Towards monitoring the englacial fracture state using virtual-reflector seismology

Lindner, Fabian; Weemstra, Cornelis; Walter, Fabian; Hadziioannou, Céline

doi:10.1093/gji/ggy156

Cited by 6 publications

(10 citation statements)

References 90 publications

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“…A properly designed interferometric observation network would be required to obtain more robust results. A denser station coverage would also invite the application of recent methodological advancements in seismic interferometry which aim at minimizing the influence of directional bias in the ambient noise source distribution (Lindner and others, 2018).…”

Section: Resultsmentioning

confidence: 99%

Seismic characterization of a rapidly-rising jökulhlaup cycle at the A.P. Olsen Ice Cap, NE-Greenland

et al. 2020

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Rapidly-rising jökulhlaups, or glacial outburst floods, are a phenomenon with a high potential for damage. The initiation and propagation processes of a rapidly-rising jökulhlaup are still not fully understood. Seismic monitoring can contribute to an improved process understanding, but comprehensive long-term seismic monitoring campaigns capturing the dynamics of a rapidly-rising jökulhlaup have not been reported so far. To fill this gap, we installed a seismic network at the marginal, ice-dammed lake of the A.P. Olsen Ice Cap (APO) in NE-Greenland. Episodic outbursts from the lake cause flood waves in the Zackenberg river, characterized by a rapid discharge increase within a few hours. Our 6 months long seismic dataset comprises the whole fill-and-drain cycle of the ice-dammed lake in 2012 and includes one of the most destructive floods recorded so far for the Zackenberg river. Seismic event detection and localization reveals abundant surface crevassing and correlates with changes of the river discharge. Seismic interferometry suggests the existence of a thin basal sedimentary layer. We show that the ballistic part of the first surface waves can potentially be used to infer medium changes in both the ice body and the basal layer. Interpretation of time-lapse interferograms is challenged by a varying ambient noise source distribution.

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Section: Resultsmentioning

confidence: 99%

Seismic characterization of a rapidly-rising jökulhlaup cycle at the A.P. Olsen Ice Cap, NE-Greenland

et al. 2020

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“…(B3). and Lindner et al (2018) both use this method to obtain dispersion curves of Rayleigh wave speeds from cross-correlations of on-ice seismic records.…”

Section: B2 Aki's Spectral Methodsmentioning

confidence: 99%

“…MDD processing then enables us to remove the imprint of the (nonuniform) source distribution from the correlation responses and improves the quality of the retrieved GF. We follow Lindner et al (2018) and use the outer receiver contour of the Glacier d'Argentière array (black triangles in Fig. 12a) as virtual boundaries for MDD of the icequake correlations computed at one pair of sensors and sorted for a 2 d window with 50 % overlap.…”

Section: Implications For Glacier Monitoringmentioning

confidence: 99%

“…They recorded thousands of point source events which offered an idealized spatial source distribution around one pair of seismic sensors and could obtain accurate GF estimates. To overcome the situation of a skewed illumination pattern often arising from icequake locations, Lindner et al (2018) used multidimensional deconvolution (Wapenaar et al, 2011;Weemstra et al, 2017) that relies on a contour of receivers enclosing the region of interest (see also Sect. 6.2).…”

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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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“…(c) The real part of the cross-spectrum (dots) with the linear combination of third-order polynomials that best fits their behaviour overlain (solid lines) for both station couples. (d) Velocity values (triangles) for which the zeros of a zeroth order Bessel function of the first kind coincide with the zeros of the least-squares fits in (c) [the procedure is similar to the approach by Ekström et al (2009) and explained in detail in Lindner et al (2018)]. Rayleigh wave fundamental-mode phase velocities for the preliminary reference earth model (PREM, but with the oceanic layer removed; Dziewonski & Anderson 1981) are given by the grey dashed curve.…”

Section: Figure S6mentioning

confidence: 99%

Systematic recovery of instrumental timing and phase errors using interferometric surface-waves retrieved from large-N seismic arrays

Weemstra

Laat

Verdel

et al. 2020

Geophysical Journal International

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Summary Instrumental timing and phase errors are a notorious problem in seismic data acquisition and processing. These can be frequency independent, for example due to clock drift, but may also be frequency dependent, for example due to imperfectly known instrument responses. A technique is presented that allows both types of errors to be recovered in a systematic fashion. The methodology relies on the time-symmetry usually inherent in time-averaged crosscorrelations of ambient seismic noise: the difference between the arrival time of the direct surface wave at positive time and the arrival time of the direct surface wave at negative time is quantified. Doing this for all eligible receiver-receiver pairs of a large-N seismic array, including one or more receivers devoid of instrumental timing errors, the instrumental timing errors of all incorrectly timed receivers can be determined uniquely. Most notably, this is accomplished by means of a weighted least-squares inversion. The weights are based on the receiver-receiver distances and decrease the adverse effect of inhomogeneities in the noise illumination pattern on the recovered instrumental timing errors. Inversion results are furthermore optimized by limiting the inversion to receiver couples that (i) exceed a specific receiver-receiver distance threshold and (ii) whose time-averaged crosscorrelations exceed a specific signal-to-noise ratio threshold. Potential frequency dependence of the timing errors is incorporated by means of an iterative, frequency-dependent approach. The proposed methodology is validated using synthetic recordings of ambient seismic surface-wave noise due to an arbitrary non-uniform illumination pattern. The methodology is successfully applied to time-averaged crosscorrelations of field recordings of ambient seismic noise on and around the Reykjanes peninsula, SW Iceland.

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Towards monitoring the englacial fracture state using virtual-reflector seismology

Cited by 6 publications

References 90 publications

Seismic characterization of a rapidly-rising jökulhlaup cycle at the A.P. Olsen Ice Cap, NE-Greenland

Seismic characterization of a rapidly-rising jökulhlaup cycle at the A.P. Olsen Ice Cap, NE-Greenland

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

Systematic recovery of instrumental timing and phase errors using interferometric surface-waves retrieved from large-N seismic arrays

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