial hydrology (Bartholomaus et al, 2015;Labedz et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

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Self-sufficient seismic boxes for monitoring glacier seismology

et al. 2023

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Glacier seismology is a valuable tool for investigating ice flow dynamics, but sufficient data acquisition in remote and exposed glaciated terrain remains challenging. For data acquisition on a highly crevassed and remote outlet glacier in Greenland we developed self-sufficient and easily deployable seismic stations, "SG-boxes". The SG-boxes contain their own power supply via solar panel, a three-component omni-directional geophone and a GNSS receiver. The SG-boxes can be deployed and retrieved from a hovering helicopter, allowing for deployment in difficult terrain. To assess their performance we conducted a field test comparing the SG-boxes to established on-ice geophone installations at Gornergletscher in Switzerland. Moreover, data from a first SG-box deployment in Greenland were analyzed. The SG-boxes exhibit consistently higher noise levels relative to colocated conventional geophones and a correlation between noise levels, wind and air temperature is found. Despite their noise susceptibility, the SG-boxes detected a total of 13,114 Gornergletscher icequakes over 10 days, which is 30% of the total number of icequakes detected by conventional geophone stations. Hence, even in sub-optimal weather conditions and without additional noise reduction measures, the SG-boxes can provide unique and valuable data from challenging glaciated terrain where no conventional seismic installations are possible.

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Section: Discussionmentioning

confidence: 99%

Section: Background Noise Wind and Air Temperaturementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Self-sufficient seismic boxes for monitoring glacier seismology

et al. 2023

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“…Juretzek & Hadziioannou 2016), sediment transport in rivers (Tsai et al 2012), glacier hydrology and dynamics (e.g. Aso et al 2017;Labedz et al 2022), tropical cyclones (e.g. Retailleau & Gualtieri 2019) and underground hydrothermal activity (e.g.…”

Section: Introductionmentioning

confidence: 99%

Acoustic full waveform inversion for 2-D ambient noise source imaging

Datta¹,

Shekar²,

Kumar³

2023

Preprint

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We present a method for estimating seismic ambient noise sources, by acoustic full waveform inversion of interstation cross-correlations. The method is valid at local scales for laterally heterogeneous media, and ambient noise sources confined to the Earth's surface. Synthetic tests performed using an actual field array geometry, are used to illustrate three unique aspects of our work. First: the method is able to recover noise sources of arbitrary spatial distribution, both within and outside the receiver array, with high fidelity. This holds true for complex velocity models and does not require a good initial guess for inversion, thereby bridging a clear gap in the existing research literature. Second: we analyse the extent of biases in source inversion, that arise due to inaccurate velocity models. Our findings indicate that source inversion using simplified (e.g. homogeneous) velocity models may work reliably when lateral variations in velocity structure are limited to 5 or 10\% in magnitude, but is vitiated by strong variations of 20\% or higher. Finally, our technique is implemented without the adjoint method, which is usually inextricably linked to full waveform inversion. Inversions are performed using source kernels computed for each receiver pair, and this approach is computationally tractable for real-world problems with small aperture seismic arrays.

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“…Due the co-existence of different subglacial drainage system components and their dynamic evolution over time, the interpretation of the hydro-mechanical conditions variations from borehole studies solely remain very local and challenging to extrapolate at glacier-scale. Recent studies have shown the potential of using cryoseismology to bridge the gap between observations at different scales (Podolskiy and Walter, 2016), for instance by inferring hydraulic conditions across various temporal (sub-daily to multi-year) and spatial (decametric to kilometric) scales (Bartholomaus et al, 2015;Gimbert et al, 2016;Nanni et al, 2020;Lindner et al, 2020;Labedz et al, 2022). This is based on the principle that turbulent water flow generates seismic tremor at high frequency (>1 Hz) can be used to quantify relative changes in the subglacial drainage system conditions (Gimbert et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Multi-scale variations of hydro-mechanical conditions at the base of the surge-type glacier Kongsvegen, Svalbard

Bouchayer

Nanni

Lefeuvre

et al. 2023

Preprint

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Abstract. Fast glacier flow and dynamic instabilities, such as surges, are primarily caused by changes at the ice-bed interface, where basal slip and sediment deformation drive basal glacier motion. Determining subglacial conditions and their responses to hydraulic forcing (e.g. rainfall, surface melt) remains challenging due to the difficulty of accessing the glacier bed. In this study, we monitor the interplay between surface runoff and hydro-mechanical conditions at the base of the Arctic surge-type glacier Kongsvegen, in Svalbard, over two contrasting melt seasons. Kongsvegen last surged in 1948, after which it entered a prolonged quiescent phase. Around 2014, flow speeds began to increase, sign of an imminent new fast-flow event. In 2021 we instrumented a borehole to assess subglacial conditions at the local scale and deployed seismometers to monitor the subglacial conditions at the kilometer scale. We measure both subglacial water pressure within the borehole with a water pressure sensor and till rheology with a ploughmeter inserted into the sediments at the bottom of the borehole. We use channel-flow-induced tremors recorded by a seismometer to characterize hydraulic conditions over a kilometre scale at the base of the glacier. The records cover the period from spring 2021 until summer 2022. To characterize the variations in the subglacial conditions caused by changes in surface runoff, we investigate the phase relationship (i.e. how two variables evolve in time) of the following hydro-mechanical condition proxies: water pressure, hydraulic gradient, hydraulic radius, and sediment ploughing forces. We analyse these proxies versus modelled runoff analyzed over seasonal, multi-day and diurnal time-scales. We compare our results with existing theories in terms of subglacial drainage system evolution and sediment shear strength to describe various aspects of subglacial conditions. We find apparent ambiguities in the interpretation of different variables recorded by individual sensors, thus demonstrating the importance of using multi-sensor records in a multi-scale analysis. This study highlights the different adaption of the subglacial drainage system during short, low melt intensity season in 2021, against long, high intensity melt season in 2022. In the short and low intensity melt season, we find that the subglacial drainage system evolves at equilibrium with runoff, increasing its capacity as the melt season progresses. In contrast, during the long and high intensity melt season 2022, we find that the subglacial drainage system evolves transiently to respond to the abrupt and high intensity input of precipitation and melt water conveyed to the bed. In this configuration, the subglacial channels evolution is not rapid enough to adapt immediately to the forcing conditions. The drainage capacity of the main active channels is exceeded, promoting the water to leak in poorly connected areas of the bed, increasing the water pressure, resulting in speed-up events. Another robust outcome of our analysis is, that, on a seasonal scale, till shear strength variations are mainly anti-correlated with water pressure variations (consistent with a Coulomb-plastic behavior), whereas on shorter time scales especially during speed-up events, the two variables correlate, describing a viscous rheology. To our knowledge, such contrasted behaviors of the sediment rheology and subglacial flow at the base of a glacier have not been reported before.

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Seismic Mapping of Subglacial Hydrology Reveals Previously Undetected Pressurization Event

Cited by 6 publications

References 53 publications

Self-sufficient seismic boxes for monitoring glacier seismology

Self-sufficient seismic boxes for monitoring glacier seismology

Acoustic full waveform inversion for 2-D ambient noise source imaging

Multi-scale variations of hydro-mechanical conditions at the base of the surge-type glacier Kongsvegen, Svalbard

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