Changes in Greenland ice bed conditions inferred from seismology

Toyokuni, Genti; Takenaka, Hiroshi; Takagi, Ryota; Kanao, Masaki; Tsuboi, Seiji; Tono, Yoko; Childs, Dean; Zhao, Dapeng

doi:10.1016/j.pepi.2017.10.010

Cited by 18 publications

(36 citation statements)

References 35 publications

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“…The temporal group velocities measured are reasonable, varying around our reference Rayleigh wave group velocity dispersion curve. We observe a slight velocity decrease in summer, which could be attributed to the pressure melting of ice, similar to what has been reported for station pairs in the coastal areas (Toyokuni et al 2018). It has also been suggested that an increase in ice mass during winter months could result in velocity increase due to the compaction of ice and bedrock, which changes the stress field.…”

Section: Velocity Variationssupporting

confidence: 90%

A Feasibility Study on Monitoring Crustal Structure Variations by Direct Comparison of Surface Wave Dispersion Curves from Ambient Seismic Noise

Muhumuza

2020

International Journal of Geophysics

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This work assesses the feasibility of the direct use of surface-wave dispersion curves from seismic ambient noise to gain insight into the crustal structure of Bransfield Strait and detect seasonal seismic velocity changes. We cross-correlated four years of vertical component ambient noise data recorded by a seismic array in West Antarctica. To estimate fundamental mode Rayleigh wave Green's functions, the correlations are computed in 4-hr segments, stacked over 1-year time windows and moving windows of 3 months. Rayleigh wave group dispersion curves are then measured on two spectral bands-primary (10-30 s) and secondary (5-10 s) microseisms-using frequency-time analysis. We analyze the temporal evolution of seismic velocity by comparing dispersion curves for the successive annual and 3-month correlation stacks. Our main assumption was that the Green's functions from the cross-correlations, and thus the dispersion curves, remain invariant if the crustal structure remains unchanged. Maximum amplitudes of secondary microseisms were observed during local winter when the Southern Ocean experiences winter storms. The Rayleigh wave group velocity ranges between 2.1 and 3.7 km/s, considering our period range studied. Inter-annual velocity variations are not much evident. We observe a slight velocity decrease in summer and increase in winter, which could be attributed to the pressure melting of ice and an increase in ice mass, respectively. The velocity anomalies observed within the crust and upper mantle structure correlate with the major crustal and upper mantle features known from previous studies in the area. Our results demonstrate that the direct comparison of surface wave dispersion curves extracted from ambient noise might be a useful tool in monitoring crustal structure variations.In this study, we used vertical component continuous seismic data from 4 stations in the Argentine Antarctica region from ASAIN (Antarctic Seismographic Argentine-Italian Network) in West Antarctica (Fig. 1). The stations Carlini-formerly Jubany (JUBA)-station, Esperanza (ESPZ), Orcada (ORCD) and San Martin (SMAI) are part of the 5 seismological stations that have been set under ASAIN collaborative agreement.The seismologic network provide essential data to study the internal structure of the Antarctic continent, monitor seismicity, and to monitor large-scale phenomena, such as melting of the Antarctic ice sheet, among others. We analyzed 4 years (2008-2011) of seismic data recorded recorded by the 4 stations with a sampling rate of 1 sample per second. The initial data preparation involves unpacking the raw data from its standard SEED format to obtain noise data in SAC format. We have to ensure that the two amplitudes of each record are completely consistent by running a time normalization so that the records share the same absolute time and the same amplitude information is retained. It is important to note that if the instruments of two stations are inconsistent, it is necessary to remove instrument responses from the raw data.Here ...

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Section: Velocity Variationssupporting

confidence: 90%

A Feasibility Study on Monitoring Crustal Structure Variations by Direct Comparison of Surface Wave Dispersion Curves from Ambient Seismic Noise

Muhumuza

2020

International Journal of Geophysics

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“…The recent developing seismic network has also provided a new opportunity for direct, real-time, and continuous monitoring of GrIS. A seismic interferometry study by using the broadband continuous waveform data from GrIS was carried out [30]. The GreenLand Ice Sheet monitoring Network (GLISN) is an international project by 14 countries to monitor dynamic changes in GrIS, by deploying 32 broadband seismic stations in and around Greenland [8,31].…”

Section: Oceanic Waves and Seismic Interferometrymentioning

confidence: 99%

“…The GreenLand Ice Sheet monitoring Network (GLISN) is an international project by 14 countries to monitor dynamic changes in GrIS, by deploying 32 broadband seismic stations in and around Greenland [8,31]. Daily cross-correlation functions (CCFs) for all possible pairs of The ambient noise surface wave data were utilized from seismic stations all over Greenland for a 4.5-year period to detect changes in Rayleigh wave phase velocity between the seismic station pairs [30] (Figure 3). They observed clear seasonal and long-term velocity changes for many pairs and proposed a plausible mechanism for these changes.…”

Section: Oceanic Waves and Seismic Interferometrymentioning

confidence: 99%

“…(Left) Seismic surface (Rayleigh) wave phase velocity changes at three station pairs over 4.5 years in Greenland. (Right) Comparison with estimated GrIS basal temperature[34] (modified after[30]). Open Access Journal (CC BY 3.0) (one of the authors is M. Kanao).A New Trend in Cryoseismology: A Proxy for Detecting the Polar Surface Environment http://dx.doi.org/10.5772/intechopen.78557 the GLISN stations were computed.…”

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A New Trend in Cryoseismology: A Proxy for Detecting the Polar Surface Environment

Kanao¹

2018

Polar Seismology - Advances and Impact

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"Cryoseismology" is a new branch of interdisciplinary science, which treats glacierrelated seismic events and their dynamics associated with the variable phenomenon of the Earth's surface. Cryoseismology is considered to be one of the proxies for detecting environmental variations, particularly in the polar region, which contains the majority volume of the cryosphere of the planet. Various kinds of cryoseismic signals recently reported are reviewed by classifying them into several categories on the basis of their occurrence locations and focal dynamics. Temporal-spatial variations in cryoseismic activities and their wave propagation characteristics could demonstrate a new image of cryodynamics, which have not yet been known well before but have a significant impact on the global environment and human activities.

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“…For the cryosphere, few studies have successfully used oceanic ambient noise at permanent broadband stations deployed on the rocky margins of glaciers or up to 500 km away on polar ice sheets to monitor the subsurface processes. Mordret et al (2016) and Toyokuni et al (2018) tracked the strain evolution in the upper 5 km of the Earth's crust beneath the GIS due to seasonal loading and unloading of the overlaying melting ice mass. More recently, Zhan (2019) detected slowing down of surface wave velocities up to 2 % in the basal till layer of the largest North American glacier (Bering Glacier, 20 km wide) during a surge, likely due to the switch of the subglacial drainage from channelized to distributed.…”

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confidence: 99%

On the Green's function emergence from interferometry of seismic wave fields generated in high-melt glaciers: implications for passive imaging and monitoring

Sergeant

Chmiel²,

Lindner³

et al. 2020

The Cryosphere

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Abstract. Ambient noise seismology has revolutionized seismic characterization of the Earth's crust from local to global scales. The estimate of Green's function (GF) between two receivers, representing the impulse response of elastic media, can be reconstructed via cross-correlation of the ambient noise seismograms. A homogenized wave field illuminating the propagation medium in all directions is a prerequisite for obtaining an accurate GF. For seismic data recorded on glaciers, this condition imposes strong limitations on GF convergence because of minimal seismic scattering in homogeneous ice and limitations in network coverage. We address this difficulty by investigating three patterns of seismic wave fields: a favorable distribution of icequakes and noise sources recorded on a dense array of 98 sensors on Glacier d'Argentière (France), a dominant noise source constituted by a moulin within a smaller seismic array on the Greenland Ice Sheet, and crevasse-generated scattering at Gornergletscher (Switzerland). In Glacier d'Argentière, surface melt routing through englacial channels produces turbulent water flow, creating sustained ambient seismic sources and thus favorable conditions for GF estimates. Analysis of the cross-correlation functions reveals non-equally distributed noise sources outside and within the recording network. The dense sampling of sensors allows for spatial averaging and accurate GF estimates when stacked on lines of receivers. The averaged GFs contain high-frequency (>30 Hz) direct and refracted P waves in addition to the fundamental mode of dispersive Rayleigh waves above 1 Hz. From seismic velocity measurements, we invert bed properties and depth profiles and map seismic anisotropy, which is likely introduced by crevassing. In Greenland, we employ an advanced preprocessing scheme which includes match-field processing and eigenspectral equalization of the cross spectra to remove the moulin source signature and reduce the effect of inhomogeneous wave fields on the GFs. At Gornergletscher, cross-correlations of icequake coda waves show evidence for homogenized incident directions of the scattered wave field. Optimization of coda correlation windows via a Bayesian inversion based on the GF cross coherency and symmetry further promotes the GF estimate convergence. This study presents new processing schemes on suitable array geometries for passive seismic imaging and monitoring of glaciers and ice sheets.

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Changes in Greenland ice bed conditions inferred from seismology

Cited by 18 publications

References 35 publications

A Feasibility Study on Monitoring Crustal Structure Variations by Direct Comparison of Surface Wave Dispersion Curves from Ambient Seismic Noise

A Feasibility Study on Monitoring Crustal Structure Variations by Direct Comparison of Surface Wave Dispersion Curves from Ambient Seismic Noise

A New Trend in Cryoseismology: A Proxy for Detecting the Polar Surface Environment

On the Green's function emergence from interferometry of seismic wave fields generated in high-melt glaciers: implications for passive imaging and monitoring

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